Defer repeat expr `Copy` checks to end of type checking #137045

BoxyUwU · 2025-02-14T21:52:27Z

Defers repeat expr checks that the element type is Copy when the length is > 1 (or generic) to end of typeck so that under generic_arg_infer repeat exprs are able to have an inferred count, e.g. let a: [_; 1] = [String::new(); _];.

Currently the deferring is gated under generic_arg_infer though I intend to separately types FCP deferring the checks even outside of generic_arg_infer if we wind up not going with an alternative.

BoxyUwU · 2025-02-14T21:52:34Z

@bors try

bors · 2025-02-14T21:53:46Z

⌛ Trying commit c09f183 with merge 9053a8a...

…<try> Defer repeat expr `Copy` checks to end of type checking Fixes rust-lang#110443 r? `@ghost`

BoxyUwU · 2025-02-14T21:58:43Z

tests/ui/repeat-expr/infer-eager.rs

+
+fn main() {
+    let x = [Foo(PhantomData); 2];
+    //~^ ERROR: type annotations needed


always deferring the check is a breaking change in cases where the Copy impl has inference constraints that are then used in order to perform method lookup (or any other kind of hir typeck check that relies on matching on a type).

want to crater this to see how breaking it is but it would be very easy to just not break this and think that is my preference :3

I think my preference now is actually to either always defer and eat the breaking change or do a less-hacky attempt to avoid the breaking change by introducing a new goal kind for repeat expr checks that can be deferred exactly as long as is necessary and no furthur

bors · 2025-02-14T23:40:31Z

☀️ Try build successful - checks-actions
Build commit: 9053a8a (9053a8ad740a9e131b53ea98acecf68cf79134fe)

BoxyUwU · 2025-02-14T23:53:07Z

@craterbot check

craterbot · 2025-02-14T23:53:27Z

👌 Experiment pr-137045 created and queued.
🤖 Automatically detected try build 9053a8a
🔍 You can check out the queue and this experiment's details.

ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

craterbot · 2025-02-15T18:15:15Z

🚧 Experiment pr-137045 is now running

ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

craterbot · 2025-02-16T15:41:49Z

🎉 Experiment pr-137045 is completed!
📊 5 regressed and 3 fixed (583035 total)
📰 Open the full report.

⚠️ If you notice any spurious failure please add them to the denylist!
ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

BoxyUwU · 2025-02-16T19:12:13Z

(all spurrious)

BoxyUwU · 2025-02-18T13:01:29Z

r? @compiler-errors

BoxyUwU · 2025-02-18T13:05:44Z

compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs

+            // FIXME: Infer `?ct = {const error}`?
+            ty::Const::new_error(self.tcx, e)


There's no fcx.demand_subtype for consts yet.

You could just self.at(..).eq(ct, err)?

BoxyUwU · 2025-02-18T13:07:13Z

compiler/rustc_hir_typeck/src/lib.rs

+    // first as errors from not having inferred array lengths yet seem less confusing than errors from inference
+    // fallback arbitrarily inferring something incompatible with `Copy` inference side effects.
+    //
+    // This should also be forwards compatible with moving repeat expr checks to a custom goal kind or using


I feel somewhat hesitant to add a custom goal kind for repeat expr checks but I do think it would be "optimal" behaviour-wise as the goals could stall on the repeat count infer var and be deferred ~as long as necessary while also not delaying inference constraints from them any later than is needed.

compiler-errors · 2025-02-27T19:36:01Z

compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs

+            // FIXME: Infer `?ct = {const error}`?
+            ty::Const::new_error(self.tcx, e)


You could just self.at(..).eq(ct, err)?

compiler-errors · 2025-02-27T19:37:06Z

lgtm, r=me with or without applying the nit; i think it may not be needed b/c all it's gonna do is slightly improve duplicated/unnecessary errors.

BoxyUwU · 2025-02-27T22:35:57Z

(rebased)

@bors r=compiler-errors

bors · 2025-02-27T22:36:00Z

📌 Commit 6c3243f has been approved by compiler-errors

It is now in the queue for this repository.

bors · 2025-02-27T22:36:01Z

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

…r=compiler-errors Defer repeat expr `Copy` checks to end of type checking Fixes rust-lang#110443 Defers repeat expr checks that the element type is `Copy` when the length is > 1 (or generic) to end of typeck so that under `generic_arg_infer` repeat exprs are able to have an inferred count, e.g. `let a: [_; 1] = [String::new(); _];`. Currently the deferring is gated under `generic_arg_infer` though I intend to separately types FCP deferring the checks even outside of `generic_arg_infer` if we wind up not going with an alternative.

…iaskrgr Rollup of 11 pull requests Successful merges: - rust-lang#137045 (Defer repeat expr `Copy` checks to end of type checking) - rust-lang#137171 (Suggest swapping equality on E0277) - rust-lang#137634 (Update `compiler-builtins` to 0.1.149) - rust-lang#137686 (Handle asm const similar to inline const) - rust-lang#137689 (Use `Binder<Vec<Ty>>` instead of `Vec<Binder<Ty>>` in both solvers for sized/auto traits/etc.) - rust-lang#137718 (Use original command for showing sccache stats) - rust-lang#137723 (Make `rust.description` more general-purpose and pass `CFG_VER_DESCRIPTION`) - rust-lang#137730 (checked_ilog tests: deal with a bit of float imprecision) - rust-lang#137735 (Update E0133 docs for 2024 edition) - rust-lang#137742 (unconditionally lower match arm even if it's unneeded for never pattern in match) - rust-lang#137771 (Tweak incorrect ABI suggestion) r? `@ghost` `@rustbot` modify labels: rollup

…r=compiler-errors Defer repeat expr `Copy` checks to end of type checking Fixes rust-lang#110443 Defers repeat expr checks that the element type is `Copy` when the length is > 1 (or generic) to end of typeck so that under `generic_arg_infer` repeat exprs are able to have an inferred count, e.g. `let a: [_; 1] = [String::new(); _];`. Currently the deferring is gated under `generic_arg_infer` though I intend to separately types FCP deferring the checks even outside of `generic_arg_infer` if we wind up not going with an alternative.

…iaskrgr Rollup of 9 pull requests Successful merges: - rust-lang#137045 (Defer repeat expr `Copy` checks to end of type checking) - rust-lang#137171 (Suggest swapping equality on E0277) - rust-lang#137686 (Handle asm const similar to inline const) - rust-lang#137689 (Use `Binder<Vec<Ty>>` instead of `Vec<Binder<Ty>>` in both solvers for sized/auto traits/etc.) - rust-lang#137718 (Use original command for showing sccache stats) - rust-lang#137730 (checked_ilog tests: deal with a bit of float imprecision) - rust-lang#137735 (Update E0133 docs for 2024 edition) - rust-lang#137742 (unconditionally lower match arm even if it's unneeded for never pattern in match) - rust-lang#137771 (Tweak incorrect ABI suggestion and make suggestion verbose) Failed merges: - rust-lang#137723 (Make `rust.description` more general-purpose and pass `CFG_VER_DESCRIPTION`) r? `@ghost` `@rustbot` modify labels: rollup

Rollup merge of rust-lang#137045 - BoxyUwU:defer_repeat_expr_checks, r=compiler-errors Defer repeat expr `Copy` checks to end of type checking Fixes rust-lang#110443 Defers repeat expr checks that the element type is `Copy` when the length is > 1 (or generic) to end of typeck so that under `generic_arg_infer` repeat exprs are able to have an inferred count, e.g. `let a: [_; 1] = [String::new(); _];`. Currently the deferring is gated under `generic_arg_infer` though I intend to separately types FCP deferring the checks even outside of `generic_arg_infer` if we wind up not going with an alternative.

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 14, 2025

bors added a commit to rust-lang-ci/rust that referenced this pull request Feb 14, 2025

Auto merge of rust-lang#137045 - BoxyUwU:defer_repeat_expr_checks, r=…

9053a8a

…<try> Defer repeat expr `Copy` checks to end of type checking Fixes rust-lang#110443 r? `@ghost`

BoxyUwU commented Feb 14, 2025

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craterbot added S-waiting-on-crater Status: Waiting on a crater run to be completed. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Feb 14, 2025

BoxyUwU force-pushed the defer_repeat_expr_checks branch from c09f183 to 8966d60 Compare February 15, 2025 02:06

craterbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-crater Status: Waiting on a crater run to be completed. labels Feb 16, 2025

BoxyUwU force-pushed the defer_repeat_expr_checks branch 3 times, most recently from 75bb3ab to 1ff88a7 Compare February 18, 2025 12:58

BoxyUwU marked this pull request as ready for review February 18, 2025 13:01

rustbot assigned compiler-errors Feb 18, 2025

BoxyUwU commented Feb 18, 2025

View reviewed changes

compiler-errors approved these changes Feb 27, 2025

View reviewed changes

BoxyUwU added 3 commits February 27, 2025 20:02

Add inference constraining Copy impl test

cdd8895

Defer repeat expr Copy check

dc6db19

Bless

6c3243f

BoxyUwU force-pushed the defer_repeat_expr_checks branch from 1ff88a7 to 6c3243f Compare February 27, 2025 22:33

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 27, 2025

matthiaskrgr mentioned this pull request Feb 28, 2025

Rollup of 11 pull requests #137775

Closed

This was referenced Feb 28, 2025

Rollup of 10 pull requests #137797

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Rollup of 9 pull requests #137838

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bors merged commit 91eb721 into rust-lang:master Mar 1, 2025
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Defer repeat expr `Copy` checks to end of type checking #137045

Defer repeat expr `Copy` checks to end of type checking #137045

BoxyUwU commented Feb 14, 2025 •

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		// FIXME: Infer `?ct = {const error}`?
		ty::Const::new_error(self.tcx, e)

Defer repeat expr Copy checks to end of type checking #137045

Defer repeat expr Copy checks to end of type checking #137045

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Defer repeat expr `Copy` checks to end of type checking #137045

Defer repeat expr `Copy` checks to end of type checking #137045

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