use crate::traits::{ObligationCause, ObligationCauseCode}; use crate::ty::diagnostics::suggest_constraining_type_param; use crate::ty::print::{FmtPrinter, Printer}; use crate::ty::{self, BoundRegionKind, Region, Ty, TyCtxt}; use hir::def::DefKind; use rustc_errors::Applicability::{MachineApplicable, MaybeIncorrect}; use rustc_errors::{pluralize, Diagnostic, MultiSpan}; use rustc_hir as hir; use rustc_hir::def_id::DefId; use rustc_span::symbol::{sym, Symbol}; use rustc_span::{BytePos, Span}; use rustc_target::spec::abi; use std::borrow::Cow; use std::collections::hash_map::DefaultHasher; use std::fmt; use std::hash::{Hash, Hasher}; use std::path::PathBuf; use super::print::PrettyPrinter; #[derive(Clone, Copy, Debug, PartialEq, Eq, TypeFoldable, TypeVisitable, Lift)] pub struct ExpectedFound { pub expected: T, pub found: T, } impl ExpectedFound { pub fn new(a_is_expected: bool, a: T, b: T) -> Self { if a_is_expected { ExpectedFound { expected: a, found: b } } else { ExpectedFound { expected: b, found: a } } } } // Data structures used in type unification #[derive(Copy, Clone, Debug, TypeFoldable, TypeVisitable, Lift)] #[rustc_pass_by_value] pub enum TypeError<'tcx> { Mismatch, ConstnessMismatch(ExpectedFound), PolarityMismatch(ExpectedFound), UnsafetyMismatch(ExpectedFound), AbiMismatch(ExpectedFound), Mutability, ArgumentMutability(usize), TupleSize(ExpectedFound), FixedArraySize(ExpectedFound), ArgCount, FieldMisMatch(Symbol, Symbol), RegionsDoesNotOutlive(Region<'tcx>, Region<'tcx>), RegionsInsufficientlyPolymorphic(BoundRegionKind, Region<'tcx>), RegionsOverlyPolymorphic(BoundRegionKind, Region<'tcx>), RegionsPlaceholderMismatch, Sorts(ExpectedFound>), ArgumentSorts(ExpectedFound>, usize), IntMismatch(ExpectedFound), FloatMismatch(ExpectedFound), Traits(ExpectedFound), VariadicMismatch(ExpectedFound), /// Instantiating a type variable with the given type would have /// created a cycle (because it appears somewhere within that /// type). CyclicTy(Ty<'tcx>), CyclicConst(ty::Const<'tcx>), ProjectionMismatched(ExpectedFound), ExistentialMismatch(ExpectedFound<&'tcx ty::List>>), ConstMismatch(ExpectedFound>), IntrinsicCast, /// Safe `#[target_feature]` functions are not assignable to safe function pointers. TargetFeatureCast(DefId), } impl TypeError<'_> { pub fn involves_regions(self) -> bool { match self { TypeError::RegionsDoesNotOutlive(_, _) | TypeError::RegionsInsufficientlyPolymorphic(_, _) | TypeError::RegionsOverlyPolymorphic(_, _) | TypeError::RegionsPlaceholderMismatch => true, _ => false, } } } /// Explains the source of a type err in a short, human readable way. This is meant to be placed /// in parentheses after some larger message. You should also invoke `note_and_explain_type_err()` /// afterwards to present additional details, particularly when it comes to lifetime-related /// errors. impl<'tcx> fmt::Display for TypeError<'tcx> { fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { use self::TypeError::*; fn report_maybe_different( f: &mut fmt::Formatter<'_>, expected: &str, found: &str, ) -> fmt::Result { // A naive approach to making sure that we're not reporting silly errors such as: // (expected closure, found closure). if expected == found { write!(f, "expected {}, found a different {}", expected, found) } else { write!(f, "expected {}, found {}", expected, found) } } let br_string = |br: ty::BoundRegionKind| match br { ty::BrNamed(_, name) => format!(" {}", name), _ => String::new(), }; match *self { CyclicTy(_) => write!(f, "cyclic type of infinite size"), CyclicConst(_) => write!(f, "encountered a self-referencing constant"), Mismatch => write!(f, "types differ"), ConstnessMismatch(values) => { write!(f, "expected {} bound, found {} bound", values.expected, values.found) } PolarityMismatch(values) => { write!(f, "expected {} polarity, found {} polarity", values.expected, values.found) } UnsafetyMismatch(values) => { write!(f, "expected {} fn, found {} fn", values.expected, values.found) } AbiMismatch(values) => { write!(f, "expected {} fn, found {} fn", values.expected, values.found) } ArgumentMutability(_) | Mutability => write!(f, "types differ in mutability"), TupleSize(values) => write!( f, "expected a tuple with {} element{}, found one with {} element{}", values.expected, pluralize!(values.expected), values.found, pluralize!(values.found) ), FixedArraySize(values) => write!( f, "expected an array with a fixed size of {} element{}, found one with {} element{}", values.expected, pluralize!(values.expected), values.found, pluralize!(values.found) ), ArgCount => write!(f, "incorrect number of function parameters"), FieldMisMatch(adt, field) => write!(f, "field type mismatch: {}.{}", adt, field), RegionsDoesNotOutlive(..) => write!(f, "lifetime mismatch"), // Actually naming the region here is a bit confusing because context is lacking RegionsInsufficientlyPolymorphic(..) => { write!(f, "one type is more general than the other") } RegionsOverlyPolymorphic(br, _) => write!( f, "expected concrete lifetime, found bound lifetime parameter{}", br_string(br) ), RegionsPlaceholderMismatch => write!(f, "one type is more general than the other"), ArgumentSorts(values, _) | Sorts(values) => ty::tls::with(|tcx| { report_maybe_different( f, &values.expected.sort_string(tcx), &values.found.sort_string(tcx), ) }), Traits(values) => ty::tls::with(|tcx| { report_maybe_different( f, &format!("trait `{}`", tcx.def_path_str(values.expected)), &format!("trait `{}`", tcx.def_path_str(values.found)), ) }), IntMismatch(ref values) => { let expected = match values.expected { ty::IntVarValue::IntType(ty) => ty.name_str(), ty::IntVarValue::UintType(ty) => ty.name_str(), }; let found = match values.found { ty::IntVarValue::IntType(ty) => ty.name_str(), ty::IntVarValue::UintType(ty) => ty.name_str(), }; write!(f, "expected `{}`, found `{}`", expected, found) } FloatMismatch(ref values) => { write!( f, "expected `{}`, found `{}`", values.expected.name_str(), values.found.name_str() ) } VariadicMismatch(ref values) => write!( f, "expected {} fn, found {} function", if values.expected { "variadic" } else { "non-variadic" }, if values.found { "variadic" } else { "non-variadic" } ), ProjectionMismatched(ref values) => ty::tls::with(|tcx| { write!( f, "expected {}, found {}", tcx.def_path_str(values.expected), tcx.def_path_str(values.found) ) }), ExistentialMismatch(ref values) => report_maybe_different( f, &format!("trait `{}`", values.expected), &format!("trait `{}`", values.found), ), ConstMismatch(ref values) => { write!(f, "expected `{}`, found `{}`", values.expected, values.found) } IntrinsicCast => write!(f, "cannot coerce intrinsics to function pointers"), TargetFeatureCast(_) => write!( f, "cannot coerce functions with `#[target_feature]` to safe function pointers" ), } } } impl<'tcx> TypeError<'tcx> { pub fn must_include_note(self) -> bool { use self::TypeError::*; match self { CyclicTy(_) | CyclicConst(_) | UnsafetyMismatch(_) | ConstnessMismatch(_) | PolarityMismatch(_) | Mismatch | AbiMismatch(_) | FixedArraySize(_) | ArgumentSorts(..) | Sorts(_) | IntMismatch(_) | FloatMismatch(_) | VariadicMismatch(_) | TargetFeatureCast(_) => false, Mutability | ArgumentMutability(_) | TupleSize(_) | ArgCount | FieldMisMatch(..) | RegionsDoesNotOutlive(..) | RegionsInsufficientlyPolymorphic(..) | RegionsOverlyPolymorphic(..) | RegionsPlaceholderMismatch | Traits(_) | ProjectionMismatched(_) | ExistentialMismatch(_) | ConstMismatch(_) | IntrinsicCast => true, } } } impl<'tcx> Ty<'tcx> { pub fn sort_string(self, tcx: TyCtxt<'_>) -> Cow<'static, str> { match *self.kind() { ty::Bool | ty::Char | ty::Int(_) | ty::Uint(_) | ty::Float(_) | ty::Str | ty::Never => { format!("`{}`", self).into() } ty::Tuple(ref tys) if tys.is_empty() => format!("`{}`", self).into(), ty::Adt(def, _) => format!("{} `{}`", def.descr(), tcx.def_path_str(def.did())).into(), ty::Foreign(def_id) => format!("extern type `{}`", tcx.def_path_str(def_id)).into(), ty::Array(t, n) => { if t.is_simple_ty() { return format!("array `{}`", self).into(); } let n = tcx.lift(n).unwrap(); if let ty::ConstKind::Value(v) = n.kind() { if let Some(n) = v.try_to_machine_usize(tcx) { return format!("array of {} element{}", n, pluralize!(n)).into(); } } "array".into() } ty::Slice(ty) if ty.is_simple_ty() => format!("slice `{}`", self).into(), ty::Slice(_) => "slice".into(), ty::RawPtr(tymut) => { let tymut_string = match tymut.mutbl { hir::Mutability::Mut => tymut.to_string(), hir::Mutability::Not => format!("const {}", tymut.ty), }; if tymut_string != "_" && (tymut.ty.is_simple_text() || tymut_string.len() < "const raw pointer".len()) { format!("`*{}`", tymut_string).into() } else { // Unknown type name, it's long or has type arguments "raw pointer".into() } }, ty::Ref(_, ty, mutbl) => { let tymut = ty::TypeAndMut { ty, mutbl }; let tymut_string = tymut.to_string(); if tymut_string != "_" && (ty.is_simple_text() || tymut_string.len() < "mutable reference".len()) { format!("`&{}`", tymut_string).into() } else { // Unknown type name, it's long or has type arguments match mutbl { hir::Mutability::Mut => "mutable reference", _ => "reference", } .into() } } ty::FnDef(..) => "fn item".into(), ty::FnPtr(_) => "fn pointer".into(), ty::Dynamic(ref inner, ..) if let Some(principal) = inner.principal() => { format!("trait object `dyn {}`", tcx.def_path_str(principal.def_id())).into() } ty::Dynamic(..) => "trait object".into(), ty::Closure(..) => "closure".into(), ty::Generator(def_id, ..) => tcx.generator_kind(def_id).unwrap().descr().into(), ty::GeneratorWitness(..) => "generator witness".into(), ty::Tuple(..) => "tuple".into(), ty::Infer(ty::TyVar(_)) => "inferred type".into(), ty::Infer(ty::IntVar(_)) => "integer".into(), ty::Infer(ty::FloatVar(_)) => "floating-point number".into(), ty::Placeholder(..) => "placeholder type".into(), ty::Bound(..) => "bound type".into(), ty::Infer(ty::FreshTy(_)) => "fresh type".into(), ty::Infer(ty::FreshIntTy(_)) => "fresh integral type".into(), ty::Infer(ty::FreshFloatTy(_)) => "fresh floating-point type".into(), ty::Projection(_) => "associated type".into(), ty::Param(p) => format!("type parameter `{}`", p).into(), ty::Opaque(..) => "opaque type".into(), ty::Error(_) => "type error".into(), } } pub fn prefix_string(self, tcx: TyCtxt<'_>) -> Cow<'static, str> { match *self.kind() { ty::Infer(_) | ty::Error(_) | ty::Bool | ty::Char | ty::Int(_) | ty::Uint(_) | ty::Float(_) | ty::Str | ty::Never => "type".into(), ty::Tuple(ref tys) if tys.is_empty() => "unit type".into(), ty::Adt(def, _) => def.descr().into(), ty::Foreign(_) => "extern type".into(), ty::Array(..) => "array".into(), ty::Slice(_) => "slice".into(), ty::RawPtr(_) => "raw pointer".into(), ty::Ref(.., mutbl) => match mutbl { hir::Mutability::Mut => "mutable reference", _ => "reference", } .into(), ty::FnDef(..) => "fn item".into(), ty::FnPtr(_) => "fn pointer".into(), ty::Dynamic(..) => "trait object".into(), ty::Closure(..) => "closure".into(), ty::Generator(def_id, ..) => tcx.generator_kind(def_id).unwrap().descr().into(), ty::GeneratorWitness(..) => "generator witness".into(), ty::Tuple(..) => "tuple".into(), ty::Placeholder(..) => "higher-ranked type".into(), ty::Bound(..) => "bound type variable".into(), ty::Projection(_) => "associated type".into(), ty::Param(_) => "type parameter".into(), ty::Opaque(..) => "opaque type".into(), } } } impl<'tcx> TyCtxt<'tcx> { pub fn note_and_explain_type_err( self, diag: &mut Diagnostic, err: TypeError<'tcx>, cause: &ObligationCause<'tcx>, sp: Span, body_owner_def_id: DefId, ) { use self::TypeError::*; debug!("note_and_explain_type_err err={:?} cause={:?}", err, cause); match err { ArgumentSorts(values, _) | Sorts(values) => { match (values.expected.kind(), values.found.kind()) { (ty::Closure(..), ty::Closure(..)) => { diag.note("no two closures, even if identical, have the same type"); diag.help("consider boxing your closure and/or using it as a trait object"); } (ty::Opaque(..), ty::Opaque(..)) => { // Issue #63167 diag.note("distinct uses of `impl Trait` result in different opaque types"); } (ty::Float(_), ty::Infer(ty::IntVar(_))) if let Ok( // Issue #53280 snippet, ) = self.sess.source_map().span_to_snippet(sp) => { if snippet.chars().all(|c| c.is_digit(10) || c == '-' || c == '_') { diag.span_suggestion( sp, "use a float literal", format!("{}.0", snippet), MachineApplicable, ); } } (ty::Param(expected), ty::Param(found)) => { let generics = self.generics_of(body_owner_def_id); let e_span = self.def_span(generics.type_param(expected, self).def_id); if !sp.contains(e_span) { diag.span_label(e_span, "expected type parameter"); } let f_span = self.def_span(generics.type_param(found, self).def_id); if !sp.contains(f_span) { diag.span_label(f_span, "found type parameter"); } diag.note( "a type parameter was expected, but a different one was found; \ you might be missing a type parameter or trait bound", ); diag.note( "for more information, visit \ https://doc.rust-lang.org/book/ch10-02-traits.html\ #traits-as-parameters", ); } (ty::Projection(_), ty::Projection(_)) => { diag.note("an associated type was expected, but a different one was found"); } (ty::Param(p), ty::Projection(proj)) | (ty::Projection(proj), ty::Param(p)) if self.def_kind(proj.item_def_id) != DefKind::ImplTraitPlaceholder => { let generics = self.generics_of(body_owner_def_id); let p_span = self.def_span(generics.type_param(p, self).def_id); if !sp.contains(p_span) { diag.span_label(p_span, "this type parameter"); } let hir = self.hir(); let mut note = true; if let Some(generics) = generics .type_param(p, self) .def_id .as_local() .map(|id| hir.local_def_id_to_hir_id(id)) .and_then(|id| self.hir().find(self.hir().get_parent_node(id))) .as_ref() .and_then(|node| node.generics()) { // Synthesize the associated type restriction `Add`. // FIXME: extract this logic for use in other diagnostics. let (trait_ref, assoc_substs) = proj.trait_ref_and_own_substs(self); let path = self.def_path_str_with_substs(trait_ref.def_id, trait_ref.substs); let item_name = self.item_name(proj.item_def_id); let item_args = self.format_generic_args(assoc_substs); let path = if path.ends_with('>') { format!( "{}, {}{} = {}>", &path[..path.len() - 1], item_name, item_args, p ) } else { format!("{}<{}{} = {}>", path, item_name, item_args, p) }; note = !suggest_constraining_type_param( self, generics, diag, &format!("{}", proj.self_ty()), &path, None, ); } if note { diag.note("you might be missing a type parameter or trait bound"); } } (ty::Param(p), ty::Dynamic(..) | ty::Opaque(..)) | (ty::Dynamic(..) | ty::Opaque(..), ty::Param(p)) => { let generics = self.generics_of(body_owner_def_id); let p_span = self.def_span(generics.type_param(p, self).def_id); if !sp.contains(p_span) { diag.span_label(p_span, "this type parameter"); } diag.help("type parameters must be constrained to match other types"); if self.sess.teach(&diag.get_code().unwrap()) { diag.help( "given a type parameter `T` and a method `foo`: ``` trait Trait { fn foo(&self) -> T; } ``` the only ways to implement method `foo` are: - constrain `T` with an explicit type: ``` impl Trait for X { fn foo(&self) -> String { String::new() } } ``` - add a trait bound to `T` and call a method on that trait that returns `Self`: ``` impl Trait for X { fn foo(&self) -> T { ::default() } } ``` - change `foo` to return an argument of type `T`: ``` impl Trait for X { fn foo(&self, x: T) -> T { x } } ```", ); } diag.note( "for more information, visit \ https://doc.rust-lang.org/book/ch10-02-traits.html\ #traits-as-parameters", ); } (ty::Param(p), ty::Closure(..) | ty::Generator(..)) => { let generics = self.generics_of(body_owner_def_id); let p_span = self.def_span(generics.type_param(p, self).def_id); if !sp.contains(p_span) { diag.span_label(p_span, "this type parameter"); } diag.help(&format!( "every closure has a distinct type and so could not always match the \ caller-chosen type of parameter `{}`", p )); } (ty::Param(p), _) | (_, ty::Param(p)) => { let generics = self.generics_of(body_owner_def_id); let p_span = self.def_span(generics.type_param(p, self).def_id); if !sp.contains(p_span) { diag.span_label(p_span, "this type parameter"); } } (ty::Projection(proj_ty), _) if self.def_kind(proj_ty.item_def_id) != DefKind::ImplTraitPlaceholder => { self.expected_projection( diag, proj_ty, values, body_owner_def_id, cause.code(), ); } (_, ty::Projection(proj_ty)) if self.def_kind(proj_ty.item_def_id) != DefKind::ImplTraitPlaceholder => { let msg = format!( "consider constraining the associated type `{}` to `{}`", values.found, values.expected, ); if !(self.suggest_constraining_opaque_associated_type( diag, &msg, proj_ty, values.expected, ) || self.suggest_constraint( diag, &msg, body_owner_def_id, proj_ty, values.expected, )) { diag.help(&msg); diag.note( "for more information, visit \ https://doc.rust-lang.org/book/ch19-03-advanced-traits.html", ); } } _ => {} } debug!( "note_and_explain_type_err expected={:?} ({:?}) found={:?} ({:?})", values.expected, values.expected.kind(), values.found, values.found.kind(), ); } CyclicTy(ty) => { // Watch out for various cases of cyclic types and try to explain. if ty.is_closure() || ty.is_generator() { diag.note( "closures cannot capture themselves or take themselves as argument;\n\ this error may be the result of a recent compiler bug-fix,\n\ see issue #46062 \n\ for more information", ); } } TargetFeatureCast(def_id) => { let target_spans = self.get_attrs(def_id, sym::target_feature).map(|attr| attr.span); diag.note( "functions with `#[target_feature]` can only be coerced to `unsafe` function pointers" ); diag.span_labels(target_spans, "`#[target_feature]` added here"); } _ => {} } } fn suggest_constraint( self, diag: &mut Diagnostic, msg: &str, body_owner_def_id: DefId, proj_ty: &ty::ProjectionTy<'tcx>, ty: Ty<'tcx>, ) -> bool { let assoc = self.associated_item(proj_ty.item_def_id); let (trait_ref, assoc_substs) = proj_ty.trait_ref_and_own_substs(self); if let Some(item) = self.hir().get_if_local(body_owner_def_id) { if let Some(hir_generics) = item.generics() { // Get the `DefId` for the type parameter corresponding to `A` in `::Foo`. // This will also work for `impl Trait`. let def_id = if let ty::Param(param_ty) = proj_ty.self_ty().kind() { let generics = self.generics_of(body_owner_def_id); generics.type_param(param_ty, self).def_id } else { return false; }; let Some(def_id) = def_id.as_local() else { return false; }; // First look in the `where` clause, as this might be // `fn foo(x: T) where T: Trait`. for pred in hir_generics.bounds_for_param(def_id) { if self.constrain_generic_bound_associated_type_structured_suggestion( diag, &trait_ref, pred.bounds, &assoc, assoc_substs, ty, msg, false, ) { return true; } } } } false } /// An associated type was expected and a different type was found. /// /// We perform a few different checks to see what we can suggest: /// /// - In the current item, look for associated functions that return the expected type and /// suggest calling them. (Not a structured suggestion.) /// - If any of the item's generic bounds can be constrained, we suggest constraining the /// associated type to the found type. /// - If the associated type has a default type and was expected inside of a `trait`, we /// mention that this is disallowed. /// - If all other things fail, and the error is not because of a mismatch between the `trait` /// and the `impl`, we provide a generic `help` to constrain the assoc type or call an assoc /// fn that returns the type. fn expected_projection( self, diag: &mut Diagnostic, proj_ty: &ty::ProjectionTy<'tcx>, values: ExpectedFound>, body_owner_def_id: DefId, cause_code: &ObligationCauseCode<'_>, ) { let msg = format!( "consider constraining the associated type `{}` to `{}`", values.expected, values.found ); let body_owner = self.hir().get_if_local(body_owner_def_id); let current_method_ident = body_owner.and_then(|n| n.ident()).map(|i| i.name); // We don't want to suggest calling an assoc fn in a scope where that isn't feasible. let callable_scope = matches!( body_owner, Some( hir::Node::Item(hir::Item { kind: hir::ItemKind::Fn(..), .. }) | hir::Node::TraitItem(hir::TraitItem { kind: hir::TraitItemKind::Fn(..), .. }) | hir::Node::ImplItem(hir::ImplItem { kind: hir::ImplItemKind::Fn(..), .. }), ) ); let impl_comparison = matches!(cause_code, ObligationCauseCode::CompareImplItemObligation { .. }); let assoc = self.associated_item(proj_ty.item_def_id); if !callable_scope || impl_comparison { // We do not want to suggest calling functions when the reason of the // type error is a comparison of an `impl` with its `trait` or when the // scope is outside of a `Body`. } else { // If we find a suitable associated function that returns the expected type, we don't // want the more general suggestion later in this method about "consider constraining // the associated type or calling a method that returns the associated type". let point_at_assoc_fn = self.point_at_methods_that_satisfy_associated_type( diag, assoc.container_id(self), current_method_ident, proj_ty.item_def_id, values.expected, ); // Possibly suggest constraining the associated type to conform to the // found type. if self.suggest_constraint(diag, &msg, body_owner_def_id, proj_ty, values.found) || point_at_assoc_fn { return; } } self.suggest_constraining_opaque_associated_type(diag, &msg, proj_ty, values.found); if self.point_at_associated_type(diag, body_owner_def_id, values.found) { return; } if !impl_comparison { // Generic suggestion when we can't be more specific. if callable_scope { diag.help(&format!( "{} or calling a method that returns `{}`", msg, values.expected )); } else { diag.help(&msg); } diag.note( "for more information, visit \ https://doc.rust-lang.org/book/ch19-03-advanced-traits.html", ); } if self.sess.teach(&diag.get_code().unwrap()) { diag.help( "given an associated type `T` and a method `foo`: ``` trait Trait { type T; fn foo(&self) -> Self::T; } ``` the only way of implementing method `foo` is to constrain `T` with an explicit associated type: ``` impl Trait for X { type T = String; fn foo(&self) -> Self::T { String::new() } } ```", ); } } /// When the expected `impl Trait` is not defined in the current item, it will come from /// a return type. This can occur when dealing with `TryStream` (#71035). fn suggest_constraining_opaque_associated_type( self, diag: &mut Diagnostic, msg: &str, proj_ty: &ty::ProjectionTy<'tcx>, ty: Ty<'tcx>, ) -> bool { let assoc = self.associated_item(proj_ty.item_def_id); if let ty::Opaque(def_id, _) = *proj_ty.self_ty().kind() { let opaque_local_def_id = def_id.as_local(); let opaque_hir_ty = if let Some(opaque_local_def_id) = opaque_local_def_id { match &self.hir().expect_item(opaque_local_def_id).kind { hir::ItemKind::OpaqueTy(opaque_hir_ty) => opaque_hir_ty, _ => bug!("The HirId comes from a `ty::Opaque`"), } } else { return false; }; let (trait_ref, assoc_substs) = proj_ty.trait_ref_and_own_substs(self); self.constrain_generic_bound_associated_type_structured_suggestion( diag, &trait_ref, opaque_hir_ty.bounds, assoc, assoc_substs, ty, msg, true, ) } else { false } } fn point_at_methods_that_satisfy_associated_type( self, diag: &mut Diagnostic, assoc_container_id: DefId, current_method_ident: Option, proj_ty_item_def_id: DefId, expected: Ty<'tcx>, ) -> bool { let items = self.associated_items(assoc_container_id); // Find all the methods in the trait that could be called to construct the // expected associated type. // FIXME: consider suggesting the use of associated `const`s. let methods: Vec<(Span, String)> = items .items .iter() .filter(|(name, item)| { ty::AssocKind::Fn == item.kind && Some(**name) != current_method_ident }) .filter_map(|(_, item)| { let method = self.fn_sig(item.def_id); match *method.output().skip_binder().kind() { ty::Projection(ty::ProjectionTy { item_def_id, .. }) if item_def_id == proj_ty_item_def_id => { Some(( self.def_span(item.def_id), format!("consider calling `{}`", self.def_path_str(item.def_id)), )) } _ => None, } }) .collect(); if !methods.is_empty() { // Use a single `help:` to show all the methods in the trait that can // be used to construct the expected associated type. let mut span: MultiSpan = methods.iter().map(|(sp, _)| *sp).collect::>().into(); let msg = format!( "{some} method{s} {are} available that return{r} `{ty}`", some = if methods.len() == 1 { "a" } else { "some" }, s = pluralize!(methods.len()), are = pluralize!("is", methods.len()), r = if methods.len() == 1 { "s" } else { "" }, ty = expected ); for (sp, label) in methods.into_iter() { span.push_span_label(sp, label); } diag.span_help(span, &msg); return true; } false } fn point_at_associated_type( self, diag: &mut Diagnostic, body_owner_def_id: DefId, found: Ty<'tcx>, ) -> bool { let Some(hir_id) = body_owner_def_id.as_local() else { return false; }; let hir_id = self.hir().local_def_id_to_hir_id(hir_id); // When `body_owner` is an `impl` or `trait` item, look in its associated types for // `expected` and point at it. let parent_id = self.hir().get_parent_item(hir_id); let item = self.hir().find_by_def_id(parent_id.def_id); debug!("expected_projection parent item {:?}", item); match item { Some(hir::Node::Item(hir::Item { kind: hir::ItemKind::Trait(.., items), .. })) => { // FIXME: account for `#![feature(specialization)]` for item in &items[..] { match item.kind { hir::AssocItemKind::Type => { // FIXME: account for returning some type in a trait fn impl that has // an assoc type as a return type (#72076). if let hir::Defaultness::Default { has_value: true } = self.impl_defaultness(item.id.owner_id) { if self.type_of(item.id.owner_id) == found { diag.span_label( item.span, "associated type defaults can't be assumed inside the \ trait defining them", ); return true; } } } _ => {} } } } Some(hir::Node::Item(hir::Item { kind: hir::ItemKind::Impl(hir::Impl { items, .. }), .. })) => { for item in &items[..] { if let hir::AssocItemKind::Type = item.kind { if self.type_of(item.id.owner_id) == found { diag.span_label(item.span, "expected this associated type"); return true; } } } } _ => {} } false } /// Given a slice of `hir::GenericBound`s, if any of them corresponds to the `trait_ref` /// requirement, provide a structured suggestion to constrain it to a given type `ty`. /// /// `is_bound_surely_present` indicates whether we know the bound we're looking for is /// inside `bounds`. If that's the case then we can consider `bounds` containing only one /// trait bound as the one we're looking for. This can help in cases where the associated /// type is defined on a supertrait of the one present in the bounds. fn constrain_generic_bound_associated_type_structured_suggestion( self, diag: &mut Diagnostic, trait_ref: &ty::TraitRef<'tcx>, bounds: hir::GenericBounds<'_>, assoc: &ty::AssocItem, assoc_substs: &[ty::GenericArg<'tcx>], ty: Ty<'tcx>, msg: &str, is_bound_surely_present: bool, ) -> bool { // FIXME: we would want to call `resolve_vars_if_possible` on `ty` before suggesting. let trait_bounds = bounds.iter().filter_map(|bound| match bound { hir::GenericBound::Trait(ptr, hir::TraitBoundModifier::None) => Some(ptr), _ => None, }); let matching_trait_bounds = trait_bounds .clone() .filter(|ptr| ptr.trait_ref.trait_def_id() == Some(trait_ref.def_id)) .collect::>(); let span = match &matching_trait_bounds[..] { &[ptr] => ptr.span, &[] if is_bound_surely_present => match &trait_bounds.collect::>()[..] { &[ptr] => ptr.span, _ => return false, }, _ => return false, }; self.constrain_associated_type_structured_suggestion( diag, span, assoc, assoc_substs, ty, msg, ) } /// Given a span corresponding to a bound, provide a structured suggestion to set an /// associated type to a given type `ty`. fn constrain_associated_type_structured_suggestion( self, diag: &mut Diagnostic, span: Span, assoc: &ty::AssocItem, assoc_substs: &[ty::GenericArg<'tcx>], ty: Ty<'tcx>, msg: &str, ) -> bool { if let Ok(has_params) = self.sess.source_map().span_to_snippet(span).map(|snippet| snippet.ends_with('>')) { let (span, sugg) = if has_params { let pos = span.hi() - BytePos(1); let span = Span::new(pos, pos, span.ctxt(), span.parent()); (span, format!(", {} = {}", assoc.ident(self), ty)) } else { let item_args = self.format_generic_args(assoc_substs); (span.shrink_to_hi(), format!("<{}{} = {}>", assoc.ident(self), item_args, ty)) }; diag.span_suggestion_verbose(span, msg, sugg, MaybeIncorrect); return true; } false } pub fn short_ty_string(self, ty: Ty<'tcx>) -> (String, Option) { let width = self.sess.diagnostic_width(); let length_limit = width.saturating_sub(30); let mut type_limit = 50; let regular = FmtPrinter::new(self, hir::def::Namespace::TypeNS) .pretty_print_type(ty) .expect("could not write to `String`") .into_buffer(); if regular.len() <= width { return (regular, None); } let mut short; loop { // Look for the longest properly trimmed path that still fits in lenght_limit. short = FmtPrinter::new_with_limit( self, hir::def::Namespace::TypeNS, rustc_session::Limit(type_limit), ) .pretty_print_type(ty) .expect("could not write to `String`") .into_buffer(); if short.len() <= length_limit || type_limit == 0 { break; } type_limit -= 1; } if regular == short { return (regular, None); } // Multiple types might be shortened in a single error, ensure we create a file for each. let mut s = DefaultHasher::new(); ty.hash(&mut s); let hash = s.finish(); let path = self.output_filenames(()).temp_path_ext(&format!("long-type-{hash}.txt"), None); match std::fs::write(&path, ®ular) { Ok(_) => (short, Some(path)), Err(_) => (regular, None), } } fn format_generic_args(self, args: &[ty::GenericArg<'tcx>]) -> String { FmtPrinter::new(self, hir::def::Namespace::TypeNS) .path_generic_args(Ok, args) .expect("could not write to `String`.") .into_buffer() } }