rustc_middle/ty/print/

pretty.rs

use std::cell::Cell;
use std::fmt::{self, Write as _};
use std::iter;
use std::ops::{Deref, DerefMut};

use rustc_abi::{ExternAbi, Size};
use rustc_apfloat::Float;
use rustc_apfloat::ieee::{Double, Half, Quad, Single};
use rustc_data_structures::Limit;
use rustc_data_structures::fx::{FxIndexMap, IndexEntry};
use rustc_data_structures::unord::UnordMap;
use rustc_hir as hir;
use rustc_hir::LangItem;
use rustc_hir::def::{self, CtorKind, DefKind, Namespace};
use rustc_hir::def_id::{DefIdMap, DefIdSet, LOCAL_CRATE, ModId};
use rustc_hir::definitions::{DefKey, DefPathDataName};
use rustc_macros::{Lift, extension};
use rustc_session::cstore::{ExternCrate, ExternCrateSource};
use rustc_span::{Ident, RemapPathScopeComponents, Symbol, kw, sym};
use rustc_type_ir::{FieldInfo, Unnormalized, Upcast as _, elaborate};
use smallvec::SmallVec;

// `pretty` is a separate module only for organization.
use super::*;
use crate::mir::interpret::{AllocRange, GlobalAlloc, Pointer, Provenance, Scalar};
use crate::query::{IntoQueryKey, Providers};
use crate::ty::region::RegionExt;
use crate::ty::{
    ConstInt, Expr, GenericArgKind, ParamConst, ScalarInt, Term, TermKind, TraitPredicate,
    TypeFoldable, TypeSuperFoldable, TypeSuperVisitable, TypeVisitable, TypeVisitableExt,
};

thread_local! {
    static FORCE_IMPL_FILENAME_LINE: Cell<bool> = const { Cell::new(false) };
    static SHOULD_PREFIX_WITH_CRATE_NAME: Cell<bool> = const { Cell::new(false) };
    static SHOULD_PREFIX_WITH_CRATE: Cell<bool> = const { Cell::new(false) };
    static NO_TRIMMED_PATH: Cell<bool> = const { Cell::new(false) };
    static FORCE_TRIMMED_PATH: Cell<bool> = const { Cell::new(false) };
    static REDUCED_QUERIES: Cell<bool> = const { Cell::new(false) };
    static NO_VISIBLE_PATH: Cell<bool> = const { Cell::new(false) };
    static NO_VISIBLE_PATH_IF_DOC_HIDDEN: Cell<bool> = const { Cell::new(false) };
    static RTN_MODE: Cell<RtnMode> = const { Cell::new(RtnMode::ForDiagnostic) };
}

/// Rendering style for RTN types.
#[derive(Copy, Clone, PartialEq, Eq, Debug)]
pub enum RtnMode {
    /// Print the RTN type as an impl trait with its path, i.e.e `impl Sized { T::method(..) }`.
    ForDiagnostic,
    /// Print the RTN type as an impl trait, i.e. `impl Sized`.
    ForSignature,
    /// Print the RTN type as a value path, i.e. `T::method(..): ...`.
    ForSuggestion,
}

macro_rules! define_helper {
    ($($(#[$a:meta])* fn $name:ident($helper:ident, $tl:ident);)+) => {
        $(
            #[must_use]
            pub struct $helper(bool);

            impl $helper {
                pub fn new() -> $helper {
                    $helper($tl.replace(true))
                }
            }

            $(#[$a])*
            pub macro $name($e:expr) {
                {
                    let _guard = $helper::new();
                    $e
                }
            }

            impl Drop for $helper {
                fn drop(&mut self) {
                    $tl.set(self.0)
                }
            }

            pub fn $name() -> bool {
                $tl.get()
            }
        )+
    }
}

define_helper!(
    /// Avoids running select queries during any prints that occur
    /// during the closure. This may alter the appearance of some
    /// types (e.g. forcing verbose printing for opaque types).
    /// This method is used during some queries (e.g. `explicit_item_bounds`
    /// for opaque types), to ensure that any debug printing that
    /// occurs during the query computation does not end up recursively
    /// calling the same query.
    fn with_reduced_queries(ReducedQueriesGuard, REDUCED_QUERIES);
    /// Force us to name impls with just the filename/line number. We
    /// normally try to use types. But at some points, notably while printing
    /// cycle errors, this can result in extra or suboptimal error output,
    /// so this variable disables that check.
    fn with_forced_impl_filename_line(ForcedImplGuard, FORCE_IMPL_FILENAME_LINE);
    /// Adds the crate name prefix to paths where appropriate.
    /// Unlike `with_crate_prefix`, this unconditionally uses `tcx.crate_name` instead of sometimes
    /// using `crate::` for local items.
    ///
    /// Overrides `with_crate_prefix`.

    // This function is used by `rustc_public` and downstream rustc-driver in
    // Ferrocene. Please check with them before removing it.
    fn with_resolve_crate_name(CrateNamePrefixGuard, SHOULD_PREFIX_WITH_CRATE_NAME);
    /// Adds the `crate::` prefix to paths where appropriate.
    ///
    /// Ignored if `with_resolve_crate_name` is active.
    fn with_crate_prefix(CratePrefixGuard, SHOULD_PREFIX_WITH_CRATE);
    /// Prevent path trimming if it is turned on. Path trimming affects `Display` impl
    /// of various rustc types, for example `std::vec::Vec` would be trimmed to `Vec`,
    /// if no other `Vec` is found.
    fn with_no_trimmed_paths(NoTrimmedGuard, NO_TRIMMED_PATH);
    fn with_forced_trimmed_paths(ForceTrimmedGuard, FORCE_TRIMMED_PATH);
    /// Prevent selection of visible paths. `Display` impl of DefId will prefer
    /// visible (public) reexports of types as paths.
    fn with_no_visible_paths(NoVisibleGuard, NO_VISIBLE_PATH);
    /// Prevent selection of visible paths if the paths are through a doc hidden path.
    fn with_no_visible_paths_if_doc_hidden(NoVisibleIfDocHiddenGuard, NO_VISIBLE_PATH_IF_DOC_HIDDEN);
);

#[must_use]
pub struct RtnModeHelper(RtnMode);

impl RtnModeHelper {
    pub fn with(mode: RtnMode) -> RtnModeHelper {
        RtnModeHelper(RTN_MODE.with(|c| c.replace(mode)))
    }
}

impl Drop for RtnModeHelper {
    fn drop(&mut self) {
        RTN_MODE.with(|c| c.set(self.0))
    }
}

/// Print types for the purposes of a suggestion.
///
/// Specifically, this will render RPITITs as `T::method(..)` which is suitable for
/// things like where-clauses.
pub macro with_types_for_suggestion($e:expr) {{
    let _guard = $crate::ty::print::pretty::RtnModeHelper::with(RtnMode::ForSuggestion);
    $e
}}

/// Print types for the purposes of a signature suggestion.
///
/// Specifically, this will render RPITITs as `impl Trait` rather than `T::method(..)`.
pub macro with_types_for_signature($e:expr) {{
    let _guard = $crate::ty::print::pretty::RtnModeHelper::with(RtnMode::ForSignature);
    $e
}}

/// Avoids running any queries during prints.
pub macro with_no_queries($e:expr) {{
    $crate::ty::print::with_reduced_queries!($crate::ty::print::with_forced_impl_filename_line!(
        $crate::ty::print::with_no_trimmed_paths!($crate::ty::print::with_no_visible_paths!($e))
    ))
}}

#[derive(Copy, Clone, Debug, PartialEq, Eq)]
pub enum WrapBinderMode {
    ForAll,
    Unsafe,
}
impl WrapBinderMode {
    pub fn start_str(self) -> &'static str {
        match self {
            WrapBinderMode::ForAll => "for<",
            WrapBinderMode::Unsafe => "unsafe<",
        }
    }
}

/// The "region highlights" are used to control region printing during
/// specific error messages. When a "region highlight" is enabled, it
/// gives an alternate way to print specific regions. For now, we
/// always print those regions using a number, so something like "`'0`".
///
/// Regions not selected by the region highlight mode are presently
/// unaffected.
#[derive(Copy, Clone, Default)]
pub struct RegionHighlightMode<'tcx> {
    /// If enabled, when we see the selected region, use "`'N`"
    /// instead of the ordinary behavior.
    highlight_regions: [Option<(ty::Region<'tcx>, usize)>; 3],

    /// If set to `true`, types that include regions will always be included in the output, while
    /// other types will be free to be trimmed.
    pub keep_regions: bool,

    /// If enabled, when printing a "free region" that originated from
    /// the given `ty::BoundRegionKind`, print it as "`'1`". Free regions that would ordinarily
    /// have names print as normal.
    ///
    /// This is used when you have a signature like `fn foo(x: &u32,
    /// y: &'a u32)` and we want to give a name to the region of the
    /// reference `x`.
    highlight_bound_region: Option<(ty::BoundRegionKind<'tcx>, usize)>,
}

impl<'tcx> RegionHighlightMode<'tcx> {
    /// If `region` and `number` are both `Some`, invokes
    /// `highlighting_region`.
    pub fn maybe_highlighting_region(
        &mut self,
        region: Option<ty::Region<'tcx>>,
        number: Option<usize>,
    ) {
        self.keep_regions = true;
        if let Some(k) = region
            && let Some(n) = number
        {
            self.highlighting_region(k, n);
        }
    }

    /// Highlights the region inference variable `vid` as `'N`.
    pub fn highlighting_region(&mut self, region: ty::Region<'tcx>, number: usize) {
        let num_slots = self.highlight_regions.len();
        let first_avail_slot =
            self.highlight_regions.iter_mut().find(|s| s.is_none()).unwrap_or_else(|| {
                bug!("can only highlight {} placeholders at a time", num_slots,)
            });
        *first_avail_slot = Some((region, number));
        self.keep_regions = true;
    }

    /// Convenience wrapper for `highlighting_region`.
    pub fn highlighting_region_vid(
        &mut self,
        tcx: TyCtxt<'tcx>,
        vid: ty::RegionVid,
        number: usize,
    ) {
        self.highlighting_region(ty::Region::new_var(tcx, vid), number)
    }

    /// Returns `Some(n)` with the number to use for the given region, if any.
    fn region_highlighted(&self, region: ty::Region<'tcx>) -> Option<usize> {
        self.highlight_regions.iter().find_map(|h| match h {
            Some((r, n)) if *r == region => Some(*n),
            _ => None,
        })
    }

    /// Highlight the given bound region.
    /// We can only highlight one bound region at a time. See
    /// the field `highlight_bound_region` for more detailed notes.
    pub fn highlighting_bound_region(&mut self, br: ty::BoundRegionKind<'tcx>, number: usize) {
        assert!(self.highlight_bound_region.is_none());
        self.highlight_bound_region = Some((br, number));
    }
}

/// Trait for printers that pretty-print using `fmt::Write` to the printer.
pub trait PrettyPrinter<'tcx>: Printer<'tcx> + fmt::Write {
    /// Like `print_def_path` but for value paths.
    fn pretty_print_value_path(
        &mut self,
        def_id: DefId,
        args: &'tcx [GenericArg<'tcx>],
    ) -> Result<(), PrintError> {
        self.print_def_path(def_id, args)
    }

    fn pretty_print_in_binder<T>(&mut self, value: &ty::Binder<'tcx, T>) -> Result<(), PrintError>
    where
        T: Print<Self> + TypeFoldable<TyCtxt<'tcx>>,
    {
        value.as_ref().skip_binder().print(self)
    }

    fn wrap_binder<T, F: FnOnce(&T, &mut Self) -> Result<(), fmt::Error>>(
        &mut self,
        value: &ty::Binder<'tcx, T>,
        _mode: WrapBinderMode,
        f: F,
    ) -> Result<(), PrintError>
    where
        T: TypeFoldable<TyCtxt<'tcx>>,
    {
        f(value.as_ref().skip_binder(), self)
    }

    /// Prints comma-separated elements.
    fn comma_sep<T>(&mut self, mut elems: impl Iterator<Item = T>) -> Result<(), PrintError>
    where
        T: Print<Self>,
    {
        if let Some(first) = elems.next() {
            first.print(self)?;
            for elem in elems {
                self.write_str(", ")?;
                elem.print(self)?;
            }
        }
        Ok(())
    }

    /// Prints `{f: t}` or `{f as t}` depending on the `cast` argument
    fn typed_value(
        &mut self,
        f: impl FnOnce(&mut Self) -> Result<(), PrintError>,
        t: impl FnOnce(&mut Self) -> Result<(), PrintError>,
        conversion: &str,
    ) -> Result<(), PrintError> {
        self.write_str("{")?;
        f(self)?;
        self.write_str(conversion)?;
        t(self)?;
        self.write_str("}")?;
        Ok(())
    }

    /// Prints `(...)` around what `f` prints.
    fn parenthesized(
        &mut self,
        f: impl FnOnce(&mut Self) -> Result<(), PrintError>,
    ) -> Result<(), PrintError> {
        self.write_str("(")?;
        f(self)?;
        self.write_str(")")?;
        Ok(())
    }

    /// Prints `(...)` around what `f` prints if `parenthesized` is true, otherwise just prints `f`.
    fn maybe_parenthesized(
        &mut self,
        f: impl FnOnce(&mut Self) -> Result<(), PrintError>,
        parenthesized: bool,
    ) -> Result<(), PrintError> {
        if parenthesized {
            self.parenthesized(f)?;
        } else {
            f(self)?;
        }
        Ok(())
    }

    /// Prints `<...>` around what `f` prints.
    fn generic_delimiters(
        &mut self,
        f: impl FnOnce(&mut Self) -> Result<(), PrintError>,
    ) -> Result<(), PrintError>;

    fn should_truncate(&mut self) -> bool {
        false
    }

    /// Returns `true` if the region should be printed in optional positions,
    /// e.g., `&'a T` or `dyn Tr + 'b`. (Regions like the one in `Cow<'static, T>`
    /// will always be printed.)
    fn should_print_optional_region(&self, region: ty::Region<'tcx>) -> bool;

    fn reset_type_limit(&mut self) {}

    // Defaults (should not be overridden):

    /// If possible, this returns a global path resolving to `def_id` that is visible
    /// from at least one local module, and returns `true`. If the crate defining `def_id` is
    /// declared with an `extern crate`, the path is guaranteed to use the `extern crate`.
    fn try_print_visible_def_path(&mut self, def_id: DefId) -> Result<bool, PrintError> {
        if with_no_visible_paths() {
            return Ok(false);
        }

        let mut callers = Vec::new();
        self.try_print_visible_def_path_recur(def_id, &mut callers)
    }

    // Given a `DefId`, produce a short name. For types and traits, it prints *only* its name,
    // For associated items on traits it prints out the trait's name and the associated item's name.
    // For enum variants, if they have an unique name, then we only print the name, otherwise we
    // print the enum name and the variant name. Otherwise, we do not print anything and let the
    // caller use the `print_def_path` fallback.
    fn force_print_trimmed_def_path(&mut self, def_id: DefId) -> Result<bool, PrintError> {
        let key = self.tcx().def_key(def_id);
        let visible_parent_map = self.tcx().visible_parent_map(());
        let kind = self.tcx().def_kind(def_id);

        let get_local_name = |this: &Self, name, def_id, key: DefKey| {
            if let Some(visible_parent) = visible_parent_map.get(&def_id)
                && let actual_parent = this.tcx().opt_parent(def_id)
                && let DefPathData::TypeNs(_) = key.disambiguated_data.data
                && Some(*visible_parent) != actual_parent
            {
                this.tcx()
                    .module_children(ModId::new_unchecked(*visible_parent))
                    .iter()
                    .filter(|child| child.res.opt_def_id() == Some(def_id))
                    .find(|child| child.vis.is_public() && child.ident.name != kw::Underscore)
                    .map(|child| child.ident.name)
                    .unwrap_or(name)
            } else {
                name
            }
        };
        if let DefKind::Variant = kind
            && let Some(symbol) = self.tcx().trimmed_def_paths(()).get(&def_id)
        {
            // If `Assoc` is unique, we don't want to talk about `Trait::Assoc`.
            self.write_str(get_local_name(self, *symbol, def_id, key).as_str())?;
            return Ok(true);
        }
        if let Some(symbol) = key.get_opt_name() {
            if let DefKind::AssocConst { .. } | DefKind::AssocFn | DefKind::AssocTy = kind
                && let Some(parent) = self.tcx().opt_parent(def_id)
                && let parent_key = self.tcx().def_key(parent)
                && let Some(symbol) = parent_key.get_opt_name()
            {
                // Trait
                self.write_str(get_local_name(self, symbol, parent, parent_key).as_str())?;
                self.write_str("::")?;
            } else if let DefKind::Variant = kind
                && let Some(parent) = self.tcx().opt_parent(def_id)
                && let parent_key = self.tcx().def_key(parent)
                && let Some(symbol) = parent_key.get_opt_name()
            {
                // Enum

                // For associated items and variants, we want the "full" path, namely, include
                // the parent type in the path. For example, `Iterator::Item`.
                self.write_str(get_local_name(self, symbol, parent, parent_key).as_str())?;
                self.write_str("::")?;
            } else if let DefKind::Struct
            | DefKind::Union
            | DefKind::Enum
            | DefKind::Trait
            | DefKind::TyAlias
            | DefKind::Fn
            | DefKind::Const { .. }
            | DefKind::Static { .. } = kind
            {
            } else {
                // If not covered above, like for example items out of `impl` blocks, fallback.
                return Ok(false);
            }
            self.write_str(get_local_name(self, symbol, def_id, key).as_str())?;
            return Ok(true);
        }
        Ok(false)
    }

    /// Try to see if this path can be trimmed to a unique symbol name.
    fn try_print_trimmed_def_path(&mut self, def_id: DefId) -> Result<bool, PrintError> {
        if with_forced_trimmed_paths() && self.force_print_trimmed_def_path(def_id)? {
            return Ok(true);
        }
        if self.tcx().sess.opts.unstable_opts.trim_diagnostic_paths
            && self.tcx().sess.opts.trimmed_def_paths
            && !with_no_trimmed_paths()
            && !with_crate_prefix()
            && let Some(symbol) = self.tcx().trimmed_def_paths(()).get(&def_id)
        {
            write!(self, "{}", Ident::with_dummy_span(*symbol))?;
            Ok(true)
        } else {
            Ok(false)
        }
    }

    /// Does the work of `try_print_visible_def_path`, building the
    /// full definition path recursively before attempting to
    /// post-process it into the valid and visible version that
    /// accounts for re-exports.
    ///
    /// This method should only be called by itself or
    /// `try_print_visible_def_path`.
    ///
    /// `callers` is a chain of visible_parent's leading to `def_id`,
    /// to support cycle detection during recursion.
    ///
    /// This method returns false if we can't print the visible path, so
    /// `print_def_path` can fall back on the item's real definition path.
    fn try_print_visible_def_path_recur(
        &mut self,
        def_id: DefId,
        callers: &mut Vec<DefId>,
    ) -> Result<bool, PrintError> {
        debug!("try_print_visible_def_path: def_id={:?}", def_id);

        // If `def_id` is a direct or injected extern crate, return the
        // path to the crate followed by the path to the item within the crate.
        if let Some(cnum) = def_id.as_crate_root() {
            if cnum == LOCAL_CRATE {
                self.print_crate_name(cnum)?;
                return Ok(true);
            }

            // In local mode, when we encounter a crate other than
            // LOCAL_CRATE, execution proceeds in one of two ways:
            //
            // 1. For a direct dependency, where user added an
            //    `extern crate` manually, we put the `extern
            //    crate` as the parent. So you wind up with
            //    something relative to the current crate.
            // 2. For an extern inferred from a path or an indirect crate,
            //    where there is no explicit `extern crate`, we just prepend
            //    the crate name.
            match self.tcx().extern_crate(cnum) {
                Some(&ExternCrate { src, dependency_of, span, .. }) => match (src, dependency_of) {
                    (ExternCrateSource::Extern(def_id), LOCAL_CRATE) => {
                        // NOTE(eddyb) the only reason `span` might be dummy,
                        // that we're aware of, is that it's the `std`/`core`
                        // `extern crate` injected by default.
                        // FIXME(eddyb) find something better to key this on,
                        // or avoid ending up with `ExternCrateSource::Extern`,
                        // for the injected `std`/`core`.
                        if span.is_dummy() {
                            self.print_crate_name(cnum)?;
                            return Ok(true);
                        }

                        // Disable `try_print_trimmed_def_path` behavior within
                        // the `print_def_path` call, to avoid infinite recursion
                        // in cases where the `extern crate foo` has non-trivial
                        // parents, e.g. it's nested in `impl foo::Trait for Bar`
                        // (see also issues #55779 and #87932).
                        with_no_visible_paths!(self.print_def_path(def_id, &[])?);

                        return Ok(true);
                    }
                    (ExternCrateSource::Path, LOCAL_CRATE) => {
                        self.print_crate_name(cnum)?;
                        return Ok(true);
                    }
                    _ => {}
                },
                None => {
                    self.print_crate_name(cnum)?;
                    return Ok(true);
                }
            }
        }

        if def_id.is_local() {
            return Ok(false);
        }

        let visible_parent_map = self.tcx().visible_parent_map(());

        let mut cur_def_key = self.tcx().def_key(def_id);
        debug!("try_print_visible_def_path: cur_def_key={:?}", cur_def_key);

        // For a constructor, we want the name of its parent rather than <unnamed>.
        if let DefPathData::Ctor = cur_def_key.disambiguated_data.data {
            let parent = DefId {
                krate: def_id.krate,
                index: cur_def_key
                    .parent
                    .expect("`DefPathData::Ctor` / `VariantData` missing a parent"),
            };

            cur_def_key = self.tcx().def_key(parent);
        }

        let Some(visible_parent) = visible_parent_map.get(&def_id).cloned() else {
            return Ok(false);
        };

        if self.tcx().is_doc_hidden(visible_parent) && with_no_visible_paths_if_doc_hidden() {
            return Ok(false);
        }

        let actual_parent = self.tcx().opt_parent(def_id);
        debug!(
            "try_print_visible_def_path: visible_parent={:?} actual_parent={:?}",
            visible_parent, actual_parent,
        );

        let mut data = cur_def_key.disambiguated_data.data;
        debug!(
            "try_print_visible_def_path: data={:?} visible_parent={:?} actual_parent={:?}",
            data, visible_parent, actual_parent,
        );

        match data {
            // In order to output a path that could actually be imported (valid and visible),
            // we need to handle re-exports correctly.
            //
            // For example, take `std::os::unix::process::CommandExt`, this trait is actually
            // defined at `std::sys::unix::ext::process::CommandExt` (at time of writing).
            //
            // `std::os::unix` reexports the contents of `std::sys::unix::ext`. `std::sys` is
            // private so the "true" path to `CommandExt` isn't accessible.
            //
            // In this case, the `visible_parent_map` will look something like this:
            //
            // (child) -> (parent)
            // `std::sys::unix::ext::process::CommandExt` -> `std::sys::unix::ext::process`
            // `std::sys::unix::ext::process` -> `std::sys::unix::ext`
            // `std::sys::unix::ext` -> `std::os`
            //
            // This is correct, as the visible parent of `std::sys::unix::ext` is in fact
            // `std::os`.
            //
            // When printing the path to `CommandExt` and looking at the `cur_def_key` that
            // corresponds to `std::sys::unix::ext`, we would normally print `ext` and then go
            // to the parent - resulting in a mangled path like
            // `std::os::ext::process::CommandExt`.
            //
            // Instead, we must detect that there was a re-export and instead print `unix`
            // (which is the name `std::sys::unix::ext` was re-exported as in `std::os`). To
            // do this, we compare the parent of `std::sys::unix::ext` (`std::sys::unix`) with
            // the visible parent (`std::os`). If these do not match, then we iterate over
            // the children of the visible parent (as was done when computing
            // `visible_parent_map`), looking for the specific child we currently have and then
            // have access to the re-exported name.
            DefPathData::TypeNs(ref mut name) if Some(visible_parent) != actual_parent => {
                // Item might be re-exported several times, but filter for the one
                // that's public and whose identifier isn't `_`.
                let reexport = self
                    .tcx()
                    .module_children(ModId::new_unchecked(visible_parent))
                    .iter()
                    .filter(|child| child.res.opt_def_id() == Some(def_id))
                    .find(|child| child.vis.is_public() && child.ident.name != kw::Underscore)
                    .map(|child| child.ident.name);

                if let Some(new_name) = reexport {
                    *name = new_name;
                } else {
                    // There is no name that is public and isn't `_`, so bail.
                    return Ok(false);
                }
            }
            // Re-exported `extern crate` (#43189).
            DefPathData::CrateRoot => {
                data = DefPathData::TypeNs(self.tcx().crate_name(def_id.krate));
            }
            _ => {}
        }
        debug!("try_print_visible_def_path: data={:?}", data);

        if callers.contains(&visible_parent) {
            return Ok(false);
        }
        callers.push(visible_parent);
        // HACK(eddyb) this bypasses `print_path_with_simple`'s prefix printing to avoid
        // knowing ahead of time whether the entire path will succeed or not.
        // To support printers that do not implement `PrettyPrinter`, a `Vec` or
        // linked list on the stack would need to be built, before any printing.
        match self.try_print_visible_def_path_recur(visible_parent, callers)? {
            false => return Ok(false),
            true => {}
        }
        callers.pop();
        self.print_path_with_simple(
            |_| Ok(()),
            &DisambiguatedDefPathData { data, disambiguator: 0 },
        )?;
        Ok(true)
    }

    fn pretty_print_path_with_qualified(
        &mut self,
        self_ty: Ty<'tcx>,
        trait_ref: Option<ty::TraitRef<'tcx>>,
    ) -> Result<(), PrintError> {
        if trait_ref.is_none() {
            // Inherent impls. Try to print `Foo::bar` for an inherent
            // impl on `Foo`, but fallback to `<Foo>::bar` if self-type is
            // anything other than a simple path.
            match self_ty.kind() {
                ty::Adt(..)
                | ty::Foreign(_)
                | ty::Bool
                | ty::Char
                | ty::Str
                | ty::Int(_)
                | ty::Uint(_)
                | ty::Float(_) => {
                    return self_ty.print(self);
                }

                _ => {}
            }
        }

        self.generic_delimiters(|p| {
            self_ty.print(p)?;
            if let Some(trait_ref) = trait_ref {
                write!(p, " as ")?;
                trait_ref.print_only_trait_path().print(p)?;
            }
            Ok(())
        })
    }

    fn pretty_print_path_with_impl(
        &mut self,
        print_prefix: impl FnOnce(&mut Self) -> Result<(), PrintError>,
        self_ty: Ty<'tcx>,
        trait_ref: Option<ty::TraitRef<'tcx>>,
    ) -> Result<(), PrintError> {
        print_prefix(self)?;

        self.generic_delimiters(|p| {
            write!(p, "impl ")?;
            if let Some(trait_ref) = trait_ref {
                trait_ref.print_only_trait_path().print(p)?;
                write!(p, " for ")?;
            }
            self_ty.print(p)?;

            Ok(())
        })
    }

    fn pretty_print_closure_inner(
        &mut self,
        did: DefId,
        args: ty::GenericArgsRef<'tcx>,
    ) -> Result<(), PrintError> {
        if self.should_truncate() {
            write!(self, "@...")
        } else if self.tcx().sess.opts.unstable_opts.span_free_formats {
            write!(self, "@")?;
            self.print_def_path(did, args)
        } else if let Some(did) = did.as_local() {
            let span = self.tcx().def_span(did);
            let loc = if with_forced_trimmed_paths() {
                self.tcx()
                    .sess
                    .source_map()
                    .span_to_short_string(span, RemapPathScopeComponents::DIAGNOSTICS)
            } else {
                self.tcx().sess.source_map().span_to_diagnostic_string(span)
            };
            write!(
                self,
                "@{}",
                // This may end up in stderr diagnostics but it may also be
                // emitted into MIR. Hence we use the remapped path if
                // available
                loc
            )
        } else {
            write!(self, "@")?;
            self.print_def_path(did, args)
        }
    }

    fn pretty_print_type(&mut self, ty: Ty<'tcx>) -> Result<(), PrintError> {
        match *ty.kind() {
            ty::Bool => write!(self, "bool")?,
            ty::Char => write!(self, "char")?,
            ty::Int(t) => write!(self, "{}", t.name_str())?,
            ty::Uint(t) => write!(self, "{}", t.name_str())?,
            ty::Float(t) => write!(self, "{}", t.name_str())?,
            ty::Pat(ty, pat) => {
                write!(self, "(")?;
                ty.print(self)?;
                write!(self, ") is {pat:?}")?;
            }
            ty::RawPtr(ty, mutbl) => {
                write!(self, "*{} ", mutbl.ptr_str())?;
                ty.print(self)?;
            }
            ty::Ref(r, ty, mutbl) => {
                write!(self, "&")?;
                if self.should_print_optional_region(r) {
                    r.print(self)?;
                    write!(self, " ")?;
                }
                ty::TypeAndMut { ty, mutbl }.print(self)?;
            }
            ty::Never => write!(self, "!")?,
            ty::Tuple(tys) => {
                write!(self, "(")?;
                self.comma_sep(tys.iter())?;
                if tys.len() == 1 {
                    write!(self, ",")?;
                }
                write!(self, ")")?;
            }
            ty::FnDef(def_id, args) => {
                let args = args.no_bound_vars().unwrap();
                if with_reduced_queries() {
                    self.print_def_path(def_id, args)?;
                } else {
                    let mut sig =
                        self.tcx().fn_sig(def_id).instantiate(self.tcx(), args).skip_norm_wip();
                    if self.tcx().codegen_fn_attrs(def_id).safe_target_features {
                        write!(self, "#[target_feature(..)] ")?;
                        sig = sig.map_bound(|mut sig| {
                            sig.fn_sig_kind = sig.fn_sig_kind.set_safety(hir::Safety::Safe);
                            sig
                        });
                    }
                    sig.print(self)?;
                    write!(self, " {{")?;
                    self.pretty_print_value_path(def_id, args)?;
                    write!(self, "}}")?;
                }
            }
            ty::FnPtr(ref sig_tys, hdr) => sig_tys.with(hdr).print(self)?,
            ty::UnsafeBinder(ref bound_ty) => {
                self.wrap_binder(bound_ty, WrapBinderMode::Unsafe, |ty, p| {
                    p.pretty_print_type(*ty)
                })?;
            }
            ty::Infer(infer_ty) => {
                if self.should_print_verbose() {
                    write!(self, "{:?}", ty.kind())?;
                    return Ok(());
                }

                if let ty::TyVar(ty_vid) = infer_ty {
                    if let Some(name) = self.ty_infer_name(ty_vid) {
                        write!(self, "{name}")?;
                    } else {
                        write!(self, "{infer_ty}")?;
                    }
                } else {
                    write!(self, "{infer_ty}")?;
                }
            }
            ty::Error(_) => write!(self, "{{type error}}")?,
            ty::Param(ref param_ty) => param_ty.print(self)?,
            ty::Bound(debruijn, bound_ty) => match bound_ty.kind {
                ty::BoundTyKind::Anon => {
                    rustc_type_ir::debug_bound_var(self, debruijn, bound_ty.var)?
                }
                ty::BoundTyKind::Param(def_id) => match self.should_print_verbose() {
                    true => write!(self, "{:?}", ty.kind())?,
                    false => write!(self, "{}", self.tcx().item_name(def_id))?,
                },
            },
            ty::Adt(def, args)
                if let Some(FieldInfo { base, variant, name, .. }) =
                    def.field_representing_type_info(self.tcx(), args) =>
            {
                if let Some(variant) = variant {
                    write!(self, "field_of!({base}, {variant}.{name})")?;
                } else {
                    write!(self, "field_of!({base}, {name})")?;
                }
            }
            ty::Adt(def, args) => self.print_def_path(def.did(), args)?,
            ty::Dynamic(data, r) => {
                let print_r = self.should_print_optional_region(r);
                if print_r {
                    write!(self, "(")?;
                }
                write!(self, "dyn ")?;
                data.print(self)?;
                if print_r {
                    write!(self, " + ")?;
                    r.print(self)?;
                    write!(self, ")")?;
                }
            }
            ty::Foreign(def_id) => self.print_def_path(def_id, &[])?,
            ty::Alias(
                _,
                ref data @ ty::AliasTy {
                    kind: ty::Projection { .. } | ty::Inherent { .. } | ty::Free { .. },
                    ..
                },
            ) => data.print(self)?,
            ty::Placeholder(placeholder) => placeholder.print(self)?,
            ty::Alias(_, ty::AliasTy { kind: ty::Opaque { def_id }, args, .. }) => {
                // We use verbose printing in 'NO_QUERIES' mode, to
                // avoid needing to call `clauses_of`. This should
                // only affect certain debug messages (e.g. messages printed
                // from `rustc_middle::ty` during the computation of `tcx.clauses_of`),
                // and should have no effect on any compiler output.
                // [Unless `-Zverbose-internals` is used, e.g. in the output of
                // `tests/ui/nll/ty-outlives/impl-trait-captures.rs`, for
                // example.]
                if self.should_print_verbose() {
                    // FIXME(eddyb) print this with `print_def_path`.
                    write!(self, "Opaque({:?}, {})", def_id, args.print_as_list())?;
                    return Ok(());
                }

                let parent = self.tcx().parent(def_id);
                match self.tcx().def_kind(parent) {
                    DefKind::TyAlias | DefKind::AssocTy => {
                        // NOTE: I know we should check for NO_QUERIES here, but it's alright.
                        // `type_of` on a type alias or assoc type should never cause a cycle.
                        if let ty::Alias(_, ty::AliasTy { kind: ty::Opaque { def_id: d }, .. }) =
                            *self
                                .tcx()
                                .type_of(parent)
                                .instantiate_identity()
                                .skip_norm_wip()
                                .kind()
                        {
                            if d == def_id {
                                // If the type alias directly starts with the `impl` of the
                                // opaque type we're printing, then skip the `::{opaque#1}`.
                                self.print_def_path(parent, args)?;
                                return Ok(());
                            }
                        }
                        // Complex opaque type, e.g. `type Foo = (i32, impl Debug);`
                        self.print_def_path(def_id, args)?;
                        return Ok(());
                    }
                    _ => {
                        if with_reduced_queries() {
                            self.print_def_path(def_id, &[])?;
                            return Ok(());
                        } else {
                            return self.pretty_print_opaque_impl_type(def_id, args);
                        }
                    }
                }
            }
            ty::Str => write!(self, "str")?,
            ty::Coroutine(did, args) => {
                write!(self, "{{")?;
                let coroutine_kind = self.tcx().coroutine_kind(did).unwrap();
                let should_print_movability = self.should_print_verbose()
                    || matches!(coroutine_kind, hir::CoroutineKind::Coroutine(_));

                if should_print_movability {
                    match coroutine_kind.movability() {
                        hir::Movability::Movable => {}
                        hir::Movability::Static => write!(self, "static ")?,
                    }
                }

                if !self.should_print_verbose() {
                    write!(self, "{coroutine_kind}")?;
                    if coroutine_kind.is_fn_like() {
                        // If we are printing an `async fn` coroutine type, then give the path
                        // of the fn, instead of its span, because that will in most cases be
                        // more helpful for the reader than just a source location.
                        //
                        // This will look like:
                        //    {async fn body of some_fn()}
                        write!(self, " of ")?;
                        let did_of_the_fn_item = self.tcx().parent(did);
                        self.print_def_path(did_of_the_fn_item, args)?;
                        write!(self, "()")?;
                    } else {
                        self.pretty_print_closure_inner(did, args)?;
                    }
                } else {
                    self.print_def_path(did, args)?;
                    write!(self, " upvar_tys=")?;
                    args.as_coroutine().tupled_upvars_ty().print(self)?;
                    write!(self, " resume_ty=")?;
                    args.as_coroutine().resume_ty().print(self)?;
                    write!(self, " yield_ty=")?;
                    args.as_coroutine().yield_ty().print(self)?;
                    write!(self, " return_ty=")?;
                    args.as_coroutine().return_ty().print(self)?;
                }

                write!(self, "}}")?
            }
            ty::CoroutineWitness(did, args) => {
                write!(self, "{{")?;
                if !self.should_print_verbose() {
                    write!(self, "coroutine witness")?;
                    self.pretty_print_closure_inner(did, args)?;
                } else {
                    self.print_def_path(did, args)?;
                }
                write!(self, "}}")?
            }
            ty::Closure(did, args) => {
                write!(self, "{{")?;
                if !self.should_print_verbose() {
                    write!(self, "closure")?;
                    self.pretty_print_closure_inner(did, args)?;
                } else {
                    self.print_def_path(did, args)?;
                    write!(self, " closure_kind_ty=")?;
                    args.as_closure().kind_ty().print(self)?;
                    write!(self, " closure_sig_as_fn_ptr_ty=")?;
                    args.as_closure().sig_as_fn_ptr_ty().print(self)?;
                    write!(self, " upvar_tys=")?;
                    args.as_closure().tupled_upvars_ty().print(self)?;
                }
                write!(self, "}}")?;
            }
            ty::CoroutineClosure(did, args) => {
                write!(self, "{{")?;
                if !self.should_print_verbose() {
                    match self.tcx().coroutine_kind(self.tcx().coroutine_for_closure(did)).unwrap()
                    {
                        hir::CoroutineKind::Desugared(
                            desugaring,
                            hir::CoroutineSource::Closure,
                        ) => write!(self, "{desugaring}closure")?,
                        _ => unreachable!(
                            "coroutine from coroutine-closure should have CoroutineSource::Closure"
                        ),
                    };
                    self.pretty_print_closure_inner(did, args)?;
                } else {
                    self.print_def_path(did, args)?;
                    write!(self, " closure_kind_ty=")?;
                    args.as_coroutine_closure().kind_ty().print(self)?;
                    write!(self, " signature_parts_ty=")?;
                    args.as_coroutine_closure().signature_parts_ty().print(self)?;
                    write!(self, " upvar_tys=")?;
                    args.as_coroutine_closure().tupled_upvars_ty().print(self)?;
                    write!(self, " coroutine_captures_by_ref_ty=")?;
                    args.as_coroutine_closure().coroutine_captures_by_ref_ty().print(self)?;
                }
                write!(self, "}}")?;
            }
            ty::Array(ty, sz) => {
                write!(self, "[")?;
                ty.print(self)?;
                write!(self, "; ")?;
                sz.print(self)?;
                write!(self, "]")?;
            }
            ty::Slice(ty) => {
                write!(self, "[")?;
                ty.print(self)?;
                write!(self, "]")?;
            }
        }

        Ok(())
    }

    fn pretty_print_opaque_impl_type(
        &mut self,
        def_id: DefId,
        args: ty::GenericArgsRef<'tcx>,
    ) -> Result<(), PrintError> {
        let tcx = self.tcx();

        // Grab the "TraitA + TraitB" from `impl TraitA + TraitB`,
        // by looking up the projections associated with the def_id.
        let bounds = tcx.explicit_item_bounds(def_id);

        let mut traits = FxIndexMap::default();
        let mut fn_traits = FxIndexMap::default();
        let mut lifetimes = SmallVec::<[ty::Region<'tcx>; 1]>::new();

        let mut has_sized_bound = false;
        let mut has_negative_sized_bound = false;
        let mut has_meta_sized_bound = false;

        for (predicate, _) in
            bounds.iter_instantiated_copied(tcx, args).map(Unnormalized::skip_norm_wip)
        {
            let bound_predicate = predicate.kind();

            match bound_predicate.skip_binder() {
                ty::ClauseKind::Trait(pred) => {
                    // With `feature(sized_hierarchy)`, don't print `?Sized` as an alias for
                    // `MetaSized`, and skip sizedness bounds to be added at the end.
                    match tcx.as_lang_item(pred.def_id()) {
                        Some(LangItem::Sized) => match pred.polarity {
                            ty::PredicatePolarity::Positive => {
                                has_sized_bound = true;
                                continue;
                            }
                            ty::PredicatePolarity::Negative => has_negative_sized_bound = true,
                        },
                        Some(LangItem::MetaSized) => {
                            has_meta_sized_bound = true;
                            continue;
                        }
                        Some(LangItem::PointeeSized) => {
                            bug!("`PointeeSized` is removed during lowering");
                        }
                        _ => (),
                    }

                    self.insert_trait_and_projection(
                        bound_predicate.rebind(pred),
                        None,
                        &mut traits,
                        &mut fn_traits,
                    );
                }
                ty::ClauseKind::Projection(pred) => {
                    let proj = bound_predicate.rebind(pred);
                    let trait_ref = proj.map_bound(|proj| TraitPredicate {
                        trait_ref: proj.projection_term.trait_ref(tcx),
                        polarity: ty::PredicatePolarity::Positive,
                    });

                    self.insert_trait_and_projection(
                        trait_ref,
                        Some((proj.item_def_id(), proj.term())),
                        &mut traits,
                        &mut fn_traits,
                    );
                }
                ty::ClauseKind::TypeOutlives(outlives) => {
                    lifetimes.push(outlives.1);
                }
                _ => {}
            }
        }

        write!(self, "impl ")?;

        let mut first = true;
        // Insert parenthesis around (Fn(A, B) -> C) if the opaque ty has more than one other trait
        let paren_needed = fn_traits.len() > 1 || traits.len() > 0 || !has_sized_bound;

        for ((bound_args_and_self_ty, is_async), entry) in fn_traits {
            write!(self, "{}", if first { "" } else { " + " })?;
            write!(self, "{}", if paren_needed { "(" } else { "" })?;

            let trait_def_id = if is_async {
                tcx.async_fn_trait_kind_to_def_id(entry.kind).expect("expected AsyncFn lang items")
            } else {
                tcx.fn_trait_kind_to_def_id(entry.kind).expect("expected Fn lang items")
            };

            if let Some(return_ty) = entry.return_ty {
                self.wrap_binder(
                    &bound_args_and_self_ty,
                    WrapBinderMode::ForAll,
                    |(args, _), p| {
                        write!(p, "{}", tcx.item_name(trait_def_id))?;
                        write!(p, "(")?;

                        for (idx, ty) in args.iter().enumerate() {
                            if idx > 0 {
                                write!(p, ", ")?;
                            }
                            ty.print(p)?;
                        }

                        write!(p, ")")?;
                        if let Some(ty) = return_ty.skip_binder().as_type() {
                            if !ty.is_unit() {
                                write!(p, " -> ")?;
                                return_ty.print(p)?;
                            }
                        }
                        write!(p, "{}", if paren_needed { ")" } else { "" })?;

                        first = false;
                        Ok(())
                    },
                )?;
            } else {
                // Otherwise, render this like a regular trait.
                traits.insert(
                    bound_args_and_self_ty.map_bound(|(args, self_ty)| ty::TraitPredicate {
                        polarity: ty::PredicatePolarity::Positive,
                        trait_ref: ty::TraitRef::new(
                            tcx,
                            trait_def_id,
                            [self_ty, Ty::new_tup(tcx, args)],
                        ),
                    }),
                    FxIndexMap::default(),
                );
            }
        }

        // Print the rest of the trait types (that aren't Fn* family of traits)
        for (trait_pred, assoc_items) in traits {
            write!(self, "{}", if first { "" } else { " + " })?;

            self.wrap_binder(&trait_pred, WrapBinderMode::ForAll, |trait_pred, p| {
                if trait_pred.polarity == ty::PredicatePolarity::Negative {
                    write!(p, "!")?;
                }
                trait_pred.trait_ref.print_only_trait_name().print(p)?;

                let generics = tcx.generics_of(trait_pred.def_id());
                let own_args = generics.own_args_no_defaults(tcx, trait_pred.trait_ref.args);

                if !own_args.is_empty() || !assoc_items.is_empty() {
                    let mut first = true;

                    for ty in own_args {
                        if first {
                            write!(p, "<")?;
                            first = false;
                        } else {
                            write!(p, ", ")?;
                        }
                        ty.print(p)?;
                    }

                    for (assoc_item_def_id, term) in assoc_items {
                        if first {
                            write!(p, "<")?;
                            first = false;
                        } else {
                            write!(p, ", ")?;
                        }

                        write!(p, "{} = ", tcx.associated_item(assoc_item_def_id).name())?;

                        match term.skip_binder().kind() {
                            TermKind::Ty(ty) => ty.print(p)?,
                            TermKind::Const(c) => c.print(p)?,
                        };
                    }

                    if !first {
                        write!(p, ">")?;
                    }
                }

                first = false;
                Ok(())
            })?;
        }

        let using_sized_hierarchy = self.tcx().features().sized_hierarchy();
        let add_sized = has_sized_bound && (first || has_negative_sized_bound);
        let add_maybe_sized =
            has_meta_sized_bound && !has_negative_sized_bound && !using_sized_hierarchy;
        // Set `has_pointee_sized_bound` if there were no `Sized` or `MetaSized` bounds.
        let has_pointee_sized_bound =
            !has_sized_bound && !has_meta_sized_bound && !has_negative_sized_bound;
        if add_sized || add_maybe_sized {
            if !first {
                write!(self, " + ")?;
            }
            if add_maybe_sized {
                write!(self, "?")?;
            }
            write!(self, "Sized")?;
        } else if has_meta_sized_bound && using_sized_hierarchy {
            if !first {
                write!(self, " + ")?;
            }
            write!(self, "MetaSized")?;
        } else if has_pointee_sized_bound && using_sized_hierarchy {
            if !first {
                write!(self, " + ")?;
            }
            write!(self, "PointeeSized")?;
        }

        if !with_forced_trimmed_paths() {
            for re in lifetimes {
                write!(self, " + ")?;
                self.print_region(re)?;
            }
        }

        Ok(())
    }

    /// Insert the trait ref and optionally a projection type associated with it into either the
    /// traits map or fn_traits map, depending on if the trait is in the Fn* family of traits.
    fn insert_trait_and_projection(
        &mut self,
        trait_pred: ty::PolyTraitPredicate<'tcx>,
        proj_ty: Option<(DefId, ty::Binder<'tcx, Term<'tcx>>)>,
        traits: &mut FxIndexMap<
            ty::PolyTraitPredicate<'tcx>,
            FxIndexMap<DefId, ty::Binder<'tcx, Term<'tcx>>>,
        >,
        fn_traits: &mut FxIndexMap<
            (ty::Binder<'tcx, (&'tcx ty::List<Ty<'tcx>>, Ty<'tcx>)>, bool),
            OpaqueFnEntry<'tcx>,
        >,
    ) {
        let tcx = self.tcx();
        let trait_def_id = trait_pred.def_id();

        let fn_trait_and_async = if let Some(kind) = tcx.fn_trait_kind_from_def_id(trait_def_id) {
            Some((kind, false))
        } else if let Some(kind) = tcx.async_fn_trait_kind_from_def_id(trait_def_id) {
            Some((kind, true))
        } else {
            None
        };

        if trait_pred.polarity() == ty::PredicatePolarity::Positive
            && let Some((kind, is_async)) = fn_trait_and_async
            && let ty::Tuple(types) = *trait_pred.skip_binder().trait_ref.args.type_at(1).kind()
        {
            let entry = fn_traits
                .entry((trait_pred.rebind((types, trait_pred.skip_binder().self_ty())), is_async))
                .or_insert_with(|| OpaqueFnEntry { kind, return_ty: None });
            if kind.extends(entry.kind) {
                entry.kind = kind;
            }
            if let Some((proj_def_id, proj_ty)) = proj_ty
                && tcx.item_name(proj_def_id) == sym::Output
            {
                entry.return_ty = Some(proj_ty);
            }
            return;
        }

        // Otherwise, just group our traits and projection types.
        traits.entry(trait_pred).or_default().extend(proj_ty);
    }

    fn pretty_print_inherent_projection(
        &mut self,
        alias_term: ty::AliasTerm<'tcx>,
    ) -> Result<(), PrintError> {
        let alias_def_id = alias_term.expect_inherent_def_id();
        let def_key = self.tcx().def_key(alias_def_id);
        self.print_path_with_generic_args(
            |p| {
                p.print_path_with_simple(
                    |p| p.print_path_with_qualified(alias_term.self_ty(), None),
                    &def_key.disambiguated_data,
                )
            },
            &alias_term.args[1..],
        )
    }

    fn pretty_print_rpitit(
        &mut self,
        def_id: DefId,
        args: ty::GenericArgsRef<'tcx>,
    ) -> Result<(), PrintError> {
        let fn_args = if self.tcx().features().return_type_notation()
            && let Some(ty::ImplTraitInTraitData::Trait { fn_def_id, .. }) =
                self.tcx().opt_rpitit_info(def_id)
            && let ty::Alias(_, alias_ty) =
                self.tcx().fn_sig(fn_def_id).skip_binder().output().skip_binder().kind()
            && let Some(projection_ty) = alias_ty.try_to_projection()
            && projection_ty.kind == def_id
            && let generics = self.tcx().generics_of(fn_def_id)
            // FIXME(return_type_notation): We only support lifetime params for now.
            && generics
                .own_params
                .iter()
                .all(|param| matches!(param.kind, ty::GenericParamDefKind::Lifetime))
        {
            let num_args = generics.count();
            Some((fn_def_id, &args[..num_args]))
        } else {
            None
        };

        match (fn_args, RTN_MODE.with(|c| c.get())) {
            (Some((fn_def_id, fn_args)), RtnMode::ForDiagnostic) => {
                self.pretty_print_opaque_impl_type(def_id, args)?;
                write!(self, " {{ ")?;
                self.print_def_path(fn_def_id, fn_args)?;
                write!(self, "(..) }}")?;
            }
            (Some((fn_def_id, fn_args)), RtnMode::ForSuggestion) => {
                self.print_def_path(fn_def_id, fn_args)?;
                write!(self, "(..)")?;
            }
            _ => {
                self.pretty_print_opaque_impl_type(def_id, args)?;
            }
        }

        Ok(())
    }

    fn ty_infer_name(&self, _: ty::TyVid) -> Option<Symbol> {
        None
    }

    fn const_infer_name(&self, _: ty::ConstVid) -> Option<Symbol> {
        None
    }

    fn pretty_print_dyn_existential(
        &mut self,
        predicates: &'tcx ty::List<ty::PolyExistentialPredicate<'tcx>>,
    ) -> Result<(), PrintError> {
        // Generate the main trait ref, including associated types.
        let mut first = true;

        if let Some(bound_principal) = predicates.principal() {
            self.wrap_binder(&bound_principal, WrapBinderMode::ForAll, |principal, p| {
                p.print_def_path(principal.def_id, &[])?;

                let mut resugared = false;

                // Special-case `Fn(...) -> ...` and re-sugar it.
                let fn_trait_kind = p.tcx().fn_trait_kind_from_def_id(principal.def_id);
                if !p.should_print_verbose() && fn_trait_kind.is_some() {
                    if let ty::Tuple(tys) = principal.args.type_at(0).kind() {
                        let mut projections = predicates.projection_bounds();
                        if let (Some(proj), None) = (projections.next(), projections.next()) {
                            p.pretty_print_fn_sig(
                                tys,
                                false,
                                // FIXME(splat): support splatted arguments here?
                                None,
                                proj.skip_binder().term.as_type().expect("Return type was a const"),
                            )?;
                            resugared = true;
                        }
                    }
                }

                // HACK(eddyb) this duplicates `FmtPrinter`'s `print_path_with_generic_args`,
                // in order to place the projections inside the `<...>`.
                if !resugared {
                    let principal_with_self =
                        principal.with_self_ty(p.tcx(), p.tcx().types.trait_object_dummy_self);

                    let args = p
                        .tcx()
                        .generics_of(principal_with_self.def_id)
                        .own_args_no_defaults(p.tcx(), principal_with_self.args);

                    let bound_principal_with_self = bound_principal
                        .with_self_ty(p.tcx(), p.tcx().types.trait_object_dummy_self);

                    let clause: ty::Clause<'tcx> = bound_principal_with_self.upcast(p.tcx());
                    let super_projections: Vec<_> = elaborate::elaborate(p.tcx(), [clause])
                        .filter_only_self()
                        .filter_map(|clause| clause.as_projection_clause())
                        .collect();

                    let mut projections: Vec<_> = predicates
                        .projection_bounds()
                        .filter(|&proj| {
                            // Filter out projections that are implied by the super predicates.
                            let proj_is_implied = super_projections.iter().any(|&super_proj| {
                                let super_proj = super_proj.map_bound(|super_proj| {
                                    ty::ExistentialProjection::erase_self_ty(p.tcx(), super_proj)
                                });

                                // This function is sometimes called on types with erased and
                                // anonymized regions, but the super projections can still
                                // contain named regions. So we erase and anonymize everything
                                // here to compare the types modulo regions below.
                                let proj = p.tcx().erase_and_anonymize_regions(proj);
                                let super_proj = p.tcx().erase_and_anonymize_regions(super_proj);

                                proj == super_proj
                            });
                            !proj_is_implied
                        })
                        .map(|proj| {
                            // Skip the binder, because we don't want to print the binder in
                            // front of the associated item.
                            proj.skip_binder()
                        })
                        .collect();

                    projections
                        .sort_by_cached_key(|proj| p.tcx().item_name(proj.def_id).to_string());

                    if !args.is_empty() || !projections.is_empty() {
                        p.generic_delimiters(|p| {
                            p.comma_sep(args.iter().copied())?;
                            if !args.is_empty() && !projections.is_empty() {
                                write!(p, ", ")?;
                            }
                            p.comma_sep(projections.iter().copied())
                        })?;
                    }
                }
                Ok(())
            })?;

            first = false;
        }

        // Builtin bounds.
        // FIXME(eddyb) avoid printing twice (needed to ensure
        // that the auto traits are sorted *and* printed via p).
        let mut auto_traits: Vec<_> = predicates.auto_traits().collect();

        // The auto traits come ordered by `DefPathHash`. While
        // `DefPathHash` is *stable* in the sense that it depends on
        // neither the host nor the phase of the moon, it depends
        // "pseudorandomly" on the compiler version and the target.
        //
        // To avoid causing instabilities in compiletest
        // output, sort the auto-traits alphabetically.
        auto_traits.sort_by_cached_key(|did| with_no_trimmed_paths!(self.tcx().def_path_str(*did)));

        for def_id in auto_traits {
            if !first {
                write!(self, " + ")?;
            }
            first = false;

            self.print_def_path(def_id, &[])?;
        }

        Ok(())
    }

    fn pretty_print_fn_sig(
        &mut self,
        inputs: &[Ty<'tcx>],
        c_variadic: bool,
        splatted: Option<u8>,
        output: Ty<'tcx>,
    ) -> Result<(), PrintError> {
        write!(self, "(")?;
        let splatted_arg_index = splatted.map(usize::from);
        let mut input_iter = inputs.iter().copied();
        if let Some(index) = splatted_arg_index {
            self.comma_sep((&mut input_iter).take(usize::from(index)))?;
            write!(self, ", #[rustc_splat]")?;
            self.comma_sep(input_iter)?;
        } else {
            self.comma_sep(input_iter)?;
        }
        if c_variadic {
            if !inputs.is_empty() {
                write!(self, ", ")?;
            }
            write!(self, "...")?;
        }
        write!(self, ")")?;
        if !output.is_unit() {
            write!(self, " -> ")?;
            output.print(self)?;
        }

        Ok(())
    }

    fn pretty_print_const(
        &mut self,
        ct: ty::Const<'tcx>,
        print_ty: bool,
    ) -> Result<(), PrintError> {
        if self.should_print_verbose() {
            write!(self, "{ct:?}")?;
            return Ok(());
        }

        match ct.kind() {
            ty::ConstKind::Alias(_, ty::AliasConst { kind, args, .. }) => {
                match kind {
                    ty::AliasConstKind::Projection { def_id }
                    | ty::AliasConstKind::Inherent { def_id }
                    | ty::AliasConstKind::Free { def_id } => {
                        self.pretty_print_value_path(def_id, args)?;
                    }
                    ty::AliasConstKind::Anon { def_id } => {
                        if def_id.is_local()
                            && let span = self.tcx().def_span(def_id)
                            && let Ok(snip) = self.tcx().sess.source_map().span_to_snippet(span)
                        {
                            write!(self, "{snip}")?;
                        } else {
                            // Do not call `pretty_print_value_path` as if a parent of this anon
                            // const is an impl it will attempt to print out the impl trait ref
                            // i.e. `<T as Trait>::{constant#0}`. This would cause printing to
                            // enter an infinite recursion if the anon const is in the self type
                            // i.e. `impl<T: Default> Default for [T; 32 - 1 - 1 - 1] {` where we
                            // would try to print `<[T; /* print constant#0 again */] as //
                            // Default>::{constant#0}`.
                            write!(
                                self,
                                "{}::{}",
                                self.tcx().crate_name(def_id.krate),
                                self.tcx().def_path(def_id).to_string_no_crate_verbose()
                            )?;
                        }
                    }
                }
            }
            ty::ConstKind::Infer(infer_ct) => match infer_ct {
                ty::InferConst::Var(ct_vid) if let Some(name) = self.const_infer_name(ct_vid) => {
                    write!(self, "{name}")?;
                }
                _ => write!(self, "_")?,
            },
            ty::ConstKind::Param(ParamConst { name, .. }) => write!(self, "{name}")?,
            ty::ConstKind::Value(cv) => {
                return self.pretty_print_const_valtree(cv, print_ty);
            }

            ty::ConstKind::Bound(debruijn, bound_var) => {
                rustc_type_ir::debug_bound_var(self, debruijn, bound_var)?
            }
            ty::ConstKind::Placeholder(placeholder) => write!(self, "{placeholder:?}")?,
            // FIXME(generic_const_exprs):
            // write out some legible representation of an abstract const?
            ty::ConstKind::Expr(expr) => self.pretty_print_const_expr(expr, print_ty)?,
            ty::ConstKind::Error(_) => write!(self, "{{const error}}")?,
        };
        Ok(())
    }

    fn pretty_print_const_expr(
        &mut self,
        expr: Expr<'tcx>,
        print_ty: bool,
    ) -> Result<(), PrintError> {
        match expr.kind {
            ty::ExprKind::Binop(op) => {
                let (_, _, c1, c2) = expr.binop_args();

                let precedence = |binop: crate::mir::BinOp| binop.to_hir_binop().precedence();
                let op_precedence = precedence(op);
                let formatted_op = op.to_hir_binop().as_str();
                let (lhs_parenthesized, rhs_parenthesized) = match (c1.kind(), c2.kind()) {
                    (
                        ty::ConstKind::Expr(ty::Expr { kind: ty::ExprKind::Binop(lhs_op), .. }),
                        ty::ConstKind::Expr(ty::Expr { kind: ty::ExprKind::Binop(rhs_op), .. }),
                    ) => (precedence(lhs_op) < op_precedence, precedence(rhs_op) < op_precedence),
                    (
                        ty::ConstKind::Expr(ty::Expr { kind: ty::ExprKind::Binop(lhs_op), .. }),
                        ty::ConstKind::Expr(_),
                    ) => (precedence(lhs_op) < op_precedence, true),
                    (
                        ty::ConstKind::Expr(_),
                        ty::ConstKind::Expr(ty::Expr { kind: ty::ExprKind::Binop(rhs_op), .. }),
                    ) => (true, precedence(rhs_op) < op_precedence),
                    (ty::ConstKind::Expr(_), ty::ConstKind::Expr(_)) => (true, true),
                    (
                        ty::ConstKind::Expr(ty::Expr { kind: ty::ExprKind::Binop(lhs_op), .. }),
                        _,
                    ) => (precedence(lhs_op) < op_precedence, false),
                    (
                        _,
                        ty::ConstKind::Expr(ty::Expr { kind: ty::ExprKind::Binop(rhs_op), .. }),
                    ) => (false, precedence(rhs_op) < op_precedence),
                    (ty::ConstKind::Expr(_), _) => (true, false),
                    (_, ty::ConstKind::Expr(_)) => (false, true),
                    _ => (false, false),
                };

                self.maybe_parenthesized(
                    |this| this.pretty_print_const(c1, print_ty),
                    lhs_parenthesized,
                )?;
                write!(self, " {formatted_op} ")?;
                self.maybe_parenthesized(
                    |this| this.pretty_print_const(c2, print_ty),
                    rhs_parenthesized,
                )?;
            }
            ty::ExprKind::UnOp(op) => {
                let (_, ct) = expr.unop_args();

                use crate::mir::UnOp;
                let formatted_op = match op {
                    UnOp::Not => "!",
                    UnOp::Neg => "-",
                    UnOp::PtrMetadata => "PtrMetadata",
                };
                let parenthesized = match ct.kind() {
                    _ if op == UnOp::PtrMetadata => true,
                    ty::ConstKind::Expr(ty::Expr { kind: ty::ExprKind::UnOp(c_op), .. }) => {
                        c_op != op
                    }
                    ty::ConstKind::Expr(_) => true,
                    _ => false,
                };
                write!(self, "{formatted_op}")?;
                self.maybe_parenthesized(
                    |this| this.pretty_print_const(ct, print_ty),
                    parenthesized,
                )?
            }
            ty::ExprKind::FunctionCall => {
                let (_, fn_def, fn_args) = expr.call_args();

                write!(self, "(")?;
                self.pretty_print_const(fn_def, print_ty)?;
                write!(self, ")(")?;
                self.comma_sep(fn_args)?;
                write!(self, ")")?;
            }
            ty::ExprKind::Cast(kind) => {
                let (_, value, to_ty) = expr.cast_args();

                use ty::abstract_const::CastKind;
                if kind == CastKind::As || (kind == CastKind::Use && self.should_print_verbose()) {
                    let parenthesized = match value.kind() {
                        ty::ConstKind::Expr(ty::Expr {
                            kind: ty::ExprKind::Cast { .. }, ..
                        }) => false,
                        ty::ConstKind::Expr(_) => true,
                        _ => false,
                    };
                    self.maybe_parenthesized(
                        |this| {
                            this.typed_value(
                                |this| this.pretty_print_const(value, print_ty),
                                |this| this.pretty_print_type(to_ty),
                                " as ",
                            )
                        },
                        parenthesized,
                    )?;
                } else {
                    self.pretty_print_const(value, print_ty)?
                }
            }
        }
        Ok(())
    }

    fn pretty_print_const_scalar(
        &mut self,
        scalar: Scalar,
        ty: Ty<'tcx>,
    ) -> Result<(), PrintError> {
        match scalar {
            Scalar::Ptr(ptr, _size) => self.pretty_print_const_scalar_ptr(ptr, ty),
            Scalar::Int(int) => {
                self.pretty_print_const_scalar_int(int, ty, /* print_ty */ true)
            }
        }
    }

    fn pretty_print_const_scalar_ptr(
        &mut self,
        ptr: Pointer,
        ty: Ty<'tcx>,
    ) -> Result<(), PrintError> {
        let (prov, offset) = ptr.prov_and_relative_offset();
        match ty.kind() {
            // Byte strings (&[u8; N])
            ty::Ref(_, inner, _) => {
                if let ty::Array(elem, ct_len) = inner.kind()
                    && let ty::Uint(ty::UintTy::U8) = elem.kind()
                    && let Some(len) = ct_len.try_to_target_usize(self.tcx())
                {
                    match self.tcx().try_get_global_alloc(prov.alloc_id()) {
                        Some(GlobalAlloc::Memory(alloc)) => {
                            let range = AllocRange { start: offset, size: Size::from_bytes(len) };
                            if let Ok(byte_str) =
                                alloc.inner().get_bytes_strip_provenance(&self.tcx(), range)
                            {
                                self.pretty_print_byte_str(byte_str)?;
                            } else {
                                write!(self, "<too short allocation>")?;
                            }
                        }
                        // FIXME: for statics, vtables, and functions, we could in principle print more detail.
                        Some(GlobalAlloc::Static(def_id)) => {
                            write!(self, "<static({def_id:?})>")?;
                        }
                        Some(GlobalAlloc::Function { .. }) => write!(self, "<function>")?,
                        Some(GlobalAlloc::VTable(..)) => write!(self, "<vtable>")?,
                        Some(GlobalAlloc::TypeId { .. }) => write!(self, "<typeid>")?,
                        None => write!(self, "<dangling pointer>")?,
                    }
                    return Ok(());
                }
            }
            ty::FnPtr(..) => {
                // FIXME: We should probably have a helper method to share code with the "Byte strings"
                // printing above (which also has to handle pointers to all sorts of things).
                if let Some(GlobalAlloc::Function { instance, .. }) =
                    self.tcx().try_get_global_alloc(prov.alloc_id())
                {
                    self.typed_value(
                        |this| this.pretty_print_value_path(instance.def_id(), instance.args),
                        |this| this.print_type(ty),
                        " as ",
                    )?;
                    return Ok(());
                }
            }
            _ => {}
        }
        // Any pointer values not covered by a branch above
        self.pretty_print_const_pointer(ptr, ty)?;
        Ok(())
    }

    fn pretty_print_const_scalar_int(
        &mut self,
        int: ScalarInt,
        ty: Ty<'tcx>,
        print_ty: bool,
    ) -> Result<(), PrintError> {
        match ty.kind() {
            // Bool
            ty::Bool if int == ScalarInt::FALSE => write!(self, "false")?,
            ty::Bool if int == ScalarInt::TRUE => write!(self, "true")?,
            // Float
            ty::Float(fty) => match fty {
                ty::FloatTy::F16 => {
                    let val = Half::try_from(int).unwrap();
                    write!(self, "{}{}f16", val, if val.is_finite() { "" } else { "_" })?;
                }
                ty::FloatTy::F32 => {
                    let val = Single::try_from(int).unwrap();
                    write!(self, "{}{}f32", val, if val.is_finite() { "" } else { "_" })?;
                }
                ty::FloatTy::F64 => {
                    let val = Double::try_from(int).unwrap();
                    write!(self, "{}{}f64", val, if val.is_finite() { "" } else { "_" })?;
                }
                ty::FloatTy::F128 => {
                    let val = Quad::try_from(int).unwrap();
                    write!(self, "{}{}f128", val, if val.is_finite() { "" } else { "_" })?;
                }
            },
            // Int
            ty::Uint(_) | ty::Int(_) => {
                let int =
                    ConstInt::new(int, matches!(ty.kind(), ty::Int(_)), ty.is_ptr_sized_integral());
                if print_ty { write!(self, "{int:#?}")? } else { write!(self, "{int:?}")? }
            }
            // Char
            ty::Char if char::try_from(int).is_ok() => {
                write!(self, "{:?}", char::try_from(int).unwrap())?;
            }
            // Pointer types
            ty::Ref(..) | ty::RawPtr(_, _) | ty::FnPtr(..) => {
                let data = int.to_bits(self.tcx().data_layout.pointer_size());
                self.typed_value(
                    |this| {
                        write!(this, "0x{data:x}")?;
                        Ok(())
                    },
                    |this| this.print_type(ty),
                    " as ",
                )?;
            }
            ty::Pat(base_ty, pat) if self.tcx().validate_scalar_in_layout(int, ty) => {
                self.pretty_print_const_scalar_int(int, *base_ty, print_ty)?;
                write!(self, " is {pat:?}")?;
            }
            // Nontrivial types with scalar bit representation
            _ => {
                let print = |this: &mut Self| {
                    if int.size() == Size::ZERO {
                        write!(this, "transmute(())")?;
                    } else {
                        write!(this, "transmute(0x{int:x})")?;
                    }
                    Ok(())
                };
                if print_ty {
                    self.typed_value(print, |this| this.print_type(ty), ": ")?
                } else {
                    print(self)?
                };
            }
        }
        Ok(())
    }

    /// This is overridden for MIR printing because we only want to hide alloc ids from users, not
    /// from MIR where it is actually useful.
    fn pretty_print_const_pointer<Prov: Provenance>(
        &mut self,
        _: Pointer<Prov>,
        ty: Ty<'tcx>,
    ) -> Result<(), PrintError> {
        self.typed_value(
            |this| {
                this.write_str("&_")?;
                Ok(())
            },
            |this| this.print_type(ty),
            ": ",
        )
    }

    fn pretty_print_byte_str(&mut self, byte_str: &'tcx [u8]) -> Result<(), PrintError> {
        write!(self, "b\"{}\"", byte_str.escape_ascii())?;
        Ok(())
    }

    fn pretty_print_const_valtree(
        &mut self,
        cv: ty::Value<'tcx>,
        print_ty: bool,
    ) -> Result<(), PrintError> {
        if with_reduced_queries() || self.should_print_verbose() {
            write!(self, "ValTree({:?}: ", cv.valtree)?;
            cv.ty.print(self)?;
            write!(self, ")")?;
            return Ok(());
        }

        let u8_type = self.tcx().types.u8;
        match (*cv.valtree, *cv.ty.kind()) {
            (ty::ValTreeKind::Branch(_), ty::Ref(_, inner_ty, _)) => match inner_ty.kind() {
                ty::Slice(t) if *t == u8_type => {
                    let bytes = cv.try_to_raw_bytes(self.tcx()).unwrap_or_else(|| {
                        bug!(
                            "expected to convert valtree {:?} to raw bytes for type {:?}",
                            cv.valtree,
                            t
                        )
                    });
                    return self.pretty_print_byte_str(bytes);
                }
                ty::Str => {
                    let bytes = cv.try_to_raw_bytes(self.tcx()).unwrap_or_else(|| {
                        bug!("expected to convert valtree to raw bytes for type {:?}", cv.ty)
                    });
                    write!(self, "{:?}", String::from_utf8_lossy(bytes))?;
                    return Ok(());
                }
                _ => {
                    let cv = ty::Value { valtree: cv.valtree, ty: inner_ty };
                    write!(self, "&")?;
                    self.pretty_print_const_valtree(cv, print_ty)?;
                    return Ok(());
                }
            },
            // If it is a branch with an array, and this array can be printed as raw bytes, then dump its bytes
            (ty::ValTreeKind::Branch(_), ty::Array(t, _))
                if t == u8_type
                    && let Some(bytes) = cv.try_to_raw_bytes(self.tcx()) =>
            {
                write!(self, "*")?;
                self.pretty_print_byte_str(bytes)?;
                return Ok(());
            }
            // Otherwise, print the array separated by commas (or if it's a tuple)
            (ty::ValTreeKind::Branch(fields), ty::Array(..) | ty::Tuple(..)) => {
                let fields_iter = fields.iter();

                match *cv.ty.kind() {
                    ty::Array(..) => {
                        write!(self, "[")?;
                        self.comma_sep(fields_iter)?;
                        write!(self, "]")?;
                    }
                    ty::Tuple(..) => {
                        write!(self, "(")?;
                        self.comma_sep(fields_iter)?;
                        if fields.len() == 1 {
                            write!(self, ",")?;
                        }
                        write!(self, ")")?;
                    }
                    _ => unreachable!(),
                }
                return Ok(());
            }
            (ty::ValTreeKind::Branch(_), ty::Adt(def, args)) => {
                let contents = cv.destructure_adt_const();
                let fields = contents.fields.iter().copied();

                if def.variants().is_empty() {
                    self.typed_value(
                        |this| {
                            write!(this, "unreachable()")?;
                            Ok(())
                        },
                        |this| this.print_type(cv.ty),
                        ": ",
                    )?;
                } else {
                    let variant_idx = contents.variant;
                    let variant_def = &def.variant(variant_idx);
                    self.pretty_print_value_path(variant_def.def_id, args)?;
                    match variant_def.ctor_kind() {
                        Some(CtorKind::Const) => {}
                        Some(CtorKind::Fn) => {
                            write!(self, "(")?;
                            self.comma_sep(fields)?;
                            write!(self, ")")?;
                        }
                        None => {
                            write!(self, " {{ ")?;
                            let mut first = true;
                            for (field_def, field) in iter::zip(&variant_def.fields, fields) {
                                if !first {
                                    write!(self, ", ")?;
                                }
                                write!(self, "{}: ", field_def.name)?;
                                field.print(self)?;
                                first = false;
                            }
                            write!(self, " }}")?;
                        }
                    }
                }
                return Ok(());
            }
            (ty::ValTreeKind::Leaf(leaf), ty::Ref(_, inner_ty, _)) => {
                write!(self, "&")?;
                return self.pretty_print_const_scalar_int(*leaf, inner_ty, print_ty);
            }
            (ty::ValTreeKind::Leaf(leaf), _) => {
                return self.pretty_print_const_scalar_int(*leaf, cv.ty, print_ty);
            }
            (_, ty::FnDef(def_id, args)) => {
                // Never allowed today, but we still encounter them in invalid const args.
                // FIXME(addiesh): fix wrt late-bound stuff
                self.pretty_print_value_path(def_id, args.no_bound_vars().unwrap())?;
                return Ok(());
            }
            // FIXME(oli-obk): also pretty print arrays and other aggregate constants by reading
            // their fields instead of just dumping the memory.
            _ => {}
        }

        // fallback
        if cv.valtree.is_zst() {
            write!(self, "<ZST>")?;
        } else {
            write!(self, "{:?}", cv.valtree)?;
        }
        if print_ty {
            write!(self, ": ")?;
            cv.ty.print(self)?;
        }
        Ok(())
    }

    fn pretty_print_closure_as_impl(
        &mut self,
        closure: ty::ClosureArgs<TyCtxt<'tcx>>,
    ) -> Result<(), PrintError> {
        let sig = closure.sig();
        let kind = closure.kind_ty().to_opt_closure_kind().unwrap_or(ty::ClosureKind::Fn);

        write!(self, "impl ")?;
        self.wrap_binder(&sig, WrapBinderMode::ForAll, |sig, p| {
            write!(p, "{kind}(")?;
            for (i, arg) in sig.inputs()[0].tuple_fields().iter().enumerate() {
                if i > 0 {
                    write!(p, ", ")?;
                }
                arg.print(p)?;
            }
            write!(p, ")")?;

            if !sig.output().is_unit() {
                write!(p, " -> ")?;
                sig.output().print(p)?;
            }

            Ok(())
        })
    }

    fn pretty_print_bound_constness(
        &mut self,
        constness: ty::BoundConstness,
    ) -> Result<(), PrintError> {
        match constness {
            ty::BoundConstness::Const => write!(self, "const ")?,
            ty::BoundConstness::Maybe => write!(self, "[const] ")?,
        }
        Ok(())
    }

    fn should_print_verbose(&self) -> bool {
        self.tcx().sess.verbose_internals()
    }
}

pub(crate) fn pretty_print_const<'tcx>(
    c: ty::Const<'tcx>,
    fmt: &mut fmt::Formatter<'_>,
    print_types: bool,
) -> fmt::Result {
    ty::tls::with(|tcx| {
        let mut p = FmtPrinter::new(tcx, Namespace::ValueNS);
        p.print_alloc_ids = true;
        p.pretty_print_const(tcx.lift(c), print_types)?;
        fmt.write_str(&p.into_buffer())?;
        Ok(())
    })
}

// HACK(eddyb) boxed to avoid moving around a large struct by-value.
pub struct FmtPrinter<'a, 'tcx>(Box<FmtPrinterData<'a, 'tcx>>);

pub struct FmtPrinterData<'a, 'tcx> {
    tcx: TyCtxt<'tcx>,
    fmt: String,

    empty_path: bool,
    in_value: bool,
    pub print_alloc_ids: bool,

    // set of all named (non-anonymous) region names
    used_region_names: FxHashSet<Symbol>,

    region_index: usize,
    binder_depth: usize,
    printed_type_count: usize,
    type_length_limit: Limit,

    pub region_highlight_mode: RegionHighlightMode<'tcx>,

    pub ty_infer_name_resolver: Option<Box<dyn Fn(ty::TyVid) -> Option<Symbol> + 'a>>,
    pub const_infer_name_resolver: Option<Box<dyn Fn(ty::ConstVid) -> Option<Symbol> + 'a>>,
}

impl<'a, 'tcx> Deref for FmtPrinter<'a, 'tcx> {
    type Target = FmtPrinterData<'a, 'tcx>;
    fn deref(&self) -> &Self::Target {
        &self.0
    }
}

impl DerefMut for FmtPrinter<'_, '_> {
    fn deref_mut(&mut self) -> &mut Self::Target {
        &mut self.0
    }
}

impl<'a, 'tcx> FmtPrinter<'a, 'tcx> {
    pub fn new(tcx: TyCtxt<'tcx>, ns: Namespace) -> Self {
        let limit =
            if with_reduced_queries() { Limit::new(1048576) } else { tcx.type_length_limit() };
        Self::new_with_limit(tcx, ns, limit)
    }

    pub fn print_string(
        tcx: TyCtxt<'tcx>,
        ns: Namespace,
        f: impl FnOnce(&mut Self) -> Result<(), PrintError>,
    ) -> Result<String, PrintError> {
        let mut c = FmtPrinter::new(tcx, ns);
        f(&mut c)?;
        Ok(c.into_buffer())
    }

    pub fn new_with_limit(tcx: TyCtxt<'tcx>, ns: Namespace, type_length_limit: Limit) -> Self {
        FmtPrinter(Box::new(FmtPrinterData {
            tcx,
            // Estimated reasonable capacity to allocate upfront based on a few
            // benchmarks.
            fmt: String::with_capacity(64),
            empty_path: false,
            in_value: ns == Namespace::ValueNS,
            print_alloc_ids: false,
            used_region_names: Default::default(),
            region_index: 0,
            binder_depth: 0,
            printed_type_count: 0,
            type_length_limit,
            region_highlight_mode: RegionHighlightMode::default(),
            ty_infer_name_resolver: None,
            const_infer_name_resolver: None,
        }))
    }

    pub fn into_buffer(self) -> String {
        self.0.fmt
    }
}

fn guess_def_namespace(tcx: TyCtxt<'_>, def_id: DefId) -> Namespace {
    match tcx.def_key(def_id).disambiguated_data.data {
        DefPathData::TypeNs(..) | DefPathData::CrateRoot | DefPathData::OpaqueTy => {
            Namespace::TypeNS
        }

        DefPathData::ValueNs(..)
        | DefPathData::AnonConst
        | DefPathData::Closure
        | DefPathData::Ctor => Namespace::ValueNS,

        DefPathData::MacroNs(..) => Namespace::MacroNS,

        _ => Namespace::TypeNS,
    }
}

impl<'t> TyCtxt<'t> {
    /// Returns a string identifying this `DefId`. This string is
    /// suitable for user output.
    pub fn def_path_str(self, def_id: impl IntoQueryKey<DefId>) -> String {
        let def_id = def_id.into_query_key();
        self.def_path_str_with_args(def_id, &[])
    }

    /// For this one we determine the appropriate namespace for the `def_id`.
    pub fn def_path_str_with_args(
        self,
        def_id: impl IntoQueryKey<DefId>,
        args: &'t [GenericArg<'t>],
    ) -> String {
        let def_id = def_id.into_query_key();
        let ns = guess_def_namespace(self, def_id);
        debug!("def_path_str: def_id={:?}, ns={:?}", def_id, ns);

        FmtPrinter::print_string(self, ns, |p| p.print_def_path(def_id, args)).unwrap()
    }

    /// For this one we always use value namespace.
    pub fn value_path_str_with_args(
        self,
        def_id: impl IntoQueryKey<DefId>,
        args: &'t [GenericArg<'t>],
    ) -> String {
        let def_id = def_id.into_query_key();
        let ns = Namespace::ValueNS;
        debug!("value_path_str: def_id={:?}, ns={:?}", def_id, ns);

        FmtPrinter::print_string(self, ns, |p| p.print_def_path(def_id, args)).unwrap()
    }
}

impl fmt::Write for FmtPrinter<'_, '_> {
    fn write_str(&mut self, s: &str) -> fmt::Result {
        self.fmt.push_str(s);
        Ok(())
    }
}

impl<'tcx> Printer<'tcx> for FmtPrinter<'_, 'tcx> {
    fn tcx<'a>(&'a self) -> TyCtxt<'tcx> {
        self.tcx
    }

    fn reset_path(&mut self) -> Result<(), PrintError> {
        self.empty_path = true;
        Ok(())
    }

    fn should_omit_parent_def_path(&self, parent_def_id: DefId) -> bool {
        RTN_MODE.with(|mode| mode.get()) == RtnMode::ForSuggestion
            && matches!(
                self.tcx().def_key(parent_def_id).disambiguated_data.data,
                DefPathData::ValueNs(..) | DefPathData::Closure | DefPathData::AnonConst
            )
    }

    fn print_def_path(
        &mut self,
        def_id: DefId,
        args: &'tcx [GenericArg<'tcx>],
    ) -> Result<(), PrintError> {
        if args.is_empty() {
            match self.try_print_trimmed_def_path(def_id)? {
                true => return Ok(()),
                false => {}
            }

            match self.try_print_visible_def_path(def_id)? {
                true => return Ok(()),
                false => {}
            }
        }

        let key = self.tcx.def_key(def_id);
        if let DefPathData::Impl = key.disambiguated_data.data {
            // Always use types for non-local impls, where types are always
            // available, and filename/line-number is mostly uninteresting.
            let use_types = !def_id.is_local() || {
                // Otherwise, use filename/line-number if forced.
                let force_no_types = with_forced_impl_filename_line();
                !force_no_types
            };

            if !use_types {
                // If no type info is available, fall back to
                // pretty printing some span information. This should
                // only occur very early in the compiler pipeline.
                let parent_def_id = DefId { index: key.parent.unwrap(), ..def_id };
                let span = self.tcx.def_span(def_id);

                self.print_def_path(parent_def_id, &[])?;

                // HACK(eddyb) copy of `print_path_with_simple` to avoid
                // constructing a `DisambiguatedDefPathData`.
                if !self.empty_path {
                    write!(self, "::")?;
                }
                write!(
                    self,
                    "<impl at {}>",
                    // This may end up in stderr diagnostics but it may also be emitted
                    // into MIR. Hence we use the remapped path if available
                    self.tcx.sess.source_map().span_to_diagnostic_string(span)
                )?;
                self.empty_path = false;

                return Ok(());
            }
        }

        self.default_print_def_path(def_id, args)
    }

    fn print_region(&mut self, region: ty::Region<'tcx>) -> Result<(), PrintError> {
        self.pretty_print_region(region)
    }

    fn print_type(&mut self, ty: Ty<'tcx>) -> Result<(), PrintError> {
        let has_regions = self.region_highlight_mode.keep_regions
            && ty.has_type_flags(ty::TypeFlags::HAS_REGIONS);
        match ty.kind() {
            ty::Tuple(tys) if tys.len() == 0 => {
                // Don't truncate `()`.
                self.pretty_print_type(ty)
            }

            ty::Adt(def, args)
                if self.should_truncate()
                    && args.consts().count() < 2
                    && args.types().count() < 2
                    && {
                        // We ensure that if there's at most a single type parameter and that type
                        // *doesn't* have any parameters, to avoid printing all the names in cases
                        // like `Foo<Foo<Foo<Foo<...>>>`, instead truncating those always to
                        // `Foo<...>`.
                        if let Some(arg) = args.types().next() {
                            if let ty::Adt(_, arg_args) = arg.kind() {
                                if arg_args.consts().next().is_none()
                                    && arg_args.types().next().is_none()
                                {
                                    // Single param type with no type or const parameters:
                                    // `Foo<Bar<'a>>`.
                                    true
                                } else {
                                    // Single param type with multiple type or const parameters:
                                    // `Foo<Bar<Baz, Qux>>`. We don't want to recurse into those,
                                    // we'll replace the whole thing with `...`.
                                    false
                                }
                            } else {
                                // Single type param that *isn't* a type with parameters, like a
                                // primitive: `Foo<i32>`.
                                true
                            }
                        } else {
                            // No type param: `Foo`.
                            true
                        }
                    }
                    && self.tcx.item_name(def.did()).as_str().len() < 7 =>
            {
                // Don't fully truncate types that have "short names" and at most one type or const
                // param. We do use the short path for them (only item name instead of full path).
                with_forced_trimmed_paths!(self.pretty_print_type(ty))
            }

            ty::Alias(_, alias)
                if self.should_truncate()
                    && let ty::AliasTyKind::Opaque { def_id } = alias.kind
                    && self.region_highlight_mode.keep_regions
                    && self
                        .tcx
                        .explicit_item_bounds(def_id)
                        .iter_instantiated_copied(self.tcx, alias.args)
                        .map(Unnormalized::skip_norm_wip)
                        .any(|(value, _)| value.has_bound_vars()) =>
            {
                // `<impl for<'a> Trait as Trait>`
                self.printed_type_count += 1;
                self.pretty_print_type(ty)
            }

            ty::Adt(..)
            | ty::Foreign(_)
            | ty::Pat(..)
            | ty::RawPtr(..)
            | ty::Ref(..)
            | ty::FnDef(..)
            | ty::FnPtr(..)
            | ty::UnsafeBinder(..)
            | ty::Dynamic(..)
            | ty::CoroutineClosure(..)
            | ty::Coroutine(..)
            | ty::CoroutineWitness(..)
            | ty::Tuple(_)
            | ty::Alias(..)
            | ty::Bound(..)
            | ty::Placeholder(_)
            | ty::Error(_)
                if self.should_truncate() && !has_regions =>
            {
                // We only truncate types that we know are likely to be much longer than 3 chars.
                // There's no point in replacing `i32` or `!`.
                write!(self, "_")?;
                Ok(())
            }
            ty::Ref(..) if self.should_truncate() && has_regions => self.pretty_print_type(ty),
            ty::Closure(..) => self.pretty_print_type(ty),
            _ => {
                self.printed_type_count += 1;
                self.pretty_print_type(ty)
            }
        }
    }

    fn print_dyn_existential(
        &mut self,
        predicates: &'tcx ty::List<ty::PolyExistentialPredicate<'tcx>>,
    ) -> Result<(), PrintError> {
        self.pretty_print_dyn_existential(predicates)
    }

    fn print_const(&mut self, ct: ty::Const<'tcx>) -> Result<(), PrintError> {
        self.pretty_print_const(ct, false)
    }

    fn print_crate_name(&mut self, cnum: CrateNum) -> Result<(), PrintError> {
        self.empty_path = true;
        if cnum == LOCAL_CRATE && !with_resolve_crate_name() {
            if self.tcx.sess.at_least_rust_2018() {
                // We add the `crate::` keyword on Rust 2018, only when desired.
                if with_crate_prefix() {
                    write!(self, "{}", kw::Crate)?;
                    self.empty_path = false;
                }
            }
        } else {
            write!(self, "{}", self.tcx.crate_name(cnum))?;
            self.empty_path = false;
        }
        Ok(())
    }

    fn print_path_with_qualified(
        &mut self,
        self_ty: Ty<'tcx>,
        trait_ref: Option<ty::TraitRef<'tcx>>,
    ) -> Result<(), PrintError> {
        self.pretty_print_path_with_qualified(self_ty, trait_ref)?;
        self.empty_path = false;
        Ok(())
    }

    fn print_path_with_impl(
        &mut self,
        print_prefix: impl FnOnce(&mut Self) -> Result<(), PrintError>,
        self_ty: Ty<'tcx>,
        trait_ref: Option<ty::TraitRef<'tcx>>,
    ) -> Result<(), PrintError> {
        self.pretty_print_path_with_impl(
            |p| {
                print_prefix(p)?;
                if !p.empty_path {
                    write!(p, "::")?;
                }

                Ok(())
            },
            self_ty,
            trait_ref,
        )?;
        self.empty_path = false;
        Ok(())
    }

    fn print_path_with_simple(
        &mut self,
        print_prefix: impl FnOnce(&mut Self) -> Result<(), PrintError>,
        disambiguated_data: &DisambiguatedDefPathData,
    ) -> Result<(), PrintError> {
        print_prefix(self)?;

        // Skip `::{{extern}}` blocks and `::{{constructor}}` on tuple/unit structs.
        if let DefPathData::ForeignMod | DefPathData::Ctor = disambiguated_data.data {
            return Ok(());
        }

        let name = disambiguated_data.data.name();
        if !self.empty_path {
            write!(self, "::")?;
        }

        if let DefPathDataName::Named(name) = name {
            if Ident::with_dummy_span(name).is_raw_guess() {
                write!(self, "r#")?;
            }
        }

        let verbose = self.should_print_verbose();
        write!(self, "{}", disambiguated_data.as_sym(verbose))?;

        self.empty_path = false;

        Ok(())
    }

    fn print_path_with_generic_args(
        &mut self,
        print_prefix: impl FnOnce(&mut Self) -> Result<(), PrintError>,
        args: &[GenericArg<'tcx>],
    ) -> Result<(), PrintError> {
        print_prefix(self)?;

        if !args.is_empty() {
            if self.in_value {
                write!(self, "::")?;
            }
            self.generic_delimiters(|p| p.comma_sep(args.iter().copied()))
        } else {
            Ok(())
        }
    }
}

impl<'tcx> PrettyPrinter<'tcx> for FmtPrinter<'_, 'tcx> {
    fn ty_infer_name(&self, id: ty::TyVid) -> Option<Symbol> {
        self.0.ty_infer_name_resolver.as_ref().and_then(|func| func(id))
    }

    fn reset_type_limit(&mut self) {
        self.printed_type_count = 0;
    }

    fn const_infer_name(&self, id: ty::ConstVid) -> Option<Symbol> {
        self.0.const_infer_name_resolver.as_ref().and_then(|func| func(id))
    }

    fn pretty_print_value_path(
        &mut self,
        def_id: DefId,
        args: &'tcx [GenericArg<'tcx>],
    ) -> Result<(), PrintError> {
        let was_in_value = std::mem::replace(&mut self.in_value, true);
        self.print_def_path(def_id, args)?;
        self.in_value = was_in_value;

        Ok(())
    }

    fn pretty_print_in_binder<T>(&mut self, value: &ty::Binder<'tcx, T>) -> Result<(), PrintError>
    where
        T: Print<Self> + TypeFoldable<TyCtxt<'tcx>>,
    {
        self.wrap_binder(value, WrapBinderMode::ForAll, |new_value, this| new_value.print(this))
    }

    fn wrap_binder<T, C: FnOnce(&T, &mut Self) -> Result<(), PrintError>>(
        &mut self,
        value: &ty::Binder<'tcx, T>,
        mode: WrapBinderMode,
        f: C,
    ) -> Result<(), PrintError>
    where
        T: TypeFoldable<TyCtxt<'tcx>>,
    {
        let old_region_index = self.region_index;
        let (new_value, _) = self.name_all_regions(value, mode)?;
        f(&new_value, self)?;
        self.region_index = old_region_index;
        self.binder_depth -= 1;
        Ok(())
    }

    fn typed_value(
        &mut self,
        f: impl FnOnce(&mut Self) -> Result<(), PrintError>,
        t: impl FnOnce(&mut Self) -> Result<(), PrintError>,
        conversion: &str,
    ) -> Result<(), PrintError> {
        self.write_str("{")?;
        f(self)?;
        self.write_str(conversion)?;
        let was_in_value = std::mem::replace(&mut self.in_value, false);
        t(self)?;
        self.in_value = was_in_value;
        self.write_str("}")?;
        Ok(())
    }

    fn generic_delimiters(
        &mut self,
        f: impl FnOnce(&mut Self) -> Result<(), PrintError>,
    ) -> Result<(), PrintError> {
        write!(self, "<")?;

        let was_in_value = std::mem::replace(&mut self.in_value, false);
        f(self)?;
        self.in_value = was_in_value;

        write!(self, ">")?;
        Ok(())
    }

    fn should_truncate(&mut self) -> bool {
        !self.type_length_limit.value_within_limit(self.printed_type_count)
    }

    fn should_print_optional_region(&self, region: ty::Region<'tcx>) -> bool {
        let highlight = self.region_highlight_mode;
        if highlight.region_highlighted(region).is_some() {
            return true;
        }

        if self.should_print_verbose() {
            return true;
        }

        if with_forced_trimmed_paths() {
            return false;
        }

        let identify_regions = self.tcx.sess.opts.unstable_opts.identify_regions;

        match region.kind() {
            ty::ReEarlyParam(ref data) => data.is_named(),

            ty::ReLateParam(ty::LateParamRegion { kind, .. }) => kind.is_named(self.tcx),
            ty::ReBound(_, ty::BoundRegion { kind: br, .. })
            | ty::RePlaceholder(ty::Placeholder {
                bound: ty::BoundRegion { kind: br, .. }, ..
            }) => {
                if br.is_named(self.tcx) {
                    return true;
                }

                if let Some((region, _)) = highlight.highlight_bound_region {
                    if br == region {
                        return true;
                    }
                }

                false
            }

            ty::ReVar(_) if identify_regions => true,

            ty::ReVar(_) | ty::ReErased | ty::ReError(_) => false,

            ty::ReStatic => true,
        }
    }

    fn pretty_print_const_pointer<Prov: Provenance>(
        &mut self,
        p: Pointer<Prov>,
        ty: Ty<'tcx>,
    ) -> Result<(), PrintError> {
        let print = |this: &mut Self| {
            if this.print_alloc_ids {
                write!(this, "{p:?}")?;
            } else {
                write!(this, "&_")?;
            }
            Ok(())
        };
        self.typed_value(print, |this| this.print_type(ty), ": ")
    }
}

// HACK(eddyb) limited to `FmtPrinter` because of `region_highlight_mode`.
impl<'tcx> FmtPrinter<'_, 'tcx> {
    pub fn pretty_print_region(&mut self, region: ty::Region<'tcx>) -> Result<(), fmt::Error> {
        // Watch out for region highlights.
        let highlight = self.region_highlight_mode;
        if let Some(n) = highlight.region_highlighted(region) {
            write!(self, "'{n}")?;
            return Ok(());
        }

        if self.should_print_verbose() {
            write!(self, "{region:?}")?;
            return Ok(());
        }

        let identify_regions = self.tcx.sess.opts.unstable_opts.identify_regions;

        // These printouts are concise. They do not contain all the information
        // the user might want to diagnose an error, but there is basically no way
        // to fit that into a short string. Hence the recommendation to use
        // `explain_region()` or `note_and_explain_region()`.
        match region.kind() {
            ty::ReEarlyParam(data) => {
                write!(self, "{}", data.name)?;
                return Ok(());
            }
            ty::ReLateParam(ty::LateParamRegion { kind, .. }) => {
                if let Some(name) = kind.get_name(self.tcx) {
                    write!(self, "{name}")?;
                    return Ok(());
                }
            }
            ty::ReBound(_, ty::BoundRegion { kind: br, .. })
            | ty::RePlaceholder(ty::Placeholder {
                bound: ty::BoundRegion { kind: br, .. }, ..
            }) => {
                if let Some(name) = br.get_name(self.tcx) {
                    write!(self, "{name}")?;
                    return Ok(());
                }

                if let Some((region, counter)) = highlight.highlight_bound_region {
                    if br == region {
                        write!(self, "'{counter}")?;
                        return Ok(());
                    }
                }
            }
            ty::ReVar(region_vid) if identify_regions => {
                write!(self, "{region_vid:?}")?;
                return Ok(());
            }
            ty::ReVar(_) => {}
            ty::ReErased => {}
            ty::ReError(_) => {}
            ty::ReStatic => {
                write!(self, "'static")?;
                return Ok(());
            }
        }

        write!(self, "'_")?;

        Ok(())
    }
}

/// Folds through bound vars and placeholders, naming them
struct RegionFolder<'a, 'tcx> {
    tcx: TyCtxt<'tcx>,
    current_index: ty::DebruijnIndex,
    region_map: UnordMap<ty::BoundRegion<'tcx>, ty::Region<'tcx>>,
    name: &'a mut (
                dyn FnMut(
        Option<ty::DebruijnIndex>, // Debruijn index of the folded late-bound region
        ty::DebruijnIndex,         // Index corresponding to binder level
        ty::BoundRegion<'tcx>,
    ) -> ty::Region<'tcx>
                    + 'a
            ),
}

impl<'a, 'tcx> ty::TypeFolder<TyCtxt<'tcx>> for RegionFolder<'a, 'tcx> {
    fn cx(&self) -> TyCtxt<'tcx> {
        self.tcx
    }

    fn fold_binder<T: TypeFoldable<TyCtxt<'tcx>>>(
        &mut self,
        t: ty::Binder<'tcx, T>,
    ) -> ty::Binder<'tcx, T> {
        self.current_index.shift_in(1);
        let t = t.super_fold_with(self);
        self.current_index.shift_out(1);
        t
    }

    fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
        match *t.kind() {
            _ if t.has_vars_bound_at_or_above(self.current_index) || t.has_placeholders() => {
                return t.super_fold_with(self);
            }
            _ => {}
        }
        t
    }

    fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
        let name = &mut self.name;
        let region = match r.kind() {
            ty::ReBound(ty::BoundVarIndexKind::Bound(db), br) if db >= self.current_index => {
                *self.region_map.entry(br).or_insert_with(|| name(Some(db), self.current_index, br))
            }
            ty::RePlaceholder(ty::PlaceholderRegion {
                bound: ty::BoundRegion { kind, .. },
                ..
            }) => {
                // If this is an anonymous placeholder, don't rename. Otherwise, in some
                // async fns, we get a `for<'r> Send` bound
                match kind {
                    ty::BoundRegionKind::Anon | ty::BoundRegionKind::ClosureEnv => r,
                    _ => {
                        // Index doesn't matter, since this is just for naming and these never get bound
                        let br = ty::BoundRegion { var: ty::BoundVar::ZERO, kind };
                        *self
                            .region_map
                            .entry(br)
                            .or_insert_with(|| name(None, self.current_index, br))
                    }
                }
            }
            _ => return r,
        };
        if let ty::ReBound(ty::BoundVarIndexKind::Bound(debruijn1), br) = region.kind() {
            assert_eq!(debruijn1, ty::INNERMOST);
            ty::Region::new_bound(self.tcx, self.current_index, br)
        } else {
            region
        }
    }
}

// HACK(eddyb) limited to `FmtPrinter` because of `binder_depth`,
// `region_index` and `used_region_names`.
impl<'tcx> FmtPrinter<'_, 'tcx> {
    pub fn name_all_regions<T>(
        &mut self,
        value: &ty::Binder<'tcx, T>,
        mode: WrapBinderMode,
    ) -> Result<(T, UnordMap<ty::BoundRegion<'tcx>, ty::Region<'tcx>>), fmt::Error>
    where
        T: TypeFoldable<TyCtxt<'tcx>>,
    {
        fn name_by_region_index(
            index: usize,
            available_names: &mut Vec<Symbol>,
            num_available: usize,
        ) -> Symbol {
            if let Some(name) = available_names.pop() {
                name
            } else {
                Symbol::intern(&format!("'z{}", index - num_available))
            }
        }

        debug!("name_all_regions");

        // Replace any anonymous late-bound regions with named
        // variants, using new unique identifiers, so that we can
        // clearly differentiate between named and unnamed regions in
        // the output. We'll probably want to tweak this over time to
        // decide just how much information to give.
        if self.binder_depth == 0 {
            self.prepare_region_info(value);
        }

        debug!("self.used_region_names: {:?}", self.used_region_names);

        let mut empty = true;
        let mut start_or_continue = |p: &mut Self, start: &str, cont: &str| {
            let w = if empty {
                empty = false;
                start
            } else {
                cont
            };
            let _ = write!(p, "{w}");
        };
        let do_continue = |p: &mut Self, cont: Symbol| {
            let _ = write!(p, "{cont}");
        };

        let possible_names = ('a'..='z').rev().map(|s| Symbol::intern(&format!("'{s}")));

        let mut available_names = possible_names
            .filter(|name| !self.used_region_names.contains(name))
            .collect::<Vec<_>>();
        debug!(?available_names);
        let num_available = available_names.len();

        let mut region_index = self.region_index;
        let mut next_name = |this: &Self| {
            let mut name;

            loop {
                name = name_by_region_index(region_index, &mut available_names, num_available);
                region_index += 1;

                if !this.used_region_names.contains(&name) {
                    break;
                }
            }

            name
        };

        // If we want to print verbosely, then print *all* binders, even if they
        // aren't named. Eventually, we might just want this as the default, but
        // this is not *quite* right and changes the ordering of some output
        // anyways.
        let (new_value, map) = if self.should_print_verbose() {
            for var in value.bound_vars().iter() {
                start_or_continue(self, mode.start_str(), ", ");
                write!(self, "{var:?}")?;
            }
            // Unconditionally render `unsafe<>`.
            if value.bound_vars().is_empty() && mode == WrapBinderMode::Unsafe {
                start_or_continue(self, mode.start_str(), "");
            }
            start_or_continue(self, "", "> ");
            (value.clone().skip_binder(), UnordMap::default())
        } else {
            let tcx = self.tcx;

            let trim_path = with_forced_trimmed_paths();
            // Closure used in `RegionFolder` to create names for anonymous late-bound
            // regions. We use two `DebruijnIndex`es (one for the currently folded
            // late-bound region and the other for the binder level) to determine
            // whether a name has already been created for the currently folded region,
            // see issue #102392.
            let mut name = |lifetime_idx: Option<ty::DebruijnIndex>,
                            binder_level_idx: ty::DebruijnIndex,
                            br: ty::BoundRegion<'tcx>| {
                let (name, kind) = if let Some(name) = br.kind.get_name(tcx) {
                    (name, br.kind)
                } else {
                    let name = next_name(self);
                    (name, ty::BoundRegionKind::NamedForPrinting(name))
                };

                if let Some(lt_idx) = lifetime_idx {
                    if lt_idx > binder_level_idx {
                        return ty::Region::new_bound(
                            tcx,
                            ty::INNERMOST,
                            ty::BoundRegion { var: br.var, kind },
                        );
                    }
                }

                // Unconditionally render `unsafe<>`.
                if !trim_path || mode == WrapBinderMode::Unsafe {
                    start_or_continue(self, mode.start_str(), ", ");
                    do_continue(self, name);
                }
                ty::Region::new_bound(tcx, ty::INNERMOST, ty::BoundRegion { var: br.var, kind })
            };
            let mut folder = RegionFolder {
                tcx,
                current_index: ty::INNERMOST,
                name: &mut name,
                region_map: UnordMap::default(),
            };
            let new_value = value.clone().skip_binder().fold_with(&mut folder);
            let region_map = folder.region_map;

            if mode == WrapBinderMode::Unsafe && region_map.is_empty() {
                start_or_continue(self, mode.start_str(), "");
            }
            start_or_continue(self, "", "> ");

            (new_value, region_map)
        };

        self.binder_depth += 1;
        self.region_index = region_index;
        Ok((new_value, map))
    }

    fn prepare_region_info<T>(&mut self, value: &ty::Binder<'tcx, T>)
    where
        T: TypeFoldable<TyCtxt<'tcx>>,
    {
        struct RegionNameCollector<'tcx> {
            tcx: TyCtxt<'tcx>,
            used_region_names: FxHashSet<Symbol>,
            type_collector: SsoHashSet<Ty<'tcx>>,
        }

        impl<'tcx> RegionNameCollector<'tcx> {
            fn new(tcx: TyCtxt<'tcx>) -> Self {
                RegionNameCollector {
                    tcx,
                    used_region_names: Default::default(),
                    type_collector: SsoHashSet::new(),
                }
            }
        }

        impl<'tcx> ty::TypeVisitor<TyCtxt<'tcx>> for RegionNameCollector<'tcx> {
            fn visit_region(&mut self, r: ty::Region<'tcx>) {
                trace!("address: {:p}", r.0.0);

                // Collect all named lifetimes. These allow us to prevent duplication
                // of already existing lifetime names when introducing names for
                // anonymous late-bound regions.
                if let Some(name) = r.get_name(self.tcx) {
                    self.used_region_names.insert(name);
                }
            }

            // We collect types in order to prevent really large types from compiling for
            // a really long time. See issue #83150 for why this is necessary.
            fn visit_ty(&mut self, ty: Ty<'tcx>) {
                let not_previously_inserted = self.type_collector.insert(ty);
                if not_previously_inserted {
                    ty.super_visit_with(self)
                }
            }
        }

        let mut collector = RegionNameCollector::new(self.tcx());
        value.visit_with(&mut collector);
        self.used_region_names = collector.used_region_names;
        self.region_index = 0;
    }
}

impl<'tcx, T, P: PrettyPrinter<'tcx>> Print<P> for ty::Binder<'tcx, T>
where
    T: Print<P> + TypeFoldable<TyCtxt<'tcx>>,
{
    fn print(&self, p: &mut P) -> Result<(), PrintError> {
        p.pretty_print_in_binder(self)
    }
}

impl<'tcx, T, P: PrettyPrinter<'tcx>> Print<P> for ty::OutlivesClause<'tcx, T>
where
    T: Print<P>,
{
    fn print(&self, p: &mut P) -> Result<(), PrintError> {
        self.0.print(p)?;
        write!(p, ": ")?;
        self.1.print(p)?;
        Ok(())
    }
}

/// Wrapper type for `ty::TraitRef` which opts-in to pretty printing only
/// the trait path. That is, it will print `Trait<U>` instead of
/// `<T as Trait<U>>`.
#[derive(Copy, Clone, TypeFoldable, TypeVisitable, Lift, Hash)]
pub struct TraitRefPrintOnlyTraitPath<'tcx>(ty::TraitRef<'tcx>);

impl<'tcx> rustc_errors::IntoDiagArg for TraitRefPrintOnlyTraitPath<'tcx> {
    fn into_diag_arg(self, path: &mut Option<std::path::PathBuf>) -> rustc_errors::DiagArgValue {
        ty::tls::with(|tcx| {
            let trait_ref = tcx.short_string(tcx.lift(self), path);
            rustc_errors::DiagArgValue::Str(std::borrow::Cow::Owned(trait_ref))
        })
    }
}

impl<'tcx> fmt::Debug for TraitRefPrintOnlyTraitPath<'tcx> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        fmt::Display::fmt(self, f)
    }
}

/// Wrapper type for `ty::TraitRef` which opts-in to pretty printing only
/// the trait path, and additionally tries to "sugar" `Fn(...)` trait bounds.
#[derive(Copy, Clone, TypeFoldable, TypeVisitable, Lift, Hash)]
pub struct TraitRefPrintSugared<'tcx>(ty::TraitRef<'tcx>);

impl<'tcx> rustc_errors::IntoDiagArg for TraitRefPrintSugared<'tcx> {
    fn into_diag_arg(self, path: &mut Option<std::path::PathBuf>) -> rustc_errors::DiagArgValue {
        ty::tls::with(|tcx| {
            let trait_ref = tcx.short_string(tcx.lift(self), path);
            rustc_errors::DiagArgValue::Str(std::borrow::Cow::Owned(trait_ref))
        })
    }
}

impl<'tcx> fmt::Debug for TraitRefPrintSugared<'tcx> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        fmt::Display::fmt(self, f)
    }
}

/// Wrapper type for `ty::TraitRef` which opts-in to pretty printing only
/// the trait name. That is, it will print `Trait` instead of
/// `<T as Trait<U>>`.
#[derive(Copy, Clone, TypeFoldable, TypeVisitable, Lift)]
pub struct TraitRefPrintOnlyTraitName<'tcx>(ty::TraitRef<'tcx>);

impl<'tcx> fmt::Debug for TraitRefPrintOnlyTraitName<'tcx> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        fmt::Display::fmt(self, f)
    }
}

#[extension(pub trait PrintTraitRefExt<'tcx>)]
impl<'tcx> ty::TraitRef<'tcx> {
    fn print_only_trait_path(self) -> TraitRefPrintOnlyTraitPath<'tcx> {
        TraitRefPrintOnlyTraitPath(self)
    }

    fn print_trait_sugared(self) -> TraitRefPrintSugared<'tcx> {
        TraitRefPrintSugared(self)
    }

    fn print_only_trait_name(self) -> TraitRefPrintOnlyTraitName<'tcx> {
        TraitRefPrintOnlyTraitName(self)
    }
}

#[extension(pub trait PrintPolyTraitRefExt<'tcx>)]
impl<'tcx> ty::Binder<'tcx, ty::TraitRef<'tcx>> {
    fn print_only_trait_path(self) -> ty::Binder<'tcx, TraitRefPrintOnlyTraitPath<'tcx>> {
        self.map_bound(|tr| tr.print_only_trait_path())
    }

    fn print_trait_sugared(self) -> ty::Binder<'tcx, TraitRefPrintSugared<'tcx>> {
        self.map_bound(|tr| tr.print_trait_sugared())
    }
}

#[derive(Copy, Clone, TypeFoldable, TypeVisitable, Lift, Hash)]
pub struct TraitPredPrintModifiersAndPath<'tcx>(ty::TraitPredicate<'tcx>);

impl<'tcx> fmt::Debug for TraitPredPrintModifiersAndPath<'tcx> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        fmt::Display::fmt(self, f)
    }
}

#[extension(pub trait PrintTraitPredicateExt<'tcx>)]
impl<'tcx> ty::TraitPredicate<'tcx> {
    fn print_modifiers_and_trait_path(self) -> TraitPredPrintModifiersAndPath<'tcx> {
        TraitPredPrintModifiersAndPath(self)
    }
}

#[derive(Copy, Clone, TypeFoldable, TypeVisitable, Lift, Hash)]
pub struct TraitPredPrintWithBoundConstness<'tcx>(
    ty::TraitPredicate<'tcx>,
    Option<ty::BoundConstness>,
);

impl<'tcx> fmt::Debug for TraitPredPrintWithBoundConstness<'tcx> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        fmt::Display::fmt(self, f)
    }
}

#[extension(pub trait PrintPolyTraitPredicateExt<'tcx>)]
impl<'tcx> ty::PolyTraitPredicate<'tcx> {
    fn print_modifiers_and_trait_path(
        self,
    ) -> ty::Binder<'tcx, TraitPredPrintModifiersAndPath<'tcx>> {
        self.map_bound(TraitPredPrintModifiersAndPath)
    }

    fn print_with_bound_constness(
        self,
        constness: Option<ty::BoundConstness>,
    ) -> ty::Binder<'tcx, TraitPredPrintWithBoundConstness<'tcx>> {
        self.map_bound(|trait_pred| TraitPredPrintWithBoundConstness(trait_pred, constness))
    }
}

#[derive(Debug, Copy, Clone, Lift)]
pub struct PrintClosureAsImpl<'tcx> {
    pub closure: ty::ClosureArgs<TyCtxt<'tcx>>,
}

macro_rules! forward_display_to_print {
    ($($ty:ty),+) => {
        $(
            #[allow(unused_lifetimes, reason = "not all `$ty` have a 'tcx")]
            impl<'tcx> fmt::Display for $ty {
                fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
                    ty::tls::with(|tcx| {
                        let mut p = FmtPrinter::new(tcx, Namespace::TypeNS);
                        tcx.lift(*self)
                            .print(&mut p)?;
                        f.write_str(&p.into_buffer())?;
                        Ok(())
                    })
                }
            }
        )+
    };
}

macro_rules! define_print {
    (($self:ident, $p:ident): $($ty:ty $print:block)+) => {
        $(impl<'tcx, P: PrettyPrinter<'tcx>> Print<P> for $ty {
            fn print(&$self, $p: &mut P) -> Result<(), PrintError> {
                let _: () = $print;
                Ok(())
            }
        })+
    };
}

macro_rules! define_print_and_forward_display {
    (($self:ident, $p:ident): $($ty:ty $print:block)+) => {
        define_print!(($self, $p): $($ty $print)*);
        forward_display_to_print!($($ty),+);
    };
}

forward_display_to_print! {
    Ty<'tcx>,
    &'tcx ty::List<ty::PolyExistentialPredicate<'tcx>>,
    ty::Const<'tcx>
}

define_print! {
    (self, p):

    ty::FnSig<'tcx> {
        write!(p, "{}", self.safety().prefix_str())?;

        if self.abi() != ExternAbi::Rust {
            write!(p, "extern {} ", self.abi())?;
        }

        write!(p, "fn")?;
        p.pretty_print_fn_sig(self.inputs(), self.c_variadic(), self.splatted(), self.output())?;
    }

    ty::TraitRef<'tcx> {
        write!(p, "<{} as {}>", self.self_ty(), self.print_only_trait_path())?;
    }

    ty::AliasTy<'tcx> {
        let alias_term: ty::AliasTerm<'tcx> = (*self).into();
        alias_term.print(p)?;
    }

    ty::AliasTerm<'tcx> {
        match self.kind {
            ty::AliasTermKind::InherentTy { .. } | ty::AliasTermKind::InherentConst { .. } => {
                p.pretty_print_inherent_projection(*self)?;
            }
            ty::AliasTermKind::ProjectionTy { def_id } => {
                if !(p.should_print_verbose() || with_reduced_queries())
                    && p.tcx().is_impl_trait_in_trait(def_id)
                {
                    p.pretty_print_rpitit(def_id, self.args)?;
                } else {
                    p.print_def_path(def_id, self.args)?;
                }
            }
            ty::AliasTermKind::FreeTy { def_id }
            | ty::AliasTermKind::FreeConst { def_id }
            | ty::AliasTermKind::OpaqueTy { def_id }
            | ty::AliasTermKind::AnonConst { def_id }
            | ty::AliasTermKind::ProjectionConst { def_id } => {
                p.print_def_path(def_id, self.args)?;
            }
        }
    }

    ty::TraitPredicate<'tcx> {
        self.trait_ref.self_ty().print(p)?;
        write!(p, ": ")?;
        if let ty::PredicatePolarity::Negative = self.polarity {
            write!(p, "!")?;
        }
        self.trait_ref.print_trait_sugared().print(p)?;
    }

    ty::HostEffectPredicate<'tcx> {
        let constness = match self.constness {
            ty::BoundConstness::Const => { "const" }
            ty::BoundConstness::Maybe => { "[const]" }
        };
        self.trait_ref.self_ty().print(p)?;
        write!(p, ": {constness} ")?;
        self.trait_ref.print_trait_sugared().print(p)?;
    }

    ty::TypeAndMut<'tcx> {
        write!(p, "{}", self.mutbl.prefix_str())?;
        self.ty.print(p)?;
    }

    ty::ClauseKind<'tcx> {
        match *self {
            ty::ClauseKind::Trait(ref data) => data.print(p)?,
            ty::ClauseKind::RegionOutlives(predicate) => predicate.print(p)?,
            ty::ClauseKind::TypeOutlives(predicate) => predicate.print(p)?,
            ty::ClauseKind::Projection(predicate) => predicate.print(p)?,
            ty::ClauseKind::HostEffect(predicate) => predicate.print(p)?,
            ty::ClauseKind::ConstArgHasType(ct, ty) => {
                write!(p, "the constant `")?;
                ct.print(p)?;
                write!(p, "` has type `")?;
                ty.print(p)?;
                write!(p, "`")?;
            },
            ty::ClauseKind::WellFormed(term) => {
                term.print(p)?;
                write!(p, " well-formed")?;
            }
            ty::ClauseKind::ConstEvaluatable(ct) => {
                write!(p, "the constant `")?;
                ct.print(p)?;
                write!(p, "` can be evaluated")?;
            }
            ty::ClauseKind::UnstableFeature(symbol) => {
                write!(p, "feature({symbol}) is enabled")?;
            }
        }
    }

    ty::PredicateKind<'tcx> {
        match *self {
            ty::PredicateKind::Clause(data) => data.print(p)?,
            ty::PredicateKind::Subtype(predicate) => predicate.print(p)?,
            ty::PredicateKind::Coerce(predicate) => predicate.print(p)?,
            ty::PredicateKind::DynCompatible(trait_def_id) => {
                write!(p, "the trait `")?;
                p.print_def_path(trait_def_id, &[])?;
                write!(p, "` is dyn-compatible")?;
            }
            ty::PredicateKind::ConstEquate(c1, c2) => {
                write!(p, "the constant `")?;
                c1.print(p)?;
                write!(p, "` equals `")?;
                c2.print(p)?;
                write!(p, "`")?;
            }
            ty::PredicateKind::Ambiguous => write!(p, "ambiguous")?,
            ty::PredicateKind::NormalizesTo(data) => data.print(p)?,
        }
    }

    ty::ExistentialPredicate<'tcx> {
        match *self {
            ty::ExistentialPredicate::Trait(x) => x.print(p)?,
            ty::ExistentialPredicate::Projection(x) => x.print(p)?,
            ty::ExistentialPredicate::AutoTrait(def_id) => p.print_def_path(def_id, &[])?,
        }
    }

    ty::ExistentialTraitRef<'tcx> {
        // Dummy Self is safe to use as it can't appear in generic param defaults which is important
        // later on for correctly eliding generic args that coincide with their default.
        let trait_ref = self.with_self_ty(p.tcx(), p.tcx().types.trait_object_dummy_self);
        trait_ref.print_only_trait_path().print(p)?;
    }

    ty::ExistentialProjection<'tcx> {
        let name = p.tcx().associated_item(self.def_id).name();
        // The args don't contain the self ty (as it has been erased) but the corresp.
        // generics do as the trait always has a self ty param. We need to offset.
        let args = &self.args[p.tcx().generics_of(self.def_id).parent_count - 1..];
        p.print_path_with_generic_args(|p| write!(p, "{name}"), args)?;
        write!(p, " = ")?;
        self.term.print(p)?;
    }

    ty::ProjectionPredicate<'tcx> {
        self.projection_term.print(p)?;
        write!(p, " == ")?;
        p.reset_type_limit();
        self.term.print(p)?;
    }

    ty::SubtypePredicate<'tcx> {
        self.a.print(p)?;
        write!(p, " <: ")?;
        p.reset_type_limit();
        self.b.print(p)?;
    }

    ty::CoercePredicate<'tcx> {
        self.a.print(p)?;
        write!(p, " -> ")?;
        p.reset_type_limit();
        self.b.print(p)?;
    }

    ty::NormalizesTo<'tcx> {
        self.alias.print(p)?;
        write!(p, " normalizes-to ")?;
        p.reset_type_limit();
        self.term.print(p)?;
    }

    ty::PlaceholderType<'tcx> {
        match self.bound.kind {
            ty::BoundTyKind::Anon => write!(p, "{self:?}")?,
            ty::BoundTyKind::Param(def_id) => match p.should_print_verbose() {
                true => write!(p, "{self:?}")?,
                false => write!(p, "{}", p.tcx().item_name(def_id))?,
            },
        }
    }
}

define_print_and_forward_display! {
    (self, p):

    &'tcx ty::List<Ty<'tcx>> {
        write!(p, "{{")?;
        p.comma_sep(self.iter())?;
        write!(p, "}}")?;
    }

    TraitRefPrintOnlyTraitPath<'tcx> {
        p.print_def_path(self.0.def_id, self.0.args)?;
    }

    TraitRefPrintSugared<'tcx> {
        if !with_reduced_queries()
            && p.tcx().trait_def(self.0.def_id).paren_sugar
            && let Some(args_ty) = self.0.args.get(1).and_then(|arg| arg.as_type())
            && let ty::Tuple(args) = args_ty.kind()
        {
            write!(p, "{}(", p.tcx().item_name(self.0.def_id))?;
            for (i, arg) in args.iter().enumerate() {
                if i > 0 {
                    write!(p, ", ")?;
                }
                arg.print(p)?;
            }
            write!(p, ")")?;
        } else {
            p.print_def_path(self.0.def_id, self.0.args)?;
        }
    }

    TraitRefPrintOnlyTraitName<'tcx> {
        p.print_def_path(self.0.def_id, &[])?;
    }

    TraitPredPrintModifiersAndPath<'tcx> {
        if let ty::PredicatePolarity::Negative = self.0.polarity {
            write!(p, "!")?;
        }
        self.0.trait_ref.print_trait_sugared().print(p)?;
    }

    TraitPredPrintWithBoundConstness<'tcx> {
        self.0.trait_ref.self_ty().print(p)?;
        write!(p, ": ")?;
        if let Some(constness) = self.1 {
            p.pretty_print_bound_constness(constness)?;
        }
        if let ty::PredicatePolarity::Negative = self.0.polarity {
            write!(p, "!")?;
        }
        self.0.trait_ref.print_trait_sugared().print(p)?;
    }

    PrintClosureAsImpl<'tcx> {
        p.pretty_print_closure_as_impl(self.closure)?;
    }

    ty::ParamTy {
        write!(p, "{}", self.name)?;
    }

    ty::ParamConst {
        write!(p, "{}", self.name)?;
    }

    ty::Term<'tcx> {
      match self.kind() {
        ty::TermKind::Ty(ty) => ty.print(p)?,
        ty::TermKind::Const(c) => c.print(p)?,
      }
    }

    ty::Predicate<'tcx> {
        self.kind().print(p)?;
    }

    ty::Clause<'tcx> {
        self.kind().print(p)?;
    }

    ty::UserTypeKind<'tcx> {
        match *self {
            Self::Ty(ty) => {
                write!(p, "Ty(")?;
                ty.print(p)?;
            }
            Self::TypeOf(def_id, ty::UserArgs { args, user_self_ty }) => {
                write!(p, "TypeOf(")?;
                p.print_def_path(def_id, args)?;
                if let Some(ty::UserSelfTy { impl_def_id, self_ty }) = user_self_ty {
                    write!(p, " at <impl ")?;
                    let key = p.tcx().def_key(impl_def_id);
                    let parent_def_id = DefId { index: key.parent.unwrap(), ..impl_def_id };
                    p.print_def_path(parent_def_id, &[])?;
                    write!(p, "::<{}> for ", key.disambiguated_data.as_sym(false))?;
                    self_ty.print(p)?;
                    write!(p, ">")?;
                }
            }
        }
        write!(p, ")")?;
    }

    GenericArg<'tcx> {
        match self.kind() {
            GenericArgKind::Lifetime(lt) => lt.print(p)?,
            GenericArgKind::Type(ty) => ty.print(p)?,
            GenericArgKind::Const(ct) => ct.print(p)?,
        }
    }
}

fn for_each_def(tcx: TyCtxt<'_>, mut collect_fn: impl for<'b> FnMut(&'b Ident, Namespace, DefId)) {
    // Iterate all (non-anonymous) local crate items no matter where they are defined.
    for id in tcx.hir_free_items() {
        if tcx.def_kind(id.owner_id) == DefKind::Use {
            continue;
        }

        let item = tcx.hir_item(id);
        let Some(ident) = item.kind.ident() else { continue };

        let def_id = item.owner_id.to_def_id();
        let ns = tcx.def_kind(def_id).ns().unwrap_or(Namespace::TypeNS);
        collect_fn(&ident, ns, def_id);
    }

    // Now take care of extern crate items.
    let queue = &mut Vec::new();
    let mut seen_defs: DefIdSet = Default::default();

    for &cnum in tcx.crates(()).iter() {
        // Ignore crates that are not direct dependencies.
        match tcx.extern_crate(cnum) {
            None => continue,
            Some(extern_crate) => {
                if !extern_crate.is_direct() {
                    continue;
                }
            }
        }

        queue.push(cnum.as_def_id());
    }

    // Iterate external crate defs but be mindful about visibility
    while let Some(def) = queue.pop() {
        for child in tcx.module_children(def).iter() {
            if !child.vis.is_public() {
                continue;
            }

            match child.res {
                def::Res::Def(DefKind::AssocTy, _) => {}
                def::Res::Def(DefKind::TyAlias, _) => {}
                def::Res::Def(defkind, def_id) => {
                    // Ignore external `#[doc(hidden)]` items and their descendants.
                    // They shouldn't prevent other items from being considered
                    // unique, and should be printed with a full path if necessary.
                    if tcx.is_doc_hidden(def_id) {
                        continue;
                    }

                    if let Some(ns) = defkind.ns() {
                        collect_fn(&child.ident, ns, def_id);
                    }

                    if defkind.is_module_like() && seen_defs.insert(def_id) {
                        queue.push(def_id);
                    }
                }
                _ => {}
            }
        }
    }
}

/// The purpose of this function is to collect public symbols names that are unique across all
/// crates in the build. Later, when printing about types we can use those names instead of the
/// full exported path to them.
///
/// So essentially, if a symbol name can only be imported from one place for a type, and as
/// long as it was not glob-imported anywhere in the current crate, we can trim its printed
/// path and print only the name.
///
/// This has wide implications on error messages with types, for example, shortening
/// `std::vec::Vec` to just `Vec`, as long as there is no other `Vec` importable anywhere.
///
/// The implementation uses similar import discovery logic to that of 'use' suggestions.
///
/// See also [`with_no_trimmed_paths!`].
// this is pub to be able to intra-doc-link it
pub fn trimmed_def_paths(tcx: TyCtxt<'_>, (): ()) -> DefIdMap<Symbol> {
    // Trimming paths is expensive and not optimized, since we expect it to only be used for error
    // reporting. Record the fact that we did it, so we can abort if we later found it was
    // unnecessary.
    //
    // The `rustc_middle::ty::print::with_no_trimmed_paths` wrapper can be used to suppress this
    // checking, in exchange for full paths being formatted.
    tcx.sess.record_trimmed_def_paths();

    // Once constructed, unique namespace+symbol pairs will have a `Some(_)` entry, while
    // non-unique pairs will have a `None` entry.
    let unique_symbols_rev: &mut FxIndexMap<(Namespace, Symbol), Option<DefId>> =
        &mut FxIndexMap::default();

    for symbol_set in tcx.resolutions(()).glob_map.values() {
        for symbol in symbol_set {
            unique_symbols_rev.insert((Namespace::TypeNS, *symbol), None);
            unique_symbols_rev.insert((Namespace::ValueNS, *symbol), None);
            unique_symbols_rev.insert((Namespace::MacroNS, *symbol), None);
        }
    }

    for_each_def(tcx, |ident, ns, def_id| match unique_symbols_rev.entry((ns, ident.name)) {
        IndexEntry::Occupied(mut v) => match v.get() {
            None => {}
            Some(existing) => {
                if *existing != def_id {
                    v.insert(None);
                }
            }
        },
        IndexEntry::Vacant(v) => {
            v.insert(Some(def_id));
        }
    });

    // Put the symbol from all the unique namespace+symbol pairs into `map`.
    let mut map: DefIdMap<Symbol> = Default::default();
    for ((_, symbol), opt_def_id) in unique_symbols_rev.drain(..) {
        use std::collections::hash_map::Entry::{Occupied, Vacant};

        if let Some(def_id) = opt_def_id {
            match map.entry(def_id) {
                Occupied(mut v) => {
                    // A single DefId can be known under multiple names (e.g.,
                    // with a `pub use ... as ...;`). We need to ensure that the
                    // name placed in this map is chosen deterministically, so
                    // if we find multiple names (`symbol`) resolving to the
                    // same `def_id`, we prefer the lexicographically smallest
                    // name.
                    //
                    // Any stable ordering would be fine here though.
                    if *v.get() != symbol && v.get().as_str() > symbol.as_str() {
                        v.insert(symbol);
                    }
                }
                Vacant(v) => {
                    v.insert(symbol);
                }
            }
        }
    }

    map
}

pub fn provide(providers: &mut Providers) {
    *providers = Providers { trimmed_def_paths, ..*providers };
}

pub struct OpaqueFnEntry<'tcx> {
    kind: ty::ClosureKind,
    return_ty: Option<ty::Binder<'tcx, Term<'tcx>>>,
}