Mention implementers of unsatisfied trait #91873

estebank · 2021-12-13T20:59:10Z

When encountering an unsatisfied trait bound, if there are no other
suggestions, mention all the types that do implement that trait:

error[E0277]: the trait bound `f32: Foo` is not satisfied
  --> $DIR/impl_wf.rs:22:6
   |
LL | impl Baz<f32> for f32 { }
   |      ^^^^^^^^ the trait `Foo` is not implemented for `f32`
   |
   = help: the trait `Foo` is implemented for `i32`
note: required by a bound in `Baz`
  --> $DIR/impl_wf.rs:18:31
   |
LL | trait Baz<U: ?Sized> where U: Foo { }
   |                               ^^^ required by this bound in `Baz`

error[E0277]: the trait bound `u32: Foo` is not satisfied
  --> $DIR/associated-types-path-2.rs:29:5
   |
LL |     f1(2u32, 4u32);
   |     ^^ the trait `Foo` is not implemented for `u32`
   |
   = help: the trait `Foo` is implemented for `i32`
note: required by a bound in `f1`
  --> $DIR/associated-types-path-2.rs:13:14
   |
LL | pub fn f1<T: Foo>(a: T, x: T::A) {}
   |              ^^^ required by this bound in `f1`

Suggest dereferencing in more cases.

Fix #87437, fix #90970.

rust-highfive · 2021-12-13T20:59:13Z

r? @michaelwoerister

(rust-highfive has picked a reviewer for you, use r? to override)

fmease · 2021-12-14T04:13:50Z

Does this fix/work towards fixing #90970?

estebank · 2021-12-14T18:29:12Z

As is, it does not:

error[E0277]: expected a `FnMut<(char,)>` closure, found `u8`
 --> f23.rs:2:20
  |
2 |     s.strip_suffix(b'\n').unwrap_or(s)
  |       ------------ ^^^^^ expected an `FnMut<(char,)>` closure, found `u8`
  |       |
  |       required by a bound introduced by this call
  |
  = help: the trait `FnMut<(char,)>` is not implemented for `u8`

Looking if there's a straightforward change that can be done.

Edit: With a quick check, I managed to get the following:

error[E0277]: expected a `FnMut<(char,)>` closure, found `u8`
 --> f23.rs:2:20
  |
2 |     s.strip_suffix(b'\n').unwrap_or(s)
  |       ------------ ^^^^^ expected an `FnMut<(char,)>` closure, found `u8`
  |       |
  |       required by a bound introduced by this call
  |
  = help: the trait `FnMut<(char,)>` is not implemented for `u8`
  = note: required because of the requirements on the impl of `Pattern<'_>` for `u8`
  = note: the following other types implement `Pattern<'_>`:
            &'b String
            &'b [char; N]
            &'b [char]
            &'b str
            &'c &'b str
            [char; N]
            char
            pattern::MultiCharEqPattern<C>

I would like to iterate a bit further (and report the error higher in the obligation chain so we only talk about Pattern and not FnMut), but that will be better served by a separate PR.

What do you think?

estebank · 2021-12-15T01:05:17Z

Update: now it does cover it, slightly.

fmease · 2021-12-15T02:25:31Z

What do you think?

I think it's already an improvement that it lists those other implementations and thus likely clears up the potential confusion of the user much faster which may arise from the incorrect mention of FnMut (instead of Pattern). So thank you very much! ❤️

I first faced this error message a few years ago when I wasn't that familiar with Rust yet and I remember it took me a quite a bit of time to figure out what was going on. So any steps towards fixing this is great!

I would like to iterate a bit further (and report the error higher in the obligation chain so we only talk about Pattern and not FnMut), but that will be better served by a separate PR.

Sure! I hope you (or someone else of course) can figure out how to suppress, really, references to Fn* obligations in certain situations. From past experiences, I know that sometimes for some reason Fn* impls like to “take over” certain error messages. I don't have a concrete example at hand right now, though (apart from Pattern obviously).

michaelwoerister · 2022-01-05T15:28:21Z

Sorry for the delay. I think it might be better if someone from wg-diagnostics reviewed this.

r? rust-lang/diagnostics

davidtwco

I like the diagnostic change, couple comments on the implementation where we might be able to deduplicate things a bit.

compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs

compiler/rustc_errors/src/diagnostic.rs

compiler/rustc_middle/src/ty/mod.rs

compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs

compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs

davidtwco

r=me unless you want to squash the commits first

bors · 2022-04-01T20:54:52Z

☔ The latest upstream changes (presumably #95552) made this pull request unmergeable. Please resolve the merge conflicts.

When encountering an unsatisfied trait bound, if there are no other suggestions, mention all the types that *do* implement that trait: ``` error[E0277]: the trait bound `f32: Foo` is not satisfied --> $DIR/impl_wf.rs:22:6 | LL | impl Baz<f32> for f32 { } | ^^^^^^^^ the trait `Foo` is not implemented for `f32` | = help: the following other types implement trait `Foo`: Option<T> i32 str note: required by a bound in `Baz` --> $DIR/impl_wf.rs:18:31 | LL | trait Baz<U: ?Sized> where U: Foo { } | ^^^ required by this bound in `Baz` ``` Mention implementers of traits in `ImplObligation`s. Do not mention other `impl`s for closures, ranges and `?`.

estebank · 2022-04-04T21:14:41Z

@bors r=davidtwco

bors · 2022-04-04T21:14:43Z

📌 Commit e1ef833 has been approved by davidtwco

…ied-trait, r=davidtwco Mention implementers of unsatisfied trait When encountering an unsatisfied trait bound, if there are no other suggestions, mention all the types that *do* implement that trait: ``` error[E0277]: the trait bound `f32: Foo` is not satisfied --> $DIR/impl_wf.rs:22:6 | LL | impl Baz<f32> for f32 { } | ^^^^^^^^ the trait `Foo` is not implemented for `f32` | = help: the trait `Foo` is implemented for `i32` note: required by a bound in `Baz` --> $DIR/impl_wf.rs:18:31 | LL | trait Baz<U: ?Sized> where U: Foo { } | ^^^ required by this bound in `Baz` ``` ``` error[E0277]: the trait bound `u32: Foo` is not satisfied --> $DIR/associated-types-path-2.rs:29:5 | LL | f1(2u32, 4u32); | ^^ the trait `Foo` is not implemented for `u32` | = help: the trait `Foo` is implemented for `i32` note: required by a bound in `f1` --> $DIR/associated-types-path-2.rs:13:14 | LL | pub fn f1<T: Foo>(a: T, x: T::A) {} | ^^^ required by this bound in `f1` ``` Suggest dereferencing in more cases. Fix rust-lang#87437, fix rust-lang#90970.

Rollup of 7 pull requests Successful merges: - rust-lang#91873 (Mention implementers of unsatisfied trait) - rust-lang#95588 (explicitly distinguish pointer::addr and pointer::expose_addr) - rust-lang#95603 (Fix late-bound ICE in `dyn` return type suggestion) - rust-lang#95620 (interpret: remove MemoryExtra in favor of giving access to the Machine) - rust-lang#95630 (Update `NonNull` pointer provenance methods' documentation) - rust-lang#95631 (Refactor: remove unnecessary nested blocks) - rust-lang#95642 (`CandidateSource::XCandidate` -> `CandidateSource::X`) Failed merges: r? `@ghost` `@rustbot` modify labels: rollup

rustbot added the T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. label Dec 13, 2021

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camelid added the A-diagnostics Area: Messages for errors, warnings, and lints label Dec 13, 2021

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estebank mentioned this pull request Mar 26, 2022

Using str::contains inside of a filter leads to confusing error message. #87437

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estebank force-pushed the mention-impls-for-unsatisfied-trait branch from 38ef896 to 1bb5b95 Compare March 27, 2022 19:09

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estebank added 8 commits April 4, 2022 21:01

Fix rust-lang#90970, doesn't address rust-lang#87437

ac8cbbd

Suggest dereferncing when possible in E0277, fix rust-lang#87437

883b93c

Fix list length

e2bba07

Dedup logic and improve output for other types that impl trait

ef91519

Refer to the TraitRef::identity in the message to be clearer

3109c93

Highlight is in the message for emphasis

a6301ca

Remove hack, fix fmt and tests

e1ef833

estebank force-pushed the mention-impls-for-unsatisfied-trait branch from e2f263e to e1ef833 Compare April 4, 2022 21:14

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Dylan-DPC mentioned this pull request Apr 4, 2022

Rollup of 8 pull requests #95658

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Dylan-DPC mentioned this pull request Apr 4, 2022

Rollup of 7 pull requests #95662

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bors merged commit a5c8169 into rust-lang:master Apr 5, 2022

rustbot added this to the 1.62.0 milestone Apr 5, 2022

Dylan-DPC mentioned this pull request Apr 5, 2022

Reverts Mention implementers of unsatisfied trait #95703

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estebank deleted the mention-impls-for-unsatisfied-trait branch November 9, 2023 05:14

fmease mentioned this pull request Jan 23, 2024

Other missing bounds required to meet a trait's blanket impl are displayed too prominently #118779

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Mention implementers of unsatisfied trait #91873

Mention implementers of unsatisfied trait #91873

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Mention implementers of unsatisfied trait #91873

Mention implementers of unsatisfied trait #91873

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