raise ambiguity error on attribute macro that could be tool attribute by mejrs · Pull Request #162597 · rust-lang/rust

mejrs · 2026-09-10T14:37:19Z

See #162597 (comment) for clean crater run; the errors are unrelated/spurious.

We need some sort of ambiguity error in other to implement the register tool rfc:

Fixing name resolution errors

Note that register_tool changes name resolution, and may give errors if you have a crate named some_tool.
The compiler will suggest ways to fix the new errors.

If a tool name conflicts with a crate name, you can disambiguate the crate with ::some_tool:
#![register_tool(some_tool)]
extern crate some_tool;

#[some_tool::attribute] //~ ERROR: is this the tool or a proc-macro?
fn bar() {
   // ...
}

#[::some_tool::attribute] // OK: This is the proc-macro defined in the crate.
fn foo() {
  // ...
}
However, if you want to go on to use a tool attribute,
you must rename the crate so it doesn't conflict:
#![register_tool(some_tool)]
extern crate some_tool as my_library;

#[some_tool::attribute] // OK: This is the attribute specified by the tool.
fn bar() {
   // ...
}
Alternatively, if you only want to use lints, you can use register_lint_tool instead of register_tool, which will avoid resolution errors.

Overlaps like this are expected to be rare in practice.

This PR implements the ambiguity error (not the "leading :: to disambiguate" part).

This is a breaking change if:

someone has a crate or module named diagnostic|miri|rust_analyzer|clippy|rustfmt and exports an attribute macro from it
it is then used it as #[(diagnostic|miri|rust_analyzer|clippy|rustfmt)::attr_macro] (rather than use module_or_crate::attr_macro; #[attr_macro])
the same applies for tools registered with register_tool, but that's unstable.

See #158146 for context. This is a simpler version of that PR.

This does not implement unconditionally resolving these as tool attributes but does reserve the ability to do so. This would allow things like this to compile:

mod rustfmt {}

#[rustfmt::skip]
fn main() {}

and see also #98291 for a case where it would be nice to assume e.g. #[rustfmt::skip] is actually a tool attribute and thus inert.

mejrs · 2026-09-10T14:37:30Z

@bors try

raise ambiguity error on attribute macro that could be tool attribute

rust-bors · 2026-09-10T15:43:53Z

☀️ Try build successful (CI)
Build commit: 8c2ec58 (8c2ec5867b7cd0db3869fc1c128b867c2e8c0129)
Base parent: c4c4a57 (c4c4a576936e9e67717d0deb8e74e02dd5dd10de)

mejrs · 2026-09-10T21:04:24Z

@bors try

raise ambiguity error on attribute macro that could be tool attribute

rust-bors · 2026-09-10T22:03:51Z

☀️ Try build successful (CI)
Build commit: be3da1e (be3da1e8c043bb6f1f335463d3b1335cdf50b03c)
Base parent: 018018e (018018e881e2db0956f229dbb543e21f058d1ce7)

mejrs · 2026-09-10T22:22:21Z

@craterbot check

craterbot · 2026-09-10T22:22:55Z

👌 Experiment pr-162597 created and queued.
🤖 Automatically detected try build be3da1e
🔍 You can check out the queue and this experiment's details.

ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

craterbot · 2026-09-16T04:00:07Z

🚧 Experiment pr-162597 is now running

ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

craterbot · 2026-09-18T20:06:09Z

🎉 Experiment pr-162597 is completed!
📊 3 regressed and 1 fixed (1108363 total)
📊 6349 spurious results on the retry-regressed-list.txt, consider a retry¹ if this is a significant amount.
📰 Open the summary report.

⚠️ If you notice any spurious failure please add them to the denylist!
ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

re-run the experiment with crates=https://crater-reports.s3.amazonaws.com/pr-162597/retry-regressed-list.txt ↩

mejrs · 2026-09-18T22:31:18Z

Looks like the crater run is clean, so I guess we can do this (If the lang team agrees, of course)

r? @petrochenkov

petrochenkov · 2026-09-25T16:29:12Z

So the main drawback here is the same as with built-in attributes - with these rules you cannot add a new built-in tool module without a breakage (maybe theoretical).

But if register_tool is stabilized, then new built-in tools are hopefully never added, and most of existing built-in tools are migrated to explicit registration in the next edition, so this is not going to be a big problem.

theemathas · 2026-10-24T18:00:45Z

I am assuming that it's intended that the diagnostic namespace thingy is treated the same way as tool attributes.

petrochenkov · 2026-10-26T16:06:01Z

@bors r+

rust-bors · 2026-10-26T16:06:04Z

📋 This PR cannot be approved because it currently has the following labels: S-waiting-on-t-lang, needs-reference-pr.

petrochenkov · 2026-10-26T16:07:59Z

Ok, waiting on the reference PR.
@rustbot author

mejrs · 2026-10-27T12:43:50Z

Reference PR is open at rust-lang/reference#2397

petrochenkov · 2026-10-27T13:37:01Z

@bors r+

rust-bors · 2026-10-27T13:37:05Z

📌 Commit 168e53d has been approved by petrochenkov

It is now in the queue for this repository.

raise ambiguity error on attribute macro that could be tool attribute See rust-lang#162597 (comment) for clean crater run; the errors are unrelated/spurious. We need some sort of ambiguity error in other to implement the [register tool rfc](https://rust-lang.github.io/rfcs/3808-register-tool.html#fixing-name-resolution-errors): > #### Fixing name resolution errors > >Note that `register_tool` changes name resolution, and may give errors if you have a crate named `some_tool`. The compiler will suggest ways to fix the new errors. > >If a tool name conflicts with a crate name, you can disambiguate the crate with `::some_tool`: >```rust >#![register_tool(some_tool)] >extern crate some_tool; > >#[some_tool::attribute] //~ ERROR: is this the tool or a proc-macro? >fn bar() { > // ... >} > >#[::some_tool::attribute] // OK: This is the proc-macro defined in the crate. >fn foo() { > // ... >} >``` >However, if you want to go on to use a tool attribute, >you must rename the crate so it doesn't conflict: >```rust >#![register_tool(some_tool)] >extern crate some_tool as my_library; > >#[some_tool::attribute] // OK: This is the attribute specified by the tool. >fn bar() { > // ... >} >``` >Alternatively, if you only want to use lints, you can use `register_lint_tool` instead of `register_tool`, which will avoid resolution errors. > >Overlaps like this are expected to be rare in practice. This PR implements the ambiguity error (**not** the "leading `::` to disambiguate" part). This is a breaking change if: - someone has a crate or module named diagnostic|miri|rust_analyzer|clippy|rustfmt and exports an attribute macro from it - it is then used it as `#[(diagnostic|miri|rust_analyzer|clippy|rustfmt)::attr_macro]` (rather than `use module_or_crate::attr_macro; #[attr_macro]`) - the same applies for tools registered with `register_tool`, but that's unstable. See rust-lang#158146 for context. This is a simpler version of that PR. This does not implement unconditionally resolving these as tool attributes but does reserve the ability to do so. This would allow things like this to compile: ```rust mod rustfmt {} #[rustfmt::skip] fn main() {} ``` and see also rust-lang#98291 for a case where it would be nice to assume e.g. `#[rustfmt::skip]` is actually a tool attribute and thus inert.

…uwer Rollup of 22 pull requests Successful merges: - #159580 (Reject cfg on expressions that cannot be safely removed) - #162597 (raise ambiguity error on attribute macro that could be tool attribute) - #162808 (Enable `--generate-link-to-definition` rustdoc option on std docs) - #163059 (Recover invalid return type until `{`, `}` or `;`) - #163672 (Use runCodeGen Abstraction for new LLVM) - #164028 (Add a future incompat warning for #[no_link]) - #164188 (Suggest adding lifetime for `dyn Trait` in return type) - #164345 (fix: handle `false` in root contexts) - #164494 (drop ands which are a superset of other ands) - #164766 (Unstably introduce MVP edition migration lint `unmarked_unchecked_type_aliases` together with bikeshed attribute `#[rustc_unchecked_type_alias]`) - #164785 (delegation: emit error when there is no field for `Self` mapping) - #164799 (Don't use `IntoIterator` in parallel API) - #164871 (Refactor call argument codegen) - #164648 (parse inline and rustc_force_inline with same parser) - #164811 (fix: Prevent ICE when comparing EII impl against generic declaration) - #164900 (make tool_attrs method to retrieve tool attributes.) - #164993 (copy_nonoverlapping: dont skip ovelrap check when src is fully uninit) - #164996 (miri: add missing alignment check in write_bytes) - #165012 (Remove Span::eq_ctxt()) - #165013 ([tiny] Add missing backticks around lifetime name) - #165024 (rustdoc-search: rank re-export lower) - #165028 (Update enzyme to fix one bug related to higher-order derivatives) > [!WARNING] > This rollup conflicts with pending auto build #165042 and may need to be recreated if the pending build succeeds.

…uwer Rollup of 21 pull requests Successful merges: - #159580 (Reject cfg on expressions that cannot be safely removed) - #162597 (raise ambiguity error on attribute macro that could be tool attribute) - #162808 (Enable `--generate-link-to-definition` rustdoc option on std docs) - #163059 (Recover invalid return type until `{`, `}` or `;`) - #163672 (Use runCodeGen Abstraction for new LLVM) - #164028 (Add a future incompat warning for #[no_link]) - #164188 (Suggest adding lifetime for `dyn Trait` in return type) - #164345 (fix: handle `false` in root contexts) - #164494 (drop ands which are a superset of other ands) - #164785 (delegation: emit error when there is no field for `Self` mapping) - #164799 (Don't use `IntoIterator` in parallel API) - #164871 (Refactor call argument codegen) - #164648 (parse inline and rustc_force_inline with same parser) - #164811 (fix: Prevent ICE when comparing EII impl against generic declaration) - #164900 (make tool_attrs method to retrieve tool attributes.) - #164993 (copy_nonoverlapping: dont skip ovelrap check when src is fully uninit) - #164996 (miri: add missing alignment check in write_bytes) - #165012 (Remove Span::eq_ctxt()) - #165013 ([tiny] Add missing backticks around lifetime name) - #165024 (rustdoc-search: rank re-export lower) - #165028 (Update enzyme to fix one bug related to higher-order derivatives)

Rollup merge of #162597 - mejrs:ambiguity, r=petrochenkov raise ambiguity error on attribute macro that could be tool attribute See #162597 (comment) for clean crater run; the errors are unrelated/spurious. We need some sort of ambiguity error in other to implement the [register tool rfc](https://rust-lang.github.io/rfcs/3808-register-tool.html#fixing-name-resolution-errors): > #### Fixing name resolution errors > >Note that `register_tool` changes name resolution, and may give errors if you have a crate named `some_tool`. The compiler will suggest ways to fix the new errors. > >If a tool name conflicts with a crate name, you can disambiguate the crate with `::some_tool`: >```rust >#![register_tool(some_tool)] >extern crate some_tool; > >#[some_tool::attribute] //~ ERROR: is this the tool or a proc-macro? >fn bar() { > // ... >} > >#[::some_tool::attribute] // OK: This is the proc-macro defined in the crate. >fn foo() { > // ... >} >``` >However, if you want to go on to use a tool attribute, >you must rename the crate so it doesn't conflict: >```rust >#![register_tool(some_tool)] >extern crate some_tool as my_library; > >#[some_tool::attribute] // OK: This is the attribute specified by the tool. >fn bar() { > // ... >} >``` >Alternatively, if you only want to use lints, you can use `register_lint_tool` instead of `register_tool`, which will avoid resolution errors. > >Overlaps like this are expected to be rare in practice. This PR implements the ambiguity error (**not** the "leading `::` to disambiguate" part). This is a breaking change if: - someone has a crate or module named diagnostic|miri|rust_analyzer|clippy|rustfmt and exports an attribute macro from it - it is then used it as `#[(diagnostic|miri|rust_analyzer|clippy|rustfmt)::attr_macro]` (rather than `use module_or_crate::attr_macro; #[attr_macro]`) - the same applies for tools registered with `register_tool`, but that's unstable. See #158146 for context. This is a simpler version of that PR. This does not implement unconditionally resolving these as tool attributes but does reserve the ability to do so. This would allow things like this to compile: ```rust mod rustfmt {} #[rustfmt::skip] fn main() {} ``` and see also #98291 for a case where it would be nice to assume e.g. `#[rustfmt::skip]` is actually a tool attribute and thus inert.

mejrs added the needs-crater This change needs a crater run to check for possible breakage in the ecosystem. label Sep 10, 2026

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Auto merge of #162597 - mejrs:ambiguity, r=<try>

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raise ambiguity error on attribute macro that could be tool attribute

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mejrs force-pushed the ambiguity branch from 27a7b29 to 087e8bf Compare September 10, 2026 20:39

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Auto merge of #162597 - mejrs:ambiguity, r=<try>

be3da1e

raise ambiguity error on attribute macro that could be tool attribute

craterbot added S-waiting-on-crater Status: Waiting on a crater run to be completed. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Sep 10, 2026

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rustbot assigned petrochenkov Sep 18, 2026

mejrs marked this pull request as ready for review September 18, 2026 22:31

petrochenkov reviewed Sep 25, 2026

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Document tool attribute ambiguity error rust-lang/reference#2397

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Rollup of 24 pull requests #165038

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Rollup of 22 pull requests #165051

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Rollup of 21 pull requests #165056

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Fixing name resolution errors

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