bjoernager/rust
bjoernager/rust
1
Fork 0
Code Activity

Rollup merge of #117914 - estebank:issue-85843, r=wesleywiser

Browse source 
On borrow return type, suggest borrowing from arg or owned return type

When we encounter a function with a return type that has an anonymous lifetime with no argument to borrow from, besides suggesting the `'static` lifetime we now also suggest changing the arguments to be borrows or changing the return type to be an owned type.

```
error[E0106]: missing lifetime specifier
  --> $DIR/variadic-ffi-6.rs:7:6
   |
LL | ) -> &usize {
   |      ^ expected named lifetime parameter
   |
   = help: this function's return type contains a borrowed value, but there is no value for it to be borrowed from
help: consider using the `'static` lifetime, but this is uncommon unless you're returning a borrowed value from a `const` or a `static`
   |
LL | ) -> &'static usize {
   |       +++++++
help: instead, you are more likely to want to change one of the arguments to be borrowed...
   |
LL |     x: &usize,
   |        +
help: ...or alternatively, to want to return an owned value
   |
LL - ) -> &usize {
LL + ) -> usize {
   |
```

Fix #85843.
This commit is contained in:
Matthias Krüger 2023-12-12 17:40:53 +01:00 • committed by GitHub
commit ffdb471872
No known key found for this signature in database
GPG key ID: 4AEE18F83AFDEB23
19 changed files with 450 additions and 55 deletions
Download patch file Download diff file Expand all files Collapse all files

271
compiler/rustc_resolve/src/late/diagnostics.rs
View file

@ -8,7 +8,7 @@ use crate::{PathResult, PathSource, Segment};
use rustc_hir::def::Namespace::{self, *};
use rustc_ast::ptr::P;
use rustc_ast::visit::{FnCtxt, FnKind, LifetimeCtxt};
use rustc_ast::visit::{walk_ty, FnCtxt, FnKind, LifetimeCtxt, Visitor};
use rustc_ast::{
self as ast, AssocItemKind, Expr, ExprKind, GenericParam, GenericParamKind, Item, ItemKind,
MethodCall, NodeId, Path, Ty, TyKind, DUMMY_NODE_ID,
@ -2830,6 +2830,7 @@ impl<'a: 'ast, 'ast, 'tcx> LateResolutionVisitor<'a, '_, 'ast, 'tcx> {
.collect();
debug!(?in_scope_lifetimes);
let mut maybe_static = false;
debug!(?function_param_lifetimes);
if let Some((param_lifetimes, params)) = &function_param_lifetimes {
let elided_len = param_lifetimes.len();
@ -2868,10 +2869,11 @@ impl<'a: 'ast, 'ast, 'tcx> LateResolutionVisitor<'a, '_, 'ast, 'tcx> {
if num_params == 0 {
err.help(
"this function's return type contains a borrowed value, \
but there is no value for it to be borrowed from",
"this function's return type contains a borrowed value, but there is no value \
for it to be borrowed from",
);
if in_scope_lifetimes.is_empty() {
maybe_static = true;
in_scope_lifetimes = vec![(
Ident::with_dummy_span(kw::StaticLifetime),
(DUMMY_NODE_ID, LifetimeRes::Static),
@ -2879,11 +2881,11 @@ impl<'a: 'ast, 'ast, 'tcx> LateResolutionVisitor<'a, '_, 'ast, 'tcx> {
}
} else if elided_len == 0 {
err.help(
"this function's return type contains a borrowed value with \
an elided lifetime, but the lifetime cannot be derived from \
the arguments",
"this function's return type contains a borrowed value with an elided \
lifetime, but the lifetime cannot be derived from the arguments",
);
if in_scope_lifetimes.is_empty() {
maybe_static = true;
in_scope_lifetimes = vec![(
Ident::with_dummy_span(kw::StaticLifetime),
(DUMMY_NODE_ID, LifetimeRes::Static),
@ -2891,13 +2893,13 @@ impl<'a: 'ast, 'ast, 'tcx> LateResolutionVisitor<'a, '_, 'ast, 'tcx> {
}
} else if num_params == 1 {
err.help(format!(
"this function's return type contains a borrowed value, \
but the signature does not say which {m} it is borrowed from"
"this function's return type contains a borrowed value, but the signature does \
not say which {m} it is borrowed from",
));
} else {
err.help(format!(
"this function's return type contains a borrowed value, \
but the signature does not say whether it is borrowed from {m}"
"this function's return type contains a borrowed value, but the signature does \
not say whether it is borrowed from {m}",
));
}
}
@ -2962,11 +2964,238 @@ impl<'a: 'ast, 'ast, 'tcx> LateResolutionVisitor<'a, '_, 'ast, 'tcx> {
);
}
1 => {
let post = if maybe_static {
let owned = if let [lt] = &lifetime_refs[..]
&& lt.kind != MissingLifetimeKind::Ampersand
{
", or if you will only have owned values"
} else {
""
};
format!(
", but this is uncommon unless you're returning a borrowed value from a \
`const` or a `static`{owned}",
)
} else {
String::new()
};
err.multipart_suggestion_verbose(
format!("consider using the `{existing_name}` lifetime"),
format!("consider using the `{existing_name}` lifetime{post}"),
spans_suggs,
Applicability::MaybeIncorrect,
);
if maybe_static {
// FIXME: what follows are general suggestions, but we'd want to perform some
// minimal flow analysis to provide more accurate suggestions. For example, if
// we identified that the return expression references only one argument, we
// would suggest borrowing only that argument, and we'd skip the prior
// "use `'static`" suggestion entirely.
if let [lt] = &lifetime_refs[..]
&& (lt.kind == MissingLifetimeKind::Ampersand
|| lt.kind == MissingLifetimeKind::Underscore)
{
let pre = if lt.kind == MissingLifetimeKind::Ampersand
&& let Some((kind, _span)) = self.diagnostic_metadata.current_function
&& let FnKind::Fn(_, _, sig, _, _, _) = kind
&& !sig.decl.inputs.is_empty()
&& let sugg = sig
.decl
.inputs
.iter()
.filter_map(|param| {
if param.ty.span.contains(lt.span) {
// We don't want to suggest `fn elision(_: &fn() -> &i32)`
// when we have `fn elision(_: fn() -> &i32)`
None
} else if let TyKind::CVarArgs = param.ty.kind {
// Don't suggest `&...` for ffi fn with varargs
None
} else if let TyKind::ImplTrait(..) = &param.ty.kind {
// We handle these in the next `else if` branch.
None
} else {
Some((param.ty.span.shrink_to_lo(), "&".to_string()))
}
})
.collect::<Vec<_>>()
&& !sugg.is_empty()
{
let (the, s) = if sig.decl.inputs.len() == 1 {
("the", "")
} else {
("one of the", "s")
};
err.multipart_suggestion_verbose(
format!(
"instead, you are more likely to want to change {the} \
argument{s} to be borrowed...",
),
sugg,
Applicability::MaybeIncorrect,
);
"...or alternatively, you might want"
} else if (lt.kind == MissingLifetimeKind::Ampersand
|| lt.kind == MissingLifetimeKind::Underscore)
&& let Some((kind, _span)) = self.diagnostic_metadata.current_function
&& let FnKind::Fn(_, _, sig, _, _, _) = kind
&& let ast::FnRetTy::Ty(ret_ty) = &sig.decl.output
&& !sig.decl.inputs.is_empty()
&& let arg_refs = sig
.decl
.inputs
.iter()
.filter_map(|param| match &param.ty.kind {
TyKind::ImplTrait(_, bounds) => Some(bounds),
_ => None,
})
.flat_map(|bounds| bounds.into_iter())
.collect::<Vec<_>>()
&& !arg_refs.is_empty()
{
// We have a situation like
// fn g(mut x: impl Iterator<Item = &()>) -> Option<&()>
// So we look at every ref in the trait bound. If there's any, we
// suggest
// fn g<'a>(mut x: impl Iterator<Item = &'a ()>) -> Option<&'a ()>
let mut lt_finder =
LifetimeFinder { lifetime: lt.span, found: None, seen: vec![] };
for bound in arg_refs {
if let ast::GenericBound::Trait(trait_ref, _) = bound {
lt_finder.visit_trait_ref(&trait_ref.trait_ref);
}
}
lt_finder.visit_ty(ret_ty);
let spans_suggs: Vec<_> = lt_finder
.seen
.iter()
.filter_map(|ty| match &ty.kind {
TyKind::Ref(_, mut_ty) => {
let span = ty.span.with_hi(mut_ty.ty.span.lo());
Some((span, "&'a ".to_string()))
}
_ => None,
})
.collect();
self.suggest_introducing_lifetime(
err,
None,
|err, higher_ranked, span, message, intro_sugg| {
err.multipart_suggestion_verbose(
message,
std::iter::once((span, intro_sugg))
.chain(spans_suggs.iter().cloned())
.collect(),
Applicability::MaybeIncorrect,
);
higher_ranked
},
);
"alternatively, you might want"
} else {
"instead, you are more likely to want"
};
let mut owned_sugg = lt.kind == MissingLifetimeKind::Ampersand;
let mut sugg = vec![(lt.span, String::new())];
if let Some((kind, _span)) = self.diagnostic_metadata.current_function
&& let FnKind::Fn(_, _, sig, _, _, _) = kind
&& let ast::FnRetTy::Ty(ty) = &sig.decl.output
{
let mut lt_finder =
LifetimeFinder { lifetime: lt.span, found: None, seen: vec![] };
lt_finder.visit_ty(&ty);
if let [Ty { span, kind: TyKind::Ref(_, mut_ty), .. }] =
&lt_finder.seen[..]
{
// We might have a situation like
// fn g(mut x: impl Iterator<Item = &'_ ()>) -> Option<&'_ ()>
// but `lt.span` only points at `'_`, so to suggest `-> Option<()>`
// we need to find a more accurate span to end up with
// fn g<'a>(mut x: impl Iterator<Item = &'_ ()>) -> Option<()>
sugg = vec![(span.with_hi(mut_ty.ty.span.lo()), String::new())];
owned_sugg = true;
}
if let Some(ty) = lt_finder.found {
if let TyKind::Path(None, path) = &ty.kind {
// Check if the path being borrowed is likely to be owned.
let path: Vec<_> = Segment::from_path(path);
match self.resolve_path(&path, Some(TypeNS), None) {
PathResult::Module(ModuleOrUniformRoot::Module(module)) => {
match module.res() {
Some(Res::PrimTy(PrimTy::Str)) => {
// Don't suggest `-> str`, suggest `-> String`.
sugg = vec![(
lt.span.with_hi(ty.span.hi()),
"String".to_string(),
)];
}
Some(Res::PrimTy(..)) => {}
Some(Res::Def(
DefKind::Struct
| DefKind::Union
| DefKind::Enum
| DefKind::ForeignTy
| DefKind::AssocTy
| DefKind::OpaqueTy
| DefKind::TyParam,
_,
)) => {}
_ => {
// Do not suggest in all other cases.
owned_sugg = false;
}
}
}
PathResult::NonModule(res) => {
match res.base_res() {
Res::PrimTy(PrimTy::Str) => {
// Don't suggest `-> str`, suggest `-> String`.
sugg = vec![(
lt.span.with_hi(ty.span.hi()),
"String".to_string(),
)];
}
Res::PrimTy(..) => {}
Res::Def(
DefKind::Struct
| DefKind::Union
| DefKind::Enum
| DefKind::ForeignTy
| DefKind::AssocTy
| DefKind::OpaqueTy
| DefKind::TyParam,
_,
) => {}
_ => {
// Do not suggest in all other cases.
owned_sugg = false;
}
}
}
_ => {
// Do not suggest in all other cases.
owned_sugg = false;
}
}
}
if let TyKind::Slice(inner_ty) = &ty.kind {
// Don't suggest `-> [T]`, suggest `-> Vec<T>`.
sugg = vec![
(lt.span.with_hi(inner_ty.span.lo()), "Vec<".to_string()),
(ty.span.with_lo(inner_ty.span.hi()), ">".to_string()),
];
}
}
}
if owned_sugg {
err.multipart_suggestion_verbose(
format!("{pre} to return an owned value"),
sugg,
Applicability::MaybeIncorrect,
);
}
}
}
// Record as using the suggested resolution.
let (_, (_, res)) = in_scope_lifetimes[0];
@ -2996,7 +3225,7 @@ impl<'a: 'ast, 'ast, 'tcx> LateResolutionVisitor<'a, '_, 'ast, 'tcx> {
fn mk_where_bound_predicate(
path: &Path,
poly_trait_ref: &ast::PolyTraitRef,
ty: &ast::Ty,
ty: &Ty,
) -> Option<ast::WhereBoundPredicate> {
use rustc_span::DUMMY_SP;
let modified_segments = {
@ -3073,6 +3302,24 @@ pub(super) fn signal_lifetime_shadowing(sess: &Session, orig: Ident, shadower: I
err.emit();
}
struct LifetimeFinder<'ast> {
lifetime: Span,
found: Option<&'ast Ty>,
seen: Vec<&'ast Ty>,
}
impl<'ast> Visitor<'ast> for LifetimeFinder<'ast> {
fn visit_ty(&mut self, t: &'ast Ty) {
if let TyKind::Ref(_, mut_ty) = &t.kind {
self.seen.push(t);
if t.span.lo() == self.lifetime.lo() {
self.found = Some(&mut_ty.ty);
}
}
walk_ty(self, t)
}
}
/// Shadowing involving a label is only a warning for historical reasons.
//FIXME: make this a proper lint.
pub(super) fn signal_label_shadowing(sess: &Session, orig: Span, shadower: Ident) {