Lint against `Iterator::map` receiving a callable that returns `()` #107890

obeis · 2023-02-10T16:27:03Z

Close #106991

rustbot · 2023-02-10T16:27:11Z

r? @cjgillot

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rustbot · 2023-02-10T16:27:15Z

rustc_error_messages was changed

cc @davidtwco, @compiler-errors, @JohnTitor, @TaKO8Ki

compiler/rustc_lint/src/map_unit_fn.rs

tests/ui/lint/unused-braces-while-let-with-mutable-value.rs

cjgillot · 2023-02-10T21:54:58Z

Also, I wonder if we should just make Iterator::map a #[must_use] method, and integrate the suggestion into the must-use lint?

cjgillot

I still have my question about #[must_use].

compiler/rustc_lint/src/map_unit_fn.rs

scottmcm · 2023-02-14T07:15:42Z

If this were to go in must_use, it wouldn't go on the function, but as an update to

rust/library/core/src/iter/adapters/map.rs

Line 58 in c3c6d73

#[must_use = "iterators are lazy and do nothing unless consumed"]

rustbot · 2023-02-16T20:18:28Z

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obeis · 2023-02-17T11:48:21Z

@rustbot ready

cjgillot · 2023-02-18T11:19:07Z

Could you add a test that the example in #106991 (comment) diagnoses both the type error and the lint?

There is a redundancy between the unused_must_use message (see https://play.rust-lang.org/?version=nightly&mode=debug&edition=2021&gist=e7043cad0b9bfadca3718b3843ed725f) and this lint. Is there any way to avoid this?

bors · 2023-02-22T19:11:54Z

☔ The latest upstream changes (presumably #103042) made this pull request unmergeable. Please resolve the merge conflicts.

cjgillot · 2023-02-25T16:37:57Z

@bors r+

bors · 2023-02-25T16:37:59Z

📌 Commit 99344a8 has been approved by cjgillot

It is now in the queue for this repository.

Lint against `Iterator::map` receiving a callable that returns `()` Close rust-lang#106991

…iaskrgr Rollup of 8 pull requests Successful merges: - rust-lang#107062 (Do some cleanup of doc/index.md) - rust-lang#107890 (Lint against `Iterator::map` receiving a callable that returns `()`) - rust-lang#108431 (Add regression test for rust-lang#107918) - rust-lang#108432 (test: drop unused deps) - rust-lang#108436 (make "proc macro panicked" translatable) - rust-lang#108444 (docs/test: add UI test and docs for `E0476`) - rust-lang#108449 (Do not lint ineffective unstable trait impl for unresolved trait) - rust-lang#108456 (Complete migrating `ast_passes` to derive diagnostics) Failed merges: r? `@ghost` `@rustbot` modify labels: rollup

estebank · 2023-02-27T17:04:39Z

tests/ui/lint/issue-106991.stderr

+error[E0271]: expected `foo` to be a fn item that returns `i32`, but it returns `()`
+  --> $DIR/issue-106991.rs:5:13
+   |
+LL | fn bar() -> impl Iterator<Item = i32> {
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^ expected `()`, found `i32`
+   |
+   = note: required for `Map<std::slice::IterMut<'_, Vec<u8>>, for<'a> fn(&'a mut Vec<u8>) {foo}>` to implement `Iterator`


This is a case where we should be doing more than we are now. A similar explanation to the lint's would be necessary to properly convey to users what the problem was. At least pointing at the return expression with nothing else would be an improvement.

rustbot assigned cjgillot Feb 10, 2023

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obeis added 5 commits February 23, 2023 13:57

Add lint against Iterator::map receiving a callable that returns ()

a914f37

Add ui test for map_unit_fn lint

ddd7d10

Emit map_unit_fn lint in closure case

a87443a

Add ui test for map_unit_fn lint in closure case

b93d545

Add ui test for E0271 error

99344a8

obeis force-pushed the mapping-to-unit branch from a97f486 to 99344a8 Compare February 23, 2023 11:03

bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Feb 25, 2023

compiler-errors added a commit to compiler-errors/rust that referenced this pull request Feb 25, 2023

Rollup merge of rust-lang#107890 - obeis:mapping-to-unit, r=cjgillot

9960a3e

Lint against `Iterator::map` receiving a callable that returns `()` Close rust-lang#106991

compiler-errors mentioned this pull request Feb 25, 2023

Rollup of 9 pull requests #108465

Closed

compiler-errors added a commit to compiler-errors/rust that referenced this pull request Feb 25, 2023

Rollup merge of rust-lang#107890 - obeis:mapping-to-unit, r=cjgillot

ec961db

Lint against `Iterator::map` receiving a callable that returns `()` Close rust-lang#106991

compiler-errors mentioned this pull request Feb 25, 2023

Rollup of 9 pull requests #108466

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matthiaskrgr mentioned this pull request Feb 25, 2023

Rollup of 8 pull requests #108473

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bors merged commit fa10a21 into rust-lang:master Feb 26, 2023

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compiler-errors mentioned this pull request Mar 14, 2023

ICE: Err on value: "core", map_unit_fn.rs #109152

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Lint against `Iterator::map` receiving a callable that returns `()` #107890

Lint against `Iterator::map` receiving a callable that returns `()` #107890

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Lint against Iterator::map receiving a callable that returns () #107890

Lint against Iterator::map receiving a callable that returns () #107890

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Lint against `Iterator::map` receiving a callable that returns `()` #107890

Lint against `Iterator::map` receiving a callable that returns `()` #107890

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