Detect bad number of generics caused by bad derive by estebank · Pull Request #160695 · rust-lang/rust

estebank · 2026-08-07T12:21:50Z

When a derive macro expands the annotated item's name directly using quote!, it keep the item's Span context (instead of having a new context). This means that the generic Span context machinery which provides feedback that an error happened due to a derive doesn't kick in.

If a derive macro isn't written to take into account the existence of type parameters, an error for "mismatched number of type parameters" will be emitted. We now detect the case when this happens due to the derive macro, and customize the output to point that out, as well as avoid giving suggestions that will always be wrong.

Partially address #160463 (this doesn't detect a nameres error caused by referencing type parameter within a derive).

error[E0107]: missing generics for enum `A`
 --> bar.rs:8:6
  |
7 | #[derive(A)]
  |          - it looks like this derive macro might not support items with generic parameters
8 | enum A<T> {
  |      ^

I did not use an LLM to create a change in this PR.
I used an LLM to create a change in this PR, and I have explained below how it was used.

r? @petrochenkov

rustbot · 2026-08-07T12:21:54Z

HIR ty lowering was modified

cc @fmease

@petrochenkov

…chenkov Do not continue past `rustc_resolve` when encountering duplicated items Duplicated items cause *lots* of confusing knock down errors. This change side-steps some known ICEs, and reduces the verbosity of crates with duplicated items at the cost of not emitting every error that we could. Noticed just how problematic these can be while looking at rust-lang#160695, as `#[derive]`s are particularly prone to the kind of confusion these duplicates cause. Fix rust-lang#120873, fix rust-lang#123690. r? @petrochenkov

@petrochenkov

…chenkov Do not continue past `rustc_resolve` when encountering duplicated items Duplicated items cause *lots* of confusing knock down errors. This change side-steps some known ICEs, and reduces the verbosity of crates with duplicated items at the cost of not emitting every error that we could. Noticed just how problematic these can be while looking at rust-lang#160695, as `#[derive]`s are particularly prone to the kind of confusion these duplicates cause. Fix rust-lang#120873, fix rust-lang#123690. r? @petrochenkov

@petrochenkov

…chenkov Do not continue past `rustc_resolve` when encountering duplicated items Duplicated items cause *lots* of confusing knock down errors. This change side-steps some known ICEs, and reduces the verbosity of crates with duplicated items at the cost of not emitting every error that we could. Noticed just how problematic these can be while looking at rust-lang#160695, as `#[derive]`s are particularly prone to the kind of confusion these duplicates cause. Fix rust-lang#120873, fix rust-lang#123690. r? @petrochenkov

@petrochenkov

Rollup merge of #162831 - estebank:duplicated-items, r=petrochenkov Do not continue past `rustc_resolve` when encountering duplicated items Duplicated items cause *lots* of confusing knock down errors. This change side-steps some known ICEs, and reduces the verbosity of crates with duplicated items at the cost of not emitting every error that we could. Noticed just how problematic these can be while looking at #160695, as `#[derive]`s are particularly prone to the kind of confusion these duplicates cause. Fix #120873, fix #123690. r? @petrochenkov

@petrochenkov

Do not continue past `rustc_resolve` when encountering duplicated items Duplicated items cause *lots* of confusing knock down errors. This change side-steps some known ICEs, and reduces the verbosity of crates with duplicated items at the cost of not emitting every error that we could. Noticed just how problematic these can be while looking at rust-lang/rust#160695, as `#[derive]`s are particularly prone to the kind of confusion these duplicates cause. Fix rust-lang/rust#120873, fix rust-lang/rust#123690. r? @petrochenkov

rustbot · 2026-09-25T16:07:20Z

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

estebank · 2026-09-25T16:07:42Z

@petrochenkov addressed your comments in the last commit (and shortened the label).

petrochenkov · 2026-09-25T16:11:59Z

r=me after squashing commits.
@rustbot author

rustbot · 2026-09-25T16:12:05Z

Reminder, once the PR becomes ready for a review, use @rustbot ready.

When a derive macro expands the annotated item's name directly using `quote!`, it keep the item's Span context (instead of having a new context). This means that the generic Span context machinery which provides feedback that an error happened due to a derive doesn't kick in. If a derive macro isn't written to take into account the existence of type parameters, an error for "mismatched number of type parameters" will be emitted. We now detect the case when this happens due to the derive macro, and customize the output to point that out, as well as avoid giving suggestions that will always be wrong.

estebank · 2026-09-25T23:06:57Z

@bors r=petrochenkov

rust-bors · 2026-09-25T23:07:00Z

📌 Commit 49276b0 has been approved by petrochenkov

It is now in the queue for this repository.

rust-bors · 2026-09-26T01:05:41Z

⚠️ A new commit 565857be19fa709280bf461ae658b5df33863f8a was pushed.

This pull request was unapproved.

estebank · 2026-09-26T04:54:22Z

@bors r=petrochenkov

rust-bors · 2026-09-26T04:54:25Z

📌 Commit 49276b0 has been approved by petrochenkov

It is now in the queue for this repository.

Rollup of 13 pull requests Successful merges: - #160695 (Detect bad number of generics caused by bad derive) - #162883 (No longer auto-inline `f16` and `f128` on well-supported platforms) - #163133 ([rustdoc] Fix invalid jump to def link when `#[rustc_allow_incoherent_impl]` is involved) - #163215 (Fix suggestion for Option to bool with proper precedence handling) - #163266 (More deferred liveness cleanups) - #163274 (Support -Z merge-functions with gcc and add stack-protector asm tests) - #163290 (Merge `ForceWarning`/`Allow`/`Expect` into `Warning`) - #163298 (Don't emit sugg for pub-reexport extern std) - #163312 (Add rustdoc regression test for glob import of a crate that re-exports) - #163357 (Borrowck cleanups part trois) - #161710 (Stabilize `mem::conjure_zst`) - #163332 (Add some docs to `Global`) - #163362 (simplify ndk compiler test)

@petrochenkov

Rollup merge of #160695 - estebank:issue-160463, r=petrochenkov Detect bad number of generics caused by bad derive When a derive macro expands the annotated item's name directly using `quote!`, it keep the item's Span context (instead of having a new context). This means that the generic Span context machinery which provides feedback that an error happened due to a derive doesn't kick in. If a derive macro isn't written to take into account the existence of type parameters, an error for "mismatched number of type parameters" will be emitted. We now detect the case when this happens due to the derive macro, and customize the output to point that out, as well as avoid giving suggestions that will always be wrong. Partially address #160463 (this doesn't detect a nameres error caused by referencing type parameter within a derive). ``` error[E0107]: missing generics for enum `A` --> bar.rs:8:6 | 7 | #[derive(A)] | - it looks like this derive macro might not support items with generic parameters 8 | enum A<T> { | ^ ``` r? @petrochenkov

Rollup of 13 pull requests Successful merges: - rust-lang/rust#160695 (Detect bad number of generics caused by bad derive) - rust-lang/rust#162883 (No longer auto-inline `f16` and `f128` on well-supported platforms) - rust-lang/rust#163133 ([rustdoc] Fix invalid jump to def link when `#[rustc_allow_incoherent_impl]` is involved) - rust-lang/rust#163215 (Fix suggestion for Option to bool with proper precedence handling) - rust-lang/rust#163266 (More deferred liveness cleanups) - rust-lang/rust#163274 (Support -Z merge-functions with gcc and add stack-protector asm tests) - rust-lang/rust#163290 (Merge `ForceWarning`/`Allow`/`Expect` into `Warning`) - rust-lang/rust#163298 (Don't emit sugg for pub-reexport extern std) - rust-lang/rust#163312 (Add rustdoc regression test for glob import of a crate that re-exports) - rust-lang/rust#163357 (Borrowck cleanups part trois) - rust-lang/rust#161710 (Stabilize `mem::conjure_zst`) - rust-lang/rust#163332 (Add some docs to `Global`) - rust-lang/rust#163362 (simplify ndk compiler test)

rustbot added A-run-make Area: port run-make Makefiles to rmake.rs 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 Aug 7, 2026

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estebank force-pushed the issue-160463 branch from ad10299 to b7358ef Compare August 7, 2026 12:47

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Comment thread tests/ui/derives/auxiliary/derive-no-generics.rs

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estebank force-pushed the issue-160463 branch from b7358ef to 7f323b4 Compare September 15, 2026 22:04

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estebank mentioned this pull request Sep 15, 2026

Do not continue past rustc_resolve when encountering duplicated items #162831

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estebank force-pushed the issue-160463 branch 2 times, most recently from d717072 to a8a03d8 Compare September 20, 2026 18:21

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estebank added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Sep 20, 2026

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Comment thread compiler/rustc_hir_analysis/src/diagnostics/wrong_number_of_generic_args.rs

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petrochenkov added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Sep 25, 2026

estebank force-pushed the issue-160463 branch from a8a03d8 to d0ca44e Compare September 25, 2026 16:07

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estebank force-pushed the issue-160463 branch from d0ca44e to e7ca4a4 Compare September 25, 2026 21:38

estebank force-pushed the issue-160463 branch from e7ca4a4 to 49276b0 Compare September 25, 2026 21:43

estebank mentioned this pull request Sep 25, 2026

Rustc incorrectly suggests adding generic arguments to an enum that already has them when using enum-map-derive =1.0.0 #160463

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estebank force-pushed the issue-160463 branch from 565857b to 49276b0 Compare September 26, 2026 01:06

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jhpratt mentioned this pull request Sep 26, 2026

Rollup of 13 pull requests #163363

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rust-bors Bot merged commit 06568dc into rust-lang:main Sep 26, 2026
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estebank mentioned this pull request Sep 26, 2026

Tweak "name not found" resolution error when it happens from within a derive expansion #163380

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