rustc_middle/ty/diagnostics.rs
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//! Diagnostics related methods for `Ty`.
use std::borrow::Cow;
use std::fmt::Write;
use std::ops::ControlFlow;
use rustc_data_structures::fx::FxHashMap;
use rustc_errors::{Applicability, Diag, DiagArgValue, IntoDiagArg, into_diag_arg_using_display};
use rustc_hir::def::DefKind;
use rustc_hir::def_id::DefId;
use rustc_hir::{self as hir, LangItem, PredicateOrigin, WherePredicate};
use rustc_span::{BytePos, Span};
use rustc_type_ir::TyKind::*;
use crate::ty::{
self, AliasTy, Const, ConstKind, FallibleTypeFolder, InferConst, InferTy, Opaque,
PolyTraitPredicate, Projection, Ty, TyCtxt, TypeFoldable, TypeSuperFoldable,
TypeSuperVisitable, TypeVisitable, TypeVisitor,
};
into_diag_arg_using_display! {
Ty<'_>,
ty::Region<'_>,
}
impl<'tcx> Ty<'tcx> {
/// Similar to `Ty::is_primitive`, but also considers inferred numeric values to be primitive.
pub fn is_primitive_ty(self) -> bool {
matches!(
self.kind(),
Bool | Char
| Str
| Int(_)
| Uint(_)
| Float(_)
| Infer(
InferTy::IntVar(_)
| InferTy::FloatVar(_)
| InferTy::FreshIntTy(_)
| InferTy::FreshFloatTy(_)
)
)
}
/// Whether the type is succinctly representable as a type instead of just referred to with a
/// description in error messages. This is used in the main error message.
pub fn is_simple_ty(self) -> bool {
match self.kind() {
Bool
| Char
| Str
| Int(_)
| Uint(_)
| Float(_)
| Infer(
InferTy::IntVar(_)
| InferTy::FloatVar(_)
| InferTy::FreshIntTy(_)
| InferTy::FreshFloatTy(_),
) => true,
Ref(_, x, _) | Array(x, _) | Slice(x) => x.peel_refs().is_simple_ty(),
Tuple(tys) if tys.is_empty() => true,
_ => false,
}
}
/// Whether the type is succinctly representable as a type instead of just referred to with a
/// description in error messages. This is used in the primary span label. Beyond what
/// `is_simple_ty` includes, it also accepts ADTs with no type arguments and references to
/// ADTs with no type arguments.
pub fn is_simple_text(self, tcx: TyCtxt<'tcx>) -> bool {
match self.kind() {
Adt(def, args) => args.non_erasable_generics(tcx, def.did()).next().is_none(),
Ref(_, ty, _) => ty.is_simple_text(tcx),
_ => self.is_simple_ty(),
}
}
}
pub trait IsSuggestable<'tcx>: Sized {
/// Whether this makes sense to suggest in a diagnostic.
///
/// We filter out certain types and constants since they don't provide
/// meaningful rendered suggestions when pretty-printed. We leave some
/// nonsense, such as region vars, since those render as `'_` and are
/// usually okay to reinterpret as elided lifetimes.
///
/// Only if `infer_suggestable` is true, we consider type and const
/// inference variables to be suggestable.
fn is_suggestable(self, tcx: TyCtxt<'tcx>, infer_suggestable: bool) -> bool;
fn make_suggestable(
self,
tcx: TyCtxt<'tcx>,
infer_suggestable: bool,
placeholder: Option<Ty<'tcx>>,
) -> Option<Self>;
}
impl<'tcx, T> IsSuggestable<'tcx> for T
where
T: TypeVisitable<TyCtxt<'tcx>> + TypeFoldable<TyCtxt<'tcx>>,
{
#[tracing::instrument(level = "debug", skip(tcx))]
fn is_suggestable(self, tcx: TyCtxt<'tcx>, infer_suggestable: bool) -> bool {
self.visit_with(&mut IsSuggestableVisitor { tcx, infer_suggestable }).is_continue()
}
fn make_suggestable(
self,
tcx: TyCtxt<'tcx>,
infer_suggestable: bool,
placeholder: Option<Ty<'tcx>>,
) -> Option<T> {
self.try_fold_with(&mut MakeSuggestableFolder { tcx, infer_suggestable, placeholder }).ok()
}
}
pub fn suggest_arbitrary_trait_bound<'tcx>(
tcx: TyCtxt<'tcx>,
generics: &hir::Generics<'_>,
err: &mut Diag<'_>,
trait_pred: PolyTraitPredicate<'tcx>,
associated_ty: Option<(&'static str, Ty<'tcx>)>,
) -> bool {
if !trait_pred.is_suggestable(tcx, false) {
return false;
}
let param_name = trait_pred.skip_binder().self_ty().to_string();
let mut constraint = trait_pred.to_string();
if let Some((name, term)) = associated_ty {
// FIXME: this case overlaps with code in TyCtxt::note_and_explain_type_err.
// That should be extracted into a helper function.
if constraint.ends_with('>') {
constraint = format!("{}, {} = {}>", &constraint[..constraint.len() - 1], name, term);
} else {
constraint.push_str(&format!("<{name} = {term}>"));
}
}
let param = generics.params.iter().find(|p| p.name.ident().as_str() == param_name);
// Skip, there is a param named Self
if param.is_some() && param_name == "Self" {
return false;
}
// Suggest a where clause bound for a non-type parameter.
err.span_suggestion_verbose(
generics.tail_span_for_predicate_suggestion(),
format!(
"consider {} `where` clause, but there might be an alternative better way to express \
this requirement",
if generics.where_clause_span.is_empty() { "introducing a" } else { "extending the" },
),
format!("{} {constraint}", generics.add_where_or_trailing_comma()),
Applicability::MaybeIncorrect,
);
true
}
#[derive(Debug)]
enum SuggestChangingConstraintsMessage<'a> {
RestrictBoundFurther,
RestrictType { ty: &'a str },
RestrictTypeFurther { ty: &'a str },
RemoveMaybeUnsized,
ReplaceMaybeUnsizedWithSized,
}
fn suggest_changing_unsized_bound(
generics: &hir::Generics<'_>,
suggestions: &mut Vec<(Span, String, SuggestChangingConstraintsMessage<'_>)>,
param: &hir::GenericParam<'_>,
def_id: Option<DefId>,
) {
// See if there's a `?Sized` bound that can be removed to suggest that.
// First look at the `where` clause because we can have `where T: ?Sized`,
// then look at params.
for (where_pos, predicate) in generics.predicates.iter().enumerate() {
let WherePredicate::BoundPredicate(predicate) = predicate else {
continue;
};
if !predicate.is_param_bound(param.def_id.to_def_id()) {
continue;
};
let unsized_bounds = predicate
.bounds
.iter()
.enumerate()
.filter(|(_, bound)| {
if let hir::GenericBound::Trait(poly, hir::TraitBoundModifier::Maybe) = bound
&& poly.trait_ref.trait_def_id() == def_id
{
true
} else {
false
}
})
.collect::<Vec<_>>();
if unsized_bounds.is_empty() {
continue;
}
let mut push_suggestion = |sp, msg| suggestions.push((sp, String::new(), msg));
if predicate.bounds.len() == unsized_bounds.len() {
// All the bounds are unsized bounds, e.g.
// `T: ?Sized + ?Sized` or `_: impl ?Sized + ?Sized`,
// so in this case:
// - if it's an impl trait predicate suggest changing the
// the first bound to sized and removing the rest
// - Otherwise simply suggest removing the entire predicate
if predicate.origin == PredicateOrigin::ImplTrait {
let first_bound = unsized_bounds[0].1;
let first_bound_span = first_bound.span();
if first_bound_span.can_be_used_for_suggestions() {
let question_span =
first_bound_span.with_hi(first_bound_span.lo() + BytePos(1));
push_suggestion(
question_span,
SuggestChangingConstraintsMessage::ReplaceMaybeUnsizedWithSized,
);
for (pos, _) in unsized_bounds.iter().skip(1) {
let sp = generics.span_for_bound_removal(where_pos, *pos);
push_suggestion(sp, SuggestChangingConstraintsMessage::RemoveMaybeUnsized);
}
}
} else {
let sp = generics.span_for_predicate_removal(where_pos);
push_suggestion(sp, SuggestChangingConstraintsMessage::RemoveMaybeUnsized);
}
} else {
// Some of the bounds are other than unsized.
// So push separate removal suggestion for each unsized bound
for (pos, _) in unsized_bounds {
let sp = generics.span_for_bound_removal(where_pos, pos);
push_suggestion(sp, SuggestChangingConstraintsMessage::RemoveMaybeUnsized);
}
}
}
}
/// Suggest restricting a type param with a new bound.
///
/// If `span_to_replace` is provided, then that span will be replaced with the
/// `constraint`. If one wasn't provided, then the full bound will be suggested.
pub fn suggest_constraining_type_param(
tcx: TyCtxt<'_>,
generics: &hir::Generics<'_>,
err: &mut Diag<'_>,
param_name: &str,
constraint: &str,
def_id: Option<DefId>,
span_to_replace: Option<Span>,
) -> bool {
suggest_constraining_type_params(
tcx,
generics,
err,
[(param_name, constraint, def_id)].into_iter(),
span_to_replace,
)
}
/// Suggest restricting a type param with a new bound.
pub fn suggest_constraining_type_params<'a>(
tcx: TyCtxt<'_>,
generics: &hir::Generics<'_>,
err: &mut Diag<'_>,
param_names_and_constraints: impl Iterator<Item = (&'a str, &'a str, Option<DefId>)>,
span_to_replace: Option<Span>,
) -> bool {
let mut grouped = FxHashMap::default();
param_names_and_constraints.for_each(|(param_name, constraint, def_id)| {
grouped.entry(param_name).or_insert(Vec::new()).push((constraint, def_id))
});
let mut applicability = Applicability::MachineApplicable;
let mut suggestions = Vec::new();
for (param_name, mut constraints) in grouped {
let param = generics.params.iter().find(|p| p.name.ident().as_str() == param_name);
let Some(param) = param else { return false };
{
let mut sized_constraints = constraints.extract_if(|(_, def_id)| {
def_id.is_some_and(|def_id| tcx.is_lang_item(def_id, LangItem::Sized))
});
if let Some((_, def_id)) = sized_constraints.next() {
applicability = Applicability::MaybeIncorrect;
err.span_label(param.span, "this type parameter needs to be `Sized`");
suggest_changing_unsized_bound(generics, &mut suggestions, param, def_id);
}
}
// in the scenario like impl has stricter requirements than trait,
// we should not suggest restrict bound on the impl, here we double check
// the whether the param already has the constraint by checking `def_id`
let bound_trait_defs: Vec<DefId> = generics
.bounds_for_param(param.def_id)
.flat_map(|bound| {
bound.bounds.iter().flat_map(|b| b.trait_ref().and_then(|t| t.trait_def_id()))
})
.collect();
constraints
.retain(|(_, def_id)| def_id.map_or(true, |def| !bound_trait_defs.contains(&def)));
if constraints.is_empty() {
continue;
}
let mut constraint = constraints.iter().map(|&(c, _)| c).collect::<Vec<_>>();
constraint.sort();
constraint.dedup();
let constraint = constraint.join(" + ");
let mut suggest_restrict = |span, bound_list_non_empty, open_paren_sp| {
let suggestion = if span_to_replace.is_some() {
constraint.clone()
} else if constraint.starts_with('<') {
constraint.to_string()
} else if bound_list_non_empty {
format!(" + {constraint}")
} else {
format!(" {constraint}")
};
use SuggestChangingConstraintsMessage::RestrictBoundFurther;
if let Some(open_paren_sp) = open_paren_sp {
suggestions.push((open_paren_sp, "(".to_string(), RestrictBoundFurther));
suggestions.push((span, format!("){suggestion}"), RestrictBoundFurther));
} else {
suggestions.push((span, suggestion, RestrictBoundFurther));
}
};
if let Some(span) = span_to_replace {
suggest_restrict(span, true, None);
continue;
}
// When the type parameter has been provided bounds
//
// Message:
// fn foo<T>(t: T) where T: Foo { ... }
// ^^^^^^
// |
// help: consider further restricting this bound with `+ Bar`
//
// Suggestion:
// fn foo<T>(t: T) where T: Foo { ... }
// ^
// |
// replace with: ` + Bar`
//
// Or, if user has provided some bounds, suggest restricting them:
//
// fn foo<T: Foo>(t: T) { ... }
// ---
// |
// help: consider further restricting this bound with `+ Bar`
//
// Suggestion for tools in this case is:
//
// fn foo<T: Foo>(t: T) { ... }
// --
// |
// replace with: `T: Bar +`
if let Some((span, open_paren_sp)) = generics.bounds_span_for_suggestions(param.def_id) {
suggest_restrict(span, true, open_paren_sp);
continue;
}
if generics.has_where_clause_predicates {
// This part is a bit tricky, because using the `where` clause user can
// provide zero, one or many bounds for the same type parameter, so we
// have following cases to consider:
//
// When the type parameter has been provided zero bounds
//
// Message:
// fn foo<X, Y>(x: X, y: Y) where Y: Foo { ... }
// - help: consider restricting this type parameter with `where X: Bar`
//
// Suggestion:
// fn foo<X, Y>(x: X, y: Y) where Y: Foo { ... }
// - insert: `, X: Bar`
suggestions.push((
generics.tail_span_for_predicate_suggestion(),
constraints.iter().fold(String::new(), |mut string, &(constraint, _)| {
write!(string, ", {param_name}: {constraint}").unwrap();
string
}),
SuggestChangingConstraintsMessage::RestrictTypeFurther { ty: param_name },
));
continue;
}
// Additionally, there may be no `where` clause but the generic parameter has a default:
//
// Message:
// trait Foo<T=()> {... }
// - help: consider further restricting this type parameter with `where T: Zar`
//
// Suggestion:
// trait Foo<T=()> {... }
// - insert: `where T: Zar`
if matches!(param.kind, hir::GenericParamKind::Type { default: Some(_), .. }) {
// If we are here and the where clause span is of non-zero length
// it means we're dealing with an empty where clause like this:
// fn foo<X>(x: X) where { ... }
// In that case we don't want to add another "where" (Fixes #120838)
let where_prefix = if generics.where_clause_span.is_empty() { " where" } else { "" };
// Suggest a bound, but there is no existing `where` clause *and* the type param has a
// default (`<T=Foo>`), so we suggest adding `where T: Bar`.
suggestions.push((
generics.tail_span_for_predicate_suggestion(),
format!("{where_prefix} {param_name}: {constraint}"),
SuggestChangingConstraintsMessage::RestrictTypeFurther { ty: param_name },
));
continue;
}
// If user has provided a colon, don't suggest adding another:
//
// fn foo<T:>(t: T) { ... }
// - insert: consider restricting this type parameter with `T: Foo`
if let Some(colon_span) = param.colon_span {
suggestions.push((
colon_span.shrink_to_hi(),
format!(" {constraint}"),
SuggestChangingConstraintsMessage::RestrictType { ty: param_name },
));
continue;
}
// If user hasn't provided any bounds, suggest adding a new one:
//
// fn foo<T>(t: T) { ... }
// - help: consider restricting this type parameter with `T: Foo`
suggestions.push((
param.span.shrink_to_hi(),
format!(": {constraint}"),
SuggestChangingConstraintsMessage::RestrictType { ty: param_name },
));
}
// FIXME: remove the suggestions that are from derive, as the span is not correct
suggestions = suggestions
.into_iter()
.filter(|(span, _, _)| !span.in_derive_expansion())
.collect::<Vec<_>>();
if suggestions.len() == 1 {
let (span, suggestion, msg) = suggestions.pop().unwrap();
let msg = match msg {
SuggestChangingConstraintsMessage::RestrictBoundFurther => {
Cow::from("consider further restricting this bound")
}
SuggestChangingConstraintsMessage::RestrictType { ty } => {
Cow::from(format!("consider restricting type parameter `{ty}`"))
}
SuggestChangingConstraintsMessage::RestrictTypeFurther { ty } => {
Cow::from(format!("consider further restricting type parameter `{ty}`"))
}
SuggestChangingConstraintsMessage::RemoveMaybeUnsized => {
Cow::from("consider removing the `?Sized` bound to make the type parameter `Sized`")
}
SuggestChangingConstraintsMessage::ReplaceMaybeUnsizedWithSized => {
Cow::from("consider replacing `?Sized` with `Sized`")
}
};
err.span_suggestion_verbose(span, msg, suggestion, applicability);
} else if suggestions.len() > 1 {
err.multipart_suggestion_verbose(
"consider restricting type parameters",
suggestions.into_iter().map(|(span, suggestion, _)| (span, suggestion)).collect(),
applicability,
);
}
true
}
/// Collect al types that have an implicit `'static` obligation that we could suggest `'_` for.
pub struct TraitObjectVisitor<'tcx>(pub Vec<&'tcx hir::Ty<'tcx>>, pub crate::hir::map::Map<'tcx>);
impl<'v> hir::intravisit::Visitor<'v> for TraitObjectVisitor<'v> {
fn visit_ty(&mut self, ty: &'v hir::Ty<'v>) {
match ty.kind {
hir::TyKind::TraitObject(
_,
hir::Lifetime {
res:
hir::LifetimeName::ImplicitObjectLifetimeDefault | hir::LifetimeName::Static,
..
},
_,
)
| hir::TyKind::OpaqueDef(..) => self.0.push(ty),
_ => {}
}
hir::intravisit::walk_ty(self, ty);
}
}
/// Collect al types that have an implicit `'static` obligation that we could suggest `'_` for.
pub struct StaticLifetimeVisitor<'tcx>(pub Vec<Span>, pub crate::hir::map::Map<'tcx>);
impl<'v> hir::intravisit::Visitor<'v> for StaticLifetimeVisitor<'v> {
fn visit_lifetime(&mut self, lt: &'v hir::Lifetime) {
if let hir::LifetimeName::ImplicitObjectLifetimeDefault | hir::LifetimeName::Static = lt.res
{
self.0.push(lt.ident.span);
}
}
}
pub struct IsSuggestableVisitor<'tcx> {
tcx: TyCtxt<'tcx>,
infer_suggestable: bool,
}
impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for IsSuggestableVisitor<'tcx> {
type Result = ControlFlow<()>;
fn visit_ty(&mut self, t: Ty<'tcx>) -> Self::Result {
match *t.kind() {
Infer(InferTy::TyVar(_)) if self.infer_suggestable => {}
FnDef(..)
| Closure(..)
| Infer(..)
| Coroutine(..)
| CoroutineWitness(..)
| Bound(_, _)
| Placeholder(_)
| Error(_) => {
return ControlFlow::Break(());
}
Alias(Opaque, AliasTy { def_id, .. }) => {
let parent = self.tcx.parent(def_id);
let parent_ty = self.tcx.type_of(parent).instantiate_identity();
if let DefKind::TyAlias | DefKind::AssocTy = self.tcx.def_kind(parent)
&& let Alias(Opaque, AliasTy { def_id: parent_opaque_def_id, .. }) =
*parent_ty.kind()
&& parent_opaque_def_id == def_id
{
// Okay
} else {
return ControlFlow::Break(());
}
}
Alias(Projection, AliasTy { def_id, .. }) => {
if self.tcx.def_kind(def_id) != DefKind::AssocTy {
return ControlFlow::Break(());
}
}
Param(param) => {
// FIXME: It would be nice to make this not use string manipulation,
// but it's pretty hard to do this, since `ty::ParamTy` is missing
// sufficient info to determine if it is synthetic, and we don't
// always have a convenient way of getting `ty::Generics` at the call
// sites we invoke `IsSuggestable::is_suggestable`.
if param.name.as_str().starts_with("impl ") {
return ControlFlow::Break(());
}
}
_ => {}
}
t.super_visit_with(self)
}
fn visit_const(&mut self, c: Const<'tcx>) -> Self::Result {
match c.kind() {
ConstKind::Infer(InferConst::Var(_)) if self.infer_suggestable => {}
// effect variables are always suggestable, because they are not visible
ConstKind::Infer(InferConst::EffectVar(_)) => {}
ConstKind::Infer(..)
| ConstKind::Bound(..)
| ConstKind::Placeholder(..)
| ConstKind::Error(..) => {
return ControlFlow::Break(());
}
_ => {}
}
c.super_visit_with(self)
}
}
pub struct MakeSuggestableFolder<'tcx> {
tcx: TyCtxt<'tcx>,
infer_suggestable: bool,
placeholder: Option<Ty<'tcx>>,
}
impl<'tcx> FallibleTypeFolder<TyCtxt<'tcx>> for MakeSuggestableFolder<'tcx> {
type Error = ();
fn cx(&self) -> TyCtxt<'tcx> {
self.tcx
}
fn try_fold_ty(&mut self, t: Ty<'tcx>) -> Result<Ty<'tcx>, Self::Error> {
let t = match *t.kind() {
Infer(InferTy::TyVar(_)) if self.infer_suggestable => t,
FnDef(def_id, args) if self.placeholder.is_none() => {
Ty::new_fn_ptr(self.tcx, self.tcx.fn_sig(def_id).instantiate(self.tcx, args))
}
Closure(..)
| FnDef(..)
| Infer(..)
| Coroutine(..)
| CoroutineWitness(..)
| Bound(_, _)
| Placeholder(_)
| Error(_) => {
if let Some(placeholder) = self.placeholder {
// We replace these with infer (which is passed in from an infcx).
placeholder
} else {
return Err(());
}
}
Alias(Opaque, AliasTy { def_id, .. }) => {
let parent = self.tcx.parent(def_id);
let parent_ty = self.tcx.type_of(parent).instantiate_identity();
if let hir::def::DefKind::TyAlias | hir::def::DefKind::AssocTy =
self.tcx.def_kind(parent)
&& let Alias(Opaque, AliasTy { def_id: parent_opaque_def_id, .. }) =
*parent_ty.kind()
&& parent_opaque_def_id == def_id
{
t
} else {
return Err(());
}
}
Param(param) => {
// FIXME: It would be nice to make this not use string manipulation,
// but it's pretty hard to do this, since `ty::ParamTy` is missing
// sufficient info to determine if it is synthetic, and we don't
// always have a convenient way of getting `ty::Generics` at the call
// sites we invoke `IsSuggestable::is_suggestable`.
if param.name.as_str().starts_with("impl ") {
return Err(());
}
t
}
_ => t,
};
t.try_super_fold_with(self)
}
fn try_fold_const(&mut self, c: Const<'tcx>) -> Result<Const<'tcx>, ()> {
let c = match c.kind() {
ConstKind::Infer(InferConst::Var(_)) if self.infer_suggestable => c,
ConstKind::Infer(..)
| ConstKind::Bound(..)
| ConstKind::Placeholder(..)
| ConstKind::Error(..) => {
return Err(());
}
_ => c,
};
c.try_super_fold_with(self)
}
}