Add a diagnostic attribute for special casing const bound errors for non-const impls #148641

oli-obk · 2025-11-07T10:39:43Z

Somewhat of a follow-up to #144194

My plan is to resolve

https://github.com/rust-lang/rust/blob/f4e19c68786211f3c3cf2593442629599678800a/compiler/rustc_hir_typeck/src/callee.rs#L907-913

but doing so without being able to mark impls the way I do in this PR wrould cause all nice diagnostics about for loops and pointer comparisons to just be a *const u32 does not implement [const] PartialEq errors.

rustbot · 2025-11-07T10:39:46Z

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

cc @jdonszelmann

rustbot · 2025-11-07T10:39:48Z

r? @jackh726

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estebank · 2025-11-07T17:27:52Z

compiler/rustc_passes/src/check_attr.rs

+    /// Checks if `#[diagnostic::on_const]` is applied to a trait impl
+    fn check_diagnostic_on_const(&self, attr_span: Span, hir_id: HirId, target: Target) {
+        if !matches!(target, Target::Impl { of_trait: true }) {
+            self.tcx.emit_node_span_lint(
+                MISPLACED_DIAGNOSTIC_ATTRIBUTES,
+                hir_id,
+                attr_span,
+                DiagnosticOnConstOnlyForTraitImpls,
+            );
+        }
+    }


Should we also check that the impl is not const? Otherwise the annotation is fully inert in that case, right?

tests/ui/feature-gates/feature-gate-diagnostic-on-const.rs

rustbot · 2025-11-21T11:28:11Z

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.

jackh726 · 2025-11-26T01:59:25Z

r=me after rebase

…non-const impls

oli-obk · 2025-11-26T21:02:51Z

@bors r=jackh726

bors · 2025-11-26T21:02:54Z

📌 Commit 9218298 has been approved by jackh726

It is now in the queue for this repository.

Add a diagnostic attribute for special casing const bound errors for non-const impls Somewhat of a follow-up to rust-lang#144194 My plan is to resolve https://github.com/rust-lang/rust/blob/f4e19c68786211f3c3cf2593442629599678800a/compiler/rustc_hir_typeck/src/callee.rs#L907-913 but doing so without being able to mark impls the way I do in this PR wrould cause all nice diagnostics about for loops and pointer comparisons to just be a `*const u32 does not implement [const] PartialEq` errors.

Rollup of 19 pull requests Successful merges: - #148048 (Stabilize `maybe_uninit_write_slice`) - #148641 (Add a diagnostic attribute for special casing const bound errors for non-const impls) - #148765 (std: split up the `thread` module) - #149074 (Add Command::get_env_clear) - #149097 (num: Implement `uint_gather_scatter_bits` feature for unsigned integers) - #149131 (optimize `slice::Iter::next_chunk`) - #149190 (Forbid `CHECK: br` and `CHECK-NOT: br` in codegen tests (suggest `br {{.*}}` instead)) - #149239 (clarify float min/max behavios for NaNs and signed zeros) - #149243 (Fix typo and clarify bootstrap change tracker entry) - #149270 (implement `Iterator::{exactly_one, collect_array}`) - #149295 (Suggest _bytes versions of endian-converting methods) - #149301 (Motor OS: make decode_error_kind more comprehensive) - #149306 (bootstrap: Miri now handles jemalloc like everything else) - #149325 (rustdoc: add regression test for #140968) - #149332 (fix rustdoc search says “Consider searching for "null" instead.” #149324) - #149349 (Fix typo in comment.) - #149353 (Tidying up UI tests [3/N]) - #149355 (Document that `build.description` affects symbol mangling and crate IDs) - #149360 (Enable CI download for windows-gnullvm) r? `@ghost` `@rustbot` modify labels: rollup

rustbot assigned jackh726 Nov 7, 2025