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Suggest adding a new lifetime parameter when two elided lifetimes should match up for traits and impls. #94464

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merged 3 commits into from
Mar 2, 2022
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Suggest adding a new lifetime parameter when two elided lifetimes should match up for traits and impls. #94464

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abcccc9
Suggest adding a new lifetime parameter when two elided lifetimes sho…
kckeiks Feb 28, 2022
270730f
add suggestion to update trait if error is in impl
kckeiks Mar 1, 2022
1b08cba
update (bless) test results
kckeiks Mar 1, 2022
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106 changes: 54 additions & 52 deletions compiler/rustc_infer/src/infer/error_reporting/nice_region_error/different_lifetimes.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -166,59 +166,61 @@ impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
if lifetime_sub.name.is_elided() && lifetime_sup.name.is_elided() {
if let Some(anon_reg) = self.tcx().is_suitable_region(sub) {
let hir_id = self.tcx().hir().local_def_id_to_hir_id(anon_reg.def_id);
if let hir::Node::Item(&hir::Item {
kind: hir::ItemKind::Fn(_, ref generics, ..),
..
}) = self.tcx().hir().get(hir_id)
{
let (suggestion_param_name, introduce_new) = generics
.params
.iter()
.find(|p| matches!(p.kind, GenericParamKind::Lifetime { .. }))
.and_then(|p| self.tcx().sess.source_map().span_to_snippet(p.span).ok())
.map(|name| (name, false))
.unwrap_or_else(|| ("'a".to_string(), true));

let mut suggestions = vec![
if let hir::LifetimeName::Underscore = lifetime_sub.name {
(lifetime_sub.span, suggestion_param_name.clone())
} else {
(
lifetime_sub.span.shrink_to_hi(),
suggestion_param_name.clone() + " ",
)
},
if let hir::LifetimeName::Underscore = lifetime_sup.name {
(lifetime_sup.span, suggestion_param_name.clone())
} else {
(
lifetime_sup.span.shrink_to_hi(),
suggestion_param_name.clone() + " ",
)
},
];

if introduce_new {
let new_param_suggestion = match &generics.params {
[] => (generics.span, format!("<{}>", suggestion_param_name)),
[first, ..] => (
first.span.shrink_to_lo(),
format!("{}, ", suggestion_param_name),
),
};

suggestions.push(new_param_suggestion);
}

err.multipart_suggestion(
"consider introducing a named lifetime parameter",
suggestions,
Applicability::MaybeIncorrect,
);
err.note(
"each elided lifetime in input position becomes a distinct lifetime",
);

let node = self.tcx().hir().get(hir_id);
let is_impl = matches!(&node, hir::Node::ImplItem(_));
let generics = match node {
hir::Node::Item(&hir::Item {
kind: hir::ItemKind::Fn(_, ref generics, ..),
..
})
| hir::Node::TraitItem(&hir::TraitItem { ref generics, .. })
| hir::Node::ImplItem(&hir::ImplItem { ref generics, .. }) => generics,
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We should handle the impl case specifically with extra wording in the suggestion to let people know that they'll have to modify the trait as well. This is likely not a problem in practice, but I'd like us to be thorough and avoid confusing people.

It might be enough to just have a boolean flag that you use to modify the suggestion description with extra wording.

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Good call. I'll make that change.

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How about this for impl?

help: consider introducing a named lifetime parameter and update trait if needed
   |
32 |     fn foo<'a>(&'a self, x: &i32, z: &'a i32) -> Option<&i32> {
   |           ++++  ++                    ++

error: aborting due to previous error

For more information about this error, try `rustc --explain E0623`.

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Ideally we would have something like "consider introducing a named lifetime parameter and update trait TraitName as necessary", by getting the TraitName from the parent DefId, but that can be left as follow up work.

_ => return,
};

let (suggestion_param_name, introduce_new) = generics
.params
.iter()
.find(|p| matches!(p.kind, GenericParamKind::Lifetime { .. }))
.and_then(|p| self.tcx().sess.source_map().span_to_snippet(p.span).ok())
.map(|name| (name, false))
.unwrap_or_else(|| ("'a".to_string(), true));

let mut suggestions = vec![
if let hir::LifetimeName::Underscore = lifetime_sub.name {
(lifetime_sub.span, suggestion_param_name.clone())
} else {
(lifetime_sub.span.shrink_to_hi(), suggestion_param_name.clone() + " ")
},
if let hir::LifetimeName::Underscore = lifetime_sup.name {
(lifetime_sup.span, suggestion_param_name.clone())
} else {
(lifetime_sup.span.shrink_to_hi(), suggestion_param_name.clone() + " ")
},
];

if introduce_new {
let new_param_suggestion = match &generics.params {
[] => (generics.span, format!("<{}>", suggestion_param_name)),
[first, ..] => {
(first.span.shrink_to_lo(), format!("{}, ", suggestion_param_name))
}
};

suggestions.push(new_param_suggestion);
}

let mut sugg = String::from("consider introducing a named lifetime parameter");
if is_impl {
sugg.push_str(" and update trait if needed");
}
err.multipart_suggestion(
sugg.as_str(),
suggestions,
Applicability::MaybeIncorrect,
);
err.note("each elided lifetime in input position becomes a distinct lifetime");
}
}
}
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6 changes: 6 additions & 0 deletions src/test/ui/issues/issue-17728.stderr
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Original file line number Diff line number Diff line change
Expand Up @@ -8,6 +8,12 @@ LL | fn attemptTraverse(&self, room: &Room, directionStr: &str) -> Result<&R
...
LL | Some(entry) => Ok(entry),
| ^^^^^^^^^ ...but data from `room` is returned here
|
= note: each elided lifetime in input position becomes a distinct lifetime
help: consider introducing a named lifetime parameter
|
LL | fn attemptTraverse<'a>(&'a self, room: &'a Room, directionStr: &str) -> Result<&Room, &str> {
| ++++ ++ ++

error[E0308]: `match` arms have incompatible types
--> $DIR/issue-17728.rs:109:14
Expand Down
6 changes: 6 additions & 0 deletions src/test/ui/lifetimes/lifetime-errors/ex3-both-anon-regions-return-type-is-anon.stderr
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Expand Up @@ -7,6 +7,12 @@ LL | fn foo<'a>(&self, x: &i32) -> &i32 {
| this parameter and the return type are declared with different lifetimes...
LL | x
| ^ ...but data from `x` is returned here
|
= note: each elided lifetime in input position becomes a distinct lifetime
help: consider introducing a named lifetime parameter and update trait if needed
|
LL | fn foo<'a>(&'a self, x: &'a i32) -> &i32 {
| ++ ++

error: aborting due to previous error

Expand Down
6 changes: 6 additions & 0 deletions src/test/ui/lifetimes/lifetime-errors/ex3-both-anon-regions-self-is-anon.stderr
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Original file line number Diff line number Diff line change
Expand Up @@ -7,6 +7,12 @@ LL | fn foo<'a>(&self, x: &Foo) -> &Foo {
| this parameter and the return type are declared with different lifetimes...
LL | if true { x } else { self }
| ^ ...but data from `x` is returned here
|
= note: each elided lifetime in input position becomes a distinct lifetime
help: consider introducing a named lifetime parameter and update trait if needed
|
LL | fn foo<'a>(&'a self, x: &'a Foo) -> &Foo {
| ++ ++

error: aborting due to previous error

Expand Down
6 changes: 6 additions & 0 deletions src/test/ui/lifetimes/lifetime-errors/ex3-both-anon-regions-using-impl-items.stderr
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Expand Up @@ -5,6 +5,12 @@ LL | fn foo(x: &mut Vec<&u8>, y: &u8) {
| --- --- these two types are declared with different lifetimes...
LL | x.push(y);
| ^ ...but data from `y` flows into `x` here
|
= note: each elided lifetime in input position becomes a distinct lifetime
help: consider introducing a named lifetime parameter and update trait if needed
|
LL | fn foo<'a>(x: &mut Vec<&'a u8>, y: &'a u8) {
| ++++ ++ ++

error: aborting due to previous error

Expand Down
12 changes: 12 additions & 0 deletions src/test/ui/self/arbitrary_self_types_pin_lifetime_mismatch.stderr
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Expand Up @@ -5,6 +5,12 @@ LL | fn a(self: Pin<&Foo>, f: &Foo) -> &Foo { f }
| ---- ---- ^ ...but data from `f` is returned here
| |
| this parameter and the return type are declared with different lifetimes...
|
= note: each elided lifetime in input position becomes a distinct lifetime
help: consider introducing a named lifetime parameter and update trait if needed
|
LL | fn a<'a>(self: Pin<&'a Foo>, f: &'a Foo) -> &Foo { f }
| ++++ ++ ++

error[E0623]: lifetime mismatch
--> $DIR/arbitrary_self_types_pin_lifetime_mismatch.rs:8:76
Expand All @@ -13,6 +19,12 @@ LL | fn c(self: Pin<&Self>, f: &Foo, g: &Foo) -> (Pin<&Foo>, &Foo) { (self,
| ---- ----------------- ^ ...but data from `f` is returned here
| |
| this parameter and the return type are declared with different lifetimes...
|
= note: each elided lifetime in input position becomes a distinct lifetime
help: consider introducing a named lifetime parameter and update trait if needed
|
LL | fn c<'a>(self: Pin<&'a Self>, f: &'a Foo, g: &Foo) -> (Pin<&Foo>, &Foo) { (self, f) }
| ++++ ++ ++

error[E0623]: lifetime mismatch
--> $DIR/arbitrary_self_types_pin_lifetime_mismatch.rs:13:58
Expand Down
36 changes: 36 additions & 0 deletions src/test/ui/self/elision/lt-ref-self.stderr
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Expand Up @@ -7,6 +7,12 @@ LL | fn ref_self(&self, f: &u32) -> &u32 {
| this parameter and the return type are declared with different lifetimes...
LL | f
| ^ ...but data from `f` is returned here
|
= note: each elided lifetime in input position becomes a distinct lifetime
help: consider introducing a named lifetime parameter and update trait if needed
|
LL | fn ref_self<'a>(&'a self, f: &'a u32) -> &u32 {
| ++++ ++ ++

error[E0623]: lifetime mismatch
--> $DIR/lt-ref-self.rs:17:9
Expand All @@ -17,6 +23,12 @@ LL | fn ref_Self(self: &Self, f: &u32) -> &u32 {
| this parameter and the return type are declared with different lifetimes...
LL | f
| ^ ...but data from `f` is returned here
|
= note: each elided lifetime in input position becomes a distinct lifetime
help: consider introducing a named lifetime parameter and update trait if needed
|
LL | fn ref_Self<'a>(self: &'a Self, f: &'a u32) -> &u32 {
| ++++ ++ ++

error[E0623]: lifetime mismatch
--> $DIR/lt-ref-self.rs:21:9
Expand All @@ -27,6 +39,12 @@ LL | fn box_ref_Self(self: Box<&Self>, f: &u32) -> &u32 {
| this parameter and the return type are declared with different lifetimes...
LL | f
| ^ ...but data from `f` is returned here
|
= note: each elided lifetime in input position becomes a distinct lifetime
help: consider introducing a named lifetime parameter and update trait if needed
|
LL | fn box_ref_Self<'a>(self: Box<&'a Self>, f: &'a u32) -> &u32 {
| ++++ ++ ++

error[E0623]: lifetime mismatch
--> $DIR/lt-ref-self.rs:25:9
Expand All @@ -37,6 +55,12 @@ LL | fn pin_ref_Self(self: Pin<&Self>, f: &u32) -> &u32 {
| this parameter and the return type are declared with different lifetimes...
LL | f
| ^ ...but data from `f` is returned here
|
= note: each elided lifetime in input position becomes a distinct lifetime
help: consider introducing a named lifetime parameter and update trait if needed
|
LL | fn pin_ref_Self<'a>(self: Pin<&'a Self>, f: &'a u32) -> &u32 {
| ++++ ++ ++

error[E0623]: lifetime mismatch
--> $DIR/lt-ref-self.rs:29:9
Expand All @@ -47,6 +71,12 @@ LL | fn box_box_ref_Self(self: Box<Box<&Self>>, f: &u32) -> &u32 {
| this parameter and the return type are declared with different lifetimes...
LL | f
| ^ ...but data from `f` is returned here
|
= note: each elided lifetime in input position becomes a distinct lifetime
help: consider introducing a named lifetime parameter and update trait if needed
|
LL | fn box_box_ref_Self<'a>(self: Box<Box<&'a Self>>, f: &'a u32) -> &u32 {
| ++++ ++ ++

error[E0623]: lifetime mismatch
--> $DIR/lt-ref-self.rs:33:9
Expand All @@ -57,6 +87,12 @@ LL | fn box_pin_Self(self: Box<Pin<&Self>>, f: &u32) -> &u32 {
| this parameter and the return type are declared with different lifetimes...
LL | f
| ^ ...but data from `f` is returned here
|
= note: each elided lifetime in input position becomes a distinct lifetime
help: consider introducing a named lifetime parameter and update trait if needed
|
LL | fn box_pin_Self<'a>(self: Box<Pin<&'a Self>>, f: &'a u32) -> &u32 {
| ++++ ++ ++

error: aborting due to 6 previous errors

Expand Down
36 changes: 36 additions & 0 deletions src/test/ui/self/elision/ref-mut-self.stderr
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Original file line number Diff line number Diff line change
Expand Up @@ -7,6 +7,12 @@ LL | fn ref_self(&mut self, f: &u32) -> &u32 {
| this parameter and the return type are declared with different lifetimes...
LL | f
| ^ ...but data from `f` is returned here
|
= note: each elided lifetime in input position becomes a distinct lifetime
help: consider introducing a named lifetime parameter and update trait if needed
|
LL | fn ref_self<'a>(&'a mut self, f: &'a u32) -> &u32 {
| ++++ ++ ++

error[E0623]: lifetime mismatch
--> $DIR/ref-mut-self.rs:17:9
Expand All @@ -17,6 +23,12 @@ LL | fn ref_Self(self: &mut Self, f: &u32) -> &u32 {
| this parameter and the return type are declared with different lifetimes...
LL | f
| ^ ...but data from `f` is returned here
|
= note: each elided lifetime in input position becomes a distinct lifetime
help: consider introducing a named lifetime parameter and update trait if needed
|
LL | fn ref_Self<'a>(self: &'a mut Self, f: &'a u32) -> &u32 {
| ++++ ++ ++

error[E0623]: lifetime mismatch
--> $DIR/ref-mut-self.rs:21:9
Expand All @@ -27,6 +39,12 @@ LL | fn box_ref_Self(self: Box<&mut Self>, f: &u32) -> &u32 {
| this parameter and the return type are declared with different lifetimes...
LL | f
| ^ ...but data from `f` is returned here
|
= note: each elided lifetime in input position becomes a distinct lifetime
help: consider introducing a named lifetime parameter and update trait if needed
|
LL | fn box_ref_Self<'a>(self: Box<&'a mut Self>, f: &'a u32) -> &u32 {
| ++++ ++ ++

error[E0623]: lifetime mismatch
--> $DIR/ref-mut-self.rs:25:9
Expand All @@ -37,6 +55,12 @@ LL | fn pin_ref_Self(self: Pin<&mut Self>, f: &u32) -> &u32 {
| this parameter and the return type are declared with different lifetimes...
LL | f
| ^ ...but data from `f` is returned here
|
= note: each elided lifetime in input position becomes a distinct lifetime
help: consider introducing a named lifetime parameter and update trait if needed
|
LL | fn pin_ref_Self<'a>(self: Pin<&'a mut Self>, f: &'a u32) -> &u32 {
| ++++ ++ ++

error[E0623]: lifetime mismatch
--> $DIR/ref-mut-self.rs:29:9
Expand All @@ -47,6 +71,12 @@ LL | fn box_box_ref_Self(self: Box<Box<&mut Self>>, f: &u32) -> &u32 {
| this parameter and the return type are declared with different lifetimes...
LL | f
| ^ ...but data from `f` is returned here
|
= note: each elided lifetime in input position becomes a distinct lifetime
help: consider introducing a named lifetime parameter and update trait if needed
|
LL | fn box_box_ref_Self<'a>(self: Box<Box<&'a mut Self>>, f: &'a u32) -> &u32 {
| ++++ ++ ++

error[E0623]: lifetime mismatch
--> $DIR/ref-mut-self.rs:33:9
Expand All @@ -57,6 +87,12 @@ LL | fn box_pin_ref_Self(self: Box<Pin<&mut Self>>, f: &u32) -> &u32 {
| this parameter and the return type are declared with different lifetimes...
LL | f
| ^ ...but data from `f` is returned here
|
= note: each elided lifetime in input position becomes a distinct lifetime
help: consider introducing a named lifetime parameter and update trait if needed
|
LL | fn box_pin_ref_Self<'a>(self: Box<Pin<&'a mut Self>>, f: &'a u32) -> &u32 {
| ++++ ++ ++

error: aborting due to 6 previous errors

Expand Down
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