Introduce #[diagnostic::on_move(message)] #150935

rperier · 2026-01-10T18:09:26Z

This is a first proposal. I have deliberately kept it simpler than diagnostic::on_unimplemented.

Few questions/remarks:

Do I need to move the OnMoveDirective logic into a dedicated module perhaps ? let's say into compiler/rustc_borrowck/src/diagnostics/on_move.rs
No problems to depend on crates like rustc_ast from the borrowck ?
Notes are not supported yet. While message and label are very static , in the sense that they are emitted in the same way from the same place in the borrowck, it is not the case for the notes. It would make the code more complex. But, I can add support for notes if it does make sense.

Suggestions are welcomed !

rustbot · 2026-01-10T18:09:30Z

These commits modify the Cargo.lock file. Unintentional changes to Cargo.lock can be introduced when switching branches and rebasing PRs.

If this was unintentional then you should revert the changes before this PR is merged.
Otherwise, you can ignore this comment.

Some changes occurred in compiler/rustc_passes/src/check_attr.rs

cc @jdonszelmann

rustbot · 2026-01-10T18:09:32Z

r? @JonathanBrouwer

rustbot has assigned @JonathanBrouwer.
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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rperier · 2026-01-10T18:11:08Z

r? @estebank

compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs

mejrs · 2026-01-13T18:28:02Z

I'm currently working on migrating the existing diagnostic attribute infrastructure, can you do this PR after that? It's going to be quite a mess to resolve that conflict.

Is this meant to be only used by the standard library or also by users? If only by std, I think you should forego the attribute and instead check whether T implements UseCloned and recommend a clone (or .use if on nightly).

rperier · 2026-01-14T07:05:01Z

Yeah I can completly wait until you finished your work and do my PR after that, It was my intention to be honest . Resolving conflicts or rebasing is not an issue for me.

rustbot · 2026-01-21T19:15:46Z

Some changes occurred in compiler/rustc_attr_parsing

cc @jdonszelmann, @JonathanBrouwer

Changes to the size of AST and/or HIR nodes.

cc @nnethercote

Some changes occurred in compiler/rustc_hir/src/attrs

cc @jdonszelmann, @JonathanBrouwer

rperier · 2026-01-21T19:16:23Z

I have reworked my code and moved everything to rustc_attr_parsing and rustc_hir/src/attrs/data_structures.rs. Few questions/remarks remain:

Perhaps, It would make sense to allow this diagnostic attribute to be used only for nightly, for now, what do you think ?
I can wait until some refactoring for attributes are merged upstream, and wait for my PR being merged after that, if it helps, no problems for me

tests/ui/stats/input-stats.stderr

This might be helpful for smart pointers to explains why they aren't Copy and what to do instead or just to let the user know that .clone() is very cheap and can be called without a performance penalty.

rustbot · 2026-01-22T19:23:24Z

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.

rperier · 2026-01-22T19:23:55Z

Rebased onto main, I have also fixed the size of AttributeKind::OnMove

mejrs · 2026-01-22T23:12:30Z

tests/ui/diagnostic_namespace/on_move/report_warning_on_malformed_options.rs

+#[diagnostic::on_move(
+    message = Foo,
+    //~^ERROR expected a literal (`1u8`, `1.0f32`, `"string"`, etc.) here, found expression
+    label = "Bar",
+)]
+#[diagnostic::on_move(
+    message = "Foo"
+    label = "Bar",
+    //~^ERROR expected `,`, found `label`
+)]


This can't be an error; this must be a lint. But you will need #151516 to do so.

mejrs · 2026-01-22T23:52:27Z

compiler/rustc_hir/src/attrs/data_structures.rs

+#[derive(Clone, Debug, Encodable, Decodable, HashStable_Generic, PrintAttribute)]
+pub struct OnMoveAttrArg {
+    pub symbol: Symbol,
+    pub format_ranges: ThinVec<(usize, usize)>,
+}


I plan on moving a fair bit of the format and string stuff that on_unimplemented uses into rustc_hir; you should be able to reuse some of that in this PR :)

Sure, I will do

rustbot added A-attributes Area: Attributes (`#[…]`, `#![…]`) S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Jan 10, 2026

rustbot assigned JonathanBrouwer Jan 10, 2026

rustbot added the T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. label Jan 10, 2026

rustbot assigned estebank and unassigned JonathanBrouwer Jan 10, 2026

fmease reviewed Jan 10, 2026

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JonathanBrouwer mentioned this pull request Jan 13, 2026

Port diagnostic::do_not_recommend to new attr parsing #151056

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rperier force-pushed the provide_diagnostic_on_move_for_smart_pointers branch from 9a0162d to 8071a7d Compare January 21, 2026 19:15

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rperier force-pushed the provide_diagnostic_on_move_for_smart_pointers branch from 8071a7d to 09506a4 Compare January 21, 2026 19:26

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Introduce #[diagnostic::on_move]

829651a

This might be helpful for smart pointers to explains why they aren't Copy and what to do instead or just to let the user know that .clone() is very cheap and can be called without a performance penalty.

rperier force-pushed the provide_diagnostic_on_move_for_smart_pointers branch from 09506a4 to 829651a Compare January 22, 2026 19:23

mejrs reviewed Jan 22, 2026

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Introduce #[diagnostic::on_move(message)] #150935

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Introduce #[diagnostic::on_move(message)] #150935

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