pattern_analysis: rework how we hide empty private fields #121000
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| /// Fake extra constructor that indicates that we should skip the column entirely. This is used | ||
| /// when a private field is empty, so that we don't observe its emptiness. Only used for | ||
| /// specialization. | ||
| Skip, |
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I wonder if we should give this a more descriptive name (PrivateUninhabited) or something
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yeah I like that, will rename
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@bors r+ |
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Ty! |
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…llaumeGomez Rollup of 7 pull requests Successful merges: - rust-lang#119748 (Increase visibility of `join_path` and `split_paths`) - rust-lang#120820 (Enable CMPXCHG16B, SSE3, SAHF/LAHF and 128-bit Atomics (in nightly) in Windows x64) - rust-lang#121000 (pattern_analysis: rework how we hide empty private fields) - rust-lang#121376 (Skip unnecessary comparison with half-open range patterns) - rust-lang#121596 (Use volatile access instead of `#[used]` for `on_tls_callback`) - rust-lang#121669 (Count stashed errors again) - rust-lang#121783 (Emitter cleanups) r? `@ghost` `@rustbot` modify labels: rollup
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Rollup merge of rust-lang#121000 - Nadrieril:keep_all_fields, r=compiler-errors pattern_analysis: rework how we hide empty private fields Consider this: ```rust mod foo { pub struct Bar { pub a: bool, b: !, } } fn match_a_bar(bar: foo::Bar) -> bool { match bar { Bar { a, .. } => a, } } ``` Because the field `b` is private, matches outside the module are not allowed to observe the fact that `Bar` is empty. In particular `match bar {}` is valid within the module `foo` but an error outside (assuming `exhaustive_patterns`). We currently handle this by hiding the field `b` when it's both private and empty. This means that the pattern `Bar { a, .. }` is lowered to `Bar(a, _)` if we're inside of `foo` and to `Bar(a)` outside. This involves a bit of a dance to keep field indices straight. But most importantly this makes pattern lowering depend on the module. In this PR, I instead do nothing special when lowering. Only during analysis do we track whether a place must be skipped. r? `@compiler-errors`
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Consider this:
Because the field
bis private, matches outside the module are not allowed to observe the fact thatBaris empty. In particularmatch bar {}is valid within the modulefoobut an error outside (assumingexhaustive_patterns).We currently handle this by hiding the field
bwhen it's both private and empty. This means that the patternBar { a, .. }is lowered toBar(a, _)if we're inside offooand toBar(a)outside. This involves a bit of a dance to keep field indices straight. But most importantly this makes pattern lowering depend on the module.In this PR, I instead do nothing special when lowering. Only during analysis do we track whether a place must be skipped.
r? @compiler-errors