Highlight the `const fn` if error happened because of a bound on the impl block#88907

WaffleLapkin · 2021-09-13T14:38:38Z

Currently, for the following code, the compiler produces the errors like the
following:

struct Type<T>(T);

impl<T: Clone> Type<T> {
    const fn f() {}
}

error[E0658]: trait bounds other than `Sized` on const fn parameters are unstable
 --> ./test.rs:3:6
  |
3 | impl<T: Clone> Type<T> {
  |      ^
  |
  = note: see issue #57563 <https://github.com/rust-lang/rust/issues/57563> for more information
  = help: add `#![feature(const_fn_trait_bound)]` to the crate attributes to enable

This can be confusing (especially to newcomers) since the error mentions "const fn parameters", but highlights only the impl.

This PR adds function highlighting, changing the error to the following:

error[E0658]: trait bounds other than `Sized` on const fn parameters are unstable
 --> ./test.rs:3:6
  |
3 | impl<T: Clone> Type<T> {
  |      ^
4 |     pub const fn f() {}
  |     ---------------- function declared as const here
  |
  = note: see issue #57563 <https://github.com/rust-lang/rust/issues/57563> for more information
  = help: add `#![feature(const_fn_trait_bound)]` to the crate attributes to enable

I've originally wanted to point directly to const token, but couldn't find a way to get it's span. It seems like this span is lost during the AST -> HIR lowering.

Also, since the errors for object casts in const fns (&T -> &dyn Trait) seem to trigger the same error, this PR accidentally changes these errors too. Not sure if it's desired or how to fix this.

P.S. it's my first time contributing to diagnostics, so feedback is very appreciated!

r? @estebank

@rustbot label: +A-diagnostics

…the impl block Currently, for the following code, the compiler produces the errors like the following error: ```rust struct Type<T> impl<T: Clone> Type<T> { fn const f() {} } ``` ```text error[E0658]: trait bounds other than `Sized` on const fn parameters are unstable --> ./test.rs:3:6 | 3 | impl<T: Clone> Type<T> { | ^ | = note: see issue rust-lang#57563 <rust-lang#57563> for more information = help: add `#![feature(const_fn_trait_bound)]` to the crate attributes to enable ``` This can be confusing (especially to newcomers) since the error mentions "const fn parameters", but highlights only the impl. This commits adds function highlighting, changing the error to the following: ```text error[E0658]: trait bounds other than `Sized` on const fn parameters are unstable --> ./test.rs:3:6 | 3 | impl<T: Clone> Type<T> { | ^ 4 | pub const fn f() {} | ---------------- function declared as const here | = note: see issue rust-lang#57563 <rust-lang#57563> for more information = help: add `#![feature(const_fn_trait_bound)]` to the crate attributes to enable ```

estebank

Also, since the errors for object casts in const fns (&T -> &dyn Trait) seem to trigger the same error, this PR accidentally changes these errors too. Not sure if it's desired or how to fix this.

Those should probably get their own errors instead of these, as they are today they are a bit confusing, but I think your changes are worth it.

estebank · 2021-09-14T11:59:59Z

compiler/rustc_const_eval/src/transform/check_consts/ops.rs


        fn build_error(&self, ccx: &ConstCx<'_, 'tcx>, span: Span) -> DiagnosticBuilder<'tcx> {
-            feature_err(
+            let mut builder = feature_err(


The common naming convention for these is usually err, or less commonly, diag.

estebank · 2021-09-14T12:04:46Z

@bors r+

bors · 2021-09-14T12:04:48Z

📌 Commit 6ec7255 has been approved by estebank

…_a_bound_in_impl_block_error, r=estebank Highlight the `const fn` if error happened because of a bound on the impl block Currently, for the following code, the compiler produces the errors like the following: ```rust struct Type<T>(T); impl<T: Clone> Type<T> { const fn f() {} } ``` ```text error[E0658]: trait bounds other than `Sized` on const fn parameters are unstable --> ./test.rs:3:6 | 3 | impl<T: Clone> Type<T> { | ^ | = note: see issue rust-lang#57563 <rust-lang#57563> for more information = help: add `#![feature(const_fn_trait_bound)]` to the crate attributes to enable ``` This can be confusing (especially to newcomers) since the error mentions "const fn parameters", but highlights only the impl. This PR adds function highlighting, changing the error to the following: ```text error[E0658]: trait bounds other than `Sized` on const fn parameters are unstable --> ./test.rs:3:6 | 3 | impl<T: Clone> Type<T> { | ^ 4 | pub const fn f() {} | ---------------- function declared as const here | = note: see issue rust-lang#57563 <rust-lang#57563> for more information = help: add `#![feature(const_fn_trait_bound)]` to the crate attributes to enable ``` --- I've originally wanted to point directly to `const` token, but couldn't find a way to get it's span. It seems like this span is lost during the AST -> HIR lowering. Also, since the errors for object casts in `const fn`s (`&T` -> `&dyn Trait`) seem to trigger the same error, this PR accidentally changes these errors too. Not sure if it's desired or how to fix this. P.S. it's my first time contributing to diagnostics, so feedback is very appreciated! --- r? `@estebank` `@rustbot` label: +A-diagnostics

…_a_bound_in_impl_block_error, r=estebank Highlight the `const fn` if error happened because of a bound on the impl block Currently, for the following code, the compiler produces the errors like the following: ```rust struct Type<T>(T); impl<T: Clone> Type<T> { const fn f() {} } ``` ```text error[E0658]: trait bounds other than `Sized` on const fn parameters are unstable --> ./test.rs:3:6 | 3 | impl<T: Clone> Type<T> { | ^ | = note: see issue rust-lang#57563 <rust-lang#57563> for more information = help: add `#![feature(const_fn_trait_bound)]` to the crate attributes to enable ``` This can be confusing (especially to newcomers) since the error mentions "const fn parameters", but highlights only the impl. This PR adds function highlighting, changing the error to the following: ```text error[E0658]: trait bounds other than `Sized` on const fn parameters are unstable --> ./test.rs:3:6 | 3 | impl<T: Clone> Type<T> { | ^ 4 | pub const fn f() {} | ---------------- function declared as const here | = note: see issue rust-lang#57563 <rust-lang#57563> for more information = help: add `#![feature(const_fn_trait_bound)]` to the crate attributes to enable ``` --- I've originally wanted to point directly to `const` token, but couldn't find a way to get it's span. It seems like this span is lost during the AST -> HIR lowering. Also, since the errors for object casts in `const fn`s (`&T` -> `&dyn Trait`) seem to trigger the same error, this PR accidentally changes these errors too. Not sure if it's desired or how to fix this. P.S. it's my first time contributing to diagnostics, so feedback is very appreciated! --- r? ``@estebank`` ``@rustbot`` label: +A-diagnostics

…arth Rollup of 8 pull requests Successful merges: - rust-lang#87320 (Introduce -Z remap-cwd-prefix switch) - rust-lang#88690 (Accept `m!{ .. }.method()` and `m!{ .. }?` statements. ) - rust-lang#88775 (Revert anon union parsing) - rust-lang#88841 (feat(rustc_typeck): suggest removing bad parens in `(recv.method)()`) - rust-lang#88907 (Highlight the `const fn` if error happened because of a bound on the impl block) - rust-lang#88915 (`Wrapping<T>` has the same layout and ABI as `T`) - rust-lang#88933 (Remove implementation of `min_align_of` intrinsic) - rust-lang#88951 (Update books) Failed merges: r? `@ghost` `@rustbot` modify labels: rollup

…_trait_in_const_fn, r=estebank Add a separate error for `dyn Trait` in `const fn` Previously "trait bounds other than `Sized` on const fn parameters are unstable" error was used for both trait bounds (`<T: Trait>`) and trait objects (`dyn Trait`). This was pretty confusing. This PR adds a separate error for trait objects: "trait objects in const fn are unstable". The error for trait bounds is otherwise intact. This is follow up to rust-lang#88907 r? `@estebank` `@rustbot` label: +A-diagnostics

…_trait_in_const_fn, r=estebank Add a separate error for `dyn Trait` in `const fn` Previously "trait bounds other than `Sized` on const fn parameters are unstable" error was used for both trait bounds (`<T: Trait>`) and trait objects (`dyn Trait`). This was pretty confusing. This PR adds a separate error for trait objects: "trait objects in const fn are unstable". The error for trait bounds is otherwise intact. This is follow up to rust-lang#88907 r? ``@estebank`` ``@rustbot`` label: +A-diagnostics

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

rust-highfive assigned estebank Sep 13, 2021

rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Sep 13, 2021

estebank approved these changes Sep 14, 2021

View reviewed changes

bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Sep 14, 2021

Manishearth mentioned this pull request Sep 14, 2021

Rollup of 8 pull requests #88948

Closed

Manishearth mentioned this pull request Sep 15, 2021

Rollup of 7 pull requests #88958

Closed

Manishearth mentioned this pull request Sep 15, 2021

Rollup of 8 pull requests #88992

Merged

bors merged commit e1acdf5 into rust-lang:master Sep 16, 2021

rustbot added this to the 1.57.0 milestone Sep 16, 2021

WaffleLapkin mentioned this pull request Sep 16, 2021

Add a separate error for dyn Trait in const fn #89021

Merged

WaffleLapkin deleted the targeted_const_fn_with_a_bound_in_impl_block_error branch September 19, 2021 22:31

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Highlight the `const fn` if error happened because of a bound on the impl block#88907