Fix suggestion span for `?Sized` when param type has default #120915

OdenShirataki · 2024-02-11T06:05:59Z

Fixes #120878

Diagnostic suggests adding : ?Sized in an incorrect place if a type parameter default is present

rustbot · 2024-02-11T06:06:06Z

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fmease

Please address my suggestions, then we are good to go unless you'd also like to fix the other bug I just found.

fmease · 2024-02-11T20:00:21Z

tests/ui/traits/issue-120878.rs

Thanks for adding a test! Could you move it into tests/ui/trait-bounds/ though? I think that'd be a better fit. I would also rename to something more descriptive like suggest-maybe-sized-bound.rs and add the issue number as a comment // issue: 120878.

Note that there already exists trait-bounds/unsized-bound.rs but that one's more about removing ?Sized bounds rather than adding them, so I wouldn't extend it.

I noticed that the following code also leads to an incorrect suggestion although that very likely hits a different code path:

trait Trait { type P<X>; } impl Trait for () { type P<X> = [u8]; }

trait Trait { type P: ?Sized<X>; } ++++++++

If you have time & interest in fixing this, too, while you're at it, go for it (and just amend the existing test file)!

Thank you for the review and for suggesting interesting assignments.

I think I can fix it, so I'll give it a try.

when param type has default and type in trait is generic.

fmease · 2024-02-13T23:55:17Z

compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs

@@ -3054,7 +3054,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                            let (span, separator) = if let [.., last] = bounds {
                                (last.span().shrink_to_hi(), " +")
                            } else {
-                                (ident.span.shrink_to_hi(), ":")
+                                (generics.span.shrink_to_hi(), ":")


Right, and if there are no generic params, this is still correct since the span will be a zero-sized span located directly after the ident 👍

fmease · 2024-02-13T23:55:57Z

Great, thanks a lot!
@bors r+ rollup

bors · 2024-02-13T23:56:00Z

📌 Commit 4ac90e2 has been approved by fmease

It is now in the queue for this repository.

Rollup of 13 pull requests Successful merges: - rust-lang#116387 (Additional doc links and explanation of `Wake`.) - rust-lang#118738 (Netbsd10 update) - rust-lang#118890 (Clarify the lifetimes of allocations returned by the `Allocator` trait) - rust-lang#120498 (Uplift `TypeVisitableExt` into `rustc_type_ir`) - rust-lang#120530 (Be less confident when `dyn` suggestion is not checked for object safety) - rust-lang#120915 (Fix suggestion span for `?Sized` when param type has default) - rust-lang#121015 (Optimize `delayed_bug` handling.) - rust-lang#121024 (implement `Default` for `AsciiChar`) - rust-lang#121039 (Correctly compute adjustment casts in GVN) - rust-lang#121045 (Fix two UI tests with incorrect directive / invalid revision) - rust-lang#121049 (Do not point at `#[allow(_)]` as the reason for compat lint triggering) - rust-lang#121071 (Use fewer delayed bugs.) - rust-lang#121073 (Fix typos in `OneLock` doc) r? `@ghost` `@rustbot` modify labels: rollup

Rollup merge of rust-lang#120915 - OdenShirataki:master, r=fmease Fix suggestion span for `?Sized` when param type has default Fixes rust-lang#120878 Diagnostic suggests adding `: ?Sized` in an incorrect place if a type parameter default is present r? `@fmease`

rustbot assigned fmease Feb 11, 2024

rustbot added 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 Feb 11, 2024