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rust/tests/ui/self/elision
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Esteban Küber 1775e7b93d Tweak suggested lifetimes to modify return type instead of &self receiver 
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 {
  |                 ++
```
2024-05-17 20:31:13 +00:00
..
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 Run rustfmt on modified tests 2024-05-17 20:31:13 +00:00
lt-ref-self-async.rs Run rustfmt on modified tests 2024-05-17 20:31:13 +00:00
lt-ref-self-async.stderr Run rustfmt on modified tests 2024-05-17 20:31:13 +00:00
lt-ref-self.fixed Tweak suggested lifetimes to modify return type instead of &self receiver 2024-05-17 20:31:13 +00:00
lt-ref-self.rs Run rustfmt on modified tests 2024-05-17 20:31:13 +00:00
lt-ref-self.stderr Tweak suggested lifetimes to modify return type instead of &self receiver 2024-05-17 20:31:13 +00:00
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 Tweak suggested lifetimes to modify return type instead of &self receiver 2024-05-17 20:31:13 +00:00
ref-mut-self.rs Run rustfmt on modified tests 2024-05-17 20:31:13 +00:00
ref-mut-self.stderr Tweak suggested lifetimes to modify return type instead of &self receiver 2024-05-17 20:31:13 +00:00
ref-mut-struct-async.rs
ref-mut-struct-async.stderr
ref-mut-struct.fixed Tweak suggested lifetimes to modify return type instead of &self receiver 2024-05-17 20:31:13 +00:00
ref-mut-struct.rs Run rustfmt on modified tests 2024-05-17 20:31:13 +00:00
ref-mut-struct.stderr Tweak suggested lifetimes to modify return type instead of &self receiver 2024-05-17 20:31:13 +00:00
ref-self-async.rs
ref-self-async.stderr
ref-self.fixed Tweak suggested lifetimes to modify return type instead of &self receiver 2024-05-17 20:31:13 +00:00
ref-self.rs Run rustfmt on modified tests 2024-05-17 20:31:13 +00:00
ref-self.stderr Tweak suggested lifetimes to modify return type instead of &self receiver 2024-05-17 20:31:13 +00:00
ref-struct-async.rs
ref-struct-async.stderr
ref-struct.fixed Tweak suggested lifetimes to modify return type instead of &self receiver 2024-05-17 20:31:13 +00:00
ref-struct.rs Run rustfmt on modified tests 2024-05-17 20:31:13 +00:00
ref-struct.stderr Tweak suggested lifetimes to modify return type instead of &self receiver 2024-05-17 20:31:13 +00:00
self-async.rs
self.rs
struct-async.rs
struct.rs

README.md

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: XXX
  • self: 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