Commit Graph

4 Commits

Author SHA1 Message Date
Esteban Küber
f0c93117ed Use root obligation on E0277 for some cases
When encountering trait bound errors that satisfy some heuristics that
tell us that the relevant trait for the user comes from the root
obligation and not the current obligation, we use the root predicate for
the main message.

This allows to talk about "X doesn't implement Pattern<'_>" over the
most specific case that just happened to fail, like  "char doesn't
implement Fn(&mut char)" in
`tests/ui/traits/suggest-dereferences/root-obligation.rs`

The heuristics are:

 - the type of the leaf predicate is (roughly) the same as the type
   from the root predicate, as a proxy for "we care about the root"
 - the leaf trait and the root trait are different, so as to avoid
   talking about `&mut T: Trait` and instead remain talking about
   `T: Trait` instead
 - the root trait is not `Unsize`, as to avoid talking about it in
   `tests/ui/coercion/coerce-issue-49593-box-never.rs`.

```
error[E0277]: the trait bound `&char: Pattern<'_>` is not satisfied
  --> $DIR/root-obligation.rs:6:38
   |
LL |         .filter(|c| "aeiou".contains(c))
   |                             -------- ^ the trait `Fn<(char,)>` is not implemented for `&char`, which is required by `&char: Pattern<'_>`
   |                             |
   |                             required by a bound introduced by this call
   |
   = note: required for `&char` to implement `FnOnce<(char,)>`
   = note: required for `&char` to implement `Pattern<'_>`
note: required by a bound in `core::str::<impl str>::contains`
  --> $SRC_DIR/core/src/str/mod.rs:LL:COL
help: consider dereferencing here
   |
LL |         .filter(|c| "aeiou".contains(*c))
   |                                      +
```

Fix #79359, fix #119983, fix #118779, cc #118415 (the suggestion needs
to change).
2024-03-03 18:53:35 +00:00
Esteban Küber
6efddac288 Provide more context on derived obligation error primary label
Expand the primary span of E0277 when the immediate unmet bound is not what the user wrote:

```
error[E0277]: the trait bound `i32: Bar` is not satisfied
 --> f100.rs:6:6
  |
6 |     <i32 as Foo>::foo();
  |      ^^^ the trait `Bar` is not implemented for `i32`, which is required by `i32: Foo`
  |
help: this trait has no implementations, consider adding one
 --> f100.rs:2:1
  |
2 | trait Bar {}
  | ^^^^^^^^^
note: required for `i32` to implement `Foo`
 --> f100.rs:3:14
  |
3 | impl<T: Bar> Foo for T {}
  |         ---  ^^^     ^
  |         |
  |         unsatisfied trait bound introduced here
```

Fix #40120.
2024-01-30 21:28:18 +00:00
Nilstrieb
41e8d152dc Show number in error message even for one error
Co-authored-by: Adrian <adrian.iosdev@gmail.com>
2023-11-24 19:15:52 +01:00
Alan Egerton
540bd986aa
Do not ICE on unmet trait alias bounds 2023-02-16 11:18:08 +00:00