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Show crate root path in misplaced crate-level attribute diagnostic#157025

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Show crate root path in misplaced crate-level attribute diagnostic#157025
Dnreikronos wants to merge 4 commits into
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Dnreikronos:fix/crate-root-path-help-in-attr-style-diagnostic

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@Dnreikronos Dnreikronos commented May 27, 2026 •
edited by rustbot
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Fixes #157001

If you put #![feature(...)] inside a non-root module, the diagnostic tells you it can only be used at the crate root, but never says where the crate root actually is. Not great if you're new to Rust or working in a big workspace with nested modules.

Now the diagnostic includes a help line with the crate root file path when the misplaced attribute is an inner attribute. Outer attributes already get a span note pointing at what they're applied to, so they don't need this. Path goes through RemapPathScopeComponents::DIAGNOSTICS so --remap-path-prefix is respected.

warning: the `#![feature]` attribute can only be used at the crate root
  --> src/foo.rs:1:1
   |
LL | #![feature(test)]
   | ^^^^^^^^^^^^^^^^^
   |
   = help: the crate root is at `src/main.rs`

@Dnreikronos
Show crate root path in misplaced crate-level attribute diagnostic
6a51d20 
When a crate-level attribute like `#![feature(...)]` is used as an inner
attribute inside a non-root module, the diagnostic now includes a help
message pointing to the crate root file path, making it easier for users
to find where the attribute should be placed.
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rustbot commented May 27, 2026

Some changes occurred in compiler/rustc_attr_parsing

cc @jdonszelmann, @JonathanBrouwer

@rustbot 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 May 27, 2026
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rustbot commented May 27, 2026

r? @oli-obk

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JonathanBrouwer
JonathanBrouwer requested changes May 27, 2026
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Comment thread tests/ui/attributes/attr-mix-new.stderr Outdated
LL | #![feature(globs)]
| ^^^^^^^^^^^^^^^^^^
|
= help: the crate root is at `$DIR/attr-mix-new.rs`
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@JonathanBrouwer JonathanBrouwer May 27, 2026 •
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Hmmm, can we remove or adjust this suggestion if the crate root is in the same file? I don't the help message is useful in that case

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I think that all changed tests have the crate root being in the same file, so then please add a new test that triggers this help message in a different file

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Good catch, done! Suppressed the help when the attribute is already in the crate root file. Added a cross-file test too (crate root + submodule in a separate file) so we still have coverage for the case where the help actually matters.

@rustbot rustbot 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 May 27, 2026
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rustbot commented May 27, 2026

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

@Dnreikronos
Suppress crate-root help when attribute is in same file
1e62f5a 
Skip the "the crate root is at ..." help message when the misplaced
crate-level attribute is already in the crate root file, since it
adds no useful information in that case. Add a cross-file test to
verify the help still appears when the attribute is in a different
file from the crate root.
@Dnreikronos
Remove trailing whitespace left by deleted annotations
bb92226
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oli-obk commented May 27, 2026

r? @JonathanBrouwer (feel free to assign back, but you seem to be on top of this already)

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rust-bors Bot commented May 27, 2026

@Dnreikronos: 🔑 Insufficient privileges: not in review users

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Dnreikronos commented May 27, 2026

@rustbot ready

@rustbot rustbot 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 May 27, 2026
JonathanBrouwer
JonathanBrouwer requested changes May 27, 2026
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Comment thread tests/ui/attributes/crate-root-path-in-different-file/crate-root-path-in-different-file.rs
@@ -0,0 +1,7 @@
#![deny(unused_attributes)]
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@JonathanBrouwer JonathanBrouwer May 27, 2026 •
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The preferred structure is afaik that:

  • submod.rs is in the tests/ui/attributes/auxiliary folder (the file then doesn't need the //@ ignote-auxiliary
  • The crate-root-path-in-different-file.rs is in the tests/ui/attributes folder. I think the file might then need an aux-build annotation? I forgot how this works exactly, lmk if you can't figure it out then I'll take a look

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Other than that I think the PR is good now :)

@rustbot rustbot 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 May 27, 2026
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actual "crate root" file not identified in diagnostics

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