Improve `declare_features!` macro error by mejrs · Pull Request #157931 · rust-lang/rust

mejrs · 2026-06-15T19:09:18Z

I got mildly annoyed when I went to add a new feature, and the fix for this is relatively simple.

Current error:

error[E0425]: cannot find value `better_rust` in module `sym`                                                                                                                                                                                                                           
   --> compiler\rustc_feature\src\unstable.rs:240:16
    |
157 |                 name: sym::$feature,
    |                            -------- due to this macro variable
...
240 |     (internal, better_rust, "2.0.0", None),
    |                ^^^^^^^^^^^ not found in `sym`

For more information about this error, try `rustc --explain E0425`

Previous error:

error[E0425]: cannot find value `better_rust` in module `sym`                                                                                                                                                                                                                           
   --> compiler\rustc_feature\src\unstable.rs:240:16
    |
157 |                 name: sym::$feature,
    |                            -------- due to this macro variable
...
240 |     (internal, better_rust, "2.0.0", None),
    |                ^^^^^^^^^^^ not found in `sym`

error[E0531]: cannot find unit struct, unit variant or constant `better_rust` in module `sym`
   --> compiler\rustc_feature\src\unstable.rs:240:16
    |
157 |                 name: sym::$feature,
    |                            -------- due to this macro variable
...
240 |     (internal, better_rust, "2.0.0", None),
    |                ^^^^^^^^^^^ not found in `sym`

Some errors have detailed explanations: E0425, E0531.

rustbot · 2026-06-15T19:09:26Z

r? @jieyouxu

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jieyouxu

While the change itself looks reasonable, do we know if this is one of the resolve errors that we should be suppressing (for the second instance)?

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mejrs · 2026-06-17T09:25:23Z

That is unwarranted in my eyes.

The existing deduplication that already happens here is not done by the resolver, it's done in rustc_errors. Which just compares the errors by hashing them.

I don't want to make such changes in the resolver, nor does a smarter deduplication mechanism in rustc_error seem worth it. Especially when there are already several easy tricks to avoid error duplication by rewriting the macro slightly (like what i did here, or by binding the metavariable to a local and using that)

jieyouxu

Thanks, this seems reasonable.
@bors r+ rollup

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rust-bors · 2026-06-17T09:27:02Z

📌 Commit 3ae0f01 has been approved by jieyouxu

It is now in the queue for this repository.

rust-bors · 2026-06-17T09:30:03Z

⌛ Testing commit 3ae0f01 with merge f9279b5...

Workflow: https://github.com/rust-lang/rust/actions/runs/27679398121

Improve `declare_features!` macro error I got mildly annoyed when I went to add a new feature, and the fix for this is relatively simple. Current error: ``` error[E0425]: cannot find value `better_rust` in module `sym` --> compiler\rustc_feature\src\unstable.rs:240:16 | 157 | name: sym::$feature, | -------- due to this macro variable ... 240 | (internal, better_rust, "2.0.0", None), | ^^^^^^^^^^^ not found in `sym` For more information about this error, try `rustc --explain E0425` ``` Previous error: ``` error[E0425]: cannot find value `better_rust` in module `sym` --> compiler\rustc_feature\src\unstable.rs:240:16 | 157 | name: sym::$feature, | -------- due to this macro variable ... 240 | (internal, better_rust, "2.0.0", None), | ^^^^^^^^^^^ not found in `sym` error[E0531]: cannot find unit struct, unit variant or constant `better_rust` in module `sym` --> compiler\rustc_feature\src\unstable.rs:240:16 | 157 | name: sym::$feature, | -------- due to this macro variable ... 240 | (internal, better_rust, "2.0.0", None), | ^^^^^^^^^^^ not found in `sym` Some errors have detailed explanations: E0425, E0531. ```

JonathanBrouwer · 2026-06-17T09:34:07Z

@bors yield
Yielding to enclosing rollup

rust-bors · 2026-06-17T09:34:12Z

Auto build was cancelled. Cancelled workflows:

https://github.com/rust-lang/rust/actions/runs/27679398121

The next pull request likely to be tested is #158015.

…uwer Rollup of 3 pull requests Successful merges: - #157931 (Improve `declare_features!` macro error) - #157992 (tidy: revisions inherit global directives) - #158010 (renovate: Pin GitHub Action digests to SemVer)

Rollup merge of #157931 - mejrs:feature_macro, r=jieyouxu Improve `declare_features!` macro error I got mildly annoyed when I went to add a new feature, and the fix for this is relatively simple. Current error: ``` error[E0425]: cannot find value `better_rust` in module `sym` --> compiler\rustc_feature\src\unstable.rs:240:16 | 157 | name: sym::$feature, | -------- due to this macro variable ... 240 | (internal, better_rust, "2.0.0", None), | ^^^^^^^^^^^ not found in `sym` For more information about this error, try `rustc --explain E0425` ``` Previous error: ``` error[E0425]: cannot find value `better_rust` in module `sym` --> compiler\rustc_feature\src\unstable.rs:240:16 | 157 | name: sym::$feature, | -------- due to this macro variable ... 240 | (internal, better_rust, "2.0.0", None), | ^^^^^^^^^^^ not found in `sym` error[E0531]: cannot find unit struct, unit variant or constant `better_rust` in module `sym` --> compiler\rustc_feature\src\unstable.rs:240:16 | 157 | name: sym::$feature, | -------- due to this macro variable ... 240 | (internal, better_rust, "2.0.0", None), | ^^^^^^^^^^^ not found in `sym` Some errors have detailed explanations: E0425, E0531. ```

Improve declare_features! macro error

3ae0f01

rustbot assigned jieyouxu Jun 15, 2026

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Jun 15, 2026

jieyouxu reviewed Jun 16, 2026

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jieyouxu approved these changes Jun 17, 2026

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rust-bors Bot 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 Jun 17, 2026

JonathanBrouwer mentioned this pull request Jun 17, 2026

Rollup of 3 pull requests #158015

Merged

rust-bors Bot merged commit 854fdba into rust-lang:main Jun 17, 2026
13 of 14 checks passed

rustbot added this to the 1.98.0 milestone Jun 17, 2026

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Improve `declare_features!` macro error#157931

Improve `declare_features!` macro error#157931
rust-bors[bot] merged 1 commit into
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mejrs:feature_macro

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