Correctly check `never_type` feature gating #120552

GuillaumeGomez · 2024-02-01T13:58:54Z

Fixes #120542.

The feature wasn't tested on return type of a generic function type, so it got under the radar in #120316.

compiler-errors

Can you check if this also works for RPIT? Or dyn Fn() -> !?

compiler-errors · 2024-02-01T15:32:33Z

Also, instead of keeping this "in generics" state as part of the visitor, please just modify this line to check for ! manually, and leave a comment saying "in generic args, we don't allow -> !" or something:

https://github.com/rust-lang/rust/pull/120316/files#diff-90854f27d73f89fc2997be31fa36f58cb9af532d1387ac39751134afdd2ff8e2R505

compiler-errors · 2024-02-01T15:40:31Z

This will also likely require a beta backport depending on the timing of when this lands. I'll nominate it pre-emptively so we don't forget. This should be backported to 1.77, so if this lands on 1.77 then we're good.

GuillaumeGomez · 2024-02-01T15:56:52Z

Also, instead of keeping this "in generics" state as part of the visitor, please just modify this line to check for ! manually, and leave a comment saying "in generic args, we don't allow -> !" or something:

https://github.com/rust-lang/rust/pull/120316/files#diff-90854f27d73f89fc2997be31fa36f58cb9af532d1387ac39751134afdd2ff8e2R505

Except this is the "default" implementation. It should call the visitor method and not the walk_ one. That's what my PR fixed originally. The problem here lies in the implementation of PostExpansionVisitor.

compiler-errors · 2024-02-01T16:01:48Z

Yes, I understand clearly what the problem is. There's a discrepancy between what hir::RetTy::Return should do when it's exactly a ! type between fn decl/fn ptr position, and bound position.

I don't understand what point you're trying to make here though -- there's still no reason to introduce is_in_generics here, and the fix can be a lot more localized.

For the record, the approach that you've taken also breaks this code which compiles on stable:

trait X<const N: i32> {}

fn hello<T: X<{ fn hello() -> ! { loop {} } 1 }>>() {}

fn main() {}

GuillaumeGomez · 2024-02-01T16:05:47Z

Then I misunderstood what you meant. I understood that you said to revert the change on this line and to add a code comment. However, this would not only impact PostExpansionVisitor but also all types implementing this visitor, which seems wrong to me. What were you suggesting instead?

compiler-errors · 2024-02-01T16:05:52Z

Actually, that's not the right line that I suggested anyways. Just modify the visit_generic_args impl in the specific feature gate detection walker to check for Parenthesized generics, and manually look for RetTy::Return with a Never type. If you don't want to do this, I can put up a PR myself.

The manual tracking of a boolean in a walker imo is an anti-pattern, because it's very easy to get wrong with nested items and other AST nodes.

GuillaumeGomez · 2024-02-01T16:07:20Z

No I'm fine with doing it. Just didn't understand what you meant.

GuillaumeGomez · 2024-02-01T16:35:50Z

Applied your suggestions. Added more ui tests and also the case which should work.

compiler-errors

r=me after applying changes

compiler-errors · 2024-02-01T17:14:43Z

compiler/rustc_ast_passes/src/feature_gate.rs

@@ -362,6 +362,16 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
        }
    }

+    fn visit_generic_args(&mut self, args: &'a ast::GenericArgs) {
+        if let ast::GenericArgs::Parenthesized(generic_args) = args


pls leave a comment explaining why this is being checked here

Good point!

compiler-errors · 2024-02-01T17:15:40Z

tests/ui/never_type/const-context.rs

+
+trait X<const N: i32> {}
+
+fn hello<T: X<{ fn hello() -> ! { loop {} } 1 }>>() {}


could you rename this? it's not really that it's in a "const context", it's more about it being in a nested item.

Maybe never-type-in-nested-fn-decl

GuillaumeGomez · 2024-02-01T19:13:31Z

@bors r=compiler-errors

bors · 2024-02-01T19:13:35Z

📌 Commit 0f21e45 has been approved by compiler-errors

It is now in the queue for this repository.

bors · 2024-02-01T19:13:35Z

🌲 The tree is currently closed for pull requests below priority 100. This pull request will be tested once the tree is reopened.

…gate, r=compiler-errors Correctly check `never_type` feature gating Fixes rust-lang#120542. The feature wasn't tested on return type of a generic function type, so it got under the radar in rust-lang#120316. r? `@compiler-errors`

…gate, r=compiler-errors Correctly check `never_type` feature gating Fixes rust-lang#120542. The feature wasn't tested on return type of a generic function type, so it got under the radar in rust-lang#120316. r? ``@compiler-errors``

…iaskrgr Rollup of 9 pull requests Successful merges: - rust-lang#119759 (Add FileCheck annotations to dataflow-const-prop tests) - rust-lang#120323 (On E0277 be clearer about implicit `Sized` bounds on type params and assoc types) - rust-lang#120473 (Only suggest removal of `as_*` and `to_` conversion methods on E0308) - rust-lang#120520 (Some cleanups around diagnostic levels.) - rust-lang#120540 (add test for try-block-in-match-arm) - rust-lang#120547 (`#![feature(inline_const_pat)]` is no longer incomplete) - rust-lang#120552 (Correctly check `never_type` feature gating) - rust-lang#120555 (put pnkfelix (me) back on the review queue.) - rust-lang#120556 (Improve the diagnostics for unused generic parameters) r? `@ghost` `@rustbot` modify labels: rollup

…iaskrgr Rollup of 8 pull requests Successful merges: - rust-lang#119759 (Add FileCheck annotations to dataflow-const-prop tests) - rust-lang#120323 (On E0277 be clearer about implicit `Sized` bounds on type params and assoc types) - rust-lang#120473 (Only suggest removal of `as_*` and `to_` conversion methods on E0308) - rust-lang#120540 (add test for try-block-in-match-arm) - rust-lang#120547 (`#![feature(inline_const_pat)]` is no longer incomplete) - rust-lang#120552 (Correctly check `never_type` feature gating) - rust-lang#120555 (put pnkfelix (me) back on the review queue.) - rust-lang#120556 (Improve the diagnostics for unused generic parameters) r? `@ghost` `@rustbot` modify labels: rollup

Rollup merge of rust-lang#120552 - GuillaumeGomez:never-type-feature-gate, r=compiler-errors Correctly check `never_type` feature gating Fixes rust-lang#120542. The feature wasn't tested on return type of a generic function type, so it got under the radar in rust-lang#120316. r? ```@compiler-errors```

apiraino · 2024-02-08T15:19:51Z

Beta backport accepted as per compiler team on Zulip

@rustbot label +beta-accepted

[beta] backports - Correct paths for hexagon-unknown-none-elf platform doc rust-lang#120533 - CI: Use ninja on apple builders rust-lang#120543 - Correctly check `never_type` feature gating rust-lang#120552 - Revert unsound libcore changes of 119911 rust-lang#120562 r? cuviper

[beta] backports - Correct paths for hexagon-unknown-none-elf platform doc rust-lang#120533 - CI: Use ninja on apple builders rust-lang#120543 - Correctly check `never_type` feature gating rust-lang#120552 - Revert unsound libcore changes of 119911 rust-lang#120562 - Downgrade xcode rust-lang#120914 r? cuviper

[beta] backports - Correct paths for hexagon-unknown-none-elf platform doc rust-lang#120533 - CI: Use ninja on apple builders rust-lang#120543 - Correctly check `never_type` feature gating rust-lang#120552 - Revert unsound libcore changes of 119911 rust-lang#120562 - Downgrade xcode rust-lang#120914 - Update jobserver-rs to 0.1.28 rust-lang#120846 - [beta] Update LLVM submodule rust-lang#121132 r? cuviper

rustbot assigned compiler-errors Feb 1, 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 1, 2024

compiler-errors requested changes Feb 1, 2024

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rustbot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Feb 1, 2024

compiler-errors added the beta-nominated Nominated for backporting to the compiler in the beta channel. label Feb 1, 2024

GuillaumeGomez force-pushed the never-type-feature-gate branch from e450f16 to aee9d60 Compare February 1, 2024 16:35

compiler-errors approved these changes Feb 1, 2024

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GuillaumeGomez added 2 commits February 1, 2024 20:01

Correctly check never_type feature gating

2c0030f

Update never_type feature gate ui test

0f21e45

GuillaumeGomez force-pushed the never-type-feature-gate branch from aee9d60 to 0f21e45 Compare February 1, 2024 19:01

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-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Feb 1, 2024

matthiaskrgr mentioned this pull request Feb 1, 2024

Rollup of 9 pull requests #120560

Closed

matthiaskrgr mentioned this pull request Feb 1, 2024

Rollup of 9 pull requests #120561

Closed

GuillaumeGomez mentioned this pull request Feb 2, 2024

No feature gate error for -> ! used in a trait bound #120542

Closed

matthiaskrgr mentioned this pull request Feb 4, 2024

Rollup of 8 pull requests #120649

Merged

bors merged commit c2ad283 into rust-lang:master Feb 5, 2024

rustbot added this to the 1.78.0 milestone Feb 5, 2024

GuillaumeGomez deleted the never-type-feature-gate branch February 5, 2024 10:15

rustbot added the beta-accepted Accepted for backporting to the compiler in the beta channel. label Feb 8, 2024

cuviper mentioned this pull request Feb 14, 2024

[beta] backports #121069

Merged

cuviper modified the milestones: 1.78.0, 1.77.0 Feb 14, 2024

cuviper removed the beta-nominated Nominated for backporting to the compiler in the beta channel. label Feb 14, 2024

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Correctly check `never_type` feature gating #120552

Correctly check `never_type` feature gating #120552

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		trait X<const N: i32> {}

		fn hello<T: X<{ fn hello() -> ! { loop {} } 1 }>>() {}

Correctly check never_type feature gating #120552

Correctly check never_type feature gating #120552

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Correctly check `never_type` feature gating #120552

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