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use more descriptive names
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@TaKO8Ki
TaKO8Ki committed Aug 20, 2022
1 parent 64b3e4a commit a311b8a
Showing 1 changed file with 95 additions and 93 deletions.
188 changes: 95 additions & 93 deletions compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -908,111 +908,113 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
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 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);
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_ref_self_ty_satisfies_pred = mk_result(trait_pred_and_imm_ref);
let mut_ref_self_ty_satisfies_pred = mk_result(trait_pred_and_mut_ref);

let ref_inner_ty_result =
let (ref_inner_ty_satisfies_pred, ref_inner_ty_mut) =
if let ObligationCauseCode::ItemObligation(_) = obligation.cause.code()
&& let ty::Ref(_, ty, mutability) = old_pred.self_ty().skip_binder().kind()
{
Some((mk_result(old_pred.map_bound(|trait_pred| (trait_pred, *ty))), mutability))
(
mk_result(old_pred.map_bound(|trait_pred| (trait_pred, *ty))),
matches!(mutability, hir::Mutability::Mut),
)
} else {
None
(false, false)
};

if imm_result || mut_result || ref_inner_ty_result.map_or(false, |(result, _)| 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,
);
if imm_ref_self_ty_satisfies_pred
|| mut_ref_self_ty_satisfies_pred
|| ref_inner_ty_satisfies_pred
{
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 {
let is_mut = mut_result
|| ref_inner_ty_result.map_or(false, |(_, mutabl)| {
matches!(mutabl, hir::Mutability::Mut)
});
err.span_suggestion_verbose(
span.shrink_to_lo(),
&format!(
"consider{} borrowing here",
if is_mut { " mutably" } else { "" }
),
format!("&{}", if is_mut { "mut " } else { "" }),
Applicability::MaybeIncorrect,
);
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_ref_self_ty_satisfies_pred && mut_ref_self_ty_satisfies_pred {
err.span_suggestions(
span.shrink_to_lo(),
"consider borrowing here",
["&".to_string(), "&mut ".to_string()].into_iter(),
Applicability::MaybeIncorrect,
);
} else {
let is_mut = mut_ref_self_ty_satisfies_pred || ref_inner_ty_mut;
err.span_suggestion_verbose(
span.shrink_to_lo(),
&format!(
"consider{} borrowing here",
if is_mut { " mutably" } else { "" }
),
format!("&{}", if is_mut { "mut " } else { "" }),
Applicability::MaybeIncorrect,
);
}
}
return true;
}
return true;
}
}
return false;
};
return false;
};

if let ObligationCauseCode::ImplDerivedObligation(cause) = &*code {
try_borrowing(cause.derived.parent_trait_pred, &[])
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