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Constrain const vars to error if const types are mismatched #109336

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merged 2 commits into from
Mar 21, 2023

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@compiler-errors compiler-errors commented Mar 19, 2023

When equating two consts of different types, if either are const variables, constrain them to the correct const error kind.

This helps us avoid "successfully" matching a const against an impl signature but leaving unconstrained const vars, which will lead to incremental ICEs when we call const-eval queries during const projection.

Fixes #109296

The second commit in the stack fixes a regression in the first commit where we end up mentioning [const error] in an impl overlap error message. I think the error message changes for the better, but I could implement alternative strategies to avoid this without delaying the overlap error message...

r? @BoxyUwU

@rustbot 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 Mar 19, 2023
@@ -2,11 +2,11 @@

// An impl that has an erroneous const substitution should not specialize one
// that is well-formed.

#[derive(Clone)]
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This is necessary because otherwise, since we no longer emit a "conflict implementation" error, we then will fail b/c both impls are not WF (since S doesn't impl Clone) 🙈

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BoxyUwU commented Mar 20, 2023

@bors r+

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bors commented Mar 20, 2023

📌 Commit 9174edb has been approved by BoxyUwU

It is now in the queue for this repository.

@bors 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 Mar 20, 2023
bors added a commit to rust-lang-ci/rust that referenced this pull request Mar 21, 2023
…iaskrgr

Rollup of 8 pull requests

Successful merges:

 - rust-lang#96391 (Windows: make `Command` prefer non-verbatim paths)
 - rust-lang#108164 (Drop all messages in bounded channel when destroying the last receiver)
 - rust-lang#108729 (fix: modify the condition that `resolve_imports` stops)
 - rust-lang#109336 (Constrain const vars to error if const types are mismatched)
 - rust-lang#109403 (Avoid ICE of attempt to add with overflow in emitter)
 - rust-lang#109415 (Refactor `handle_missing_lit`.)
 - rust-lang#109441 (Only implement Fn* traits for extern "Rust" safe function pointers and items)
 - rust-lang#109446 (Do not suggest bounds restrictions for synthesized RPITITs)

Failed merges:

r? `@ghost`
`@rustbot` modify labels: rollup
@bors bors merged commit 081c607 into rust-lang:master Mar 21, 2023
@rustbot rustbot added this to the 1.70.0 milestone Mar 21, 2023
@compiler-errors compiler-errors deleted the constrain-to-ct-err branch August 11, 2023 19:57
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Successfully merging this pull request may close these issues.

ICE: const variables should not be hashed / cannot relate consts of different types
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