feat(rustc_hir_typeck): suggest impl Fn return for capturing closures#159594
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| error[E0308]: mismatched types | ||
| --> $DIR/suggest-impl-fn-return-for-capturing-closure.rs:43:5 | ||
| | | ||
| LL | fn one_arg_ref(a: i32) -> fn(&i32) -> &i32 { | ||
| | ---------------- expected `for<'a> fn(&'a i32) -> &'a i32` because of return type | ||
| LL | / |x| { | ||
| LL | | | ||
| LL | | println!("{}", a); | ||
| LL | | x | ||
| LL | | } | ||
| | |_____^ expected fn pointer, found closure | ||
| | | ||
| = note: expected fn pointer `for<'a> fn(&'a i32) -> &'a i32` | ||
| found closure `{closure@$DIR/suggest-impl-fn-return-for-capturing-closure.rs:43:5: 43:8}` | ||
| note: closures can only be coerced to `fn` types if they do not capture any variables | ||
| --> $DIR/suggest-impl-fn-return-for-capturing-closure.rs:45:24 | ||
| | | ||
| LL | println!("{}", a); | ||
| | ^ `a` captured here | ||
| help: change the return type to return a type-erased closure instead | ||
| | | ||
| LL - fn one_arg_ref(a: i32) -> fn(&i32) -> &i32 { | ||
| LL + fn one_arg_ref(a: i32) -> impl Fn(&'_ i32) -> &'_ i32 { | ||
| | |
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In this case I think it would make sense to suggest impl for<'a> Fn(&'a i32) -> &'_ i32.
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@bors r+ Let's merge, but leave the ticket open to account for more accurate lifetime handling, as well as detecting if it would need to be |
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…uwer Rollup of 18 pull requests Successful merges: - #159600 (`rust-analyzer` subtree update) - #158046 (proc_macro: preserve file module spans for inner attrs) - #159000 (Small cleanups to the incr comp session code) - #159189 (Account for type alias projections in E0308 "expected/found" shortening logic) - #159449 (Enable single Location to issue multiple borrows) - #159544 (Suggest valid command-line crate names) - #159587 (Improve `AttrItem::span`) - #159594 (feat(rustc_hir_typeck): suggest `impl Fn` return for capturing closures) - #159597 (std: use `arc4random_buf` from libc) - #159599 (Resolver: Record at least 1 ambiguous trait if main decl is not a trait.) - #158061 (Make `pin!()` more foolproof.) - #159460 (Do not mark unnormalized const aliases as rigid when normalizing param env) - #159529 (Add regression test for nested replacement ranges in `collect_tokens`) - #159571 (Remove unused bundled library lookup for the local crate) - #159585 (Minor `TokenStream` improvements) - #159586 (Separate `InterpCx` usage by `ConstAnalysis` phases) - #159602 (Remove `ItemLike`) - #159603 (Clarify `push_stream`/`push_tree`) Failed merges: - #159590 (Remove some dead code)
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Adresses #159481