Match Ergonomics 2024: update old-edition behavior of feature gates #136093
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The debug assertion ensuring that the pattern mutability cap holds assumes the presence of Rule 3, so it now checks for that. I considered going back to only tracking the mutability cap when Rule 3 is present, but since the mutability cap is used in Rule 5's implementation too, the debug assertion would still need to check which typing rules are present. This also required some changes to tests: - `ref_pat_eat_one_layer_2021.rs` had a test for Rule 3; I'll be handling tests for earlier editions in a later commit, so as a stopgap I've #[cfg]ed it out. - One test case had to be moved from `well-typed-edition-2024.rs` to `borrowck-errors.rs` in order to get borrowck to run on it and emit an error.
These come directly from the "Compare" tab of Typing Rust Patterns, though they had to be split across multiple files. They're not comprehensive, but they do provide some previously-missing coverage and are easier to check against the spec. Possibly they should be split up some more, since `pattern-errors.rs` is getting a bit unwieldy, but I'm not sure how best to go about that.
…back for inherited ref mutability mismatches I think the diagnostic could use some work, but it's more helpful than the alternative. The previous error was misleading, since it ignored the inherited reference altogether.
…e pattern doesn't match the mutability of an inner reference This is the `Deref(EatInner, FallbackToOuter)` rule in Typing Rust Patterns.
- Removes some excess parens - Removes 3 duplicated tests
This serves two purposes. First, they're additional tests that stable Rust behavior hasn't been messed with. There's plenty of other pattern tests, so this is less important, but these at least are targeted at what's being changed. Second, this helps document exactly where the new rulesets agree and disagree with stable pattern typing. This will be especially important after the new rules for old editions are updated, since they need to be strictly more permissive; any patterns well-typed on stable should also be well-typed with the same resultant bindings on the (upcoming) new new old-edition rules. The unusual test ordering on `borrowck-errors.rs` and `ref-binding-on-inh-ref-errors.rs` are to hopefully reduce how much adding new tests will mess with line numbers in their stderr.
This doesn't (or at least shouldn't!) add, remove, or change any test cases. I've grouped them by which rule variants they test.
…rules) Since there are so many ways to write these, I've opted to only include two sorts of test: simple tests that directly target the rules differing between rulesets and nuanced tests that produce different errors under different rulesets. I've also tried not to add any duplicate tests. `well-typed-edition-2024.rs` already has tests disagreeing with stable, so I've opted not to include any in this commit that are well-typed under the new rules.
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These are very bare-bones, only intended to provide some documentation of what these feature gates are and aren't yet implementing.
This also adds `#[cfg]` attributes to tests for bindings' types, to make it visually clearer which revisions type successfully.
These are superseded by the old-edition revisions on the shared tests.
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This is based on #135434; only the latest 6 commits are new. It should be fully implemented, but I'll leave this as a draft until that's merged in case it needs updates.
This updates the behavior of the feature gates
ref_pat_eat_one_layer_2024_structuralandref_pat_eat_one_layer_2024in Editions 2021 and earlier to correspond to the left and right typing rules compared here, respectively. Compared to thestable_rustrules:&patterns to eat&mutreference types (and lone&mutinherited refs) as if they're shared,&mutpatterns to eat&reference types when there's a&mutinherited reference to also eat,I think there's already tests for all of those typing rules, so I've added revisions to use the existing tests with the new rulesets. Additionally, I've added a few tests to make sure we handle mixed-edition patterns appropriately, and I've added references to the unstable book.
Relevant tracking issue: #123076
r? @ghost