Suggest `impl Trait` return type when incorrectly using a generic return type #89892

Noratrieb · 2021-10-14T20:02:34Z

When there is a type mismatch error and the return type is generic, and that generic parameter is not used in the function parameters, suggest replacing that generic with the impl Trait syntax.

r? @estebank

rust-highfive · 2021-10-14T20:02:37Z

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @estebank (or someone else) soon.

Please see the contribution instructions for more information.

Noratrieb · 2021-10-14T20:04:54Z

This is my first PR, so I hope I did everything correctly!

src/test/ui/return/return-impl-trait.stderr

C0RR1T · 2021-10-15T06:03:04Z

As a new Rust programmer, I really want this feature

Noratrieb · 2021-10-19T06:46:44Z

I'm done with the changes, you can review it again if you have time

Noratrieb · 2021-10-26T20:24:15Z

What's the status on this PR? @estebank

jyn514

This is a neat idea :) it looks in pretty good shape, just a few suggestions.

compiler/rustc_typeck/src/check/fn_ctxt/suggestions.rs

src/test/ui/return/return-impl-trait.rs

compiler/rustc_typeck/src/check/fn_ctxt/suggestions.rs

Noratrieb · 2021-11-10T18:57:45Z

I added the notes, also added // run-rustfix to test the suggestions, and squashed all commits into one, since the change is pretty small.

jyn514 · 2021-11-10T21:20:30Z

@Nilstrieb you need to add the .fixed file I think - you might be able to generate it with --bless --run-rustfix.

Noratrieb · 2021-11-10T21:33:53Z

It does have the fixed code, but the problem is that this fixed code is not compiling successfully because of bad_echo. How can I allow this?

jyn514 · 2021-11-10T21:34:40Z

@Nilstrieb I'd suggest making the rustfix test separate from the rest of the tests.

Noratrieb · 2021-11-10T21:41:39Z

I've squashed it again since this is hopefully the last change

compiler/rustc_typeck/src/check/fn_ctxt/suggestions.rs

src/test/ui/return/return-impl-trait.rs

compiler/rustc_typeck/src/check/fn_ctxt/suggestions.rs

Noratrieb · 2021-12-15T09:14:47Z

Thank you for your review, I'll implement this next week!

compiler/rustc_typeck/src/check/fn_ctxt/suggestions.rs

jackh726 · 2022-01-09T22:05:58Z

r? @jackh726

jackh726

Sorry, more reviews.

Also, can you squash the commits?

compiler/rustc_typeck/src/check/fn_ctxt/suggestions.rs

jackh726 · 2022-01-14T23:14:39Z

compiler/rustc_typeck/src/check/fn_ctxt/suggestions.rs

+                _ => ty.contains(expected, self.tcx),
+            });
+
+        if any_predicate_contains_expected_ty {


This doesn't necessarily cover cases where T appears in the bounds, right? So like Option<()>: Trait<T>

Hmm, I wasn't able to figure out how I'd do that. Do you have an idea?

Maybe instead of making contains be on Ty, you can make it a visitor. Then just visit both the ty and bounds.

For the contains I was able to use the visitor on Ty. How should I visit the PolyTraitRef in the bounds? I found hir::intravisit but wasn't able to find a good way to use it.

Sorry, thought I replied to this before.

There is a hir visitor: https://doc.rust-lang.org/stable/nightly-rustc/rustc_hir/intravisit/trait.Visitor.html

Alternatively, you could lower the trait ref.

I'm also fine it you just want to add this as a test case with a FIXME. This is just suggestion after all and doesn't have to he "perfect"

I'll just leave a fixme in a test 👍

compiler/rustc_typeck/src/check/fn_ctxt/suggestions.rs

Noratrieb · 2022-01-15T15:31:03Z

I'll squash it once it's done.

bors · 2022-01-18T14:12:50Z

☔ The latest upstream changes (presumably #87648) made this pull request unmergeable. Please resolve the merge conflicts.

Noratrieb · 2022-01-31T19:47:27Z

Finally did it, I wanted to have TyS::contains as a separate commit at first, but after a little git accident I decided to just squash them anyways

bors · 2022-02-15T14:43:29Z

☔ The latest upstream changes (presumably #93148) made this pull request unmergeable. Please resolve the merge conflicts.

jackh726 · 2022-02-15T16:51:04Z

Sorry I didn't get to this before; r=me here after rebase

jackh726 · 2022-02-15T16:51:27Z

@bors delegate+

(just do r=jackh726)

bors · 2022-02-15T16:51:29Z

✌️ @Nilstrieb can now approve this pull request

Address rust-lang#85991 Suggest the `impl Trait` return type syntax if the user tried to return a generic parameter and we get a type mismatch The suggestion is not emitted if the param appears in the function parameters, and only get the bounds that actually involve `T: ` directly It also checks whether the generic param is contained in any where bound (where it isn't the self type), and if one is found (like `Option<T>: Send`), it is not suggested. This also adds `TyS::contains`, which recursively vistits the type and looks if the other type is contained anywhere

Noratrieb · 2022-02-18T20:33:35Z

@bors r=jackh726

bors · 2022-02-18T20:33:36Z

📌 Commit 4bed748 has been approved by jackh726

…askrgr Rollup of 10 pull requests Successful merges: - rust-lang#89892 (Suggest `impl Trait` return type when incorrectly using a generic return type) - rust-lang#91675 (Add MemTagSanitizer Support) - rust-lang#92806 (Add more information to `impl Trait` error) - rust-lang#93497 (Pass `--test` flag through rustdoc to rustc so `#[test]` functions can be scraped) - rust-lang#93814 (mips64-openwrt-linux-musl: correct soft-foat) - rust-lang#93847 (kmc-solid: Use the filesystem thread-safety wrapper) - rust-lang#93877 (asm: Allow the use of r8-r14 as clobbers on Thumb1) - rust-lang#93892 (Only mark projection as ambiguous if GAT substs are constrained) - rust-lang#93915 (Implement --check-cfg option (RFC 3013), take 2) - rust-lang#93953 (Add the `known-bug` test directive, use it, and do some cleanup) Failed merges: r? `@ghost` `@rustbot` modify labels: rollup

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matthiaskrgr mentioned this pull request Feb 18, 2022

Rollup of 10 pull requests #94134

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jackh726 mentioned this pull request Feb 19, 2022

Suggest using -> impl Trait when returning type parameter -> T where T: Trait #85991

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Noratrieb deleted the suggest-return-impl-trait branch February 19, 2022 09:50

Suggest impl Trait return type when incorrectly using a generic return type #89892

Suggest impl Trait return type when incorrectly using a generic return type #89892

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Suggest `impl Trait` return type when incorrectly using a generic return type #89892

Suggest `impl Trait` return type when incorrectly using a generic return type #89892

Noratrieb commented Nov 10, 2021 •

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