Document the `rustc_on_unimplemented` attribute. by mejrs · Pull Request #163508 · rust-lang/rust

mejrs · 2026-09-29T22:50:26Z

Moves/improves rustc_on_unimplemented's docs from the dev guide to the compiler, then in the dev guide adds links to it and other relevant diagnostic/lint attributes

Rendered:

rustbot · 2026-09-29T22:50:30Z

The rustc-dev-guide subtree was changed. If your future PRs only touch the subtree, consider submitting them directly to rust-lang/rustc-dev-guide, which is where the document is primarily maintained (and has faster CI).

cc @BoxyUwU, @tshepang

Some changes occurred in compiler/rustc_attr_ir

cc @jdonszelmann, @JonathanBrouwer

rustbot · 2026-09-29T22:50:32Z

r? @TaKO8Ki

rustbot has assigned @TaKO8Ki.
They will have a look at your PR within the next two weeks and either review your PR or reassign to another reviewer.

Use r? to explicitly pick a reviewer

Why was this reviewer chosen?

The reviewer was selected based on:

Owners of files modified in this PR: compiler
compiler expanded to 77 candidates
Random selection from 17 candidates

rustbot · 2026-10-01T09:44:01Z

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.

BoxyUwU

waht's the difference between diagnostic::on_unimplemented and rustc_on_unimplemented?

View changes since this review

BoxyUwU · 2026-10-06T10:17:55Z

 /// [#160045]:https://github.com/rust-lang/rust/issues/160045 "`iter::Rev`'s `TrustedLen` impl is unsound with trait objects"
 const _: () = ();
+
+#[doc(attribute = "rustc_on_unimplemented")]


what does doc(attribute do?

like how we document keywords and builtins, this is what makes the docs show up like that

BoxyUwU · 2026-10-06T10:20:07Z

r? me
r=me after rebasing :3

mejrs · 2026-10-06T19:46:05Z

waht's the difference between diagnostic::on_unimplemented and rustc_on_unimplemented?

rustc_on_unimplemented is diagnostic::on_unimplemented, but more, the diagnostic attr only has message/label/note and only some of the formatting options

mejrs · 2026-10-06T21:31:37Z

@bors r=boxyuwu

rust-bors · 2026-10-06T21:31:40Z

📌 Commit ea97485 has been approved by boxyuwu

It is now in the queue for this repository.

… r=boxyuwu Document the `rustc_on_unimplemented` attribute. Moves/improves `rustc_on_unimplemented`'s docs from the dev guide to the compiler, then in the dev guide adds links to it and other relevant diagnostic/lint attributes Rendered: <img width="974" height="1053" alt="image" src="https://github.com/user-attachments/assets/8042f4a2-e9fe-4f4c-b5d6-1fff1bad8997" /> <img width="958" height="1207" alt="image" src="https://github.com/user-attachments/assets/c400aed7-4bac-44ac-8b86-7e155da4afac" /> <img width="942" height="764" alt="image" src="https://github.com/user-attachments/assets/103c7496-410c-4f24-9cdf-0602d4de293d" /> <img width="968" height="986" alt="image" src="https://github.com/user-attachments/assets/8ed52e6c-638d-4927-8da2-f515c11d6bb9" /> <img width="962" height="1259" alt="image" src="https://github.com/user-attachments/assets/245ad71b-1c75-4d20-b139-8b6e49a1fb7d" />

…uwer Rollup of 25 pull requests Successful merges: - #163090 (Run LLDB debuginfo tests on `x86_64-pc-windows-msvc` in CI) - #163806 (even more `tests/crashes` migration for `-Znext-solver`) - #162156 (add IBM f128 type) - #163508 (Document the `rustc_on_unimplemented` attribute.) - #163794 (Use `target_family = "wasm"` instead of `target_arch = "wasm32"`) - #163863 (use the type name instead of `Self` in constructor paths again) - #163864 (Remove CLAUDE.md) - #163877 (Add regression test for duplicated rustdoc search results between std and core) - #163916 (Shrink `PartialRes` and its alignment) - #149753 (On name resolution error in parameter list, suggest possible `const` typo and avoid unnecessary second error) - #152557 (Oneshot `is_ready`) - #157273 (Stabilize `optimize` attribute) - #162000 (peel_transparent_wrappers only works on non-1ZST) - #163257 (abby DSL: sanity checks on forall where clauses) - #163343 (`unit` and `[1 x unit]` layouts are incompatible on big-endian targets) - #163348 (perf:cache FFI safety results in improper_ctypes lint) - #163768 (Move more `rustdoc-html` tests in the right location) - #163778 (check is_indirect_first_projection when replacing in RefProp) - #163789 (cg_llvm: Avoid `as_c_char_ptr` in several places) - #163807 (Add `has_reliable_f16b` for Arm) - #163809 (Switch TLS implementation for wasi and bump SDK version to 34) - #163826 (Update books) - #163849 (ci: update to PowerShell 7.6.6) - #163869 (INSTALL.md: use UCRT64 instead of MINGW64 in MSYS2 section) - #163870 (Add if-installed:auto:spellcheck to pre-push script)

… r=boxyuwu Document the `rustc_on_unimplemented` attribute. Moves/improves `rustc_on_unimplemented`'s docs from the dev guide to the compiler, then in the dev guide adds links to it and other relevant diagnostic/lint attributes Rendered: <img width="974" height="1053" alt="image" src="https://github.com/user-attachments/assets/8042f4a2-e9fe-4f4c-b5d6-1fff1bad8997" /> <img width="958" height="1207" alt="image" src="https://github.com/user-attachments/assets/c400aed7-4bac-44ac-8b86-7e155da4afac" /> <img width="942" height="764" alt="image" src="https://github.com/user-attachments/assets/103c7496-410c-4f24-9cdf-0602d4de293d" /> <img width="968" height="986" alt="image" src="https://github.com/user-attachments/assets/8ed52e6c-638d-4927-8da2-f515c11d6bb9" /> <img width="962" height="1259" alt="image" src="https://github.com/user-attachments/assets/245ad71b-1c75-4d20-b139-8b6e49a1fb7d" />

…uwer Rollup of 24 pull requests Successful merges: - #163090 (Run LLDB debuginfo tests on `x86_64-pc-windows-msvc` in CI) - #163806 (even more `tests/crashes` migration for `-Znext-solver`) - #163508 (Document the `rustc_on_unimplemented` attribute.) - #163794 (Use `target_family = "wasm"` instead of `target_arch = "wasm32"`) - #163863 (use the type name instead of `Self` in constructor paths again) - #163864 (Remove CLAUDE.md) - #163877 (Add regression test for duplicated rustdoc search results between std and core) - #163916 (Shrink `PartialRes` and its alignment) - #149753 (On name resolution error in parameter list, suggest possible `const` typo and avoid unnecessary second error) - #152557 (Oneshot `is_ready`) - #157273 (Stabilize `optimize` attribute) - #162000 (peel_transparent_wrappers only works on non-1ZST) - #163257 (abby DSL: sanity checks on forall where clauses) - #163343 (`unit` and `[1 x unit]` layouts are incompatible on big-endian targets) - #163348 (perf:cache FFI safety results in improper_ctypes lint) - #163768 (Move more `rustdoc-html` tests in the right location) - #163778 (check is_indirect_first_projection when replacing in RefProp) - #163789 (cg_llvm: Avoid `as_c_char_ptr` in several places) - #163807 (Add `has_reliable_f16b` for Arm) - #163809 (Switch TLS implementation for wasi and bump SDK version to 34) - #163826 (Update books) - #163849 (ci: update to PowerShell 7.6.6) - #163869 (INSTALL.md: use UCRT64 instead of MINGW64 in MSYS2 section) - #163870 (Add if-installed:auto:spellcheck to pre-push script)

…uwer Rollup of 23 pull requests Successful merges: - #163090 (Run LLDB debuginfo tests on `x86_64-pc-windows-msvc` in CI) - #163806 (even more `tests/crashes` migration for `-Znext-solver`) - #163508 (Document the `rustc_on_unimplemented` attribute.) - #163794 (Use `target_family = "wasm"` instead of `target_arch = "wasm32"`) - #163863 (use the type name instead of `Self` in constructor paths again) - #163864 (Remove CLAUDE.md) - #163877 (Add regression test for duplicated rustdoc search results between std and core) - #163916 (Shrink `PartialRes` and its alignment) - #149753 (On name resolution error in parameter list, suggest possible `const` typo and avoid unnecessary second error) - #152557 (Oneshot `is_ready`) - #157273 (Stabilize `optimize` attribute) - #162000 (peel_transparent_wrappers only works on non-1ZST) - #163343 (`unit` and `[1 x unit]` layouts are incompatible on big-endian targets) - #163348 (perf:cache FFI safety results in improper_ctypes lint) - #163768 (Move more `rustdoc-html` tests in the right location) - #163778 (check is_indirect_first_projection when replacing in RefProp) - #163789 (cg_llvm: Avoid `as_c_char_ptr` in several places) - #163807 (Add `has_reliable_f16b` for Arm) - #163809 (Switch TLS implementation for wasi and bump SDK version to 34) - #163826 (Update books) - #163849 (ci: update to PowerShell 7.6.6) - #163869 (INSTALL.md: use UCRT64 instead of MINGW64 in MSYS2 section) - #163870 (Add if-installed:auto:spellcheck to pre-push script)

Rollup merge of #163508 - mejrs:rustc_on_unimplemented_docs, r=boxyuwu Document the `rustc_on_unimplemented` attribute. Moves/improves `rustc_on_unimplemented`'s docs from the dev guide to the compiler, then in the dev guide adds links to it and other relevant diagnostic/lint attributes Rendered: <img width="974" height="1053" alt="image" src="https://github.com/user-attachments/assets/8042f4a2-e9fe-4f4c-b5d6-1fff1bad8997" /> <img width="958" height="1207" alt="image" src="https://github.com/user-attachments/assets/c400aed7-4bac-44ac-8b86-7e155da4afac" /> <img width="942" height="764" alt="image" src="https://github.com/user-attachments/assets/103c7496-410c-4f24-9cdf-0602d4de293d" /> <img width="968" height="986" alt="image" src="https://github.com/user-attachments/assets/8ed52e6c-638d-4927-8da2-f515c11d6bb9" /> <img width="962" height="1259" alt="image" src="https://github.com/user-attachments/assets/245ad71b-1c75-4d20-b139-8b6e49a1fb7d" />

rust-timer · 2026-10-08T06:13:53Z

Note

This PR was benchmarked as part of triage of its containing rollup: triage URL.

Finished benchmarking commit (0033ef0): comparison URL.

Overall result: ✅ improvements - no action needed

@rustbot label: -perf-regression

Instruction count

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.1%	[-0.3%, -0.1%]	4
Improvements ✅ (secondary)	-0.2%	[-0.5%, -0.1%]	15
All ❌✅ (primary)	-0.1%	[-0.3%, -0.1%]	4

Max RSS (memory usage)

Results (secondary -2.2%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.2%	[-2.2%, -2.2%]	1
All ❌✅ (primary)	-	-	0

Cycles

This perf run didn't have relevant results for this metric.

Binary size

This perf run didn't have relevant results for this metric.

Artifact size: 408.59 MiB -> 408.63 MiB (0.01%)

JonathanBrouwer · 2026-10-08T16:24:24Z

This is noise, all PRs in the rollup have the same results

rustbot assigned TaKO8Ki Sep 29, 2026

This comment has been minimized.

Sign in to view

mejrs force-pushed the rustc_on_unimplemented_docs branch from 05c9dc2 to c55c824 Compare October 1, 2026 09:43

This comment has been minimized.

Sign in to view

BoxyUwU reviewed Oct 6, 2026

View reviewed changes

rustbot assigned BoxyUwU and unassigned TaKO8Ki Oct 6, 2026

Document the rustc_on_unimplemented attribute.

ea97485

mejrs force-pushed the rustc_on_unimplemented_docs branch from c55c824 to ea97485 Compare October 6, 2026 19:47

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 6, 2026

JonathanBrouwer mentioned this pull request Oct 7, 2026

Rollup of 25 pull requests #163919

Closed

JonathanBrouwer mentioned this pull request Oct 7, 2026

Rollup of 24 pull requests #163934

Closed

JonathanBrouwer mentioned this pull request Oct 7, 2026

Rollup of 23 pull requests #163957

Merged

rust-bors Bot merged commit d4ec7d7 into rust-lang:main Oct 8, 2026
14 checks passed

rustbot added this to the 1.101.0 milestone Oct 8, 2026

github-actions Bot mentioned this pull request Oct 9, 2026

Toolchain upgrade to nightly-2026-10-09 flux-rs/flux#1811

Draft

Conversation

mejrs commented Sep 29, 2026

Uh oh!

rustbot commented Sep 29, 2026

Uh oh!

rustbot commented Sep 29, 2026

Uh oh!

This comment has been minimized.

rustbot commented Oct 1, 2026

Uh oh!

This comment has been minimized.

BoxyUwU left a comment • edited by rustbot Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

BoxyUwU Oct 6, 2026

Choose a reason for hiding this comment

Uh oh!

mejrs Oct 6, 2026

Choose a reason for hiding this comment

Uh oh!

BoxyUwU commented Oct 6, 2026

Uh oh!

mejrs commented Oct 6, 2026

Uh oh!

mejrs commented Oct 6, 2026

Uh oh!

rust-bors Bot commented Oct 6, 2026

Uh oh!

Uh oh!

rust-timer commented Oct 8, 2026

Overall result: ✅ improvements - no action needed

Instruction count

Max RSS (memory usage)

Cycles

Binary size

Uh oh!

JonathanBrouwer commented Oct 8, 2026

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

6 participants

BoxyUwU left a comment •

edited by rustbot

Loading