match lowering: Lower bindings in a predictable order #121716
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For some reason it doesn't figure out the slice coercion.
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Rollup of 5 pull requests Successful merges: - rust-lang#120761 (Add initial support for DataFlowSanitizer) - rust-lang#121622 (Preserve same vtable pointer when cloning raw waker, to fix Waker::will_wake) - rust-lang#121716 (match lowering: Lower bindings in a predictable order) - rust-lang#121731 (Now that inlining, mir validation and const eval all use reveal-all, we won't be constraining hidden types here anymore) - rust-lang#121841 (`f16` and `f128` step 2: intrinsics) r? `@ghost` `@rustbot` modify labels: rollup
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Rollup merge of rust-lang#121716 - Nadrieril:simple-binding-order, r=matthewjasper match lowering: Lower bindings in a predictable order After the recent refactorings, we can now lower bindings in a truly predictable order. The order in rust-lang#120214 was an improvement but not very clear. With this PR, we lower bindings from left to right, with the special case that `x @ pat` is traversed as `pat @ x` (i.e. `x` is lowered after any bindings in `pat`). This description only applies in the absence of or-patterns. Or-patterns make everything complicated, because the binding place depends on the subpattern. Until I have a better idea I leave them to be handled in whatever weird order arises from today's code. r? `@matthewjasper`
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lower pattern bindings in the order they're written and base drop order on primary bindings' order To fix #142163, this PR does two things: - Makes match arms base their drop order on the first sub-branch instead of the last sub-branch. Together with the second change, this makes bindings' drop order correspond to the relative order of when each binding first appears (i.e. the order of the "primary" bindings). - Lowers pattern bindings in the order they're written (still treating the right-hand side of a ``@`` as coming before the binding on the left). In each sub-branch of a match arm, this is the order that would be obtained if the or-alternatives chosen in that sub-branch were inlined into the arm's pattern. This both affects drop order (making bindings in or-patterns not be dropped first) and fixes the issue in [this test](https://github.com/rust-lang/rust/blob/2a023bf80a6fbd6a06d5460a34eb247b986286ed/tests/ui/pattern/bindings-after-at/bind-by-copy-or-pat.rs) from #121716. My approach to the second point is admittedly a bit trickier than may be necessary. To avoid passing around a counter when building `FlatPat`s, I've instead added just enough information to recover the original structure of the pattern's bindings from a `MatchTreeSubBranch`'s path through the `Candidate` tree. Some alternatives: - We could use a counter, then sort bindings by their ordinals when making `MatchTreeSubBranch`es. - I'd like to experiment with always merging sub-candidates and removing `test_remaining_match_pairs_after_or`; that would require lowering bindings and guards in a different way. That makes it a bigger change too, though, so I figure it might be simplest to start here. - For a very big change, we could track which or-alternatives succeed at runtime to base drop order on the binding order in the particular alternatives matched. This is a breaking change. It will need a crater run, language team sign-off, and likely updates to the Reference. This will conflict with #143376 and probably also #143028, so they shouldn't be merged at the same time. r? `@matthewjasper` or `@Nadrieril`
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After the recent refactorings, we can now lower bindings in a truly predictable order. The order in #120214 was an improvement but not very clear. With this PR, we lower bindings from left to right, with the special case that
x @ patis traversed aspat @ x(i.e.xis lowered after any bindings inpat).This description only applies in the absence of or-patterns. Or-patterns make everything complicated, because the binding place depends on the subpattern. Until I have a better idea I leave them to be handled in whatever weird order arises from today's code.
r? @matthewjasper