| 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::fmt; |
| |
| #[derive(Clone, Copy, Debug, PartialEq, Eq, TypeFoldable, TypeVisitable, Lift)] |
| pub struct ExpectedFound<T> { |
| pub expected: T, |
| pub found: T, |
| } |
| |
| impl<T> ExpectedFound<T> { |
| 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<ty::BoundConstness>), |
| PolarityMismatch(ExpectedFound<ty::ImplPolarity>), |
| UnsafetyMismatch(ExpectedFound<hir::Unsafety>), |
| AbiMismatch(ExpectedFound<abi::Abi>), |
| Mutability, |
| ArgumentMutability(usize), |
| TupleSize(ExpectedFound<usize>), |
| FixedArraySize(ExpectedFound<u64>), |
| ArgCount, |
| FieldMisMatch(Symbol, Symbol), |
| |
| RegionsDoesNotOutlive(Region<'tcx>, Region<'tcx>), |
| RegionsInsufficientlyPolymorphic(BoundRegionKind, Region<'tcx>), |
| RegionsOverlyPolymorphic(BoundRegionKind, Region<'tcx>), |
| RegionsPlaceholderMismatch, |
| |
| Sorts(ExpectedFound<Ty<'tcx>>), |
| ArgumentSorts(ExpectedFound<Ty<'tcx>>, usize), |
| IntMismatch(ExpectedFound<ty::IntVarValue>), |
| FloatMismatch(ExpectedFound<ty::FloatTy>), |
| Traits(ExpectedFound<DefId>), |
| VariadicMismatch(ExpectedFound<bool>), |
| |
| /// 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<DefId>), |
| ExistentialMismatch( |
| ExpectedFound<&'tcx ty::List<ty::Binder<'tcx, ty::ExistentialPredicate<'tcx>>>>, |
| ), |
| ObjectUnsafeCoercion(DefId), |
| ConstMismatch(ExpectedFound<ty::Const<'tcx>>), |
| |
| 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" |
| ), |
| ObjectUnsafeCoercion(_) => write!(f, "coercion to object-unsafe trait object"), |
| } |
| } |
| } |
| |
| 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 |
| | ObjectUnsafeCoercion(_) => 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)) => { |
| 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<Output = Expected>`. |
| // 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<T> { fn foo(&self) -> T; } |
| ``` |
| the only ways to implement method `foo` are: |
| - constrain `T` with an explicit type: |
| ``` |
| impl Trait<String> 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<T: std::default::Default> Trait<T> for X { |
| fn foo(&self) -> T { <T as std::default::Default>::default() } |
| } |
| ``` |
| - change `foo` to return an argument of type `T`: |
| ``` |
| impl<T> Trait<T> 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 <https://github.com/rust-lang/rust/issues/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 `<A as T>::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<T>(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<Ty<'tcx>>, |
| 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<Symbol>, |
| 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::<Vec<Span>>().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::<Vec<_>>(); |
| |
| let span = match &matching_trait_bounds[..] { |
| &[ptr] => ptr.span, |
| &[] if is_bound_surely_present => match &trait_bounds.collect::<Vec<_>>()[..] { |
| &[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 |
| } |
| |
| 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() |
| } |
| } |
