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use rustc_hir::{def::DefKind, Body, Item, ItemKind, Node, TyKind};
use rustc_hir::{Path, QPath};
use rustc_infer::infer::type_variable::TypeVariableOrigin;
use rustc_infer::infer::InferCtxt;
use rustc_infer::traits::{Obligation, ObligationCause};
use rustc_middle::ty::{self, Binder, Ty, TyCtxt, TypeFoldable, TypeFolder};
use rustc_middle::ty::{EarlyBinder, TraitRef, TypeSuperFoldable};
use rustc_session::{declare_lint, impl_lint_pass};
use rustc_span::def_id::{DefId, LOCAL_CRATE};
use rustc_span::Span;
use rustc_span::{sym, symbol::kw, ExpnKind, MacroKind};
use rustc_trait_selection::infer::TyCtxtInferExt;
use rustc_trait_selection::traits::error_reporting::ambiguity::{
compute_applicable_impls_for_diagnostics, CandidateSource,
};
use crate::lints::{NonLocalDefinitionsCargoUpdateNote, NonLocalDefinitionsDiag};
use crate::{LateContext, LateLintPass, LintContext};
declare_lint! {
/// The `non_local_definitions` lint checks for `impl` blocks and `#[macro_export]`
/// macro inside bodies (functions, enum discriminant, ...).
///
/// ### Example
///
/// ```rust
/// #![warn(non_local_definitions)]
/// trait MyTrait {}
/// struct MyStruct;
///
/// fn foo() {
/// impl MyTrait for MyStruct {}
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Creating non-local definitions go against expectation and can create discrepancies
/// in tooling. It should be avoided. It may become deny-by-default in edition 2024
/// and higher, see see the tracking issue <https://github.com/rust-lang/rust/issues/120363>.
///
/// An `impl` definition is non-local if it is nested inside an item and neither
/// the type nor the trait are at the same nesting level as the `impl` block.
///
/// All nested bodies (functions, enum discriminant, array length, consts) (expect for
/// `const _: Ty = { ... }` in top-level module, which is still undecided) are checked.
pub NON_LOCAL_DEFINITIONS,
Warn,
"checks for non-local definitions",
report_in_external_macro
}
#[derive(Default)]
pub struct NonLocalDefinitions {
body_depth: u32,
}
impl_lint_pass!(NonLocalDefinitions => [NON_LOCAL_DEFINITIONS]);
// FIXME(Urgau): Figure out how to handle modules nested in bodies.
// It's currently not handled by the current logic because modules are not bodies.
// They don't even follow the correct order (check_body -> check_mod -> check_body_post)
// instead check_mod is called after every body has been handled.
impl<'tcx> LateLintPass<'tcx> for NonLocalDefinitions {
fn check_body(&mut self, _cx: &LateContext<'tcx>, _body: &'tcx Body<'tcx>) {
self.body_depth += 1;
}
fn check_body_post(&mut self, _cx: &LateContext<'tcx>, _body: &'tcx Body<'tcx>) {
self.body_depth -= 1;
}
fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'tcx>) {
if self.body_depth == 0 {
return;
}
let def_id = item.owner_id.def_id.into();
let parent = cx.tcx.parent(def_id);
let parent_def_kind = cx.tcx.def_kind(parent);
let parent_opt_item_name = cx.tcx.opt_item_name(parent);
// Per RFC we (currently) ignore anon-const (`const _: Ty = ...`) in top-level module.
if self.body_depth == 1
&& parent_def_kind == DefKind::Const
&& parent_opt_item_name == Some(kw::Underscore)
{
return;
}
let cargo_update = || {
let oexpn = item.span.ctxt().outer_expn_data();
if let Some(def_id) = oexpn.macro_def_id
&& let ExpnKind::Macro(macro_kind, macro_name) = oexpn.kind
&& def_id.krate != LOCAL_CRATE
&& rustc_session::utils::was_invoked_from_cargo()
{
Some(NonLocalDefinitionsCargoUpdateNote {
macro_kind: macro_kind.descr(),
macro_name,
crate_name: cx.tcx.crate_name(def_id.krate),
})
} else {
None
}
};
match item.kind {
ItemKind::Impl(impl_) => {
// The RFC states:
//
// > An item nested inside an expression-containing item (through any
// > level of nesting) may not define an impl Trait for Type unless
// > either the **Trait** or the **Type** is also nested inside the
// > same expression-containing item.
//
// To achieve this we get try to get the paths of the _Trait_ and
// _Type_, and we look inside thoses paths to try a find in one
// of them a type whose parent is the same as the impl definition.
//
// If that's the case this means that this impl block declaration
// is using local items and so we don't lint on it.
// We also ignore anon-const in item by including the anon-const
// parent as well.
let parent_parent = if parent_def_kind == DefKind::Const
&& parent_opt_item_name == Some(kw::Underscore)
{
Some(cx.tcx.parent(parent))
} else {
None
};
// Part 1: Is the Self type local?
let self_ty_has_local_parent = match impl_.self_ty.kind {
TyKind::Path(QPath::Resolved(_, ty_path)) => {
path_has_local_parent(ty_path, cx, parent, parent_parent)
}
TyKind::TraitObject([principle_poly_trait_ref, ..], _, _) => {
path_has_local_parent(
principle_poly_trait_ref.trait_ref.path,
cx,
parent,
parent_parent,
)
}
TyKind::TraitObject([], _, _)
| TyKind::InferDelegation(_, _)
| TyKind::Slice(_)
| TyKind::Array(_, _)
| TyKind::Ptr(_)
| TyKind::Ref(_, _)
| TyKind::BareFn(_)
| TyKind::Never
| TyKind::Tup(_)
| TyKind::Path(_)
| TyKind::Pat(..)
| TyKind::AnonAdt(_)
| TyKind::OpaqueDef(_, _, _)
| TyKind::Typeof(_)
| TyKind::Infer
| TyKind::Err(_) => false,
};
if self_ty_has_local_parent {
return;
}
// Part 2: Is the Trait local?
let of_trait_has_local_parent = impl_
.of_trait
.map(|of_trait| path_has_local_parent(of_trait.path, cx, parent, parent_parent))
.unwrap_or(false);
if of_trait_has_local_parent {
return;
}
// Part 3: Is the impl definition leaking outside it's defining scope?
//
// We always consider inherent impls to be leaking.
let impl_has_enough_non_local_candidates = cx
.tcx
.impl_trait_ref(def_id)
.map(|binder| {
impl_trait_ref_has_enough_non_local_candidates(
cx.tcx,
item.span,
def_id,
binder,
|did| did_has_local_parent(did, cx.tcx, parent, parent_parent),
)
})
.unwrap_or(false);
if impl_has_enough_non_local_candidates {
return;
}
// Get the span of the parent const item ident (if it's a not a const anon).
//
// Used to suggest changing the const item to a const anon.
let span_for_const_anon_suggestion = if self.body_depth == 1
&& parent_def_kind == DefKind::Const
&& parent_opt_item_name != Some(kw::Underscore)
&& let Some(parent) = parent.as_local()
&& let Node::Item(item) = cx.tcx.hir_node_by_def_id(parent)
&& let ItemKind::Const(ty, _, _) = item.kind
&& let TyKind::Tup(&[]) = ty.kind
{
Some(item.ident.span)
} else {
None
};
cx.emit_span_lint(
NON_LOCAL_DEFINITIONS,
item.span,
NonLocalDefinitionsDiag::Impl {
depth: self.body_depth,
body_kind_descr: cx.tcx.def_kind_descr(parent_def_kind, parent),
body_name: parent_opt_item_name
.map(|s| s.to_ident_string())
.unwrap_or_else(|| "<unnameable>".to_string()),
cargo_update: cargo_update(),
const_anon: span_for_const_anon_suggestion,
},
)
}
ItemKind::Macro(_macro, MacroKind::Bang)
if cx.tcx.has_attr(item.owner_id.def_id, sym::macro_export) =>
{
// determining we if are in a doctest context can't currently be determined
// by the code it-self (no specific attrs), but fortunatly rustdoc sets a
// perma-unstable env for libtest so we just re-use that env for now
let is_at_toplevel_doctest =
self.body_depth == 2 && std::env::var("UNSTABLE_RUSTDOC_TEST_PATH").is_ok();
cx.emit_span_lint(
NON_LOCAL_DEFINITIONS,
item.span,
NonLocalDefinitionsDiag::MacroRules {
depth: self.body_depth,
body_kind_descr: cx.tcx.def_kind_descr(parent_def_kind, parent),
body_name: parent_opt_item_name
.map(|s| s.to_ident_string())
.unwrap_or_else(|| "<unnameable>".to_string()),
cargo_update: cargo_update(),
help: (!is_at_toplevel_doctest).then_some(()),
doctest_help: is_at_toplevel_doctest.then_some(()),
notes: (),
},
)
}
_ => {}
}
}
}
// Detecting if the impl definition is leaking outside of it's defining scope.
//
// Rule: for each impl, instantiate all local types with inference vars and
// then assemble candidates for that goal, if there are more than 1 (non-private
// impls), it does not leak.
//
// https://github.com/rust-lang/rust/issues/121621#issuecomment-1976826895
fn impl_trait_ref_has_enough_non_local_candidates<'tcx>(
tcx: TyCtxt<'tcx>,
infer_span: Span,
trait_def_id: DefId,
binder: EarlyBinder<TraitRef<'tcx>>,
mut did_has_local_parent: impl FnMut(DefId) -> bool,
) -> bool {
let infcx = tcx
.infer_ctxt()
// We use the new trait solver since the obligation we are trying to
// prove here may overflow and those are fatal in the old trait solver.
// Which is unacceptable for a lint.
//
// Thanksfully the part we use here are very similar to the
// new-trait-solver-as-coherence, which is in stabilization.
//
// https://github.com/rust-lang/rust/issues/123573
.with_next_trait_solver(true)
.build();
let trait_ref = binder.instantiate(tcx, infcx.fresh_args_for_item(infer_span, trait_def_id));
let trait_ref = trait_ref.fold_with(&mut ReplaceLocalTypesWithInfer {
infcx: &infcx,
infer_span,
did_has_local_parent: &mut did_has_local_parent,
});
let poly_trait_obligation = Obligation::new(
tcx,
ObligationCause::dummy(),
ty::ParamEnv::empty(),
Binder::dummy(trait_ref),
);
let ambiguities = compute_applicable_impls_for_diagnostics(&infcx, &poly_trait_obligation);
let mut it = ambiguities.iter().filter(|ambi| match ambi {
CandidateSource::DefId(did) => !did_has_local_parent(*did),
CandidateSource::ParamEnv(_) => unreachable!(),
});
let _ = it.next();
it.next().is_some()
}
/// Replace every local type by inference variable.
///
/// ```text
/// <Global<Local> as std::cmp::PartialEq<Global<Local>>>
/// to
/// <Global<_> as std::cmp::PartialEq<Global<_>>>
/// ```
struct ReplaceLocalTypesWithInfer<'a, 'tcx, F: FnMut(DefId) -> bool> {
infcx: &'a InferCtxt<'tcx>,
did_has_local_parent: F,
infer_span: Span,
}
impl<'a, 'tcx, F: FnMut(DefId) -> bool> TypeFolder<TyCtxt<'tcx>>
for ReplaceLocalTypesWithInfer<'a, 'tcx, F>
{
fn interner(&self) -> TyCtxt<'tcx> {
self.infcx.tcx
}
fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
if let Some(def) = t.ty_adt_def()
&& (self.did_has_local_parent)(def.did())
{
self.infcx.next_ty_var(TypeVariableOrigin { param_def_id: None, span: self.infer_span })
} else {
t.super_fold_with(self)
}
}
}
/// Given a path and a parent impl def id, this checks if the if parent resolution
/// def id correspond to the def id of the parent impl definition.
///
/// Given this path, we will look at the path (and ignore any generic args):
///
/// ```text
/// std::convert::PartialEq<Foo<Bar>>
/// ^^^^^^^^^^^^^^^^^^^^^^^
/// ```
#[inline]
fn path_has_local_parent(
path: &Path<'_>,
cx: &LateContext<'_>,
impl_parent: DefId,
impl_parent_parent: Option<DefId>,
) -> bool {
path.res
.opt_def_id()
.is_some_and(|did| did_has_local_parent(did, cx.tcx, impl_parent, impl_parent_parent))
}
/// Given a def id and a parent impl def id, this checks if the parent
/// def id (modulo modules) correspond to the def id of the parent impl definition.
#[inline]
fn did_has_local_parent(
did: DefId,
tcx: TyCtxt<'_>,
impl_parent: DefId,
impl_parent_parent: Option<DefId>,
) -> bool {
did.is_local()
&& if let Some(did_parent) = tcx.opt_parent(did) {
did_parent == impl_parent
|| Some(did_parent) == impl_parent_parent
|| !did_parent.is_crate_root()
&& tcx.def_kind(did_parent) == DefKind::Mod
&& did_has_local_parent(did_parent, tcx, impl_parent, impl_parent_parent)
} else {
false
}
}