bjoernager/rust
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Suggest setting lifetime in borrowck error involving types with elided lifetimes

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```
error: lifetime may not live long enough
  --> $DIR/ex3-both-anon-regions-both-are-structs-2.rs:7:5
   |
LL | fn foo(mut x: Ref, y: Ref) {
   |        -----       - has type `Ref<'_, '1>`
   |        |
   |        has type `Ref<'_, '2>`
LL |     x.b = y.b;
   |     ^^^^^^^^^ assignment requires that `'1` must outlive `'2`
   |
help: consider introducing a named lifetime parameter
   |
LL | fn foo<'a>(mut x: Ref<'a, 'a>, y: Ref<'a, 'a>) {
   |       ++++           ++++++++        ++++++++
```

As can be seen above, it currently doesn't try to compare the `ty::Ty` lifetimes that diverged vs the `hir::Ty` to correctly suggest the following

```
help: consider introducing a named lifetime parameter
   |
LL | fn foo<'a>(mut x: Ref<'_, 'a>, y: Ref<'_, 'a>) {
   |       ++++           ++++++++        ++++++++
```

but I believe this to still be an improvement over the status quo.

CC #40990.
This commit is contained in:
Esteban Küber 2024-05-03 21:42:34 +00:00
parent 1a73979886
commit 9f730e92f2
14 changed files with 140 additions and 30 deletions
Download patch file Download diff file Expand all files Collapse all files

105
compiler/rustc_infer/src/errors/mod.rs
View file

@ -4,6 +4,7 @@ use rustc_errors::{
MultiSpan, SubdiagMessageOp, Subdiagnostic,
};
use rustc_hir as hir;
use rustc_hir::intravisit::{walk_ty, Visitor};
use rustc_hir::FnRetTy;
use rustc_macros::{Diagnostic, Subdiagnostic};
use rustc_middle::ty::print::TraitRefPrintOnlyTraitPath;
@ -355,18 +356,6 @@ impl Subdiagnostic for AddLifetimeParamsSuggestion<'_> {
_f: &F,
) {
let mut mk_suggestion = || {
let (
hir::Ty { kind: hir::TyKind::Ref(lifetime_sub, _), .. },
hir::Ty { kind: hir::TyKind::Ref(lifetime_sup, _), .. },
) = (self.ty_sub, self.ty_sup)
else {
return false;
};
if !lifetime_sub.is_anonymous() || !lifetime_sup.is_anonymous() {
return false;
};
let Some(anon_reg) = self.tcx.is_suitable_region(self.sub) else {
return false;
};
@ -393,21 +382,77 @@ impl Subdiagnostic for AddLifetimeParamsSuggestion<'_> {
let suggestion_param_name =
suggestion_param_name.map(|n| n.to_string()).unwrap_or_else(|| "'a".to_owned());
debug!(?lifetime_sup.ident.span);
debug!(?lifetime_sub.ident.span);
let make_suggestion = |ident: Ident| {
let sugg = if ident.name == kw::Empty {
format!("{suggestion_param_name}, ")
} else if ident.name == kw::UnderscoreLifetime && ident.span.is_empty() {
format!("{suggestion_param_name} ")
} else {
suggestion_param_name.clone()
};
(ident.span, sugg)
};
let mut suggestions =
vec![make_suggestion(lifetime_sub.ident), make_suggestion(lifetime_sup.ident)];
struct ImplicitLifetimeFinder {
suggestions: Vec<(Span, String)>,
suggestion_param_name: String,
}
impl<'v> Visitor<'v> for ImplicitLifetimeFinder {
fn visit_ty(&mut self, ty: &'v hir::Ty<'v>) {
let make_suggestion = |ident: Ident| {
if ident.name == kw::Empty && ident.span.is_empty() {
format!("{}, ", self.suggestion_param_name)
} else if ident.name == kw::UnderscoreLifetime && ident.span.is_empty() {
format!("{} ", self.suggestion_param_name)
} else {
self.suggestion_param_name.clone()
}
};
match ty.kind {
hir::TyKind::Path(hir::QPath::Resolved(_, path)) => {
for segment in path.segments {
if let Some(args) = segment.args {
if args.args.iter().all(|arg| {
matches!(
arg,
hir::GenericArg::Lifetime(lifetime)
if lifetime.ident.name == kw::Empty
)
}) {
self.suggestions.push((
segment.ident.span.shrink_to_hi(),
format!(
"<{}>",
args.args
.iter()
.map(|_| self.suggestion_param_name.clone())
.collect::<Vec<_>>()
.join(", ")
),
));
} else {
for arg in args.args {
if let hir::GenericArg::Lifetime(lifetime) = arg
&& lifetime.is_anonymous()
{
self.suggestions.push((
lifetime.ident.span,
make_suggestion(lifetime.ident),
));
}
}
}
}
}
}
hir::TyKind::Ref(lifetime, ..) if lifetime.is_anonymous() => {
self.suggestions
.push((lifetime.ident.span, make_suggestion(lifetime.ident)));
}
_ => {}
}
walk_ty(self, ty);
}
}
let mut visitor = ImplicitLifetimeFinder {
suggestions: vec![],
suggestion_param_name: suggestion_param_name.clone(),
};
visitor.visit_ty(self.ty_sub);
visitor.visit_ty(self.ty_sup);
if visitor.suggestions.is_empty() {
return false;
}
if introduce_new {
let new_param_suggestion = if let Some(first) =
generics.params.iter().find(|p| !p.name.ident().span.is_empty())
@ -417,15 +462,15 @@ impl Subdiagnostic for AddLifetimeParamsSuggestion<'_> {
(generics.span, format!("<{suggestion_param_name}>"))
};
suggestions.push(new_param_suggestion);
visitor.suggestions.push(new_param_suggestion);
}
diag.multipart_suggestion(
diag.multipart_suggestion_verbose(
fluent::infer_lifetime_param_suggestion,
suggestions,
visitor.suggestions,
Applicability::MaybeIncorrect,
);
diag.arg("is_impl", is_impl);
true
};
if mk_suggestion() && self.add_note {