Add FCW for derive helper attributes that will conflict with built-in attributes #151152

nik-rev · 2026-01-15T03:42:29Z

Adds a future-compatibility-warning deny-by-default lint that helps catch invalid derive helper attribute names early.

This issues the lint, saying that ignore helper will clash with the built-in ignore attribute.

#![crate_type = "proc-macro"]
#![deny(ambiguous_derive_helpers)] 
use proc_macro::TokenStream; 

#[proc_macro_derive(Trait, attributes(ignore))]
pub fn example(input: TokenStream) -> TokenStream {
    TokenStream::new()
}

If you actually tried to use that ignore helper attribute, you won't be able to due to the ambiguity:

#[derive(Trait)]
struct Foo {
    #[ignore]
    field: (),
}

Produces:

error[E0659]: `ignore` is ambiguous
 --> src/lib.rs:5:7
  |
5 |     #[ignore]
  |       ^^^^^^ ambiguous name
  |
  = note: ambiguous because of a name conflict with a builtin attribute
  = note: `ignore` could refer to a built-in attribute
note: `ignore` could also refer to the derive helper attribute defined here
 --> src/lib.rs:3:10
  |
3 | #[derive(Trait)]
  |          ^^^^^

rustbot · 2026-01-15T03:42:35Z

Some changes occurred in compiler/rustc_attr_parsing

cc @jdonszelmann, @JonathanBrouwer

rustbot · 2026-01-15T03:42:43Z

r? @chenyukang

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They will have a look at your PR within the next two weeks and either review your PR or reassign to another reviewer.

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compiler/rustc_lint_defs/src/builtin.rs

chenyukang · 2026-01-18T04:45:49Z

@bors r=chenyukang

rust-bors · 2026-01-18T04:45:52Z

📌 Commit 4dda363 has been approved by chenyukang

It is now in the queue for this repository.

petrochenkov · 2026-01-18T10:34:49Z

New deprecation lints go through language team process, and the lint name also doesn't follow naming conventions.

chenyukang · 2026-01-18T11:51:04Z

@bors r-

rust-bors · 2026-01-18T11:51:08Z

Commit 4dda363 has been unapproved.

nik-rev · 2026-01-18T13:01:58Z

@rustbot label +I-lang-nominated

I am nominating this for lang-team attention.

What name should this lint have? The current name doesn't follow the naming conventions

My main idea is allow(derive_helper_attr_with_same_name_as_a_builtin_attr), but that's quite long

rust-bors · 2026-02-10T09:21:52Z

Commit f4eca01 has been unapproved.

This PR was contained in a rollup (#152421), which was also unapproved.

… attributes

rustbot · 2026-02-10T19:39:32Z

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.

nik-rev · 2026-02-10T19:40:38Z

@bors r+

rust-bors · 2026-02-10T19:40:40Z

@nik-rev: 🔑 Insufficient privileges: not in review users

nik-rev · 2026-02-10T19:41:30Z

@bors r=JonathanBrouwer

rust-bors · 2026-02-10T19:41:33Z

@nik-rev: 🔑 Insufficient privileges: not in review users

nik-rev · 2026-02-10T19:42:26Z

@rustbot ready

JonathanBrouwer · 2026-02-10T19:42:53Z

@bors try jobs=test-various

Add FCW for derive helper attributes that will conflict with built-in attributes try-job: test-various

rust-bors · 2026-02-10T21:55:56Z

☀️ Try build successful (CI)
Build commit: 8b451e4 (8b451e434ccbe03d091c882a267b1ee8474752b3, parent: d00ba922591daa3d0a8b0f3cdf54c610097c24ea)

JonathanBrouwer · 2026-02-10T21:57:54Z

@bors r=chenyukang

rust-bors · 2026-02-10T21:57:56Z

📌 Commit 846e4ee has been approved by chenyukang

It is now in the queue for this repository.

…=chenyukang Add FCW for derive helper attributes that will conflict with built-in attributes Adds a future-compatibility-warning deny-by-default lint that helps catch invalid derive helper attribute names early. This issues the lint, saying that `ignore` helper will clash with the built-in `ignore` attribute. ```rust #![crate_type = "proc-macro"] #![deny(ambiguous_derive_helpers)] use proc_macro::TokenStream; #[proc_macro_derive(Trait, attributes(ignore))] pub fn example(input: TokenStream) -> TokenStream { TokenStream::new() } ``` If you actually tried to use that `ignore` helper attribute, you won't be able to due to the ambiguity: ```rust #[derive(Trait)] struct Foo { #[ignore] field: (), } ``` Produces: ``` error[E0659]: `ignore` is ambiguous --> src/lib.rs:5:7 | 5 | #[ignore] | ^^^^^^ ambiguous name | = note: ambiguous because of a name conflict with a builtin attribute = note: `ignore` could refer to a built-in attribute note: `ignore` could also refer to the derive helper attribute defined here --> src/lib.rs:3:10 | 3 | #[derive(Trait)] | ^^^^^ ```

Rollup of 17 pull requests Successful merges: - #142415 (Add note when inherent impl for a alias type defined outside of the crate) - #142680 (Fix passing/returning structs with the 64-bit SPARC ABI) - #150768 (Don't compute FnAbi for LLVM intrinsics in backends) - #151152 (Add FCW for derive helper attributes that will conflict with built-in attributes) - #151814 (layout: handle rigid aliases without params) - #151863 (Borrowck: simplify diagnostics for placeholders) - #152159 (Add note for `?Sized` params in int-ptr casts diag) - #152434 (Clarify names of `QueryVTable` functions for "executing" a query) - #152478 (Remove tm_factory field from CodegenContext) - #152498 (Partially revert "resolve: Update `NameBindingData::vis` in place") - #152316 (fix: add continue) - #152394 (Correctly check if a macro call is actually a macro call in rustdoc highlighter) - #152425 (Port #![test_runner] to the attribute parser) - #152481 (Use cg_ssa's produce_final_output_artifacts in cg_clif) - #152485 (fix issue#152482) - #152495 (Clean up some subdiagnostics) - #152502 (Implement `BinaryHeap::from_raw_vec`)

Rollup merge of #151152 - nik-contrib:helper_attr_builtin, r=chenyukang Add FCW for derive helper attributes that will conflict with built-in attributes Adds a future-compatibility-warning deny-by-default lint that helps catch invalid derive helper attribute names early. This issues the lint, saying that `ignore` helper will clash with the built-in `ignore` attribute. ```rust #![crate_type = "proc-macro"] #![deny(ambiguous_derive_helpers)] use proc_macro::TokenStream; #[proc_macro_derive(Trait, attributes(ignore))] pub fn example(input: TokenStream) -> TokenStream { TokenStream::new() } ``` If you actually tried to use that `ignore` helper attribute, you won't be able to due to the ambiguity: ```rust #[derive(Trait)] struct Foo { #[ignore] field: (), } ``` Produces: ``` error[E0659]: `ignore` is ambiguous --> src/lib.rs:5:7 | 5 | #[ignore] | ^^^^^^ ambiguous name | = note: ambiguous because of a name conflict with a builtin attribute = note: `ignore` could refer to a built-in attribute note: `ignore` could also refer to the derive helper attribute defined here --> src/lib.rs:3:10 | 3 | #[derive(Trait)] | ^^^^^ ```

rustbot added A-attributes Area: Attributes (`#[…]`, `#![…]`) 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 Jan 15, 2026

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nik-rev force-pushed the helper_attr_builtin branch 2 times, most recently from 54147eb to c9b7a07 Compare January 15, 2026 04:02

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nik-rev mentioned this pull request Jan 18, 2026

Tracking Issue for future-incompatibility lint ambiguous_derive_helpers #151276

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nik-rev force-pushed the helper_attr_builtin branch from c9b7a07 to 4dda363 Compare January 18, 2026 02:11

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traviscross added T-lang Relevant to the language team needs-fcp This change is insta-stable, or significant enough to need a team FCP to proceed. labels Jan 21, 2026

Add FCW for derive helper attributes that will conflict with built-in…

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nik-rev force-pushed the helper_attr_builtin branch from f4eca01 to 846e4ee Compare February 10, 2026 19:39

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Auto merge of #151152 - nik-contrib:helper_attr_builtin, r=<try>

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Add FCW for derive helper attributes that will conflict with built-in attributes try-job: test-various

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Zalathar mentioned this pull request Feb 11, 2026

[EXPERIMENT] Rollup of 9 pull requests #152476

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Zalathar mentioned this pull request Feb 11, 2026

[EXPERIMENT] Rollup of 8 pull requests #152479

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Zalathar mentioned this pull request Feb 12, 2026

[EXPERIMENT] Rollup of 18 pull requests #152513

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Rollup of 17 pull requests #152517

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Add FCW for derive helper attributes that will conflict with built-in attributes #151152

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