bjoernager/rust
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Explain HRTB + infer limitations of old solver

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This commit is contained in:
Michael Goulet 2023-09-07 02:06:20 +00:00
parent 19dd953540
commit 976d377f7f
7 changed files with 112 additions and 0 deletions
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2
compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs
View file

@ -986,6 +986,8 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
}
}
self.explain_hrtb_projection(&mut err, trait_predicate, obligation.param_env, &obligation.cause);
// Return early if the trait is Debug or Display and the invocation
// originates within a standard library macro, because the output
// is otherwise overwhelming and unhelpful (see #85844 for an

73
compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
View file

@ -406,6 +406,14 @@ pub trait TypeErrCtxtExt<'tcx> {
candidate_impls: &[ImplCandidate<'tcx>],
span: Span,
);
fn explain_hrtb_projection(
&self,
diag: &mut Diagnostic,
pred: ty::PolyTraitPredicate<'tcx>,
param_env: ty::ParamEnv<'tcx>,
cause: &ObligationCause<'tcx>,
);
}
fn predicate_constraint(generics: &hir::Generics<'_>, pred: ty::Predicate<'_>) -> (Span, String) {
@ -4027,6 +4035,71 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
}
}
}
fn explain_hrtb_projection(
&self,
diag: &mut Diagnostic,
pred: ty::PolyTraitPredicate<'tcx>,
param_env: ty::ParamEnv<'tcx>,
cause: &ObligationCause<'tcx>,
) {
if pred.skip_binder().has_escaping_bound_vars() && pred.skip_binder().has_non_region_infer()
{
self.probe(|_| {
let ocx = ObligationCtxt::new(self);
let pred = self.instantiate_binder_with_placeholders(pred);
let pred = ocx.normalize(&ObligationCause::dummy(), param_env, pred);
ocx.register_obligation(Obligation::new(
self.tcx,
ObligationCause::dummy(),
param_env,
pred,
));
if !ocx.select_where_possible().is_empty() {
// encountered errors.
return;
}
if let ObligationCauseCode::FunctionArgumentObligation {
call_hir_id,
arg_hir_id,
parent_code: _,
} = cause.code()
{
let arg_span = self.tcx.hir().span(*arg_hir_id);
let mut sp: MultiSpan = arg_span.into();
sp.push_span_label(
arg_span,
"the trait solver is unable to infer the \
generic types that should be inferred from this argument",
);
sp.push_span_label(
self.tcx.hir().span(*call_hir_id),
"add turbofish arguments to this call to \
specify the types manually, even if it's redundant",
);
diag.span_note(
sp,
"this is a known limitation of the trait solver that \
will be lifted in the future",
);
} else {
let mut sp: MultiSpan = cause.span.into();
sp.push_span_label(
cause.span,
"try adding turbofish arguments to this expression to \
specify the types manually, even if it's redundant",
);
diag.span_note(
sp,
"this is a known limitation of the trait solver that \
will be lifted in the future",
);
}
});
}
}
}
/// Add a hint to add a missing borrow or remove an unnecessary one.