diff options
Diffstat (limited to 'compiler/rustc_trait_selection/src')
13 files changed, 328 insertions, 163 deletions
diff --git a/compiler/rustc_trait_selection/src/solve/eval_ctxt.rs b/compiler/rustc_trait_selection/src/solve/eval_ctxt.rs index bd52957d162..63a73f8d50d 100644 --- a/compiler/rustc_trait_selection/src/solve/eval_ctxt.rs +++ b/compiler/rustc_trait_selection/src/solve/eval_ctxt.rs @@ -3,7 +3,8 @@ use rustc_infer::infer::at::ToTrace; use rustc_infer::infer::canonical::CanonicalVarValues; use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind}; use rustc_infer::infer::{ - DefineOpaqueTypes, InferCtxt, InferOk, LateBoundRegionConversionTime, TyCtxtInferExt, + DefineOpaqueTypes, InferCtxt, InferOk, LateBoundRegionConversionTime, RegionVariableOrigin, + TyCtxtInferExt, }; use rustc_infer::traits::query::NoSolution; use rustc_infer::traits::ObligationCause; @@ -223,18 +224,20 @@ impl<'a, 'tcx> EvalCtxt<'a, 'tcx> { { debug!("rerunning goal to check result is stable"); let (_orig_values, canonical_goal) = self.canonicalize_goal(goal); - let canonical_response = + let new_canonical_response = EvalCtxt::evaluate_canonical_goal(self.tcx(), self.search_graph, canonical_goal)?; - if !canonical_response.value.var_values.is_identity() { + if !new_canonical_response.value.var_values.is_identity() { bug!( "unstable result: re-canonicalized goal={canonical_goal:#?} \ - response={canonical_response:#?}" + first_response={canonical_response:#?} \ + second_response={new_canonical_response:#?}" ); } - if certainty != canonical_response.value.certainty { + if certainty != new_canonical_response.value.certainty { bug!( "unstable certainty: {certainty:#?} re-canonicalized goal={canonical_goal:#?} \ - response={canonical_response:#?}" + first_response={canonical_response:#?} \ + second_response={new_canonical_response:#?}" ); } } @@ -434,6 +437,10 @@ impl<'tcx> EvalCtxt<'_, 'tcx> { }) } + pub(super) fn next_region_infer(&self) -> ty::Region<'tcx> { + self.infcx.next_region_var(RegionVariableOrigin::MiscVariable(DUMMY_SP)) + } + pub(super) fn next_const_infer(&self, ty: Ty<'tcx>) -> ty::Const<'tcx> { self.infcx.next_const_var( ty, diff --git a/compiler/rustc_trait_selection/src/solve/eval_ctxt/canonical.rs b/compiler/rustc_trait_selection/src/solve/eval_ctxt/canonical.rs index 226d29687e3..67ad7fb4bd2 100644 --- a/compiler/rustc_trait_selection/src/solve/eval_ctxt/canonical.rs +++ b/compiler/rustc_trait_selection/src/solve/eval_ctxt/canonical.rs @@ -16,7 +16,7 @@ use rustc_infer::infer::canonical::query_response::make_query_region_constraints use rustc_infer::infer::canonical::CanonicalVarValues; use rustc_infer::infer::canonical::{CanonicalExt, QueryRegionConstraints}; use rustc_middle::traits::query::NoSolution; -use rustc_middle::traits::solve::{ExternalConstraints, ExternalConstraintsData}; +use rustc_middle::traits::solve::{ExternalConstraints, ExternalConstraintsData, MaybeCause}; use rustc_middle::ty::{self, BoundVar, GenericArgKind}; use rustc_span::DUMMY_SP; use std::iter; @@ -60,9 +60,27 @@ impl<'tcx> EvalCtxt<'_, 'tcx> { let certainty = certainty.unify_with(goals_certainty); - let external_constraints = self.compute_external_query_constraints()?; + let response = match certainty { + Certainty::Yes | Certainty::Maybe(MaybeCause::Ambiguity) => { + let external_constraints = self.compute_external_query_constraints()?; + Response { var_values: self.var_values, external_constraints, certainty } + } + Certainty::Maybe(MaybeCause::Overflow) => { + // If we have overflow, it's probable that we're substituting a type + // into itself infinitely and any partial substitutions in the query + // response are probably not useful anyways, so just return an empty + // query response. + // + // This may prevent us from potentially useful inference, e.g. + // 2 candidates, one ambiguous and one overflow, which both + // have the same inference constraints. + // + // Changing this to retain some constraints in the future + // won't be a breaking change, so this is good enough for now. + return Ok(self.make_ambiguous_response_no_constraints(MaybeCause::Overflow)); + } + }; - let response = Response { var_values: self.var_values, external_constraints, certainty }; let canonical = Canonicalizer::canonicalize( self.infcx, CanonicalizeMode::Response { max_input_universe: self.max_input_universe }, @@ -72,6 +90,40 @@ impl<'tcx> EvalCtxt<'_, 'tcx> { Ok(canonical) } + /// Constructs a totally unconstrained, ambiguous response to a goal. + /// + /// Take care when using this, since often it's useful to respond with + /// ambiguity but return constrained variables to guide inference. + pub(in crate::solve) fn make_ambiguous_response_no_constraints( + &self, + maybe_cause: MaybeCause, + ) -> CanonicalResponse<'tcx> { + let unconstrained_response = Response { + var_values: CanonicalVarValues { + var_values: self.tcx().mk_substs_from_iter(self.var_values.var_values.iter().map( + |arg| -> ty::GenericArg<'tcx> { + match arg.unpack() { + GenericArgKind::Lifetime(_) => self.next_region_infer().into(), + GenericArgKind::Type(_) => self.next_ty_infer().into(), + GenericArgKind::Const(ct) => self.next_const_infer(ct.ty()).into(), + } + }, + )), + }, + external_constraints: self + .tcx() + .mk_external_constraints(ExternalConstraintsData::default()), + certainty: Certainty::Maybe(maybe_cause), + }; + + Canonicalizer::canonicalize( + self.infcx, + CanonicalizeMode::Response { max_input_universe: self.max_input_universe }, + &mut Default::default(), + unconstrained_response, + ) + } + #[instrument(level = "debug", skip(self), ret)] fn compute_external_query_constraints(&self) -> Result<ExternalConstraints<'tcx>, NoSolution> { // Cannot use `take_registered_region_obligations` as we may compute the response diff --git a/compiler/rustc_trait_selection/src/solve/mod.rs b/compiler/rustc_trait_selection/src/solve/mod.rs index 19bcbd46144..d94679fef28 100644 --- a/compiler/rustc_trait_selection/src/solve/mod.rs +++ b/compiler/rustc_trait_selection/src/solve/mod.rs @@ -340,17 +340,17 @@ impl<'tcx> EvalCtxt<'_, 'tcx> { if responses.is_empty() { return Err(NoSolution); } - let certainty = responses.iter().fold(Certainty::AMBIGUOUS, |certainty, response| { - certainty.unify_with(response.value.certainty) - }); - - let response = self.evaluate_added_goals_and_make_canonical_response(certainty); - if let Ok(response) = response { - assert!(response.has_no_inference_or_external_constraints()); - Ok(response) - } else { - bug!("failed to make floundered response: {responses:?}"); - } + + let Certainty::Maybe(maybe_cause) = responses.iter().fold( + Certainty::AMBIGUOUS, + |certainty, response| { + certainty.unify_with(response.value.certainty) + }, + ) else { + bug!("expected flounder response to be ambiguous") + }; + + Ok(self.make_ambiguous_response_no_constraints(maybe_cause)) } } diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs index ce187fbdf84..69b3c1e7eff 100644 --- a/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs +++ b/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs @@ -271,7 +271,7 @@ impl<'tcx> InferCtxtExt<'tcx> for InferCtxt<'tcx> { let underscores = vec!["_"; expected_args.len()].join(", "); err.span_suggestion_verbose( closure_arg_span.unwrap_or(found_span), - &format!( + format!( "consider changing the closure to take and ignore the expected argument{}", pluralize!(expected_args.len()) ), @@ -575,7 +575,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> { Limit(0) => Limit(2), limit => limit * 2, }; - err.help(&format!( + err.help(format!( "consider increasing the recursion limit by adding a \ `#![recursion_limit = \"{}\"]` attribute to your crate (`{}`)", suggested_limit, @@ -737,7 +737,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> { if is_try_conversion && let Some(ret_span) = self.return_type_span(&obligation) { err.span_label( ret_span, - &format!( + format!( "expected `{}` because of this", trait_ref.skip_binder().self_ty() ), @@ -780,7 +780,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> { err.emit(); return; } - if let Some(ref s) = label { + if let Some(s) = label { // If it has a custom `#[rustc_on_unimplemented]` // error message, let's display it as the label! err.span_label(span, s); @@ -788,7 +788,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> { // When the self type is a type param We don't need to "the trait // `std::marker::Sized` is not implemented for `T`" as we will point // at the type param with a label to suggest constraining it. - err.help(&explanation); + err.help(explanation); } } else if let Some(custom_explanation) = safe_transmute_explanation { err.span_label(span, custom_explanation); @@ -811,13 +811,13 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> { ); if let Some((msg, span)) = type_def { - err.span_label(span, &msg); + err.span_label(span, msg); } - if let Some(ref s) = note { + if let Some(s) = note { // If it has a custom `#[rustc_on_unimplemented]` note, let's display it - err.note(s.as_str()); + err.note(s); } - if let Some(ref s) = parent_label { + if let Some(s) = parent_label { let body = obligation.cause.body_id; err.span_label(tcx.def_span(body), s); } @@ -1028,7 +1028,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> { // which bounds actually failed to hold. self.tcx.sess.struct_span_err( span, - &format!("the type `{}` is not well-formed", ty), + format!("the type `{}` is not well-formed", ty), ) } } @@ -1071,7 +1071,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> { ty::PredicateKind::Clause(ty::Clause::ConstArgHasType(ct, ty)) => { let mut diag = self.tcx.sess.struct_span_err( span, - &format!("the constant `{}` is not of type `{}`", ct, ty), + format!("the constant `{}` is not of type `{}`", ct, ty), ); self.note_type_err( &mut diag, @@ -1835,7 +1835,7 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> { candidates.sort(); candidates.dedup(); let end = if candidates.len() <= 9 { candidates.len() } else { 8 }; - err.help(&format!( + err.help(format!( "the following {other}types implement trait `{}`:{}{}", trait_ref.print_only_trait_path(), candidates[..end].join(""), @@ -2026,7 +2026,7 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> { "perhaps two different versions of crate `{}` are being used?", trait_crate ); - err.note(&crate_msg); + err.note(crate_msg); suggested = true; } suggested @@ -2158,7 +2158,7 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> { err.cancel(); return; } - err.note(&format!("cannot satisfy `{}`", predicate)); + err.note(format!("cannot satisfy `{}`", predicate)); let impl_candidates = self.find_similar_impl_candidates( predicate.to_opt_poly_trait_pred().unwrap(), ); @@ -2178,7 +2178,7 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> { err.cancel(); return; } - err.note(&format!("cannot satisfy `{}`", predicate)); + err.note(format!("cannot satisfy `{}`", predicate)); } } @@ -2223,9 +2223,9 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> { err.cancel(); err = self.tcx.sess.struct_span_err_with_code( span, - &format!( + format!( "cannot {verb} associated {noun} on trait without specifying the corresponding `impl` type", - ), + ), rustc_errors::error_code!(E0790), ); @@ -2332,7 +2332,7 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> { ErrorCode::E0284, true, ); - err.note(&format!("cannot satisfy `{}`", predicate)); + err.note(format!("cannot satisfy `{}`", predicate)); err } else { // If we can't find a substitution, just print a generic error @@ -2343,7 +2343,7 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> { "type annotations needed: cannot satisfy `{}`", predicate, ); - err.span_label(span, &format!("cannot satisfy `{}`", predicate)); + err.span_label(span, format!("cannot satisfy `{}`", predicate)); err } } @@ -2371,7 +2371,7 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> { "type annotations needed: cannot satisfy `{}`", predicate, ); - err.span_label(span, &format!("cannot satisfy `{}`", predicate)); + err.span_label(span, format!("cannot satisfy `{}`", predicate)); err } } @@ -2386,7 +2386,7 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> { "type annotations needed: cannot satisfy `{}`", predicate, ); - err.span_label(span, &format!("cannot satisfy `{}`", predicate)); + err.span_label(span, format!("cannot satisfy `{}`", predicate)); err } }; @@ -2459,13 +2459,13 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> { match (spans.len(), crates.len(), crate_names.len()) { (0, 0, 0) => { - err.note(&format!("cannot satisfy `{}`", predicate)); + err.note(format!("cannot satisfy `{}`", predicate)); } (0, _, 1) => { - err.note(&format!("{} in the `{}` crate{}", msg, crates[0], post,)); + err.note(format!("{} in the `{}` crate{}", msg, crates[0], post,)); } (0, _, _) => { - err.note(&format!( + err.note(format!( "{} in the following crates: {}{}", msg, crate_names.join(", "), @@ -2474,19 +2474,17 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> { } (_, 0, 0) => { let span: MultiSpan = spans.into(); - err.span_note(span, &msg); + err.span_note(span, msg); } (_, 1, 1) => { let span: MultiSpan = spans.into(); - err.span_note(span, &msg); - err.note( - &format!("and another `impl` found in the `{}` crate{}", crates[0], post,), - ); + err.span_note(span, msg); + err.note(format!("and another `impl` found in the `{}` crate{}", crates[0], post,)); } _ => { let span: MultiSpan = spans.into(); - err.span_note(span, &msg); - err.note(&format!( + err.span_note(span, msg); + err.note(format!( "and more `impl`s found in the following crates: {}{}", crate_names.join(", "), post, @@ -2657,7 +2655,7 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> { } err.span_help( multispan, - &format!( + format!( "you could relax the implicit `Sized` bound on `{T}` if it were \ used through indirection like `&{T}` or `Box<{T}>`", T = param.name.ident(), @@ -2882,7 +2880,7 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> { .fn_trait_kind_from_def_id(trait_ref.def_id()) .expect("expected to map DefId to ClosureKind"); if !implemented_kind.extends(selected_kind) { - err.note(&format!( + err.note(format!( "`{}` implements `{}`, but it must implement `{}`, which is more general", trait_ref.skip_binder().self_ty(), implemented_kind, @@ -2899,7 +2897,7 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> { if expected.len() != given.len() { // Note number of types that were expected and given err.note( - &format!( + format!( "expected a closure taking {} argument{}, but one taking {} argument{} was given", given.len(), pluralize!(given.len()), @@ -2942,7 +2940,7 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> { unsatisfied_const = UnsatisfiedConst(true); err.span_note( span, - &format!( + format!( "the trait `{}` is implemented for `{}`, \ but that implementation is not `const`", non_const_predicate.print_modifiers_and_trait_path(), @@ -3171,7 +3169,7 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> { let mut err = self.tcx.sess.struct_span_err(span, "unconstrained generic constant"); let const_span = self.tcx.def_span(uv.def); match self.tcx.sess.source_map().span_to_snippet(const_span) { - Ok(snippet) => err.help(&format!( + Ok(snippet) => err.help(format!( "try adding a `where` bound using this expression: `where [(); {}]:`", snippet )), diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs index c969e5d4975..3e9e497672a 100644 --- a/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs +++ b/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs @@ -515,7 +515,7 @@ fn suggest_restriction<'tcx>( err.span_suggestion_verbose( sp, - &format!("consider further restricting {}", msg), + format!("consider further restricting {}", msg), suggestion, Applicability::MachineApplicable, ); @@ -530,6 +530,10 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> { associated_ty: Option<(&'static str, Ty<'tcx>)>, mut body_id: LocalDefId, ) { + if trait_pred.skip_binder().polarity == ty::ImplPolarity::Negative { + return; + } + let trait_pred = self.resolve_numeric_literals_with_default(trait_pred); let self_ty = trait_pred.skip_binder().self_ty(); @@ -964,7 +968,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> { // a more general note. err.span_suggestion_verbose( obligation.cause.span.shrink_to_hi(), - &msg, + msg, format!("({args})"), Applicability::HasPlaceholders, ); @@ -994,7 +998,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> { } _ => return false, }; - err.help(&format!("{msg}: `{name}({args})`")); + err.help(format!("{msg}: `{name}({args})`")); } true } @@ -1334,7 +1338,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> { let msg = format!("the trait bound `{}` is not satisfied", old_pred); if has_custom_message { - err.note(&msg); + err.note(msg); } else { err.message = vec![(rustc_errors::DiagnosticMessage::Str(msg), Style::NoStyle)]; @@ -1358,7 +1362,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> { } else { let is_mut = mut_ref_self_ty_satisfies_pred || ref_inner_ty_mut; let sugg_prefix = format!("&{}", if is_mut { "mut " } else { "" }); - let sugg_msg = &format!( + let sugg_msg = format!( "consider{} borrowing here", if is_mut { " mutably" } else { "" } ); @@ -1452,7 +1456,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> { err.span_suggestion( obligation.cause.span.shrink_to_lo(), - &format!( + format!( "consider borrowing the value, since `&{self_ty}` can be coerced into `{object_ty}`" ), "&", @@ -1505,7 +1509,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> { }; err.multipart_suggestion_verbose( - &msg, + msg, suggestions, Applicability::MachineApplicable, ); @@ -1583,55 +1587,68 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> { } 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(hir::Node::Expr(expr)) = hir_id.and_then(|hir_id| hir.find(hir_id)) { - // 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. + let hir = self.tcx.hir(); + if let ObligationCauseCode::AwaitableExpr(Some(hir_id)) = obligation.cause.code().peel_derives() + && let hir::Node::Expr(expr) = hir.get(*hir_id) + { + // 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. + + // use nth(1) to skip one layer of desugaring from `IntoIter::into_iter` + if let Some((_, hir::Node::Expr(await_expr))) = hir.parent_iter(*hir_id).nth(1) + && let Some(expr_span) = expr.span.find_ancestor_inside(await_expr.span) + { + let removal_span = self.tcx + .sess + .source_map() + .span_extend_while(expr_span, char::is_whitespace) + .unwrap_or(expr_span) + .shrink_to_hi() + .to(await_expr.span.shrink_to_hi()); err.span_suggestion( - span, + removal_span, "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::Clause(ty::Clause::Trait(pred)) = - obligation.predicate.kind().skip_binder() + } else { + err.span_label(obligation.cause.span, "remove the `.await`"); + } + // FIXME: account for associated `async fn`s. + if let hir::Expr { span, kind: hir::ExprKind::Call(base, _), .. } = expr { + if let ty::PredicateKind::Clause(ty::Clause::Trait(pred)) = + obligation.predicate.kind().skip_binder() + { + err.span_label(*span, format!("this call returns `{}`", pred.self_ty())); + } + if let Some(typeck_results) = &self.typeck_results + && 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) { - err.span_label(*span, &format!("this call returns `{}`", pred.self_ty())); - } - if let Some(typeck_results) = &self.typeck_results - && 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 + 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, ); - 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, - ); - } } - } + } } } } @@ -1704,7 +1721,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> { Applicability::MachineApplicable, ); } else { - err.note(&format!( + err.note(format!( "`{}` is implemented for `{:?}`, but not for `{:?}`", trait_pred.print_modifiers_and_trait_path(), suggested_ty, @@ -1741,7 +1758,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> { { err.span_label( expr.span, - &format!( + format!( "this expression has type `{}`, which implements `{}`", ty, trait_pred.print_modifiers_and_trait_path() @@ -1933,7 +1950,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> { // Suggest `-> impl Trait`. err.span_suggestion( ret_ty.span, - &format!( + format!( "use `impl {1}` as the return type, as all return paths are of type `{}`, \ which implements `{1}`", last_ty, trait_obj, @@ -1968,13 +1985,13 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> { } 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!( + err.note(format!( "if trait `{}` were object-safe, you could return a trait object", trait_obj, )); } err.note(trait_obj_msg); - err.note(&format!( + err.note(format!( "if all the returned values were of the same type you could use `impl {}` as the \ return type", trait_obj, @@ -2014,7 +2031,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> { } else { err.span_label( expr.span, - &format!("this returned value is of type `{}`", ty), + format!("this returned value is of type `{}`", ty), ); } } @@ -2164,7 +2181,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> { ) { 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!( + err.note(format!( "{}s cannot be accessed directly on a `trait`, they can only be \ accessed through a specific `impl`", self.tcx.def_kind_descr(assoc_item.kind.as_def_kind(), item_def_id) @@ -2594,7 +2611,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> { } err.span_note( span, - &format!( + format!( "{} {} as this value is used across {}", future_or_generator, trait_explanation, an_await_or_yield ), @@ -2615,7 +2632,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> { ); err.span_note( span, - &format!( + format!( "future {not_trait} as it awaits another future which {not_trait}", not_trait = trait_explanation ), @@ -2717,7 +2734,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> { let mut span = MultiSpan::from_span(upvar_span); span.push_span_label(upvar_span, span_label); - err.span_note(span, &span_note); + err.span_note(span, span_note); } } @@ -2781,15 +2798,15 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> { 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 `{data}` is well-formed")); + err.note(format!("required so that the projection `{data}` is well-formed")); } ObligationCauseCode::ReferenceOutlivesReferent(ref_ty) => { - err.note(&format!( + err.note(format!( "required so that reference `{ref_ty}` does not outlive its referent" )); } ObligationCauseCode::ObjectTypeBound(object_ty, region) => { - err.note(&format!( + err.note(format!( "required so that the lifetime bound of `{}` for `{}` is satisfied", region, object_ty, )); @@ -2825,9 +2842,9 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> { if span.is_visible(sm) { let msg = format!("required by this bound in `{short_item_name}`"); multispan.push_span_label(span, msg); - err.span_note(multispan, &descr); + err.span_note(multispan, descr); } else { - err.span_note(tcx.def_span(item_def_id), &descr); + err.span_note(tcx.def_span(item_def_id), descr); } } ObligationCauseCode::ObjectCastObligation(concrete_ty, object_ty) => { @@ -2835,24 +2852,24 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> { self.tcx.short_ty_string(self.resolve_vars_if_possible(concrete_ty)); let (object_ty, object_file) = self.tcx.short_ty_string(self.resolve_vars_if_possible(object_ty)); - err.note(&with_forced_trimmed_paths!(format!( + err.note(with_forced_trimmed_paths!(format!( "required for the cast from `{concrete_ty}` to the object type `{object_ty}`", ))); if let Some(file) = concrete_file { - err.note(&format!( + err.note(format!( "the full name for the casted type has been written to '{}'", file.display(), )); } if let Some(file) = object_file { - err.note(&format!( + err.note(format!( "the full name for the object type has been written to '{}'", file.display(), )); } } ObligationCauseCode::Coercion { source: _, target } => { - err.note(&format!("required by cast to type `{}`", self.ty_to_string(target))); + err.note(format!("required by cast to type `{}`", self.ty_to_string(target))); } ObligationCauseCode::RepeatElementCopy { is_const_fn } => { err.note( @@ -3055,8 +3072,8 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> { )); match ty.kind() { ty::Adt(def, _) => match self.tcx.opt_item_ident(def.did()) { - Some(ident) => err.span_note(ident.span, &msg), - None => err.note(&msg), + Some(ident) => err.span_note(ident.span, msg), + None => err.note(msg), }, ty::Alias(ty::Opaque, ty::AliasTy { def_id, .. }) => { // If the previous type is async fn, this is the future generated by the body of an async function. @@ -3077,7 +3094,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> { { break 'print; } - err.span_note(self.tcx.def_span(def_id), &msg) + err.span_note(self.tcx.def_span(def_id), msg) } ty::GeneratorWitness(bound_tys) => { use std::fmt::Write; @@ -3113,7 +3130,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> { let kind = tcx.generator_kind(def_id).unwrap().descr(); err.span_note( sp, - with_forced_trimmed_paths!(&format!( + with_forced_trimmed_paths!(format!( "required because it's used within this {kind}", )), ) @@ -3123,7 +3140,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> { "required because it's used within this closure", ), ty::Str => err.note("`str` is considered to contain a `[u8]` slice for auto trait purposes"), - _ => err.note(&msg), + _ => err.note(msg), }; } } @@ -3177,7 +3194,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> { // 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); + err.span_note(ident.span, msg); } Some(Node::Item(hir::Item { kind: hir::ItemKind::Impl(hir::Impl { of_trait, self_ty, .. }), @@ -3206,15 +3223,15 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> { "unsatisfied trait bound introduced here", ); } - err.span_note(spans, &msg); + err.span_note(spans, msg); } _ => { - err.note(&msg); + err.note(msg); } }; if let Some(file) = file { - err.note(&format!( + err.note(format!( "the full type name has been written to '{}'", file.display(), )); @@ -3254,19 +3271,19 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> { parent_trait_pred = child_trait_pred; } if count > 0 { - err.note(&format!( + err.note(format!( "{} redundant requirement{} hidden", count, pluralize!(count) )); let (self_ty, file) = self.tcx.short_ty_string(parent_trait_pred.skip_binder().self_ty()); - err.note(&format!( + err.note(format!( "required for `{self_ty}` to implement `{}`", parent_trait_pred.print_modifiers_and_trait_path() )); if let Some(file) = file { - err.note(&format!( + err.note(format!( "the full type name has been written to '{}'", file.display(), )); @@ -3347,7 +3364,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> { { assoc_span.push_span_label(ident.span, "in this trait"); } - err.span_note(assoc_span, &msg); + err.span_note(assoc_span, msg); } ObligationCauseCode::TrivialBound => { err.help("see issue #48214"); @@ -3503,7 +3520,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> { if can_derive { err.span_suggestion_verbose( self.tcx.def_span(adt.did()).shrink_to_lo(), - &format!( + format!( "consider annotating `{}` with `#[derive({})]`", trait_pred.skip_binder().self_ty(), diagnostic_name, @@ -3890,7 +3907,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> { .map(|trait_ref| trait_ref.trait_ref.self_ty()) .find(|t| is_slice(*t)) { - let msg = &format!("convert the array to a `{}` slice instead", slice_ty); + let msg = format!("convert the array to a `{}` slice instead", slice_ty); if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span) { let mut suggestions = vec![]; @@ -4111,7 +4128,7 @@ fn suggest_trait_object_return_type_alternatives( ) { err.span_suggestion( ret_ty, - &format!( + 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, @@ -4121,7 +4138,7 @@ fn suggest_trait_object_return_type_alternatives( ); if is_object_safe { err.multipart_suggestion( - &format!( + format!( "use a boxed trait object if all return paths implement trait `{}`", trait_obj, ), diff --git a/compiler/rustc_trait_selection/src/traits/misc.rs b/compiler/rustc_trait_selection/src/traits/misc.rs index 63949843aed..2210ef975e6 100644 --- a/compiler/rustc_trait_selection/src/traits/misc.rs +++ b/compiler/rustc_trait_selection/src/traits/misc.rs @@ -2,13 +2,14 @@ use crate::traits::{self, ObligationCause, ObligationCtxt}; +use hir::LangItem; use rustc_data_structures::fx::FxIndexSet; use rustc_hir as hir; use rustc_infer::infer::canonical::Canonical; use rustc_infer::infer::{RegionResolutionError, TyCtxtInferExt}; use rustc_infer::traits::query::NoSolution; use rustc_infer::{infer::outlives::env::OutlivesEnvironment, traits::FulfillmentError}; -use rustc_middle::ty::{self, ParamEnv, Ty, TyCtxt, TypeVisitableExt}; +use rustc_middle::ty::{self, AdtDef, GenericArg, List, ParamEnv, Ty, TyCtxt, TypeVisitableExt}; use rustc_span::DUMMY_SP; use super::outlives_bounds::InferCtxtExt; @@ -19,6 +20,11 @@ pub enum CopyImplementationError<'tcx> { HasDestructor, } +pub enum ConstParamTyImplementationError<'tcx> { + InfrigingFields(Vec<(&'tcx ty::FieldDef, Ty<'tcx>, InfringingFieldsReason<'tcx>)>), + NotAnAdtOrBuiltinAllowed, +} + pub enum InfringingFieldsReason<'tcx> { Fulfill(Vec<FulfillmentError<'tcx>>), Regions(Vec<RegionResolutionError<'tcx>>), @@ -27,7 +33,10 @@ pub enum InfringingFieldsReason<'tcx> { /// Checks that the fields of the type (an ADT) all implement copy. /// /// If fields don't implement copy, return an error containing a list of -/// those violating fields. If it's not an ADT, returns `Err(NotAnAdt)`. +/// those violating fields. +/// +/// If it's not an ADT, int ty, `bool`, float ty, `char`, raw pointer, `!`, +/// a reference or an array returns `Err(NotAnAdt)`. pub fn type_allowed_to_implement_copy<'tcx>( tcx: TyCtxt<'tcx>, param_env: ty::ParamEnv<'tcx>, @@ -47,12 +56,82 @@ pub fn type_allowed_to_implement_copy<'tcx>( | ty::Ref(_, _, hir::Mutability::Not) | ty::Array(..) => return Ok(()), - ty::Adt(adt, substs) => (adt, substs), + &ty::Adt(adt, substs) => (adt, substs), _ => return Err(CopyImplementationError::NotAnAdt), }; - let copy_def_id = tcx.require_lang_item(hir::LangItem::Copy, Some(parent_cause.span)); + all_fields_implement_trait( + tcx, + param_env, + self_type, + adt, + substs, + parent_cause, + hir::LangItem::Copy, + ) + .map_err(CopyImplementationError::InfringingFields)?; + + if adt.has_dtor(tcx) { + return Err(CopyImplementationError::HasDestructor); + } + + Ok(()) +} + +/// Checks that the fields of the type (an ADT) all implement `ConstParamTy`. +/// +/// If fields don't implement `ConstParamTy`, return an error containing a list of +/// those violating fields. +/// +/// If it's not an ADT, int ty, `bool` or `char`, returns `Err(NotAnAdtOrBuiltinAllowed)`. +pub fn type_allowed_to_implement_const_param_ty<'tcx>( + tcx: TyCtxt<'tcx>, + param_env: ty::ParamEnv<'tcx>, + self_type: Ty<'tcx>, + parent_cause: ObligationCause<'tcx>, +) -> Result<(), ConstParamTyImplementationError<'tcx>> { + let (adt, substs) = match self_type.kind() { + // `core` provides these impls. + ty::Uint(_) + | ty::Int(_) + | ty::Bool + | ty::Char + | ty::Str + | ty::Array(..) + | ty::Slice(_) + | ty::Ref(.., hir::Mutability::Not) => return Ok(()), + + &ty::Adt(adt, substs) => (adt, substs), + + _ => return Err(ConstParamTyImplementationError::NotAnAdtOrBuiltinAllowed), + }; + + all_fields_implement_trait( + tcx, + param_env, + self_type, + adt, + substs, + parent_cause, + hir::LangItem::ConstParamTy, + ) + .map_err(ConstParamTyImplementationError::InfrigingFields)?; + + Ok(()) +} + +/// Check that all fields of a given `adt` implement `lang_item` trait. +pub fn all_fields_implement_trait<'tcx>( + tcx: TyCtxt<'tcx>, + param_env: ty::ParamEnv<'tcx>, + self_type: Ty<'tcx>, + adt: AdtDef<'tcx>, + substs: &'tcx List<GenericArg<'tcx>>, + parent_cause: ObligationCause<'tcx>, + lang_item: LangItem, +) -> Result<(), Vec<(&'tcx ty::FieldDef, Ty<'tcx>, InfringingFieldsReason<'tcx>)>> { + let trait_def_id = tcx.require_lang_item(lang_item, Some(parent_cause.span)); let mut infringing = Vec::new(); for variant in adt.variants() { @@ -93,7 +172,7 @@ pub fn type_allowed_to_implement_copy<'tcx>( // between expected and found const-generic types. Don't report an // additional copy error here, since it's not typically useful. if !normalization_errors.is_empty() || ty.references_error() { - tcx.sess.delay_span_bug(field_span, format!("couldn't normalize struct field `{unnormalized_ty}` when checking Copy implementation")); + tcx.sess.delay_span_bug(field_span, format!("couldn't normalize struct field `{unnormalized_ty}` when checking {tr} implementation", tr = tcx.def_path_str(trait_def_id))); continue; } @@ -101,7 +180,7 @@ pub fn type_allowed_to_implement_copy<'tcx>( ObligationCause::dummy_with_span(field_ty_span), param_env, ty, - copy_def_id, + trait_def_id, ); let errors = ocx.select_all_or_error(); if !errors.is_empty() { @@ -124,15 +203,7 @@ pub fn type_allowed_to_implement_copy<'tcx>( } } - if !infringing.is_empty() { - return Err(CopyImplementationError::InfringingFields(infringing)); - } - - if adt.has_dtor(tcx) { - return Err(CopyImplementationError::HasDestructor); - } - - Ok(()) + if infringing.is_empty() { Ok(()) } else { Err(infringing) } } pub fn check_tys_might_be_eq<'tcx>( diff --git a/compiler/rustc_trait_selection/src/traits/object_safety.rs b/compiler/rustc_trait_selection/src/traits/object_safety.rs index 73e2efc3b00..384b6ae93a1 100644 --- a/compiler/rustc_trait_selection/src/traits/object_safety.rs +++ b/compiler/rustc_trait_selection/src/traits/object_safety.rs @@ -525,7 +525,7 @@ fn virtual_call_violation_for_method<'tcx>( // #78372 tcx.sess.delay_span_bug( tcx.def_span(method.def_id), - &format!("error: {}\n while computing layout for type {:?}", err, ty), + format!("error: {}\n while computing layout for type {:?}", err, ty), ); None } @@ -541,7 +541,7 @@ fn virtual_call_violation_for_method<'tcx>( abi => { tcx.sess.delay_span_bug( tcx.def_span(method.def_id), - &format!( + format!( "receiver when `Self = ()` should have a Scalar ABI; found {:?}", abi ), @@ -560,7 +560,7 @@ fn virtual_call_violation_for_method<'tcx>( abi => { tcx.sess.delay_span_bug( tcx.def_span(method.def_id), - &format!( + format!( "receiver when `Self = {}` should have a ScalarPair ABI; found {:?}", trait_object_ty, abi ), diff --git a/compiler/rustc_trait_selection/src/traits/project.rs b/compiler/rustc_trait_selection/src/traits/project.rs index ea45412e47f..4369b257f5f 100644 --- a/compiler/rustc_trait_selection/src/traits/project.rs +++ b/compiler/rustc_trait_selection/src/traits/project.rs @@ -1749,7 +1749,7 @@ fn assemble_candidates_from_impls<'cx, 'tcx>( // These traits have no associated types. selcx.tcx().sess.delay_span_bug( obligation.cause.span, - &format!("Cannot project an associated type from `{:?}`", impl_source), + format!("Cannot project an associated type from `{:?}`", impl_source), ); return Err(()); } diff --git a/compiler/rustc_trait_selection/src/traits/query/type_op/custom.rs b/compiler/rustc_trait_selection/src/traits/query/type_op/custom.rs index 8f1b05c1190..1f8e756043d 100644 --- a/compiler/rustc_trait_selection/src/traits/query/type_op/custom.rs +++ b/compiler/rustc_trait_selection/src/traits/query/type_op/custom.rs @@ -79,7 +79,7 @@ pub fn scrape_region_constraints<'tcx, Op: super::TypeOp<'tcx, Output = R>, R>( if !errors.is_empty() { infcx.tcx.sess.diagnostic().delay_span_bug( DUMMY_SP, - &format!("errors selecting obligation during MIR typeck: {:?}", errors), + format!("errors selecting obligation during MIR typeck: {:?}", errors), ); } diff --git a/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs b/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs index 1db9b8ce92e..a8864f47ef0 100644 --- a/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs +++ b/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs @@ -57,6 +57,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> { if obligation.polarity() == ty::ImplPolarity::Negative { self.assemble_candidates_for_trait_alias(obligation, &mut candidates); self.assemble_candidates_from_impls(obligation, &mut candidates); + self.assemble_candidates_from_caller_bounds(stack, &mut candidates)?; } else { self.assemble_candidates_for_trait_alias(obligation, &mut candidates); @@ -187,6 +188,10 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> { // Keep only those bounds which may apply, and propagate overflow if it occurs. for bound in matching_bounds { + if bound.skip_binder().polarity != stack.obligation.predicate.skip_binder().polarity { + continue; + } + // FIXME(oli-obk): it is suspicious that we are dropping the constness and // polarity here. let wc = self.where_clause_may_apply(stack, bound.map_bound(|t| t.trait_ref))?; diff --git a/compiler/rustc_trait_selection/src/traits/select/mod.rs b/compiler/rustc_trait_selection/src/traits/select/mod.rs index 863553670de..9890e990eeb 100644 --- a/compiler/rustc_trait_selection/src/traits/select/mod.rs +++ b/compiler/rustc_trait_selection/src/traits/select/mod.rs @@ -67,7 +67,7 @@ impl IntercrateAmbiguityCause { /// Emits notes when the overlap is caused by complex intercrate ambiguities. /// See #23980 for details. pub fn add_intercrate_ambiguity_hint(&self, err: &mut Diagnostic) { - err.note(&self.intercrate_ambiguity_hint()); + err.note(self.intercrate_ambiguity_hint()); } pub fn intercrate_ambiguity_hint(&self) -> String { @@ -2449,7 +2449,7 @@ impl<'tcx> SelectionContext<'_, 'tcx> { // for a variable being generalized... let guar = self.infcx.tcx.sess.delay_span_bug( obligation.cause.span, - &format!( + format!( "Impl {:?} was matchable against {:?} but now is not", impl_def_id, obligation ), diff --git a/compiler/rustc_trait_selection/src/traits/specialize/mod.rs b/compiler/rustc_trait_selection/src/traits/specialize/mod.rs index 8546bbe52dc..233d35aed38 100644 --- a/compiler/rustc_trait_selection/src/traits/specialize/mod.rs +++ b/compiler/rustc_trait_selection/src/traits/specialize/mod.rs @@ -373,7 +373,7 @@ fn report_conflicting_impls<'tcx>( } None => format!("conflicting implementation in crate `{}`", cname), }; - err.note(&msg); + err.note(msg); } } diff --git a/compiler/rustc_trait_selection/src/traits/wf.rs b/compiler/rustc_trait_selection/src/traits/wf.rs index 40e19abc0d0..0590e02d84a 100644 --- a/compiler/rustc_trait_selection/src/traits/wf.rs +++ b/compiler/rustc_trait_selection/src/traits/wf.rs @@ -328,6 +328,13 @@ impl<'tcx> WfPredicates<'tcx> { let tcx = self.tcx; let trait_ref = &trait_pred.trait_ref; + // Negative trait predicates don't require supertraits to hold, just + // that their substs are WF. + if trait_pred.polarity == ty::ImplPolarity::Negative { + self.compute_negative_trait_pred(trait_ref); + return; + } + // if the trait predicate is not const, the wf obligations should not be const as well. let obligations = if trait_pred.constness == ty::BoundConstness::NotConst { self.nominal_obligations_without_const(trait_ref.def_id, trait_ref.substs) @@ -393,6 +400,14 @@ impl<'tcx> WfPredicates<'tcx> { ); } + // Compute the obligations that are required for `trait_ref` to be WF, + // given that it is a *negative* trait predicate. + fn compute_negative_trait_pred(&mut self, trait_ref: &ty::TraitRef<'tcx>) { + for arg in trait_ref.substs { + self.compute(arg); + } + } + /// Pushes the obligations required for `trait_ref::Item` to be WF /// into `self.out`. fn compute_projection(&mut self, data: ty::AliasTy<'tcx>) { |