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1775e7b93d
Do not suggest constraining the `&self` param, but rather the return type.
If that is wrong (because it is not sufficient), a follow up error will tell the
user to fix it. This way we lower the chances of *over* constraining, but still
get the cake of "correctly" contrained in two steps.
This is a correct suggestion:
```
error: lifetime may not live long enough
--> $DIR/ex3-both-anon-regions-return-type-is-anon.rs:9:9
|
LL | fn foo<'a>(&self, x: &i32) -> &i32 {
| - - let's call the lifetime of this reference `'1`
| |
| let's call the lifetime of this reference `'2`
LL | x
| ^ method was supposed to return data with lifetime `'2` but it is returning data with lifetime `'1`
|
help: consider introducing a named lifetime parameter and update trait if needed
|
LL | fn foo<'a>(&self, x: &'a i32) -> &'a i32 {
| ++ ++
```
While this is incomplete because it should suggestino `&'a self`
```
error: lifetime may not live long enough
--> $DIR/ex3-both-anon-regions-self-is-anon.rs:7:19
|
LL | fn foo<'a>(&self, x: &Foo) -> &Foo {
| - - let's call the lifetime of this reference `'1`
| |
| let's call the lifetime of this reference `'2`
LL | if true { x } else { self }
| ^ method was supposed to return data with lifetime `'2` but it is returning data with lifetime `'1`
|
help: consider introducing a named lifetime parameter and update trait if needed
|
LL | fn foo<'a>(&self, x: &'a Foo) -> &'a Foo {
| ++ ++
```
but the follow up error is
```
error: lifetime may not live long enough
--> tests/ui/lifetimes/lifetime-errors/ex3-both-anon-regions-self-is-anon.rs:7:30
|
6 | fn foo<'a>(&self, x: &'a Foo) -> &'a Foo {
| -- - let's call the lifetime of this reference `'1`
| |
| lifetime `'a` defined here
7 | if true { x } else { self }
| ^^^^ method was supposed to return data with lifetime `'a` but it is returning data with lifetime `'1`
|
help: consider introducing a named lifetime parameter and update trait if needed
|
6 | fn foo<'a>(&'a self, x: &'a Foo) -> &'a Foo {
| ++
```
|
||
|---|---|---|
| .. | ||
| alias-async.rs | ||
| alias.rs | ||
| assoc-async.rs | ||
| assoc.rs | ||
| lt-alias-async.rs | ||
| lt-alias.rs | ||
| lt-assoc-async.rs | ||
| lt-assoc.rs | ||
| lt-ref-self-async.fixed | ||
| lt-ref-self-async.rs | ||
| lt-ref-self-async.stderr | ||
| lt-ref-self.fixed | ||
| lt-ref-self.rs | ||
| lt-ref-self.stderr | ||
| lt-self-async.rs | ||
| lt-self.rs | ||
| lt-struct-async.rs | ||
| lt-struct.rs | ||
| multiple-ref-self-async.rs | ||
| multiple-ref-self.rs | ||
| nested-item.rs | ||
| nested-item.stderr | ||
| README.md | ||
| ref-alias-async.rs | ||
| ref-alias.rs | ||
| ref-assoc-async.rs | ||
| ref-assoc.rs | ||
| ref-mut-alias-async.rs | ||
| ref-mut-alias.rs | ||
| ref-mut-self-async.rs | ||
| ref-mut-self-async.stderr | ||
| ref-mut-self.fixed | ||
| ref-mut-self.rs | ||
| ref-mut-self.stderr | ||
| ref-mut-struct-async.rs | ||
| ref-mut-struct-async.stderr | ||
| ref-mut-struct.fixed | ||
| ref-mut-struct.rs | ||
| ref-mut-struct.stderr | ||
| ref-self-async.rs | ||
| ref-self-async.stderr | ||
| ref-self.fixed | ||
| ref-self.rs | ||
| ref-self.stderr | ||
| ref-struct-async.rs | ||
| ref-struct-async.stderr | ||
| ref-struct.fixed | ||
| ref-struct.rs | ||
| ref-struct.stderr | ||
| self-async.rs | ||
| self.rs | ||
| struct-async.rs | ||
| struct.rs | ||
Test cases intended to document behavior and try to exhaustively explore the combinations.
Confidence
These tests are not yet considered 100% normative, in that some aspects of the current behavior are not desirable. This is expressed in the "confidence" field in the following table. Values:
| Confidence | Interpretation |
|---|---|
| 100% | this will remain recommended behavior |
| 75% | unclear whether we will continue to accept this |
| 50% | this will likely be deprecated but remain valid |
| 25% | this could change in the future |
| 0% | this is definitely bogus and will likely change in the future in some way |
Tests
| Test file | Self type |
Pattern | Current elision behavior | Confidence |
|---|---|---|---|---|
self.rs |
Struct |
Self |
ignore self parameter |
100% |
struct.rs |
Struct |
Struct |
ignore self parameter |
100% |
alias.rs |
Struct |
Alias |
ignore self parameter |
100% |
ref-self.rs |
Struct |
&Self |
take lifetime from &Self |
100% |
ref-mut-self.rs |
Struct |
&mut Self |
take lifetime from &mut Self |
100% |
ref-struct.rs |
Struct |
&Struct |
take lifetime from &Self |
50% |
ref-mut-struct.rs |
Struct |
&mut Struct |
take lifetime from &mut Self |
50% |
ref-alias.rs |
Struct |
&Alias |
ignore Alias |
0% |
ref-mut-alias.rs |
Struct |
&mut Alias |
ignore Alias |
0% |
lt-self.rs |
Struct<'a> |
Self |
ignore Self (and hence 'a) |
25% |
lt-struct.rs |
Struct<'a> |
Self |
ignore Self (and hence 'a) |
0% |
lt-alias.rs |
Alias<'a> |
Self |
ignore Self (and hence 'a) |
0% |
lt-ref-self.rs |
Struct<'a> |
&Self |
take lifetime from &Self |
75% |
In each case, we test the following patterns:
self: XXXself: Box<XXX>self: Pin<XXX>self: Box<Box<XXX>>self: Box<Pin<XXX>>
In the non-reference cases, Pin causes errors so we substitute Rc.
async fn
For each of the tests above we also check that async fn behaves as an fn would.
These tests are in files named *-async.rs.
Legends:
- ✓ ⟹ Yes / Pass
- X ⟹ No
- α ⟹ lifetime mismatch
- β ⟹ cannot infer an appropriate lifetime
- γ ⟹ missing lifetime specifier
async file |
Pass? | Conforms to fn? |
How does it diverge? fn ⟶ async fn |
|---|---|---|---|
self-async.rs |
✓ | ✓ | N/A |
struct-async.rs |
✓ | ✓ | N/A |
alias-async.rs |
✓ | ✓ | N/A |
assoc-async.rs |
✓ | ✓ | N/A |
ref-self-async.rs |
X | ✓ | N/A |
ref-mut-self-async.rs |
X | ✓ | N/A |
ref-struct-async.rs |
X | ✓ | N/A |
ref-mut-struct-async.rs |
X | ✓ | N/A |
ref-alias-async.rs |
✓ | ✓ | N/A |
ref-assoc-async.rs |
✓ | ✓ | N/A |
ref-mut-alias-async.rs |
✓ | ✓ | N/A |
lt-self-async.rs |
✓ | ✓ | N/A |
lt-struct-async.rs |
✓ | ✓ | N/A |
lt-alias-async.rs |
✓ | ✓ | N/A |
lt-assoc-async.rs |
✓ | ✓ | N/A |
lt-ref-self-async.rs |
X | ✓ | N/A |