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Diffstat (limited to 'compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs')
| -rw-r--r-- | compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs | 3119 |
1 files changed, 3119 insertions, 0 deletions
diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs new file mode 100644 index 000000000..219413121 --- /dev/null +++ b/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs @@ -0,0 +1,3119 @@ +use super::{ + EvaluationResult, Obligation, ObligationCause, ObligationCauseCode, PredicateObligation, + SelectionContext, +}; + +use crate::autoderef::Autoderef; +use crate::infer::InferCtxt; +use crate::traits::normalize_to; + +use hir::HirId; +use rustc_data_structures::fx::FxHashSet; +use rustc_data_structures::stack::ensure_sufficient_stack; +use rustc_errors::{ + error_code, pluralize, struct_span_err, Applicability, Diagnostic, DiagnosticBuilder, + ErrorGuaranteed, MultiSpan, Style, +}; +use rustc_hir as hir; +use rustc_hir::def::DefKind; +use rustc_hir::def_id::DefId; +use rustc_hir::intravisit::Visitor; +use rustc_hir::lang_items::LangItem; +use rustc_hir::{AsyncGeneratorKind, GeneratorKind, Node}; +use rustc_infer::infer::TyCtxtInferExt; +use rustc_middle::hir::map; +use rustc_middle::ty::{ + self, suggest_arbitrary_trait_bound, suggest_constraining_type_param, AdtKind, DefIdTree, + GeneratorDiagnosticData, GeneratorInteriorTypeCause, Infer, InferTy, IsSuggestable, + ProjectionPredicate, ToPredicate, Ty, TyCtxt, TypeFoldable, TypeFolder, TypeSuperFoldable, + TypeVisitable, +}; +use rustc_middle::ty::{TypeAndMut, TypeckResults}; +use rustc_session::Limit; +use rustc_span::def_id::LOCAL_CRATE; +use rustc_span::symbol::{kw, sym, Ident, Symbol}; +use rustc_span::{BytePos, DesugaringKind, ExpnKind, Span, DUMMY_SP}; +use rustc_target::spec::abi; +use std::fmt; + +use super::InferCtxtPrivExt; +use crate::infer::InferCtxtExt as _; +use crate::traits::query::evaluate_obligation::InferCtxtExt as _; +use rustc_middle::ty::print::with_no_trimmed_paths; + +#[derive(Debug)] +pub enum GeneratorInteriorOrUpvar { + // span of interior type + Interior(Span), + // span of upvar + Upvar(Span), +} + +// This type provides a uniform interface to retrieve data on generators, whether it originated from +// the local crate being compiled or from a foreign crate. +#[derive(Debug)] +pub enum GeneratorData<'tcx, 'a> { + Local(&'a TypeckResults<'tcx>), + Foreign(&'tcx GeneratorDiagnosticData<'tcx>), +} + +impl<'tcx, 'a> GeneratorData<'tcx, 'a> { + // Try to get information about variables captured by the generator that matches a type we are + // looking for with `ty_matches` function. We uses it to find upvar which causes a failure to + // meet an obligation + fn try_get_upvar_span<F>( + &self, + infer_context: &InferCtxt<'a, 'tcx>, + generator_did: DefId, + ty_matches: F, + ) -> Option<GeneratorInteriorOrUpvar> + where + F: Fn(ty::Binder<'tcx, Ty<'tcx>>) -> bool, + { + match self { + GeneratorData::Local(typeck_results) => { + infer_context.tcx.upvars_mentioned(generator_did).and_then(|upvars| { + upvars.iter().find_map(|(upvar_id, upvar)| { + let upvar_ty = typeck_results.node_type(*upvar_id); + let upvar_ty = infer_context.resolve_vars_if_possible(upvar_ty); + if ty_matches(ty::Binder::dummy(upvar_ty)) { + Some(GeneratorInteriorOrUpvar::Upvar(upvar.span)) + } else { + None + } + }) + }) + } + GeneratorData::Foreign(_) => None, + } + } + + // Try to get the span of a type being awaited on that matches the type we are looking with the + // `ty_matches` function. We uses it to find awaited type which causes a failure to meet an + // obligation + fn get_from_await_ty<F>( + &self, + visitor: AwaitsVisitor, + hir: map::Map<'tcx>, + ty_matches: F, + ) -> Option<Span> + where + F: Fn(ty::Binder<'tcx, Ty<'tcx>>) -> bool, + { + match self { + GeneratorData::Local(typeck_results) => visitor + .awaits + .into_iter() + .map(|id| hir.expect_expr(id)) + .find(|await_expr| { + ty_matches(ty::Binder::dummy(typeck_results.expr_ty_adjusted(&await_expr))) + }) + .map(|expr| expr.span), + GeneratorData::Foreign(generator_diagnostic_data) => visitor + .awaits + .into_iter() + .map(|id| hir.expect_expr(id)) + .find(|await_expr| { + ty_matches(ty::Binder::dummy( + generator_diagnostic_data + .adjustments + .get(&await_expr.hir_id.local_id) + .map_or::<&[ty::adjustment::Adjustment<'tcx>], _>(&[], |a| &a[..]) + .last() + .map_or_else::<Ty<'tcx>, _, _>( + || { + generator_diagnostic_data + .nodes_types + .get(&await_expr.hir_id.local_id) + .cloned() + .unwrap_or_else(|| { + bug!( + "node_type: no type for node `{}`", + ty::tls::with(|tcx| tcx + .hir() + .node_to_string(await_expr.hir_id)) + ) + }) + }, + |adj| adj.target, + ), + )) + }) + .map(|expr| expr.span), + } + } + + /// Get the type, expression, span and optional scope span of all types + /// that are live across the yield of this generator + fn get_generator_interior_types( + &self, + ) -> ty::Binder<'tcx, &[GeneratorInteriorTypeCause<'tcx>]> { + match self { + GeneratorData::Local(typeck_result) => { + typeck_result.generator_interior_types.as_deref() + } + GeneratorData::Foreign(generator_diagnostic_data) => { + generator_diagnostic_data.generator_interior_types.as_deref() + } + } + } + + // Used to get the source of the data, note we don't have as much information for generators + // originated from foreign crates + fn is_foreign(&self) -> bool { + match self { + GeneratorData::Local(_) => false, + GeneratorData::Foreign(_) => true, + } + } +} + +// This trait is public to expose the diagnostics methods to clippy. +pub trait InferCtxtExt<'tcx> { + fn suggest_restricting_param_bound( + &self, + err: &mut Diagnostic, + trait_pred: ty::PolyTraitPredicate<'tcx>, + proj_pred: Option<ty::PolyProjectionPredicate<'tcx>>, + body_id: hir::HirId, + ); + + fn suggest_dereferences( + &self, + obligation: &PredicateObligation<'tcx>, + err: &mut Diagnostic, + trait_pred: ty::PolyTraitPredicate<'tcx>, + ) -> bool; + + fn get_closure_name(&self, def_id: DefId, err: &mut Diagnostic, msg: &str) -> Option<Symbol>; + + fn suggest_fn_call( + &self, + obligation: &PredicateObligation<'tcx>, + err: &mut Diagnostic, + trait_pred: ty::PolyTraitPredicate<'tcx>, + ) -> bool; + + fn suggest_add_reference_to_arg( + &self, + obligation: &PredicateObligation<'tcx>, + err: &mut Diagnostic, + trait_pred: ty::PolyTraitPredicate<'tcx>, + has_custom_message: bool, + ) -> bool; + + fn suggest_borrowing_for_object_cast( + &self, + err: &mut Diagnostic, + obligation: &PredicateObligation<'tcx>, + self_ty: Ty<'tcx>, + object_ty: Ty<'tcx>, + ); + + fn suggest_remove_reference( + &self, + obligation: &PredicateObligation<'tcx>, + err: &mut Diagnostic, + trait_pred: ty::PolyTraitPredicate<'tcx>, + ) -> bool; + + fn suggest_remove_await(&self, obligation: &PredicateObligation<'tcx>, err: &mut Diagnostic); + + fn suggest_change_mut( + &self, + obligation: &PredicateObligation<'tcx>, + err: &mut Diagnostic, + trait_pred: ty::PolyTraitPredicate<'tcx>, + ); + + fn suggest_semicolon_removal( + &self, + obligation: &PredicateObligation<'tcx>, + err: &mut Diagnostic, + span: Span, + trait_pred: ty::PolyTraitPredicate<'tcx>, + ) -> bool; + + fn return_type_span(&self, obligation: &PredicateObligation<'tcx>) -> Option<Span>; + + fn suggest_impl_trait( + &self, + err: &mut Diagnostic, + span: Span, + obligation: &PredicateObligation<'tcx>, + trait_pred: ty::PolyTraitPredicate<'tcx>, + ) -> bool; + + fn point_at_returns_when_relevant( + &self, + err: &mut Diagnostic, + obligation: &PredicateObligation<'tcx>, + ); + + fn report_closure_arg_mismatch( + &self, + span: Span, + found_span: Option<Span>, + found: ty::PolyTraitRef<'tcx>, + expected: ty::PolyTraitRef<'tcx>, + ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed>; + + fn suggest_fully_qualified_path( + &self, + err: &mut Diagnostic, + item_def_id: DefId, + span: Span, + trait_ref: DefId, + ); + + fn maybe_note_obligation_cause_for_async_await( + &self, + err: &mut Diagnostic, + obligation: &PredicateObligation<'tcx>, + ) -> bool; + + fn note_obligation_cause_for_async_await( + &self, + err: &mut Diagnostic, + interior_or_upvar_span: GeneratorInteriorOrUpvar, + interior_extra_info: Option<(Option<Span>, Span, Option<hir::HirId>, Option<Span>)>, + is_async: bool, + outer_generator: Option<DefId>, + trait_pred: ty::TraitPredicate<'tcx>, + target_ty: Ty<'tcx>, + typeck_results: Option<&ty::TypeckResults<'tcx>>, + obligation: &PredicateObligation<'tcx>, + next_code: Option<&ObligationCauseCode<'tcx>>, + ); + + fn note_obligation_cause_code<T>( + &self, + err: &mut Diagnostic, + predicate: &T, + param_env: ty::ParamEnv<'tcx>, + cause_code: &ObligationCauseCode<'tcx>, + obligated_types: &mut Vec<Ty<'tcx>>, + seen_requirements: &mut FxHashSet<DefId>, + ) where + T: fmt::Display; + + fn suggest_new_overflow_limit(&self, err: &mut Diagnostic); + + /// Suggest to await before try: future? => future.await? + fn suggest_await_before_try( + &self, + err: &mut Diagnostic, + obligation: &PredicateObligation<'tcx>, + trait_pred: ty::PolyTraitPredicate<'tcx>, + span: Span, + ); + + fn suggest_floating_point_literal( + &self, + obligation: &PredicateObligation<'tcx>, + err: &mut Diagnostic, + trait_ref: &ty::PolyTraitRef<'tcx>, + ); + + fn suggest_derive( + &self, + obligation: &PredicateObligation<'tcx>, + err: &mut Diagnostic, + trait_pred: ty::PolyTraitPredicate<'tcx>, + ); + + fn suggest_dereferencing_index( + &self, + obligation: &PredicateObligation<'tcx>, + err: &mut Diagnostic, + trait_pred: ty::PolyTraitPredicate<'tcx>, + ); +} + +fn predicate_constraint(generics: &hir::Generics<'_>, pred: String) -> (Span, String) { + ( + generics.tail_span_for_predicate_suggestion(), + format!("{} {}", generics.add_where_or_trailing_comma(), pred), + ) +} + +/// Type parameter needs more bounds. The trivial case is `T` `where T: Bound`, but +/// it can also be an `impl Trait` param that needs to be decomposed to a type +/// param for cleaner code. +fn suggest_restriction<'tcx>( + tcx: TyCtxt<'tcx>, + hir_id: HirId, + hir_generics: &hir::Generics<'tcx>, + msg: &str, + err: &mut Diagnostic, + fn_sig: Option<&hir::FnSig<'_>>, + projection: Option<&ty::ProjectionTy<'_>>, + trait_pred: ty::PolyTraitPredicate<'tcx>, + // When we are dealing with a trait, `super_traits` will be `Some`: + // Given `trait T: A + B + C {}` + // - ^^^^^^^^^ GenericBounds + // | + // &Ident + super_traits: Option<(&Ident, &hir::GenericBounds<'_>)>, +) { + if hir_generics.where_clause_span.from_expansion() + || hir_generics.where_clause_span.desugaring_kind().is_some() + { + return; + } + let Some(item_id) = hir_id.as_owner() else { return; }; + let generics = tcx.generics_of(item_id); + // Given `fn foo(t: impl Trait)` where `Trait` requires assoc type `A`... + if let Some((param, bound_str, fn_sig)) = + fn_sig.zip(projection).and_then(|(sig, p)| match p.self_ty().kind() { + // Shenanigans to get the `Trait` from the `impl Trait`. + ty::Param(param) => { + let param_def = generics.type_param(param, tcx); + if param_def.kind.is_synthetic() { + let bound_str = + param_def.name.as_str().strip_prefix("impl ")?.trim_start().to_string(); + return Some((param_def, bound_str, sig)); + } + None + } + _ => None, + }) + { + let type_param_name = hir_generics.params.next_type_param_name(Some(&bound_str)); + let trait_pred = trait_pred.fold_with(&mut ReplaceImplTraitFolder { + tcx, + param, + replace_ty: ty::ParamTy::new(generics.count() as u32, Symbol::intern(&type_param_name)) + .to_ty(tcx), + }); + if !trait_pred.is_suggestable(tcx, false) { + return; + } + // We know we have an `impl Trait` that doesn't satisfy a required projection. + + // Find all of the occurrences of `impl Trait` for `Trait` in the function arguments' + // types. There should be at least one, but there might be *more* than one. In that + // case we could just ignore it and try to identify which one needs the restriction, + // but instead we choose to suggest replacing all instances of `impl Trait` with `T` + // where `T: Trait`. + let mut ty_spans = vec![]; + for input in fn_sig.decl.inputs { + ReplaceImplTraitVisitor { ty_spans: &mut ty_spans, param_did: param.def_id } + .visit_ty(input); + } + // The type param `T: Trait` we will suggest to introduce. + let type_param = format!("{}: {}", type_param_name, bound_str); + + let mut sugg = vec![ + if let Some(span) = hir_generics.span_for_param_suggestion() { + (span, format!(", {}", type_param)) + } else { + (hir_generics.span, format!("<{}>", type_param)) + }, + // `fn foo(t: impl Trait)` + // ^ suggest `where <T as Trait>::A: Bound` + predicate_constraint(hir_generics, trait_pred.to_predicate(tcx).to_string()), + ]; + sugg.extend(ty_spans.into_iter().map(|s| (s, type_param_name.to_string()))); + + // Suggest `fn foo<T: Trait>(t: T) where <T as Trait>::A: Bound`. + // FIXME: once `#![feature(associated_type_bounds)]` is stabilized, we should suggest + // `fn foo(t: impl Trait<A: Bound>)` instead. + err.multipart_suggestion( + "introduce a type parameter with a trait bound instead of using `impl Trait`", + sugg, + Applicability::MaybeIncorrect, + ); + } else { + if !trait_pred.is_suggestable(tcx, false) { + return; + } + // Trivial case: `T` needs an extra bound: `T: Bound`. + let (sp, suggestion) = match ( + hir_generics + .params + .iter() + .find(|p| !matches!(p.kind, hir::GenericParamKind::Type { synthetic: true, .. })), + super_traits, + ) { + (_, None) => { + predicate_constraint(hir_generics, trait_pred.to_predicate(tcx).to_string()) + } + (None, Some((ident, []))) => ( + ident.span.shrink_to_hi(), + format!(": {}", trait_pred.print_modifiers_and_trait_path()), + ), + (_, Some((_, [.., bounds]))) => ( + bounds.span().shrink_to_hi(), + format!(" + {}", trait_pred.print_modifiers_and_trait_path()), + ), + (Some(_), Some((_, []))) => ( + hir_generics.span.shrink_to_hi(), + format!(": {}", trait_pred.print_modifiers_and_trait_path()), + ), + }; + + err.span_suggestion_verbose( + sp, + &format!("consider further restricting {}", msg), + suggestion, + Applicability::MachineApplicable, + ); + } +} + +impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> { + fn suggest_restricting_param_bound( + &self, + mut err: &mut Diagnostic, + trait_pred: ty::PolyTraitPredicate<'tcx>, + proj_pred: Option<ty::PolyProjectionPredicate<'tcx>>, + body_id: hir::HirId, + ) { + let trait_pred = self.resolve_numeric_literals_with_default(trait_pred); + + let self_ty = trait_pred.skip_binder().self_ty(); + let (param_ty, projection) = match self_ty.kind() { + ty::Param(_) => (true, None), + ty::Projection(projection) => (false, Some(projection)), + _ => (false, None), + }; + + // FIXME: Add check for trait bound that is already present, particularly `?Sized` so we + // don't suggest `T: Sized + ?Sized`. + let mut hir_id = body_id; + while let Some(node) = self.tcx.hir().find(hir_id) { + match node { + hir::Node::Item(hir::Item { + ident, + kind: hir::ItemKind::Trait(_, _, generics, bounds, _), + .. + }) if self_ty == self.tcx.types.self_param => { + assert!(param_ty); + // Restricting `Self` for a single method. + suggest_restriction( + self.tcx, + hir_id, + &generics, + "`Self`", + err, + None, + projection, + trait_pred, + Some((ident, bounds)), + ); + return; + } + + hir::Node::TraitItem(hir::TraitItem { + generics, + kind: hir::TraitItemKind::Fn(..), + .. + }) if self_ty == self.tcx.types.self_param => { + assert!(param_ty); + // Restricting `Self` for a single method. + suggest_restriction( + self.tcx, hir_id, &generics, "`Self`", err, None, projection, trait_pred, + None, + ); + return; + } + + hir::Node::TraitItem(hir::TraitItem { + generics, + kind: hir::TraitItemKind::Fn(fn_sig, ..), + .. + }) + | hir::Node::ImplItem(hir::ImplItem { + generics, + kind: hir::ImplItemKind::Fn(fn_sig, ..), + .. + }) + | hir::Node::Item(hir::Item { + kind: hir::ItemKind::Fn(fn_sig, generics, _), .. + }) if projection.is_some() => { + // Missing restriction on associated type of type parameter (unmet projection). + suggest_restriction( + self.tcx, + hir_id, + &generics, + "the associated type", + err, + Some(fn_sig), + projection, + trait_pred, + None, + ); + return; + } + hir::Node::Item(hir::Item { + kind: + hir::ItemKind::Trait(_, _, generics, ..) + | hir::ItemKind::Impl(hir::Impl { generics, .. }), + .. + }) if projection.is_some() => { + // Missing restriction on associated type of type parameter (unmet projection). + suggest_restriction( + self.tcx, + hir_id, + &generics, + "the associated type", + err, + None, + projection, + trait_pred, + None, + ); + return; + } + + hir::Node::Item(hir::Item { + kind: + hir::ItemKind::Struct(_, generics) + | hir::ItemKind::Enum(_, generics) + | hir::ItemKind::Union(_, generics) + | hir::ItemKind::Trait(_, _, generics, ..) + | hir::ItemKind::Impl(hir::Impl { generics, .. }) + | hir::ItemKind::Fn(_, generics, _) + | hir::ItemKind::TyAlias(_, generics) + | hir::ItemKind::TraitAlias(generics, _) + | hir::ItemKind::OpaqueTy(hir::OpaqueTy { generics, .. }), + .. + }) + | hir::Node::TraitItem(hir::TraitItem { generics, .. }) + | hir::Node::ImplItem(hir::ImplItem { generics, .. }) + if param_ty => + { + // We skip the 0'th subst (self) because we do not want + // to consider the predicate as not suggestible if the + // self type is an arg position `impl Trait` -- instead, + // we handle that by adding ` + Bound` below. + // FIXME(compiler-errors): It would be nice to do the same + // this that we do in `suggest_restriction` and pull the + // `impl Trait` into a new generic if it shows up somewhere + // else in the predicate. + if !trait_pred.skip_binder().trait_ref.substs[1..] + .iter() + .all(|g| g.is_suggestable(self.tcx, false)) + { + return; + } + // Missing generic type parameter bound. + let param_name = self_ty.to_string(); + let mut constraint = with_no_trimmed_paths!( + trait_pred.print_modifiers_and_trait_path().to_string() + ); + + if let Some(proj_pred) = proj_pred { + let ProjectionPredicate { projection_ty, term } = proj_pred.skip_binder(); + let item = self.tcx.associated_item(projection_ty.item_def_id); + + // 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], + item.name, + term + ); + } else { + constraint.push_str(&format!("<{}={}>", item.name, term)); + } + } + + if suggest_constraining_type_param( + self.tcx, + generics, + &mut err, + ¶m_name, + &constraint, + Some(trait_pred.def_id()), + ) { + return; + } + } + + hir::Node::Item(hir::Item { + kind: + hir::ItemKind::Struct(_, generics) + | hir::ItemKind::Enum(_, generics) + | hir::ItemKind::Union(_, generics) + | hir::ItemKind::Trait(_, _, generics, ..) + | hir::ItemKind::Impl(hir::Impl { generics, .. }) + | hir::ItemKind::Fn(_, generics, _) + | hir::ItemKind::TyAlias(_, generics) + | hir::ItemKind::TraitAlias(generics, _) + | hir::ItemKind::OpaqueTy(hir::OpaqueTy { generics, .. }), + .. + }) if !param_ty => { + // Missing generic type parameter bound. + if suggest_arbitrary_trait_bound(self.tcx, generics, &mut err, trait_pred) { + return; + } + } + hir::Node::Crate(..) => return, + + _ => {} + } + + hir_id = self.tcx.hir().local_def_id_to_hir_id(self.tcx.hir().get_parent_item(hir_id)); + } + } + + /// When after several dereferencing, the reference satisfies the trait + /// binding. This function provides dereference suggestion for this + /// specific situation. + fn suggest_dereferences( + &self, + obligation: &PredicateObligation<'tcx>, + err: &mut Diagnostic, + trait_pred: ty::PolyTraitPredicate<'tcx>, + ) -> bool { + // It only make sense when suggesting dereferences for arguments + let ObligationCauseCode::FunctionArgumentObligation { .. } = obligation.cause.code() else { + return false; + }; + let param_env = obligation.param_env; + let body_id = obligation.cause.body_id; + let span = obligation.cause.span; + let mut real_trait_pred = trait_pred; + let mut code = obligation.cause.code(); + while let Some((parent_code, parent_trait_pred)) = code.parent() { + code = parent_code; + if let Some(parent_trait_pred) = parent_trait_pred { + real_trait_pred = parent_trait_pred; + } + + // Skipping binder here, remapping below + let real_ty = real_trait_pred.self_ty().skip_binder(); + + if let ty::Ref(region, base_ty, mutbl) = *real_ty.kind() { + let mut autoderef = Autoderef::new(self, param_env, body_id, span, base_ty, span); + if let Some(steps) = autoderef.find_map(|(ty, steps)| { + // Re-add the `&` + let ty = self.tcx.mk_ref(region, TypeAndMut { ty, mutbl }); + + // Remapping bound vars here + let real_trait_pred_and_ty = + real_trait_pred.map_bound(|inner_trait_pred| (inner_trait_pred, ty)); + let obligation = self + .mk_trait_obligation_with_new_self_ty(param_env, real_trait_pred_and_ty); + Some(steps).filter(|_| self.predicate_may_hold(&obligation)) + }) { + if steps > 0 { + if let Ok(src) = self.tcx.sess.source_map().span_to_snippet(span) { + // Don't care about `&mut` because `DerefMut` is used less + // often and user will not expect autoderef happens. + if src.starts_with('&') && !src.starts_with("&mut ") { + let derefs = "*".repeat(steps); + err.span_suggestion( + span, + "consider dereferencing here", + format!("&{}{}", derefs, &src[1..]), + Applicability::MachineApplicable, + ); + return true; + } + } + } + } else if real_trait_pred != trait_pred { + // This branch addresses #87437. + + // Remapping bound vars here + let real_trait_pred_and_base_ty = + real_trait_pred.map_bound(|inner_trait_pred| (inner_trait_pred, base_ty)); + let obligation = self.mk_trait_obligation_with_new_self_ty( + param_env, + real_trait_pred_and_base_ty, + ); + if self.predicate_may_hold(&obligation) { + err.span_suggestion_verbose( + span.shrink_to_lo(), + "consider dereferencing here", + "*", + Applicability::MachineApplicable, + ); + return true; + } + } + } + } + false + } + + /// Given a closure's `DefId`, return the given name of the closure. + /// + /// This doesn't account for reassignments, but it's only used for suggestions. + fn get_closure_name(&self, def_id: DefId, err: &mut Diagnostic, msg: &str) -> Option<Symbol> { + let get_name = |err: &mut Diagnostic, kind: &hir::PatKind<'_>| -> Option<Symbol> { + // Get the local name of this closure. This can be inaccurate because + // of the possibility of reassignment, but this should be good enough. + match &kind { + hir::PatKind::Binding(hir::BindingAnnotation::Unannotated, _, ident, None) => { + Some(ident.name) + } + _ => { + err.note(msg); + None + } + } + }; + + let hir = self.tcx.hir(); + let hir_id = hir.local_def_id_to_hir_id(def_id.as_local()?); + let parent_node = hir.get_parent_node(hir_id); + match hir.find(parent_node) { + Some(hir::Node::Stmt(hir::Stmt { kind: hir::StmtKind::Local(local), .. })) => { + get_name(err, &local.pat.kind) + } + // Different to previous arm because one is `&hir::Local` and the other + // is `P<hir::Local>`. + Some(hir::Node::Local(local)) => get_name(err, &local.pat.kind), + _ => None, + } + } + + /// We tried to apply the bound to an `fn` or closure. Check whether calling it would + /// evaluate to a type that *would* satisfy the trait binding. If it would, suggest calling + /// it: `bar(foo)` → `bar(foo())`. This case is *very* likely to be hit if `foo` is `async`. + fn suggest_fn_call( + &self, + obligation: &PredicateObligation<'tcx>, + err: &mut Diagnostic, + trait_pred: ty::PolyTraitPredicate<'tcx>, + ) -> bool { + // Skipping binder here, remapping below + let self_ty = trait_pred.self_ty().skip_binder(); + + let (def_id, output_ty, callable) = match *self_ty.kind() { + ty::Closure(def_id, substs) => (def_id, substs.as_closure().sig().output(), "closure"), + ty::FnDef(def_id, _) => (def_id, self_ty.fn_sig(self.tcx).output(), "function"), + _ => return false, + }; + let msg = format!("use parentheses to call the {}", callable); + + // "We should really create a single list of bound vars from the combined vars + // from the predicate and function, but instead we just liberate the function bound vars" + let output_ty = self.tcx.liberate_late_bound_regions(def_id, output_ty); + + // Remapping bound vars here + let trait_pred_and_self = trait_pred.map_bound(|trait_pred| (trait_pred, output_ty)); + + let new_obligation = + self.mk_trait_obligation_with_new_self_ty(obligation.param_env, trait_pred_and_self); + + match self.evaluate_obligation(&new_obligation) { + Ok( + EvaluationResult::EvaluatedToOk + | EvaluationResult::EvaluatedToOkModuloRegions + | EvaluationResult::EvaluatedToOkModuloOpaqueTypes + | EvaluationResult::EvaluatedToAmbig, + ) => {} + _ => return false, + } + let hir = self.tcx.hir(); + // Get the name of the callable and the arguments to be used in the suggestion. + let (snippet, sugg) = match hir.get_if_local(def_id) { + Some(hir::Node::Expr(hir::Expr { + kind: hir::ExprKind::Closure(hir::Closure { fn_decl, fn_decl_span, .. }), + .. + })) => { + err.span_label(*fn_decl_span, "consider calling this closure"); + let Some(name) = self.get_closure_name(def_id, err, &msg) else { + return false; + }; + let args = fn_decl.inputs.iter().map(|_| "_").collect::<Vec<_>>().join(", "); + let sugg = format!("({})", args); + (format!("{}{}", name, sugg), sugg) + } + Some(hir::Node::Item(hir::Item { + ident, + kind: hir::ItemKind::Fn(.., body_id), + .. + })) => { + err.span_label(ident.span, "consider calling this function"); + let body = hir.body(*body_id); + let args = body + .params + .iter() + .map(|arg| match &arg.pat.kind { + hir::PatKind::Binding(_, _, ident, None) + // FIXME: provide a better suggestion when encountering `SelfLower`, it + // should suggest a method call. + if ident.name != kw::SelfLower => ident.to_string(), + _ => "_".to_string(), + }) + .collect::<Vec<_>>() + .join(", "); + let sugg = format!("({})", args); + (format!("{}{}", ident, sugg), sugg) + } + _ => return false, + }; + if matches!(obligation.cause.code(), ObligationCauseCode::FunctionArgumentObligation { .. }) + { + // When the obligation error has been ensured to have been caused by + // an argument, the `obligation.cause.span` points at the expression + // of the argument, so we can provide a suggestion. Otherwise, we give + // a more general note. + err.span_suggestion_verbose( + obligation.cause.span.shrink_to_hi(), + &msg, + sugg, + Applicability::HasPlaceholders, + ); + } else { + err.help(&format!("{}: `{}`", msg, snippet)); + } + true + } + + fn suggest_add_reference_to_arg( + &self, + obligation: &PredicateObligation<'tcx>, + err: &mut Diagnostic, + poly_trait_pred: ty::PolyTraitPredicate<'tcx>, + has_custom_message: bool, + ) -> bool { + let span = obligation.cause.span; + + let code = if let ObligationCauseCode::FunctionArgumentObligation { parent_code, .. } = + obligation.cause.code() + { + &parent_code + } else if let ExpnKind::Desugaring(DesugaringKind::ForLoop) = + span.ctxt().outer_expn_data().kind + { + obligation.cause.code() + } else { + return false; + }; + + // List of traits for which it would be nonsensical to suggest borrowing. + // For instance, immutable references are always Copy, so suggesting to + // borrow would always succeed, but it's probably not what the user wanted. + let mut never_suggest_borrow: Vec<_> = + [LangItem::Copy, LangItem::Clone, LangItem::Unpin, LangItem::Sized] + .iter() + .filter_map(|lang_item| self.tcx.lang_items().require(*lang_item).ok()) + .collect(); + + if let Some(def_id) = self.tcx.get_diagnostic_item(sym::Send) { + never_suggest_borrow.push(def_id); + } + + let param_env = obligation.param_env; + + // Try to apply the original trait binding obligation by borrowing. + let mut try_borrowing = + |old_pred: ty::PolyTraitPredicate<'tcx>, blacklist: &[DefId]| -> bool { + if blacklist.contains(&old_pred.def_id()) { + return false; + } + // We map bounds to `&T` and `&mut T` + let trait_pred_and_imm_ref = old_pred.map_bound(|trait_pred| { + ( + trait_pred, + self.tcx.mk_imm_ref(self.tcx.lifetimes.re_static, trait_pred.self_ty()), + ) + }); + let trait_pred_and_mut_ref = old_pred.map_bound(|trait_pred| { + ( + trait_pred, + self.tcx.mk_mut_ref(self.tcx.lifetimes.re_static, trait_pred.self_ty()), + ) + }); + + let mk_result = |trait_pred_and_new_ty| { + let obligation = + self.mk_trait_obligation_with_new_self_ty(param_env, trait_pred_and_new_ty); + self.predicate_must_hold_modulo_regions(&obligation) + }; + let imm_result = mk_result(trait_pred_and_imm_ref); + let mut_result = mk_result(trait_pred_and_mut_ref); + + if imm_result || mut_result { + if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span) { + // We have a very specific type of error, where just borrowing this argument + // might solve the problem. In cases like this, the important part is the + // original type obligation, not the last one that failed, which is arbitrary. + // Because of this, we modify the error to refer to the original obligation and + // return early in the caller. + + let msg = format!("the trait bound `{}` is not satisfied", old_pred); + if has_custom_message { + err.note(&msg); + } else { + err.message = + vec![(rustc_errors::DiagnosticMessage::Str(msg), Style::NoStyle)]; + } + if snippet.starts_with('&') { + // This is already a literal borrow and the obligation is failing + // somewhere else in the obligation chain. Do not suggest non-sense. + return false; + } + err.span_label( + span, + &format!( + "expected an implementor of trait `{}`", + old_pred.print_modifiers_and_trait_path(), + ), + ); + + // This if is to prevent a special edge-case + if matches!( + span.ctxt().outer_expn_data().kind, + ExpnKind::Root | ExpnKind::Desugaring(DesugaringKind::ForLoop) + ) { + // We don't want a borrowing suggestion on the fields in structs, + // ``` + // struct Foo { + // the_foos: Vec<Foo> + // } + // ``` + + if imm_result && mut_result { + err.span_suggestions( + span.shrink_to_lo(), + "consider borrowing here", + ["&".to_string(), "&mut ".to_string()].into_iter(), + Applicability::MaybeIncorrect, + ); + } else { + err.span_suggestion_verbose( + span.shrink_to_lo(), + &format!( + "consider{} borrowing here", + if mut_result { " mutably" } else { "" } + ), + format!("&{}", if mut_result { "mut " } else { "" }), + Applicability::MaybeIncorrect, + ); + } + } + return true; + } + } + return false; + }; + + if let ObligationCauseCode::ImplDerivedObligation(cause) = &*code { + try_borrowing(cause.derived.parent_trait_pred, &[]) + } else if let ObligationCauseCode::BindingObligation(_, _) + | ObligationCauseCode::ItemObligation(_) = code + { + try_borrowing(poly_trait_pred, &never_suggest_borrow) + } else { + false + } + } + + // Suggest borrowing the type + fn suggest_borrowing_for_object_cast( + &self, + err: &mut Diagnostic, + obligation: &PredicateObligation<'tcx>, + self_ty: Ty<'tcx>, + object_ty: Ty<'tcx>, + ) { + let ty::Dynamic(predicates, _) = object_ty.kind() else { return; }; + let self_ref_ty = self.tcx.mk_imm_ref(self.tcx.lifetimes.re_erased, self_ty); + + for predicate in predicates.iter() { + if !self.predicate_must_hold_modulo_regions( + &obligation.with(predicate.with_self_ty(self.tcx, self_ref_ty)), + ) { + return; + } + } + + err.span_suggestion( + obligation.cause.span.shrink_to_lo(), + &format!( + "consider borrowing the value, since `&{self_ty}` can be coerced into `{object_ty}`" + ), + "&", + Applicability::MaybeIncorrect, + ); + } + + /// Whenever references are used by mistake, like `for (i, e) in &vec.iter().enumerate()`, + /// suggest removing these references until we reach a type that implements the trait. + fn suggest_remove_reference( + &self, + obligation: &PredicateObligation<'tcx>, + err: &mut Diagnostic, + trait_pred: ty::PolyTraitPredicate<'tcx>, + ) -> bool { + let span = obligation.cause.span; + + let mut suggested = false; + if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span) { + let refs_number = + snippet.chars().filter(|c| !c.is_whitespace()).take_while(|c| *c == '&').count(); + if let Some('\'') = snippet.chars().filter(|c| !c.is_whitespace()).nth(refs_number) { + // Do not suggest removal of borrow from type arguments. + return false; + } + + // Skipping binder here, remapping below + let mut suggested_ty = trait_pred.self_ty().skip_binder(); + + for refs_remaining in 0..refs_number { + let ty::Ref(_, inner_ty, _) = suggested_ty.kind() else { + break; + }; + suggested_ty = *inner_ty; + + // Remapping bound vars here + let trait_pred_and_suggested_ty = + trait_pred.map_bound(|trait_pred| (trait_pred, suggested_ty)); + + let new_obligation = self.mk_trait_obligation_with_new_self_ty( + obligation.param_env, + trait_pred_and_suggested_ty, + ); + + if self.predicate_may_hold(&new_obligation) { + let sp = self + .tcx + .sess + .source_map() + .span_take_while(span, |c| c.is_whitespace() || *c == '&'); + + let remove_refs = refs_remaining + 1; + + let msg = if remove_refs == 1 { + "consider removing the leading `&`-reference".to_string() + } else { + format!("consider removing {} leading `&`-references", remove_refs) + }; + + err.span_suggestion_short(sp, &msg, "", Applicability::MachineApplicable); + suggested = true; + break; + } + } + } + suggested + } + + fn suggest_remove_await(&self, obligation: &PredicateObligation<'tcx>, err: &mut Diagnostic) { + let span = obligation.cause.span; + + if let ObligationCauseCode::AwaitableExpr(hir_id) = obligation.cause.code().peel_derives() { + let hir = self.tcx.hir(); + if let Some(node) = hir_id.and_then(|hir_id| hir.find(hir_id)) { + if let hir::Node::Expr(expr) = node { + // FIXME: use `obligation.predicate.kind()...trait_ref.self_ty()` to see if we have `()` + // and if not maybe suggest doing something else? If we kept the expression around we + // could also check if it is an fn call (very likely) and suggest changing *that*, if + // it is from the local crate. + err.span_suggestion_verbose( + expr.span.shrink_to_hi().with_hi(span.hi()), + "remove the `.await`", + "", + Applicability::MachineApplicable, + ); + // FIXME: account for associated `async fn`s. + if let hir::Expr { span, kind: hir::ExprKind::Call(base, _), .. } = expr { + if let ty::PredicateKind::Trait(pred) = + obligation.predicate.kind().skip_binder() + { + err.span_label( + *span, + &format!("this call returns `{}`", pred.self_ty()), + ); + } + if let Some(typeck_results) = + self.in_progress_typeck_results.map(|t| t.borrow()) + && let ty = typeck_results.expr_ty_adjusted(base) + && let ty::FnDef(def_id, _substs) = ty.kind() + && let Some(hir::Node::Item(hir::Item { ident, span, vis_span, .. })) = + hir.get_if_local(*def_id) + { + let msg = format!( + "alternatively, consider making `fn {}` asynchronous", + ident + ); + if vis_span.is_empty() { + err.span_suggestion_verbose( + span.shrink_to_lo(), + &msg, + "async ", + Applicability::MaybeIncorrect, + ); + } else { + err.span_suggestion_verbose( + vis_span.shrink_to_hi(), + &msg, + " async", + Applicability::MaybeIncorrect, + ); + } + } + } + } + } + } + } + + /// Check if the trait bound is implemented for a different mutability and note it in the + /// final error. + fn suggest_change_mut( + &self, + obligation: &PredicateObligation<'tcx>, + err: &mut Diagnostic, + trait_pred: ty::PolyTraitPredicate<'tcx>, + ) { + let points_at_arg = matches!( + obligation.cause.code(), + ObligationCauseCode::FunctionArgumentObligation { .. }, + ); + + let span = obligation.cause.span; + if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span) { + let refs_number = + snippet.chars().filter(|c| !c.is_whitespace()).take_while(|c| *c == '&').count(); + if let Some('\'') = snippet.chars().filter(|c| !c.is_whitespace()).nth(refs_number) { + // Do not suggest removal of borrow from type arguments. + return; + } + let trait_pred = self.resolve_vars_if_possible(trait_pred); + if trait_pred.has_infer_types_or_consts() { + // Do not ICE while trying to find if a reborrow would succeed on a trait with + // unresolved bindings. + return; + } + + // Skipping binder here, remapping below + if let ty::Ref(region, t_type, mutability) = *trait_pred.skip_binder().self_ty().kind() + { + let suggested_ty = match mutability { + hir::Mutability::Mut => self.tcx.mk_imm_ref(region, t_type), + hir::Mutability::Not => self.tcx.mk_mut_ref(region, t_type), + }; + + // Remapping bound vars here + let trait_pred_and_suggested_ty = + trait_pred.map_bound(|trait_pred| (trait_pred, suggested_ty)); + + let new_obligation = self.mk_trait_obligation_with_new_self_ty( + obligation.param_env, + trait_pred_and_suggested_ty, + ); + let suggested_ty_would_satisfy_obligation = self + .evaluate_obligation_no_overflow(&new_obligation) + .must_apply_modulo_regions(); + if suggested_ty_would_satisfy_obligation { + let sp = self + .tcx + .sess + .source_map() + .span_take_while(span, |c| c.is_whitespace() || *c == '&'); + if points_at_arg && mutability == hir::Mutability::Not && refs_number > 0 { + err.span_suggestion_verbose( + sp, + "consider changing this borrow's mutability", + "&mut ", + Applicability::MachineApplicable, + ); + } else { + err.note(&format!( + "`{}` is implemented for `{:?}`, but not for `{:?}`", + trait_pred.print_modifiers_and_trait_path(), + suggested_ty, + trait_pred.skip_binder().self_ty(), + )); + } + } + } + } + } + + fn suggest_semicolon_removal( + &self, + obligation: &PredicateObligation<'tcx>, + err: &mut Diagnostic, + span: Span, + trait_pred: ty::PolyTraitPredicate<'tcx>, + ) -> bool { + let hir = self.tcx.hir(); + let parent_node = hir.get_parent_node(obligation.cause.body_id); + let node = hir.find(parent_node); + if let Some(hir::Node::Item(hir::Item { kind: hir::ItemKind::Fn(sig, _, body_id), .. })) = node + && let hir::ExprKind::Block(blk, _) = &hir.body(*body_id).value.kind + && sig.decl.output.span().overlaps(span) + && blk.expr.is_none() + && trait_pred.self_ty().skip_binder().is_unit() + && let Some(stmt) = blk.stmts.last() + && let hir::StmtKind::Semi(expr) = stmt.kind + // Only suggest this if the expression behind the semicolon implements the predicate + && let Some(typeck_results) = self.in_progress_typeck_results + && let Some(ty) = typeck_results.borrow().expr_ty_opt(expr) + && self.predicate_may_hold(&self.mk_trait_obligation_with_new_self_ty( + obligation.param_env, trait_pred.map_bound(|trait_pred| (trait_pred, ty)) + )) + { + err.span_label( + expr.span, + &format!( + "this expression has type `{}`, which implements `{}`", + ty, + trait_pred.print_modifiers_and_trait_path() + ) + ); + err.span_suggestion( + self.tcx.sess.source_map().end_point(stmt.span), + "remove this semicolon", + "", + Applicability::MachineApplicable + ); + return true; + } + false + } + + fn return_type_span(&self, obligation: &PredicateObligation<'tcx>) -> Option<Span> { + let hir = self.tcx.hir(); + let parent_node = hir.get_parent_node(obligation.cause.body_id); + let Some(hir::Node::Item(hir::Item { kind: hir::ItemKind::Fn(sig, ..), .. })) = hir.find(parent_node) else { + return None; + }; + + if let hir::FnRetTy::Return(ret_ty) = sig.decl.output { Some(ret_ty.span) } else { None } + } + + /// If all conditions are met to identify a returned `dyn Trait`, suggest using `impl Trait` if + /// applicable and signal that the error has been expanded appropriately and needs to be + /// emitted. + fn suggest_impl_trait( + &self, + err: &mut Diagnostic, + span: Span, + obligation: &PredicateObligation<'tcx>, + trait_pred: ty::PolyTraitPredicate<'tcx>, + ) -> bool { + match obligation.cause.code().peel_derives() { + // Only suggest `impl Trait` if the return type is unsized because it is `dyn Trait`. + ObligationCauseCode::SizedReturnType => {} + _ => return false, + } + + let hir = self.tcx.hir(); + let fn_hir_id = hir.get_parent_node(obligation.cause.body_id); + let node = hir.find(fn_hir_id); + let Some(hir::Node::Item(hir::Item { + kind: hir::ItemKind::Fn(sig, _, body_id), + .. + })) = node + else { + return false; + }; + let body = hir.body(*body_id); + let trait_pred = self.resolve_vars_if_possible(trait_pred); + let ty = trait_pred.skip_binder().self_ty(); + let is_object_safe = match ty.kind() { + ty::Dynamic(predicates, _) => { + // If the `dyn Trait` is not object safe, do not suggest `Box<dyn Trait>`. + predicates + .principal_def_id() + .map_or(true, |def_id| self.tcx.object_safety_violations(def_id).is_empty()) + } + // We only want to suggest `impl Trait` to `dyn Trait`s. + // For example, `fn foo() -> str` needs to be filtered out. + _ => return false, + }; + + let hir::FnRetTy::Return(ret_ty) = sig.decl.output else { + return false; + }; + + // Use `TypeVisitor` instead of the output type directly to find the span of `ty` for + // cases like `fn foo() -> (dyn Trait, i32) {}`. + // Recursively look for `TraitObject` types and if there's only one, use that span to + // suggest `impl Trait`. + + // Visit to make sure there's a single `return` type to suggest `impl Trait`, + // otherwise suggest using `Box<dyn Trait>` or an enum. + let mut visitor = ReturnsVisitor::default(); + visitor.visit_body(&body); + + let typeck_results = self.in_progress_typeck_results.map(|t| t.borrow()).unwrap(); + let Some(liberated_sig) = typeck_results.liberated_fn_sigs().get(fn_hir_id).copied() else { return false; }; + + let ret_types = visitor + .returns + .iter() + .filter_map(|expr| Some((expr.span, typeck_results.node_type_opt(expr.hir_id)?))) + .map(|(expr_span, ty)| (expr_span, self.resolve_vars_if_possible(ty))); + let (last_ty, all_returns_have_same_type, only_never_return) = ret_types.clone().fold( + (None, true, true), + |(last_ty, mut same, only_never_return): (std::option::Option<Ty<'_>>, bool, bool), + (_, ty)| { + let ty = self.resolve_vars_if_possible(ty); + same &= + !matches!(ty.kind(), ty::Error(_)) + && last_ty.map_or(true, |last_ty| { + // FIXME: ideally we would use `can_coerce` here instead, but `typeck` comes + // *after* in the dependency graph. + match (ty.kind(), last_ty.kind()) { + (Infer(InferTy::IntVar(_)), Infer(InferTy::IntVar(_))) + | (Infer(InferTy::FloatVar(_)), Infer(InferTy::FloatVar(_))) + | (Infer(InferTy::FreshIntTy(_)), Infer(InferTy::FreshIntTy(_))) + | ( + Infer(InferTy::FreshFloatTy(_)), + Infer(InferTy::FreshFloatTy(_)), + ) => true, + _ => ty == last_ty, + } + }); + (Some(ty), same, only_never_return && matches!(ty.kind(), ty::Never)) + }, + ); + let mut spans_and_needs_box = vec![]; + + match liberated_sig.output().kind() { + ty::Dynamic(predicates, _) => { + let cause = ObligationCause::misc(ret_ty.span, fn_hir_id); + let param_env = ty::ParamEnv::empty(); + + if !only_never_return { + for (expr_span, return_ty) in ret_types { + let self_ty_satisfies_dyn_predicates = |self_ty| { + predicates.iter().all(|predicate| { + let pred = predicate.with_self_ty(self.tcx, self_ty); + let obl = Obligation::new(cause.clone(), param_env, pred); + self.predicate_may_hold(&obl) + }) + }; + + if let ty::Adt(def, substs) = return_ty.kind() + && def.is_box() + && self_ty_satisfies_dyn_predicates(substs.type_at(0)) + { + spans_and_needs_box.push((expr_span, false)); + } else if self_ty_satisfies_dyn_predicates(return_ty) { + spans_and_needs_box.push((expr_span, true)); + } else { + return false; + } + } + } + } + _ => return false, + }; + + let sm = self.tcx.sess.source_map(); + if !ret_ty.span.overlaps(span) { + return false; + } + let snippet = if let hir::TyKind::TraitObject(..) = ret_ty.kind { + if let Ok(snippet) = sm.span_to_snippet(ret_ty.span) { + snippet + } else { + return false; + } + } else { + // Substitute the type, so we can print a fixup given `type Alias = dyn Trait` + let name = liberated_sig.output().to_string(); + let name = + name.strip_prefix('(').and_then(|name| name.strip_suffix(')')).unwrap_or(&name); + if !name.starts_with("dyn ") { + return false; + } + name.to_owned() + }; + + err.code(error_code!(E0746)); + err.set_primary_message("return type cannot have an unboxed trait object"); + err.children.clear(); + let impl_trait_msg = "for information on `impl Trait`, see \ + <https://doc.rust-lang.org/book/ch10-02-traits.html\ + #returning-types-that-implement-traits>"; + let trait_obj_msg = "for information on trait objects, see \ + <https://doc.rust-lang.org/book/ch17-02-trait-objects.html\ + #using-trait-objects-that-allow-for-values-of-different-types>"; + + let has_dyn = snippet.split_whitespace().next().map_or(false, |s| s == "dyn"); + let trait_obj = if has_dyn { &snippet[4..] } else { &snippet }; + if only_never_return { + // No return paths, probably using `panic!()` or similar. + // Suggest `-> T`, `-> impl Trait`, and if `Trait` is object safe, `-> Box<dyn Trait>`. + suggest_trait_object_return_type_alternatives( + err, + ret_ty.span, + trait_obj, + is_object_safe, + ); + } else if let (Some(last_ty), true) = (last_ty, all_returns_have_same_type) { + // Suggest `-> impl Trait`. + err.span_suggestion( + ret_ty.span, + &format!( + "use `impl {1}` as the return type, as all return paths are of type `{}`, \ + which implements `{1}`", + last_ty, trait_obj, + ), + format!("impl {}", trait_obj), + Applicability::MachineApplicable, + ); + err.note(impl_trait_msg); + } else { + if is_object_safe { + // Suggest `-> Box<dyn Trait>` and `Box::new(returned_value)`. + err.multipart_suggestion( + "return a boxed trait object instead", + vec![ + (ret_ty.span.shrink_to_lo(), "Box<".to_string()), + (span.shrink_to_hi(), ">".to_string()), + ], + Applicability::MaybeIncorrect, + ); + for (span, needs_box) in spans_and_needs_box { + if needs_box { + err.multipart_suggestion( + "... and box this value", + vec![ + (span.shrink_to_lo(), "Box::new(".to_string()), + (span.shrink_to_hi(), ")".to_string()), + ], + Applicability::MaybeIncorrect, + ); + } + } + } else { + // This is currently not possible to trigger because E0038 takes precedence, but + // leave it in for completeness in case anything changes in an earlier stage. + err.note(&format!( + "if trait `{}` were object-safe, you could return a trait object", + trait_obj, + )); + } + err.note(trait_obj_msg); + err.note(&format!( + "if all the returned values were of the same type you could use `impl {}` as the \ + return type", + trait_obj, + )); + err.note(impl_trait_msg); + err.note("you can create a new `enum` with a variant for each returned type"); + } + true + } + + fn point_at_returns_when_relevant( + &self, + err: &mut Diagnostic, + obligation: &PredicateObligation<'tcx>, + ) { + match obligation.cause.code().peel_derives() { + ObligationCauseCode::SizedReturnType => {} + _ => return, + } + + let hir = self.tcx.hir(); + let parent_node = hir.get_parent_node(obligation.cause.body_id); + let node = hir.find(parent_node); + if let Some(hir::Node::Item(hir::Item { kind: hir::ItemKind::Fn(_, _, body_id), .. })) = + node + { + let body = hir.body(*body_id); + // Point at all the `return`s in the function as they have failed trait bounds. + let mut visitor = ReturnsVisitor::default(); + visitor.visit_body(&body); + let typeck_results = self.in_progress_typeck_results.map(|t| t.borrow()).unwrap(); + for expr in &visitor.returns { + if let Some(returned_ty) = typeck_results.node_type_opt(expr.hir_id) { + let ty = self.resolve_vars_if_possible(returned_ty); + err.span_label(expr.span, &format!("this returned value is of type `{}`", ty)); + } + } + } + } + + fn report_closure_arg_mismatch( + &self, + span: Span, + found_span: Option<Span>, + found: ty::PolyTraitRef<'tcx>, + expected: ty::PolyTraitRef<'tcx>, + ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> { + pub(crate) fn build_fn_sig_ty<'tcx>( + tcx: TyCtxt<'tcx>, + trait_ref: ty::PolyTraitRef<'tcx>, + ) -> Ty<'tcx> { + let inputs = trait_ref.skip_binder().substs.type_at(1); + let sig = match inputs.kind() { + ty::Tuple(inputs) + if tcx.fn_trait_kind_from_lang_item(trait_ref.def_id()).is_some() => + { + tcx.mk_fn_sig( + inputs.iter(), + tcx.mk_ty_infer(ty::TyVar(ty::TyVid::from_u32(0))), + false, + hir::Unsafety::Normal, + abi::Abi::Rust, + ) + } + _ => tcx.mk_fn_sig( + std::iter::once(inputs), + tcx.mk_ty_infer(ty::TyVar(ty::TyVid::from_u32(0))), + false, + hir::Unsafety::Normal, + abi::Abi::Rust, + ), + }; + + tcx.mk_fn_ptr(trait_ref.rebind(sig)) + } + + let argument_kind = match expected.skip_binder().self_ty().kind() { + ty::Closure(..) => "closure", + ty::Generator(..) => "generator", + _ => "function", + }; + let mut err = struct_span_err!( + self.tcx.sess, + span, + E0631, + "type mismatch in {argument_kind} arguments", + ); + + err.span_label(span, "expected due to this"); + + let found_span = found_span.unwrap_or(span); + err.span_label(found_span, "found signature defined here"); + + let expected = build_fn_sig_ty(self.tcx, expected); + let found = build_fn_sig_ty(self.tcx, found); + + let (expected_str, found_str) = + self.tcx.infer_ctxt().enter(|infcx| infcx.cmp(expected, found)); + + let signature_kind = format!("{argument_kind} signature"); + err.note_expected_found(&signature_kind, expected_str, &signature_kind, found_str); + + err + } + + fn suggest_fully_qualified_path( + &self, + err: &mut Diagnostic, + item_def_id: DefId, + span: Span, + trait_ref: DefId, + ) { + if let Some(assoc_item) = self.tcx.opt_associated_item(item_def_id) { + if let ty::AssocKind::Const | ty::AssocKind::Type = assoc_item.kind { + err.note(&format!( + "{}s cannot be accessed directly on a `trait`, they can only be \ + accessed through a specific `impl`", + assoc_item.kind.as_def_kind().descr(item_def_id) + )); + err.span_suggestion( + span, + "use the fully qualified path to an implementation", + format!("<Type as {}>::{}", self.tcx.def_path_str(trait_ref), assoc_item.name), + Applicability::HasPlaceholders, + ); + } + } + } + + /// Adds an async-await specific note to the diagnostic when the future does not implement + /// an auto trait because of a captured type. + /// + /// ```text + /// note: future does not implement `Qux` as this value is used across an await + /// --> $DIR/issue-64130-3-other.rs:17:5 + /// | + /// LL | let x = Foo; + /// | - has type `Foo` + /// LL | baz().await; + /// | ^^^^^^^^^^^ await occurs here, with `x` maybe used later + /// LL | } + /// | - `x` is later dropped here + /// ``` + /// + /// When the diagnostic does not implement `Send` or `Sync` specifically, then the diagnostic + /// is "replaced" with a different message and a more specific error. + /// + /// ```text + /// error: future cannot be sent between threads safely + /// --> $DIR/issue-64130-2-send.rs:21:5 + /// | + /// LL | fn is_send<T: Send>(t: T) { } + /// | ---- required by this bound in `is_send` + /// ... + /// LL | is_send(bar()); + /// | ^^^^^^^ future returned by `bar` is not send + /// | + /// = help: within `impl std::future::Future`, the trait `std::marker::Send` is not + /// implemented for `Foo` + /// note: future is not send as this value is used across an await + /// --> $DIR/issue-64130-2-send.rs:15:5 + /// | + /// LL | let x = Foo; + /// | - has type `Foo` + /// LL | baz().await; + /// | ^^^^^^^^^^^ await occurs here, with `x` maybe used later + /// LL | } + /// | - `x` is later dropped here + /// ``` + /// + /// Returns `true` if an async-await specific note was added to the diagnostic. + #[instrument(level = "debug", skip_all, fields(?obligation.predicate, ?obligation.cause.span))] + fn maybe_note_obligation_cause_for_async_await( + &self, + err: &mut Diagnostic, + obligation: &PredicateObligation<'tcx>, + ) -> bool { + let hir = self.tcx.hir(); + + // Attempt to detect an async-await error by looking at the obligation causes, looking + // for a generator to be present. + // + // When a future does not implement a trait because of a captured type in one of the + // generators somewhere in the call stack, then the result is a chain of obligations. + // + // Given an `async fn` A that calls an `async fn` B which captures a non-send type and that + // future is passed as an argument to a function C which requires a `Send` type, then the + // chain looks something like this: + // + // - `BuiltinDerivedObligation` with a generator witness (B) + // - `BuiltinDerivedObligation` with a generator (B) + // - `BuiltinDerivedObligation` with `std::future::GenFuture` (B) + // - `BuiltinDerivedObligation` with `impl std::future::Future` (B) + // - `BuiltinDerivedObligation` with `impl std::future::Future` (B) + // - `BuiltinDerivedObligation` with a generator witness (A) + // - `BuiltinDerivedObligation` with a generator (A) + // - `BuiltinDerivedObligation` with `std::future::GenFuture` (A) + // - `BuiltinDerivedObligation` with `impl std::future::Future` (A) + // - `BuiltinDerivedObligation` with `impl std::future::Future` (A) + // - `BindingObligation` with `impl_send (Send requirement) + // + // The first obligation in the chain is the most useful and has the generator that captured + // the type. The last generator (`outer_generator` below) has information about where the + // bound was introduced. At least one generator should be present for this diagnostic to be + // modified. + let (mut trait_ref, mut target_ty) = match obligation.predicate.kind().skip_binder() { + ty::PredicateKind::Trait(p) => (Some(p), Some(p.self_ty())), + _ => (None, None), + }; + let mut generator = None; + let mut outer_generator = None; + let mut next_code = Some(obligation.cause.code()); + + let mut seen_upvar_tys_infer_tuple = false; + + while let Some(code) = next_code { + debug!(?code); + match code { + ObligationCauseCode::FunctionArgumentObligation { parent_code, .. } => { + next_code = Some(parent_code); + } + ObligationCauseCode::ImplDerivedObligation(cause) => { + let ty = cause.derived.parent_trait_pred.skip_binder().self_ty(); + debug!( + parent_trait_ref = ?cause.derived.parent_trait_pred, + self_ty.kind = ?ty.kind(), + "ImplDerived", + ); + + match *ty.kind() { + ty::Generator(did, ..) => { + generator = generator.or(Some(did)); + outer_generator = Some(did); + } + ty::GeneratorWitness(..) => {} + ty::Tuple(_) if !seen_upvar_tys_infer_tuple => { + // By introducing a tuple of upvar types into the chain of obligations + // of a generator, the first non-generator item is now the tuple itself, + // we shall ignore this. + + seen_upvar_tys_infer_tuple = true; + } + _ if generator.is_none() => { + trait_ref = Some(cause.derived.parent_trait_pred.skip_binder()); + target_ty = Some(ty); + } + _ => {} + } + + next_code = Some(&cause.derived.parent_code); + } + ObligationCauseCode::DerivedObligation(derived_obligation) + | ObligationCauseCode::BuiltinDerivedObligation(derived_obligation) => { + let ty = derived_obligation.parent_trait_pred.skip_binder().self_ty(); + debug!( + parent_trait_ref = ?derived_obligation.parent_trait_pred, + self_ty.kind = ?ty.kind(), + ); + + match *ty.kind() { + ty::Generator(did, ..) => { + generator = generator.or(Some(did)); + outer_generator = Some(did); + } + ty::GeneratorWitness(..) => {} + ty::Tuple(_) if !seen_upvar_tys_infer_tuple => { + // By introducing a tuple of upvar types into the chain of obligations + // of a generator, the first non-generator item is now the tuple itself, + // we shall ignore this. + + seen_upvar_tys_infer_tuple = true; + } + _ if generator.is_none() => { + trait_ref = Some(derived_obligation.parent_trait_pred.skip_binder()); + target_ty = Some(ty); + } + _ => {} + } + + next_code = Some(&derived_obligation.parent_code); + } + _ => break, + } + } + + // Only continue if a generator was found. + debug!(?generator, ?trait_ref, ?target_ty); + let (Some(generator_did), Some(trait_ref), Some(target_ty)) = (generator, trait_ref, target_ty) else { + return false; + }; + + let span = self.tcx.def_span(generator_did); + + let in_progress_typeck_results = self.in_progress_typeck_results.map(|t| t.borrow()); + let generator_did_root = self.tcx.typeck_root_def_id(generator_did); + debug!( + ?generator_did, + ?generator_did_root, + in_progress_typeck_results.hir_owner = ?in_progress_typeck_results.as_ref().map(|t| t.hir_owner), + ?span, + ); + + let generator_body = generator_did + .as_local() + .and_then(|def_id| hir.maybe_body_owned_by(def_id)) + .map(|body_id| hir.body(body_id)); + let is_async = match generator_did.as_local() { + Some(_) => generator_body + .and_then(|body| body.generator_kind()) + .map(|generator_kind| matches!(generator_kind, hir::GeneratorKind::Async(..))) + .unwrap_or(false), + None => self + .tcx + .generator_kind(generator_did) + .map(|generator_kind| matches!(generator_kind, hir::GeneratorKind::Async(..))) + .unwrap_or(false), + }; + let mut visitor = AwaitsVisitor::default(); + if let Some(body) = generator_body { + visitor.visit_body(body); + } + debug!(awaits = ?visitor.awaits); + + // Look for a type inside the generator interior that matches the target type to get + // a span. + let target_ty_erased = self.tcx.erase_regions(target_ty); + let ty_matches = |ty| -> bool { + // Careful: the regions for types that appear in the + // generator interior are not generally known, so we + // want to erase them when comparing (and anyway, + // `Send` and other bounds are generally unaffected by + // the choice of region). When erasing regions, we + // also have to erase late-bound regions. This is + // because the types that appear in the generator + // interior generally contain "bound regions" to + // represent regions that are part of the suspended + // generator frame. Bound regions are preserved by + // `erase_regions` and so we must also call + // `erase_late_bound_regions`. + let ty_erased = self.tcx.erase_late_bound_regions(ty); + let ty_erased = self.tcx.erase_regions(ty_erased); + let eq = ty_erased == target_ty_erased; + debug!(?ty_erased, ?target_ty_erased, ?eq); + eq + }; + + let mut interior_or_upvar_span = None; + let mut interior_extra_info = None; + + // Get the typeck results from the infcx if the generator is the function we are currently + // type-checking; otherwise, get them by performing a query. This is needed to avoid + // cycles. If we can't use resolved types because the generator comes from another crate, + // we still provide a targeted error but without all the relevant spans. + let generator_data: Option<GeneratorData<'tcx, '_>> = match &in_progress_typeck_results { + Some(t) if t.hir_owner.to_def_id() == generator_did_root => { + Some(GeneratorData::Local(&t)) + } + _ if generator_did.is_local() => { + Some(GeneratorData::Local(self.tcx.typeck(generator_did.expect_local()))) + } + _ => self + .tcx + .generator_diagnostic_data(generator_did) + .as_ref() + .map(|generator_diag_data| GeneratorData::Foreign(generator_diag_data)), + }; + + if let Some(generator_data) = generator_data.as_ref() { + interior_or_upvar_span = + generator_data.try_get_upvar_span(&self, generator_did, ty_matches); + + // The generator interior types share the same binders + if let Some(cause) = + generator_data.get_generator_interior_types().skip_binder().iter().find( + |ty::GeneratorInteriorTypeCause { ty, .. }| { + ty_matches(generator_data.get_generator_interior_types().rebind(*ty)) + }, + ) + { + let from_awaited_ty = generator_data.get_from_await_ty(visitor, hir, ty_matches); + let ty::GeneratorInteriorTypeCause { span, scope_span, yield_span, expr, .. } = + cause; + + interior_or_upvar_span = Some(GeneratorInteriorOrUpvar::Interior(*span)); + interior_extra_info = Some((*scope_span, *yield_span, *expr, from_awaited_ty)); + } + + if interior_or_upvar_span.is_none() && generator_data.is_foreign() { + interior_or_upvar_span = Some(GeneratorInteriorOrUpvar::Interior(span)); + } + } + + if let Some(interior_or_upvar_span) = interior_or_upvar_span { + let typeck_results = generator_data.and_then(|generator_data| match generator_data { + GeneratorData::Local(typeck_results) => Some(typeck_results), + GeneratorData::Foreign(_) => None, + }); + self.note_obligation_cause_for_async_await( + err, + interior_or_upvar_span, + interior_extra_info, + is_async, + outer_generator, + trait_ref, + target_ty, + typeck_results, + obligation, + next_code, + ); + true + } else { + false + } + } + + /// Unconditionally adds the diagnostic note described in + /// `maybe_note_obligation_cause_for_async_await`'s documentation comment. + #[instrument(level = "debug", skip_all)] + fn note_obligation_cause_for_async_await( + &self, + err: &mut Diagnostic, + interior_or_upvar_span: GeneratorInteriorOrUpvar, + interior_extra_info: Option<(Option<Span>, Span, Option<hir::HirId>, Option<Span>)>, + is_async: bool, + outer_generator: Option<DefId>, + trait_pred: ty::TraitPredicate<'tcx>, + target_ty: Ty<'tcx>, + typeck_results: Option<&ty::TypeckResults<'tcx>>, + obligation: &PredicateObligation<'tcx>, + next_code: Option<&ObligationCauseCode<'tcx>>, + ) { + let source_map = self.tcx.sess.source_map(); + + let (await_or_yield, an_await_or_yield) = + if is_async { ("await", "an await") } else { ("yield", "a yield") }; + let future_or_generator = if is_async { "future" } else { "generator" }; + + // Special case the primary error message when send or sync is the trait that was + // not implemented. + let hir = self.tcx.hir(); + let trait_explanation = if let Some(name @ (sym::Send | sym::Sync)) = + self.tcx.get_diagnostic_name(trait_pred.def_id()) + { + let (trait_name, trait_verb) = + if name == sym::Send { ("`Send`", "sent") } else { ("`Sync`", "shared") }; + + err.clear_code(); + err.set_primary_message(format!( + "{} cannot be {} between threads safely", + future_or_generator, trait_verb + )); + + let original_span = err.span.primary_span().unwrap(); + let mut span = MultiSpan::from_span(original_span); + + let message = outer_generator + .and_then(|generator_did| { + Some(match self.tcx.generator_kind(generator_did).unwrap() { + GeneratorKind::Gen => format!("generator is not {}", trait_name), + GeneratorKind::Async(AsyncGeneratorKind::Fn) => self + .tcx + .parent(generator_did) + .as_local() + .map(|parent_did| hir.local_def_id_to_hir_id(parent_did)) + .and_then(|parent_hir_id| hir.opt_name(parent_hir_id)) + .map(|name| { + format!("future returned by `{}` is not {}", name, trait_name) + })?, + GeneratorKind::Async(AsyncGeneratorKind::Block) => { + format!("future created by async block is not {}", trait_name) + } + GeneratorKind::Async(AsyncGeneratorKind::Closure) => { + format!("future created by async closure is not {}", trait_name) + } + }) + }) + .unwrap_or_else(|| format!("{} is not {}", future_or_generator, trait_name)); + + span.push_span_label(original_span, message); + err.set_span(span); + + format!("is not {}", trait_name) + } else { + format!("does not implement `{}`", trait_pred.print_modifiers_and_trait_path()) + }; + + let mut explain_yield = |interior_span: Span, + yield_span: Span, + scope_span: Option<Span>| { + let mut span = MultiSpan::from_span(yield_span); + if let Ok(snippet) = source_map.span_to_snippet(interior_span) { + // #70935: If snippet contains newlines, display "the value" instead + // so that we do not emit complex diagnostics. + let snippet = &format!("`{}`", snippet); + let snippet = if snippet.contains('\n') { "the value" } else { snippet }; + // note: future is not `Send` as this value is used across an await + // --> $DIR/issue-70935-complex-spans.rs:13:9 + // | + // LL | baz(|| async { + // | ______________- + // | | + // | | + // LL | | foo(tx.clone()); + // LL | | }).await; + // | | - ^^^^^^ await occurs here, with value maybe used later + // | |__________| + // | has type `closure` which is not `Send` + // note: value is later dropped here + // LL | | }).await; + // | | ^ + // + span.push_span_label( + yield_span, + format!("{} occurs here, with {} maybe used later", await_or_yield, snippet), + ); + span.push_span_label( + interior_span, + format!("has type `{}` which {}", target_ty, trait_explanation), + ); + // If available, use the scope span to annotate the drop location. + let mut scope_note = None; + if let Some(scope_span) = scope_span { + let scope_span = source_map.end_point(scope_span); + + let msg = format!("{} is later dropped here", snippet); + if source_map.is_multiline(yield_span.between(scope_span)) { + span.push_span_label(scope_span, msg); + } else { + scope_note = Some((scope_span, msg)); + } + } + err.span_note( + span, + &format!( + "{} {} as this value is used across {}", + future_or_generator, trait_explanation, an_await_or_yield + ), + ); + if let Some((span, msg)) = scope_note { + err.span_note(span, &msg); + } + } + }; + match interior_or_upvar_span { + GeneratorInteriorOrUpvar::Interior(interior_span) => { + if let Some((scope_span, yield_span, expr, from_awaited_ty)) = interior_extra_info { + if let Some(await_span) = from_awaited_ty { + // The type causing this obligation is one being awaited at await_span. + let mut span = MultiSpan::from_span(await_span); + span.push_span_label( + await_span, + format!( + "await occurs here on type `{}`, which {}", + target_ty, trait_explanation + ), + ); + err.span_note( + span, + &format!( + "future {not_trait} as it awaits another future which {not_trait}", + not_trait = trait_explanation + ), + ); + } else { + // Look at the last interior type to get a span for the `.await`. + debug!( + generator_interior_types = ?format_args!( + "{:#?}", typeck_results.as_ref().map(|t| &t.generator_interior_types) + ), + ); + explain_yield(interior_span, yield_span, scope_span); + } + + if let Some(expr_id) = expr { + let expr = hir.expect_expr(expr_id); + debug!("target_ty evaluated from {:?}", expr); + + let parent = hir.get_parent_node(expr_id); + if let Some(hir::Node::Expr(e)) = hir.find(parent) { + let parent_span = hir.span(parent); + let parent_did = parent.owner.to_def_id(); + // ```rust + // impl T { + // fn foo(&self) -> i32 {} + // } + // T.foo(); + // ^^^^^^^ a temporary `&T` created inside this method call due to `&self` + // ``` + // + let is_region_borrow = if let Some(typeck_results) = typeck_results { + typeck_results + .expr_adjustments(expr) + .iter() + .any(|adj| adj.is_region_borrow()) + } else { + false + }; + + // ```rust + // struct Foo(*const u8); + // bar(Foo(std::ptr::null())).await; + // ^^^^^^^^^^^^^^^^^^^^^ raw-ptr `*T` created inside this struct ctor. + // ``` + debug!(parent_def_kind = ?self.tcx.def_kind(parent_did)); + let is_raw_borrow_inside_fn_like_call = + match self.tcx.def_kind(parent_did) { + DefKind::Fn | DefKind::Ctor(..) => target_ty.is_unsafe_ptr(), + _ => false, + }; + if let Some(typeck_results) = typeck_results { + if (typeck_results.is_method_call(e) && is_region_borrow) + || is_raw_borrow_inside_fn_like_call + { + err.span_help( + parent_span, + "consider moving this into a `let` \ + binding to create a shorter lived borrow", + ); + } + } + } + } + } + } + GeneratorInteriorOrUpvar::Upvar(upvar_span) => { + // `Some(ref_ty)` if `target_ty` is `&T` and `T` fails to impl `Sync` + let refers_to_non_sync = match target_ty.kind() { + ty::Ref(_, ref_ty, _) => match self.evaluate_obligation(&obligation) { + Ok(eval) if !eval.may_apply() => Some(ref_ty), + _ => None, + }, + _ => None, + }; + + let (span_label, span_note) = match refers_to_non_sync { + // if `target_ty` is `&T` and `T` fails to impl `Sync`, + // include suggestions to make `T: Sync` so that `&T: Send` + Some(ref_ty) => ( + format!( + "has type `{}` which {}, because `{}` is not `Sync`", + target_ty, trait_explanation, ref_ty + ), + format!( + "captured value {} because `&` references cannot be sent unless their referent is `Sync`", + trait_explanation + ), + ), + None => ( + format!("has type `{}` which {}", target_ty, trait_explanation), + format!("captured value {}", trait_explanation), + ), + }; + + let mut span = MultiSpan::from_span(upvar_span); + span.push_span_label(upvar_span, span_label); + err.span_note(span, &span_note); + } + } + + // Add a note for the item obligation that remains - normally a note pointing to the + // bound that introduced the obligation (e.g. `T: Send`). + debug!(?next_code); + self.note_obligation_cause_code( + err, + &obligation.predicate, + obligation.param_env, + next_code.unwrap(), + &mut Vec::new(), + &mut Default::default(), + ); + } + + fn note_obligation_cause_code<T>( + &self, + err: &mut Diagnostic, + predicate: &T, + param_env: ty::ParamEnv<'tcx>, + cause_code: &ObligationCauseCode<'tcx>, + obligated_types: &mut Vec<Ty<'tcx>>, + seen_requirements: &mut FxHashSet<DefId>, + ) where + T: fmt::Display, + { + let tcx = self.tcx; + match *cause_code { + ObligationCauseCode::ExprAssignable + | ObligationCauseCode::MatchExpressionArm { .. } + | ObligationCauseCode::Pattern { .. } + | ObligationCauseCode::IfExpression { .. } + | ObligationCauseCode::IfExpressionWithNoElse + | ObligationCauseCode::MainFunctionType + | ObligationCauseCode::StartFunctionType + | ObligationCauseCode::IntrinsicType + | ObligationCauseCode::MethodReceiver + | ObligationCauseCode::ReturnNoExpression + | ObligationCauseCode::UnifyReceiver(..) + | ObligationCauseCode::OpaqueType + | ObligationCauseCode::MiscObligation + | ObligationCauseCode::WellFormed(..) + | ObligationCauseCode::MatchImpl(..) + | ObligationCauseCode::ReturnType + | ObligationCauseCode::ReturnValue(_) + | ObligationCauseCode::BlockTailExpression(_) + | ObligationCauseCode::AwaitableExpr(_) + | ObligationCauseCode::ForLoopIterator + | ObligationCauseCode::QuestionMark + | ObligationCauseCode::CheckAssociatedTypeBounds { .. } + | ObligationCauseCode::LetElse + | ObligationCauseCode::BinOp { .. } => {} + ObligationCauseCode::SliceOrArrayElem => { + err.note("slice and array elements must have `Sized` type"); + } + ObligationCauseCode::TupleElem => { + err.note("only the last element of a tuple may have a dynamically sized type"); + } + ObligationCauseCode::ProjectionWf(data) => { + err.note(&format!("required so that the projection `{}` is well-formed", data,)); + } + ObligationCauseCode::ReferenceOutlivesReferent(ref_ty) => { + err.note(&format!( + "required so that reference `{}` does not outlive its referent", + ref_ty, + )); + } + ObligationCauseCode::ObjectTypeBound(object_ty, region) => { + err.note(&format!( + "required so that the lifetime bound of `{}` for `{}` is satisfied", + region, object_ty, + )); + } + ObligationCauseCode::ItemObligation(_item_def_id) => { + // We hold the `DefId` of the item introducing the obligation, but displaying it + // doesn't add user usable information. It always point at an associated item. + } + ObligationCauseCode::BindingObligation(item_def_id, span) => { + let item_name = tcx.def_path_str(item_def_id); + let mut multispan = MultiSpan::from(span); + if let Some(ident) = tcx.opt_item_ident(item_def_id) { + let sm = tcx.sess.source_map(); + let same_line = + match (sm.lookup_line(ident.span.hi()), sm.lookup_line(span.lo())) { + (Ok(l), Ok(r)) => l.line == r.line, + _ => true, + }; + if !ident.span.overlaps(span) && !same_line { + multispan.push_span_label(ident.span, "required by a bound in this"); + } + } + let descr = format!("required by a bound in `{}`", item_name); + if span != DUMMY_SP { + let msg = format!("required by this bound in `{}`", item_name); + multispan.push_span_label(span, msg); + err.span_note(multispan, &descr); + } else { + err.span_note(tcx.def_span(item_def_id), &descr); + } + } + ObligationCauseCode::ObjectCastObligation(concrete_ty, object_ty) => { + err.note(&format!( + "required for the cast from `{}` to the object type `{}`", + self.ty_to_string(concrete_ty), + self.ty_to_string(object_ty) + )); + } + ObligationCauseCode::Coercion { source: _, target } => { + err.note(&format!("required by cast to type `{}`", self.ty_to_string(target))); + } + ObligationCauseCode::RepeatElementCopy { is_const_fn } => { + err.note( + "the `Copy` trait is required because this value will be copied for each element of the array", + ); + + if is_const_fn { + err.help( + "consider creating a new `const` item and initializing it with the result \ + of the function call to be used in the repeat position, like \ + `const VAL: Type = const_fn();` and `let x = [VAL; 42];`", + ); + } + + if self.tcx.sess.is_nightly_build() && is_const_fn { + err.help( + "create an inline `const` block, see RFC #2920 \ + <https://github.com/rust-lang/rfcs/pull/2920> for more information", + ); + } + } + ObligationCauseCode::VariableType(hir_id) => { + let parent_node = self.tcx.hir().get_parent_node(hir_id); + match self.tcx.hir().find(parent_node) { + Some(Node::Local(hir::Local { + init: Some(hir::Expr { kind: hir::ExprKind::Index(_, _), span, .. }), + .. + })) => { + // When encountering an assignment of an unsized trait, like + // `let x = ""[..];`, provide a suggestion to borrow the initializer in + // order to use have a slice instead. + err.span_suggestion_verbose( + span.shrink_to_lo(), + "consider borrowing here", + "&", + Applicability::MachineApplicable, + ); + err.note("all local variables must have a statically known size"); + } + Some(Node::Param(param)) => { + err.span_suggestion_verbose( + param.ty_span.shrink_to_lo(), + "function arguments must have a statically known size, borrowed types \ + always have a known size", + "&", + Applicability::MachineApplicable, + ); + } + _ => { + err.note("all local variables must have a statically known size"); + } + } + if !self.tcx.features().unsized_locals { + err.help("unsized locals are gated as an unstable feature"); + } + } + ObligationCauseCode::SizedArgumentType(sp) => { + if let Some(span) = sp { + err.span_suggestion_verbose( + span.shrink_to_lo(), + "function arguments must have a statically known size, borrowed types \ + always have a known size", + "&", + Applicability::MachineApplicable, + ); + } else { + err.note("all function arguments must have a statically known size"); + } + if tcx.sess.opts.unstable_features.is_nightly_build() + && !self.tcx.features().unsized_fn_params + { + err.help("unsized fn params are gated as an unstable feature"); + } + } + ObligationCauseCode::SizedReturnType => { + err.note("the return type of a function must have a statically known size"); + } + ObligationCauseCode::SizedYieldType => { + err.note("the yield type of a generator must have a statically known size"); + } + ObligationCauseCode::SizedBoxType => { + err.note("the type of a box expression must have a statically known size"); + } + ObligationCauseCode::AssignmentLhsSized => { + err.note("the left-hand-side of an assignment must have a statically known size"); + } + ObligationCauseCode::TupleInitializerSized => { + err.note("tuples must have a statically known size to be initialized"); + } + ObligationCauseCode::StructInitializerSized => { + err.note("structs must have a statically known size to be initialized"); + } + ObligationCauseCode::FieldSized { adt_kind: ref item, last, span } => { + match *item { + AdtKind::Struct => { + if last { + err.note( + "the last field of a packed struct may only have a \ + dynamically sized type if it does not need drop to be run", + ); + } else { + err.note( + "only the last field of a struct may have a dynamically sized type", + ); + } + } + AdtKind::Union => { + err.note("no field of a union may have a dynamically sized type"); + } + AdtKind::Enum => { + err.note("no field of an enum variant may have a dynamically sized type"); + } + } + err.help("change the field's type to have a statically known size"); + err.span_suggestion( + span.shrink_to_lo(), + "borrowed types always have a statically known size", + "&", + Applicability::MachineApplicable, + ); + err.multipart_suggestion( + "the `Box` type always has a statically known size and allocates its contents \ + in the heap", + vec![ + (span.shrink_to_lo(), "Box<".to_string()), + (span.shrink_to_hi(), ">".to_string()), + ], + Applicability::MachineApplicable, + ); + } + ObligationCauseCode::ConstSized => { + err.note("constant expressions must have a statically known size"); + } + ObligationCauseCode::InlineAsmSized => { + err.note("all inline asm arguments must have a statically known size"); + } + ObligationCauseCode::ConstPatternStructural => { + err.note("constants used for pattern-matching must derive `PartialEq` and `Eq`"); + } + ObligationCauseCode::SharedStatic => { + err.note("shared static variables must have a type that implements `Sync`"); + } + ObligationCauseCode::BuiltinDerivedObligation(ref data) => { + let parent_trait_ref = self.resolve_vars_if_possible(data.parent_trait_pred); + let ty = parent_trait_ref.skip_binder().self_ty(); + if parent_trait_ref.references_error() { + // NOTE(eddyb) this was `.cancel()`, but `err` + // is borrowed, so we can't fully defuse it. + err.downgrade_to_delayed_bug(); + return; + } + + // If the obligation for a tuple is set directly by a Generator or Closure, + // then the tuple must be the one containing capture types. + let is_upvar_tys_infer_tuple = if !matches!(ty.kind(), ty::Tuple(..)) { + false + } else { + if let ObligationCauseCode::BuiltinDerivedObligation(data) = &*data.parent_code + { + let parent_trait_ref = + self.resolve_vars_if_possible(data.parent_trait_pred); + let nested_ty = parent_trait_ref.skip_binder().self_ty(); + matches!(nested_ty.kind(), ty::Generator(..)) + || matches!(nested_ty.kind(), ty::Closure(..)) + } else { + false + } + }; + + let from_generator = tcx.lang_items().from_generator_fn().unwrap(); + + // Don't print the tuple of capture types + 'print: { + if !is_upvar_tys_infer_tuple { + let msg = format!("required because it appears within the type `{}`", ty); + match ty.kind() { + ty::Adt(def, _) => { + // `gen_future` is used in all async functions; it doesn't add any additional info. + if self.tcx.is_diagnostic_item(sym::gen_future, def.did()) { + break 'print; + } + match self.tcx.opt_item_ident(def.did()) { + Some(ident) => err.span_note(ident.span, &msg), + None => err.note(&msg), + } + } + ty::Opaque(def_id, _) => { + // Avoid printing the future from `core::future::from_generator`, it's not helpful + if tcx.parent(*def_id) == from_generator { + break 'print; + } + + // If the previous type is `from_generator`, this is the future generated by the body of an async function. + // Avoid printing it twice (it was already printed in the `ty::Generator` arm below). + let is_future = tcx.ty_is_opaque_future(ty); + debug!( + ?obligated_types, + ?is_future, + "note_obligation_cause_code: check for async fn" + ); + if is_future + && obligated_types.last().map_or(false, |ty| match ty.kind() { + ty::Opaque(last_def_id, _) => { + tcx.parent(*last_def_id) == from_generator + } + _ => false, + }) + { + break 'print; + } + err.span_note(self.tcx.def_span(def_id), &msg) + } + ty::GeneratorWitness(bound_tys) => { + use std::fmt::Write; + + // FIXME: this is kind of an unusual format for rustc, can we make it more clear? + // Maybe we should just remove this note altogether? + // FIXME: only print types which don't meet the trait requirement + let mut msg = + "required because it captures the following types: ".to_owned(); + for ty in bound_tys.skip_binder() { + write!(msg, "`{}`, ", ty).unwrap(); + } + err.note(msg.trim_end_matches(", ")) + } + ty::Generator(def_id, _, _) => { + let sp = self.tcx.def_span(def_id); + + // Special-case this to say "async block" instead of `[static generator]`. + let kind = tcx.generator_kind(def_id).unwrap(); + err.span_note( + sp, + &format!("required because it's used within this {}", kind), + ) + } + ty::Closure(def_id, _) => err.span_note( + self.tcx.def_span(def_id), + &format!("required because it's used within this closure"), + ), + _ => err.note(&msg), + }; + } + } + + obligated_types.push(ty); + + let parent_predicate = parent_trait_ref.to_predicate(tcx); + if !self.is_recursive_obligation(obligated_types, &data.parent_code) { + // #74711: avoid a stack overflow + ensure_sufficient_stack(|| { + self.note_obligation_cause_code( + err, + &parent_predicate, + param_env, + &data.parent_code, + obligated_types, + seen_requirements, + ) + }); + } else { + ensure_sufficient_stack(|| { + self.note_obligation_cause_code( + err, + &parent_predicate, + param_env, + cause_code.peel_derives(), + obligated_types, + seen_requirements, + ) + }); + } + } + ObligationCauseCode::ImplDerivedObligation(ref data) => { + let mut parent_trait_pred = + self.resolve_vars_if_possible(data.derived.parent_trait_pred); + parent_trait_pred.remap_constness_diag(param_env); + let parent_def_id = parent_trait_pred.def_id(); + let msg = format!( + "required because of the requirements on the impl of `{}` for `{}`", + parent_trait_pred.print_modifiers_and_trait_path(), + parent_trait_pred.skip_binder().self_ty() + ); + let mut is_auto_trait = false; + match self.tcx.hir().get_if_local(data.impl_def_id) { + Some(Node::Item(hir::Item { + kind: hir::ItemKind::Trait(is_auto, ..), + ident, + .. + })) => { + // FIXME: we should do something else so that it works even on crate foreign + // auto traits. + is_auto_trait = matches!(is_auto, hir::IsAuto::Yes); + err.span_note(ident.span, &msg) + } + Some(Node::Item(hir::Item { + kind: hir::ItemKind::Impl(hir::Impl { of_trait, self_ty, .. }), + .. + })) => { + let mut spans = Vec::with_capacity(2); + if let Some(trait_ref) = of_trait { + spans.push(trait_ref.path.span); + } + spans.push(self_ty.span); + err.span_note(spans, &msg) + } + _ => err.note(&msg), + }; + + let mut parent_predicate = parent_trait_pred.to_predicate(tcx); + let mut data = &data.derived; + let mut count = 0; + seen_requirements.insert(parent_def_id); + if is_auto_trait { + // We don't want to point at the ADT saying "required because it appears within + // the type `X`", like we would otherwise do in test `supertrait-auto-trait.rs`. + while let ObligationCauseCode::BuiltinDerivedObligation(derived) = + &*data.parent_code + { + let child_trait_ref = + self.resolve_vars_if_possible(derived.parent_trait_pred); + let child_def_id = child_trait_ref.def_id(); + if seen_requirements.insert(child_def_id) { + break; + } + data = derived; + parent_predicate = child_trait_ref.to_predicate(tcx); + parent_trait_pred = child_trait_ref; + } + } + while let ObligationCauseCode::ImplDerivedObligation(child) = &*data.parent_code { + // Skip redundant recursive obligation notes. See `ui/issue-20413.rs`. + let child_trait_pred = + self.resolve_vars_if_possible(child.derived.parent_trait_pred); + let child_def_id = child_trait_pred.def_id(); + if seen_requirements.insert(child_def_id) { + break; + } + count += 1; + data = &child.derived; + parent_predicate = child_trait_pred.to_predicate(tcx); + parent_trait_pred = child_trait_pred; + } + if count > 0 { + err.note(&format!( + "{} redundant requirement{} hidden", + count, + pluralize!(count) + )); + err.note(&format!( + "required because of the requirements on the impl of `{}` for `{}`", + parent_trait_pred.print_modifiers_and_trait_path(), + parent_trait_pred.skip_binder().self_ty() + )); + } + // #74711: avoid a stack overflow + ensure_sufficient_stack(|| { + self.note_obligation_cause_code( + err, + &parent_predicate, + param_env, + &data.parent_code, + obligated_types, + seen_requirements, + ) + }); + } + ObligationCauseCode::DerivedObligation(ref data) => { + let parent_trait_ref = self.resolve_vars_if_possible(data.parent_trait_pred); + let parent_predicate = parent_trait_ref.to_predicate(tcx); + // #74711: avoid a stack overflow + ensure_sufficient_stack(|| { + self.note_obligation_cause_code( + err, + &parent_predicate, + param_env, + &data.parent_code, + obligated_types, + seen_requirements, + ) + }); + } + ObligationCauseCode::FunctionArgumentObligation { + arg_hir_id, + call_hir_id, + ref parent_code, + } => { + let hir = self.tcx.hir(); + if let Some(Node::Expr(expr @ hir::Expr { kind: hir::ExprKind::Block(..), .. })) = + hir.find(arg_hir_id) + { + let in_progress_typeck_results = + self.in_progress_typeck_results.map(|t| t.borrow()); + let parent_id = hir.get_parent_item(arg_hir_id); + let typeck_results: &TypeckResults<'tcx> = match &in_progress_typeck_results { + Some(t) if t.hir_owner == parent_id => t, + _ => self.tcx.typeck(parent_id), + }; + let ty = typeck_results.expr_ty_adjusted(expr); + let span = expr.peel_blocks().span; + if Some(span) != err.span.primary_span() { + err.span_label( + span, + &if ty.references_error() { + String::new() + } else { + format!("this tail expression is of type `{:?}`", ty) + }, + ); + } + } + if let Some(Node::Expr(hir::Expr { + kind: + hir::ExprKind::Call(hir::Expr { span, .. }, _) + | hir::ExprKind::MethodCall( + hir::PathSegment { ident: Ident { span, .. }, .. }, + .., + ), + .. + })) = hir.find(call_hir_id) + { + if Some(*span) != err.span.primary_span() { + err.span_label(*span, "required by a bound introduced by this call"); + } + } + ensure_sufficient_stack(|| { + self.note_obligation_cause_code( + err, + predicate, + param_env, + &parent_code, + obligated_types, + seen_requirements, + ) + }); + } + ObligationCauseCode::CompareImplItemObligation { trait_item_def_id, kind, .. } => { + let item_name = self.tcx.item_name(trait_item_def_id); + let msg = format!( + "the requirement `{}` appears on the `impl`'s {kind} `{}` but not on the \ + corresponding trait's {kind}", + predicate, item_name, + ); + let sp = self + .tcx + .opt_item_ident(trait_item_def_id) + .map(|i| i.span) + .unwrap_or_else(|| self.tcx.def_span(trait_item_def_id)); + let mut assoc_span: MultiSpan = sp.into(); + assoc_span.push_span_label( + sp, + format!("this trait's {kind} doesn't have the requirement `{}`", predicate), + ); + if let Some(ident) = self + .tcx + .opt_associated_item(trait_item_def_id) + .and_then(|i| self.tcx.opt_item_ident(i.container_id(self.tcx))) + { + assoc_span.push_span_label(ident.span, "in this trait"); + } + err.span_note(assoc_span, &msg); + } + ObligationCauseCode::TrivialBound => { + err.help("see issue #48214"); + if tcx.sess.opts.unstable_features.is_nightly_build() { + err.help("add `#![feature(trivial_bounds)]` to the crate attributes to enable"); + } + } + ObligationCauseCode::OpaqueReturnType(expr_info) => { + if let Some((expr_ty, expr_span)) = expr_info { + let expr_ty = self.resolve_vars_if_possible(expr_ty); + err.span_label( + expr_span, + format!("return type was inferred to be `{expr_ty}` here"), + ); + } + } + } + } + + fn suggest_new_overflow_limit(&self, err: &mut Diagnostic) { + let suggested_limit = match self.tcx.recursion_limit() { + Limit(0) => Limit(2), + limit => limit * 2, + }; + err.help(&format!( + "consider increasing the recursion limit by adding a \ + `#![recursion_limit = \"{}\"]` attribute to your crate (`{}`)", + suggested_limit, + self.tcx.crate_name(LOCAL_CRATE), + )); + } + + #[instrument( + level = "debug", skip(self, err), fields(trait_pred.self_ty = ?trait_pred.self_ty()) + )] + fn suggest_await_before_try( + &self, + err: &mut Diagnostic, + obligation: &PredicateObligation<'tcx>, + trait_pred: ty::PolyTraitPredicate<'tcx>, + span: Span, + ) { + let body_hir_id = obligation.cause.body_id; + let item_id = self.tcx.hir().get_parent_node(body_hir_id); + + if let Some(body_id) = + self.tcx.hir().maybe_body_owned_by(self.tcx.hir().local_def_id(item_id)) + { + let body = self.tcx.hir().body(body_id); + if let Some(hir::GeneratorKind::Async(_)) = body.generator_kind { + let future_trait = self.tcx.require_lang_item(LangItem::Future, None); + + let self_ty = self.resolve_vars_if_possible(trait_pred.self_ty()); + let impls_future = self.type_implements_trait( + future_trait, + self.tcx.erase_late_bound_regions(self_ty), + ty::List::empty(), + obligation.param_env, + ); + if !impls_future.must_apply_modulo_regions() { + return; + } + + let item_def_id = self.tcx.associated_item_def_ids(future_trait)[0]; + // `<T as Future>::Output` + let projection_ty = trait_pred.map_bound(|trait_pred| { + self.tcx.mk_projection( + item_def_id, + // Future::Output has no substs + self.tcx.mk_substs_trait(trait_pred.self_ty(), &[]), + ) + }); + let projection_ty = normalize_to( + &mut SelectionContext::new(self), + obligation.param_env, + obligation.cause.clone(), + projection_ty, + &mut vec![], + ); + + debug!( + normalized_projection_type = ?self.resolve_vars_if_possible(projection_ty) + ); + let try_obligation = self.mk_trait_obligation_with_new_self_ty( + obligation.param_env, + trait_pred.map_bound(|trait_pred| (trait_pred, projection_ty.skip_binder())), + ); + debug!(try_trait_obligation = ?try_obligation); + if self.predicate_may_hold(&try_obligation) + && let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span) + && snippet.ends_with('?') + { + err.span_suggestion_verbose( + span.with_hi(span.hi() - BytePos(1)).shrink_to_hi(), + "consider `await`ing on the `Future`", + ".await", + Applicability::MaybeIncorrect, + ); + } + } + } + } + + fn suggest_floating_point_literal( + &self, + obligation: &PredicateObligation<'tcx>, + err: &mut Diagnostic, + trait_ref: &ty::PolyTraitRef<'tcx>, + ) { + let rhs_span = match obligation.cause.code() { + ObligationCauseCode::BinOp { rhs_span: Some(span), is_lit, .. } if *is_lit => span, + _ => return, + }; + match ( + trait_ref.skip_binder().self_ty().kind(), + trait_ref.skip_binder().substs.type_at(1).kind(), + ) { + (ty::Float(_), ty::Infer(InferTy::IntVar(_))) => { + err.span_suggestion_verbose( + rhs_span.shrink_to_hi(), + "consider using a floating-point literal by writing it with `.0`", + ".0", + Applicability::MaybeIncorrect, + ); + } + _ => {} + } + } + + fn suggest_derive( + &self, + obligation: &PredicateObligation<'tcx>, + err: &mut Diagnostic, + trait_pred: ty::PolyTraitPredicate<'tcx>, + ) { + let Some(diagnostic_name) = self.tcx.get_diagnostic_name(trait_pred.def_id()) else { + return; + }; + let (adt, substs) = match trait_pred.skip_binder().self_ty().kind() { + ty::Adt(adt, substs) if adt.did().is_local() => (adt, substs), + _ => return, + }; + let can_derive = { + let is_derivable_trait = match diagnostic_name { + sym::Default => !adt.is_enum(), + sym::PartialEq | sym::PartialOrd => { + let rhs_ty = trait_pred.skip_binder().trait_ref.substs.type_at(1); + trait_pred.skip_binder().self_ty() == rhs_ty + } + sym::Eq | sym::Ord | sym::Clone | sym::Copy | sym::Hash | sym::Debug => true, + _ => false, + }; + is_derivable_trait && + // Ensure all fields impl the trait. + adt.all_fields().all(|field| { + let field_ty = field.ty(self.tcx, substs); + let trait_substs = match diagnostic_name { + sym::PartialEq | sym::PartialOrd => { + self.tcx.mk_substs_trait(field_ty, &[field_ty.into()]) + } + _ => self.tcx.mk_substs_trait(field_ty, &[]), + }; + let trait_pred = trait_pred.map_bound_ref(|tr| ty::TraitPredicate { + trait_ref: ty::TraitRef { + substs: trait_substs, + ..trait_pred.skip_binder().trait_ref + }, + ..*tr + }); + let field_obl = Obligation::new( + obligation.cause.clone(), + obligation.param_env, + trait_pred.to_predicate(self.tcx), + ); + self.predicate_must_hold_modulo_regions(&field_obl) + }) + }; + if can_derive { + err.span_suggestion_verbose( + self.tcx.def_span(adt.did()).shrink_to_lo(), + &format!( + "consider annotating `{}` with `#[derive({})]`", + trait_pred.skip_binder().self_ty(), + diagnostic_name, + ), + format!("#[derive({})]\n", diagnostic_name), + Applicability::MaybeIncorrect, + ); + } + } + + fn suggest_dereferencing_index( + &self, + obligation: &PredicateObligation<'tcx>, + err: &mut Diagnostic, + trait_pred: ty::PolyTraitPredicate<'tcx>, + ) { + if let ObligationCauseCode::ImplDerivedObligation(_) = obligation.cause.code() + && self.tcx.is_diagnostic_item(sym::SliceIndex, trait_pred.skip_binder().trait_ref.def_id) + && let ty::Slice(_) = trait_pred.skip_binder().trait_ref.substs.type_at(1).kind() + && let ty::Ref(_, inner_ty, _) = trait_pred.skip_binder().self_ty().kind() + && let ty::Uint(ty::UintTy::Usize) = inner_ty.kind() + { + err.span_suggestion_verbose( + obligation.cause.span.shrink_to_lo(), + "dereference this index", + '*', + Applicability::MachineApplicable, + ); + } + } +} + +/// Collect all the returned expressions within the input expression. +/// Used to point at the return spans when we want to suggest some change to them. +#[derive(Default)] +pub struct ReturnsVisitor<'v> { + pub returns: Vec<&'v hir::Expr<'v>>, + in_block_tail: bool, +} + +impl<'v> Visitor<'v> for ReturnsVisitor<'v> { + fn visit_expr(&mut self, ex: &'v hir::Expr<'v>) { + // Visit every expression to detect `return` paths, either through the function's tail + // expression or `return` statements. We walk all nodes to find `return` statements, but + // we only care about tail expressions when `in_block_tail` is `true`, which means that + // they're in the return path of the function body. + match ex.kind { + hir::ExprKind::Ret(Some(ex)) => { + self.returns.push(ex); + } + hir::ExprKind::Block(block, _) if self.in_block_tail => { + self.in_block_tail = false; + for stmt in block.stmts { + hir::intravisit::walk_stmt(self, stmt); + } + self.in_block_tail = true; + if let Some(expr) = block.expr { + self.visit_expr(expr); + } + } + hir::ExprKind::If(_, then, else_opt) if self.in_block_tail => { + self.visit_expr(then); + if let Some(el) = else_opt { + self.visit_expr(el); + } + } + hir::ExprKind::Match(_, arms, _) if self.in_block_tail => { + for arm in arms { + self.visit_expr(arm.body); + } + } + // We need to walk to find `return`s in the entire body. + _ if !self.in_block_tail => hir::intravisit::walk_expr(self, ex), + _ => self.returns.push(ex), + } + } + + fn visit_body(&mut self, body: &'v hir::Body<'v>) { + assert!(!self.in_block_tail); + if body.generator_kind().is_none() { + if let hir::ExprKind::Block(block, None) = body.value.kind { + if block.expr.is_some() { + self.in_block_tail = true; + } + } + } + hir::intravisit::walk_body(self, body); + } +} + +/// Collect all the awaited expressions within the input expression. +#[derive(Default)] +struct AwaitsVisitor { + awaits: Vec<hir::HirId>, +} + +impl<'v> Visitor<'v> for AwaitsVisitor { + fn visit_expr(&mut self, ex: &'v hir::Expr<'v>) { + if let hir::ExprKind::Yield(_, hir::YieldSource::Await { expr: Some(id) }) = ex.kind { + self.awaits.push(id) + } + hir::intravisit::walk_expr(self, ex) + } +} + +pub trait NextTypeParamName { + fn next_type_param_name(&self, name: Option<&str>) -> String; +} + +impl NextTypeParamName for &[hir::GenericParam<'_>] { + fn next_type_param_name(&self, name: Option<&str>) -> String { + // This is the list of possible parameter names that we might suggest. + let name = name.and_then(|n| n.chars().next()).map(|c| c.to_string().to_uppercase()); + let name = name.as_deref(); + let possible_names = [name.unwrap_or("T"), "T", "U", "V", "X", "Y", "Z", "A", "B", "C"]; + let used_names = self + .iter() + .filter_map(|p| match p.name { + hir::ParamName::Plain(ident) => Some(ident.name), + _ => None, + }) + .collect::<Vec<_>>(); + + possible_names + .iter() + .find(|n| !used_names.contains(&Symbol::intern(n))) + .unwrap_or(&"ParamName") + .to_string() + } +} + +fn suggest_trait_object_return_type_alternatives( + err: &mut Diagnostic, + ret_ty: Span, + trait_obj: &str, + is_object_safe: bool, +) { + err.span_suggestion( + ret_ty, + "use some type `T` that is `T: Sized` as the return type if all return paths have the \ + same type", + "T", + Applicability::MaybeIncorrect, + ); + err.span_suggestion( + ret_ty, + &format!( + "use `impl {}` as the return type if all return paths have the same type but you \ + want to expose only the trait in the signature", + trait_obj, + ), + format!("impl {}", trait_obj), + Applicability::MaybeIncorrect, + ); + if is_object_safe { + err.multipart_suggestion( + &format!( + "use a boxed trait object if all return paths implement trait `{}`", + trait_obj, + ), + vec![ + (ret_ty.shrink_to_lo(), "Box<".to_string()), + (ret_ty.shrink_to_hi(), ">".to_string()), + ], + Applicability::MaybeIncorrect, + ); + } +} + +/// Collect the spans that we see the generic param `param_did` +struct ReplaceImplTraitVisitor<'a> { + ty_spans: &'a mut Vec<Span>, + param_did: DefId, +} + +impl<'a, 'hir> hir::intravisit::Visitor<'hir> for ReplaceImplTraitVisitor<'a> { + fn visit_ty(&mut self, t: &'hir hir::Ty<'hir>) { + if let hir::TyKind::Path(hir::QPath::Resolved( + None, + hir::Path { res: hir::def::Res::Def(_, segment_did), .. }, + )) = t.kind + { + if self.param_did == *segment_did { + // `fn foo(t: impl Trait)` + // ^^^^^^^^^^ get this to suggest `T` instead + + // There might be more than one `impl Trait`. + self.ty_spans.push(t.span); + return; + } + } + + hir::intravisit::walk_ty(self, t); + } +} + +// Replace `param` with `replace_ty` +struct ReplaceImplTraitFolder<'tcx> { + tcx: TyCtxt<'tcx>, + param: &'tcx ty::GenericParamDef, + replace_ty: Ty<'tcx>, +} + +impl<'tcx> TypeFolder<'tcx> for ReplaceImplTraitFolder<'tcx> { + fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> { + if let ty::Param(ty::ParamTy { index, .. }) = t.kind() { + if self.param.index == *index { + return self.replace_ty; + } + } + t.super_fold_with(self) + } + + fn tcx(&self) -> TyCtxt<'tcx> { + self.tcx + } +} |