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Trying to suggest additional lifetime parameter #102323

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merged 6 commits into from
Oct 10, 2022
Merged

Trying to suggest additional lifetime parameter #102323

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887515a
Trying to suggest additional lifetime parameter
Stoozy Sep 26, 2022
365457b
Using multipart suggestion
Stoozy Sep 27, 2022
24c8e27
Properly formatting the multipart suggestion
Stoozy Sep 27, 2022
e7cb6ad
Proper span for new generic param suggestion
Stoozy Sep 28, 2022
ef930a2
Emitting error regardless of new param suggestion
Stoozy Sep 29, 2022
2657f9d
Removed unnecessary for loop
Stoozy Oct 1, 2022
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50 changes: 43 additions & 7 deletions compiler/rustc_resolve/src/late/lifetimes.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1318,13 +1318,49 @@ impl<'a, 'tcx> LifetimeContext<'a, 'tcx> {
&& let hir::IsAsync::NotAsync = self.tcx.asyncness(lifetime_ref.hir_id.owner.def_id)
&& !self.tcx.features().anonymous_lifetime_in_impl_trait
{
rustc_session::parse::feature_err(
&self.tcx.sess.parse_sess,
sym::anonymous_lifetime_in_impl_trait,
lifetime_ref.span,
"anonymous lifetimes in `impl Trait` are unstable",
).emit();
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You can keep this a feature error. You can keep this line, but instead of calling emit immediately, store it in a mut variable diag, decorate it using span_... methods, and call emit when you're done.

return;

match self.tcx.hir().get_generics(lifetime_ref.hir_id.owner.def_id) {
Some(generics) => {
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Now you have generics you want 2 things to know where to suggest the lifetime parameter param_span, and in what form param_sugg.
Once you have that, you call

diag.multipart_suggestion(
  "consider introducing a named lifetime parameter",
  vec![
    (lifetime_ref.span, "'a".to_owned()), // this is at the use site
    (param_span, param_sugg), // this is in generics
  ],
)

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it seems if I put "'a" for the message, it replaces the ampersand symbol from the original posters input. Should I keep this?

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You can use lifetime_ref.span.shrink_to_hi() instead then.

for i in 0..generics.params.len() {
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You only use a single parameter. Could you separate the choice of param from the suggestion / move the suggestion code out of the loop?


if !generics.span.contains(generics.params[i].span) {

let mut diag = rustc_session::parse::feature_err(
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This code is common to both branches. Could you move it above the match?

&self.tcx.sess.parse_sess,
sym::anonymous_lifetime_in_impl_trait,
lifetime_ref.span,
"anonymous lifetimes in `impl Trait` are unstable",
);

diag.span_label(lifetime_ref.span, "expected named lifetime parameter");
diag.multipart_suggestion("consider introducing a named lifetime parameter",
vec![
(lifetime_ref.span.shrink_to_hi(), "'a ".to_owned()),
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This suggestion is only correct if you have a &, but it's a good start 😄. You can also have an elided lifetime with the '_ syntax, or in a path Ref<u8> instead of Ref<'_, u8> for instance.

match generics.span_for_param_suggestion() {
Some(_) => {
(self.tcx.sess.source_map().span_through_char(generics.span, '<').shrink_to_hi(), "'a, ".to_owned())
}
None => (generics.span, "<'a>".to_owned()),

}
], rustc_errors::Applicability::MaybeIncorrect);
diag.emit();
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This is also common to both branches. Could you move this below the match?


return;
}
}
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},
None => {
rustc_session::parse::feature_err(
&self.tcx.sess.parse_sess,
sym::anonymous_lifetime_in_impl_trait,
lifetime_ref.span,
"anonymous lifetimes in `impl Trait` are unstable",
).emit();
return;
}
}

}
scope = s;
}
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12 changes: 10 additions & 2 deletions src/test/ui/suggestions/impl-trait-missing-lifetime-gated.stderr
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Original file line number Diff line number Diff line change
Expand Up @@ -26,17 +26,25 @@ error[E0658]: anonymous lifetimes in `impl Trait` are unstable
--> $DIR/impl-trait-missing-lifetime-gated.rs:5:31
|
LL | fn f(_: impl Iterator<Item = &'_ ()>) {}
| ^^
| ^^ expected named lifetime parameter
|
= help: add `#![feature(anonymous_lifetime_in_impl_trait)]` to the crate attributes to enable
help: consider introducing a named lifetime parameter
|
LL | fn f<'a>(_: impl Iterator<Item = &'_'a ()>) {}
| ++++ ++

error[E0658]: anonymous lifetimes in `impl Trait` are unstable
--> $DIR/impl-trait-missing-lifetime-gated.rs:8:31
|
LL | fn g(x: impl Iterator<Item = &'_ ()>) -> Option<&'_ ()> { x.next() }
| ^^
| ^^ expected named lifetime parameter
|
= help: add `#![feature(anonymous_lifetime_in_impl_trait)]` to the crate attributes to enable
help: consider introducing a named lifetime parameter
|
LL | fn g<'a>(x: impl Iterator<Item = &'_'a ()>) -> Option<&'_ ()> { x.next() }
| ++++ ++
Comment on lines +44 to +47
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Looking at the resulting code here, the .shrink_to_hi() of the span without checking whether the span covers only & or '_ causes invalid code to be produced. It also seems like we might also want to replace the anon lifetime in the return type?

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Replacing the anon lifetime in the return type seems like an outsized change. I'd rather stabilize this feature sooner, to get rid of the question.

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Is there anything else I should do?

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The question is: do you want to take a bit more time in this PR to fix the '_'a situation?


error: aborting due to 4 previous errors

Expand Down