bjoernager/rust
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fix syntax error in suggesting generic constraint in trait parameter

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suggest `where T: Foo` for the first bound on a trait, then suggest
`, T: Foo` when the suggested bound would add to an existing set of
`where` clauses. `where T: Foo` may be the first bound if `T` has a
default, because we'd rather suggest
```
trait A<T=()> where T: Copy
```
than
```
trait A<T: Copy=()>
```
for legibility reasons.
This commit is contained in:
iximeow 2020-09-13 20:55:06 -07:00
parent dd33766e4a
commit 0eac38b7a6
5 changed files with 105 additions and 22 deletions
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66
compiler/rustc_middle/src/ty/diagnostics.rs
View file

@ -202,33 +202,59 @@ pub fn suggest_constraining_type_param(
// Suggestion:
// fn foo<T>(t: T) where T: Foo, T: Bar {... }
// - insert: `, T: Zar`
//
// Additionally, there may be no `where` clause whatsoever in the case that this was
// reached becauase the generic parameter has a default:
//
// Message:
// trait Foo<T=()> {... }
// - help: consider further restricting this type parameter with `where T: Zar`
//
// Suggestion:
// trait Foo<T=()> where T: Zar {... }
// - insert: `where T: Zar`
let mut param_spans = Vec::new();
if matches!(param.kind, hir::GenericParamKind::Type { default: Some(_), .. })
&& generics.where_clause.predicates.len() == 0
{
// Suggest a bound, but there are no existing where clauses for this `<T=Foo>`, so
// suggest adding one.
err.span_suggestion_verbose(
generics.where_clause.tail_span_for_suggestion(),
&msg_restrict_type_further,
format!(" where {}: {}", param_name, constraint),
Applicability::MachineApplicable,
);
} else {
let mut param_spans = Vec::new();
for predicate in generics.where_clause.predicates {
if let WherePredicate::BoundPredicate(WhereBoundPredicate {
span, bounded_ty, ..
}) = predicate
{
if let TyKind::Path(QPath::Resolved(_, path)) = &bounded_ty.kind {
if let Some(segment) = path.segments.first() {
if segment.ident.to_string() == param_name {
param_spans.push(span);
for predicate in generics.where_clause.predicates {
if let WherePredicate::BoundPredicate(WhereBoundPredicate {
span,
bounded_ty,
..
}) = predicate
{
if let TyKind::Path(QPath::Resolved(_, path)) = &bounded_ty.kind {
if let Some(segment) = path.segments.first() {
if segment.ident.to_string() == param_name {
param_spans.push(span);
}
}
}
}
}
}
match &param_spans[..] {
&[&param_span] => suggest_restrict(param_span.shrink_to_hi()),
_ => {
err.span_suggestion_verbose(
generics.where_clause.tail_span_for_suggestion(),
&msg_restrict_type_further,
format!(", {}: {}", param_name, constraint),
Applicability::MachineApplicable,
);
match &param_spans[..] {
&[&param_span] => suggest_restrict(param_span.shrink_to_hi()),
_ => {
err.span_suggestion_verbose(
generics.where_clause.tail_span_for_suggestion(),
&msg_restrict_type_further,
format!(", {}: {}", param_name, constraint),
Applicability::MachineApplicable,
);
}
}
}