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Add documentation for the no_main and repr attributes - #163627

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Add documentation for the no_main and repr attributes#163627
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literally-user:docs-repr-no_main_attribute

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@literally-user literally-user commented Oct 1, 2026 •
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Part of #157604.

This PR documents no_main and repr attributes in library/core/src/attribute_docs.rs with some examples.

Tested with: ./x doc

@rustbot rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-libs Relevant to the library team, which will review and decide on the PR/issue. labels Oct 1, 2026
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r? @JohnTitor

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@rustbot rustbot added has-merge-commits PR has merge commits, merge with caution. S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Oct 1, 2026
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literally-user force-pushed the docs-repr-no_main_attribute branch from b207bc2 to a09c4c7 Compare October 1, 2026 23:26
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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.

@rustbot rustbot removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. has-merge-commits PR has merge commits, merge with caution. labels Oct 1, 2026
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bushrat011899
bushrat011899 requested changes Oct 2, 2026
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Good documentation in general! Just some minor mistakes to fix up.

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Comment thread library/core/src/attribute_docs.rs Outdated
/// [representation]: ../reference/type-layout.html#representations
/// [`Rust`]: ../reference/type-layout.html#the-rust-representation
/// [`C`]: ../reference/type-layout.html#the-c-representation
/// [primitive representations]: ../reference/type-layout.html#primitiv

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Suggested change
/// [primitive representations]: ../reference/type-layout.html#primitiv
/// [primitive representations]: ../reference/type-layout.html#primitive-representations

I assume this is the link you're aiming for?

Comment thread library/core/src/attribute_docs.rs Outdated
Comment on lines +492 to +493
///
///

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Suggested change
///
///

Added lines appear superfluous.

Comment thread library/core/src/attribute_docs.rs Outdated
Comment on lines +417 to +418
/// If you define it yourself, it must use the platform's C ABI and be exported under an
/// unmangled name with the [`no_mangle` attribute]:

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Is this actually true? I agree it's almost certainly what you should do, but I don't know if it's a "must" (e.g., you could use a naked ABI).

@literally-user literally-user Oct 2, 2026 •
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So, there's no strict requirement for this, I think I'll rewrite this part. Good point, thanks!

Comment thread library/core/src/attribute_docs.rs Outdated
/// If you define it yourself, it must use the platform's C ABI and be exported under an
/// unmangled name with the [`no_mangle` attribute]:
///
/// ```rust,ignore (needs to be built as a binary crate)

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Suggested change
/// ```rust,ignore (needs to be built as a binary crate)
/// ```standalone_crate

I believe standalone_crate is sufficient to have this test compile?

Comment thread library/core/src/attribute_docs.rs
Comment thread library/core/src/attribute_docs.rs
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Reminder, once the PR becomes ready for a review, use @rustbot ready.

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literally-user force-pushed the docs-repr-no_main_attribute branch from 294f5d8 to e9ff173 Compare October 2, 2026 07:09
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@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 Oct 2, 2026
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Thanks for fixing that up, looks good to me!

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📌 Commit 4abaac9 has been approved by bushrat011899

It is now in the queue for this repository.

@rust-bors 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 Oct 2, 2026
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@rustbot ready

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@bors try jobs=dist-various-1,test-various,test-x86_64-gnu-aux,test-x86_64-msvc-1,test-aarch64-apple-1,test-aarch64-apple-2,test-x86_64-mingw-1,test-i686-msvc,test-armhf-gnu

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rust-bors Bot pushed a commit that referenced this pull request Oct 3, 2026
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Auto merge of #163627 - literally-user:docs-repr-no_main_attribute, r…
1b01c33 
…=<try>

Add documentation for the `no_main` and `repr` attributes


try-job: dist-various-1
try-job: test-various
try-job: test-x86_64-gnu-aux
try-job: test-x86_64-msvc-1
try-job: test-aarch64-apple-1
try-job: test-aarch64-apple-2
try-job: test-x86_64-mingw-1
try-job: test-i686-msvc
try-job: test-armhf-gnu
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literally-user force-pushed the docs-repr-no_main_attribute branch from 3d16c35 to f679d53 Compare October 3, 2026 13:28
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@JonathanBrouwer Can you run them again, please?

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@bors try jobs=dist-various-1,test-various,test-x86_64-gnu-aux,test-x86_64-msvc-1,test-aarch64-apple-1,test-aarch64-apple-2,test-x86_64-mingw-1,test-i686-msvc,test-armhf-gnu

rust-bors Bot pushed a commit that referenced this pull request Oct 3, 2026
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Auto merge of #163627 - literally-user:docs-repr-no_main_attribute, r…
8587fed 
…=<try>

Add documentation for the `no_main` and `repr` attributes


try-job: dist-various-1
try-job: test-various
try-job: test-x86_64-gnu-aux
try-job: test-x86_64-msvc-1
try-job: test-aarch64-apple-1
try-job: test-aarch64-apple-2
try-job: test-x86_64-mingw-1
try-job: test-i686-msvc
try-job: test-armhf-gnu
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☀️ Try build successful (CI)
Build commit: 8587fed (8587feda3991a1b0739792e0602b94f03fd1d909)
Base parent: d6b6dc7 (d6b6dc7982ef5d9117d96d018dfd83098d0471a1)

JonathanBrouwer
JonathanBrouwer reviewed Oct 3, 2026
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Comment thread library/core/src/attribute_docs.rs Outdated
/// If you define an entry point symbol that is suitable for your target, it must also be exported
/// under an unmangled name using the [`no_mangle` attribute]:
///
/// ```rust, ignore (no_main)

@JonathanBrouwer JonathanBrouwer Oct 3, 2026 •
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Would it work to make this no_run instead of ignore?
Then we can at least test that the example checks

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@literally-user literally-user Oct 3, 2026

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This is actually good idea

@literally-user
Add documentation for the and attributes
17f3f9c 
Fix test-tidy

review changes

review changes

review changes

fix llvm build

ignore attribute documentation example

fix tidy

use no_run instead of ignore
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literally-user force-pushed the docs-repr-no_main_attribute branch from f679d53 to 17f3f9c Compare October 3, 2026 22:26
@JonathanBrouwer

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@bors try jobs=test-various

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rust-bors Bot pushed a commit that referenced this pull request Oct 4, 2026
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Auto merge of #163627 - literally-user:docs-repr-no_main_attribute, r…
a46c290 
…=<try>

Add documentation for the `no_main` and `repr` attributes


try-job: test-various
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☀️ Try build successful (CI)
Build commit: a46c290 (a46c2901cc0ebd89d7262523ca634d44d35b129a)
Base parent: 56343b1 (56343b1a7d3fed3f349a5c2dc474f65b504f5221)

@JonathanBrouwer

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@bors r=bushrat011899,JonathanBrouwer rollup

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📌 Commit 17f3f9c has been approved by bushrat011899,JonathanBrouwer

It is now in the queue for this repository.

@rust-bors 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 Oct 4, 2026
@JonathanBrouwer JonathanBrouwer mentioned this pull request Oct 4, 2026
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Auto merge of #163754 - JonathanBrouwer:rollup-fdgcPnD, r=JonathanBro…
f48b3e6 
…uwer

Rollup of 6 pull requests

Successful merges:

 - #162974 (FCW for `#[panic_handler]` on `unsafe fn`.)
 - #163627 (Add documentation for the `no_main` and `repr` attributes)
 - #163671 (Add `--frontend-threads` option to `./x perf`)
 - #163694 (c_str_alloc_error test: mention why this is mostly Miri-only)
 - #163711 (Stabilize `CStr::display`)
 - #163723 ([tiny] Remove useless `.into()` calls)
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rust-bors Bot merged commit 593a42b into rust-lang:main Oct 4, 2026
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@rustbot rustbot added this to the 1.101.0 milestone Oct 4, 2026
rust-bors Bot pushed a commit that referenced this pull request Oct 4, 2026
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Unrolled build for #163627 in rollup 163754
5059fc0 
Rollup merge of #163627 - literally-user:docs-repr-no_main_attribute, r=bushrat011899,JonathanBrouwer

Add documentation for the `no_main` and `repr` attributes

Part of #157604.

This PR documents `no_main` and `repr` attributes in `library/core/src/attribute_docs.rs` with some examples.

Tested with: `./x doc`
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