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59bb9505bc
Allow partially moved values in match
This PR attempts to unify the behaviour between `let _ = PLACE`, `let _: TY = PLACE;` and `match PLACE { _ => {} }`.
The logical conclusion is that the `match` version should not check for uninitialised places nor check that borrows are still live.
The `match PLACE {}` case is handled by keeping a `FakeRead` in the unreachable fallback case to verify that `PLACE` has a legal value.
Schematically, `match PLACE { arms }` in surface rust becomes in MIR:
```rust
PlaceMention(PLACE)
match PLACE {
// Decision tree for the explicit arms
arms,
// An extra fallback arm
_ => {
FakeRead(ForMatchedPlace, PLACE);
unreachable
}
}
```
`match *borrow { _ => {} }` continues to check that `*borrow` is live, but does not read the value.
`match *borrow {}` both checks that `*borrow` is live, and fake-reads the value.
Continuation of ~https://github.com/rust-lang/rust/pull/102256~ ~https://github.com/rust-lang/rust/pull/104844~
Fixes https://github.com/rust-lang/rust/issues/99180 https://github.com/rust-lang/rust/issues/53114
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| .. | ||
| rfc-0107-bind-by-move-pattern-guards | ||
| rfc-1014-stdout-existential-crisis | ||
| rfc-1445-restrict-constants-in-patterns | ||
| rfc-1623-static | ||
| rfc-1717-dllimport | ||
| rfc-1789-as-cell | ||
| rfc-1857-stabilize-drop-order | ||
| rfc-1937-termination-trait | ||
| rfc-2005-default-binding-mode | ||
| rfc-2008-non-exhaustive | ||
| rfc-2027-object-safe-for-dispatch | ||
| rfc-2091-track-caller | ||
| rfc-2093-infer-outlives | ||
| rfc-2126-crate-paths | ||
| rfc-2126-extern-absolute-paths | ||
| rfc-2151-raw-identifiers | ||
| rfc-2175-or-if-while-let | ||
| rfc-2294-if-let-guard | ||
| rfc-2302-self-struct-ctor | ||
| rfc-2306-convert-id | ||
| rfc-2361-dbg-macro | ||
| rfc-2396-target_feature-11 | ||
| rfc-2397-do-not-recommend | ||
| rfc-2421-unreserve-pure-offsetof-sizeof-alignof | ||
| rfc-2457-non-ascii-idents | ||
| rfc-2497-if-let-chains | ||
| rfc-2528-type-changing-struct-update | ||
| rfc-2565-param-attrs | ||
| rfc-2627-raw-dylib | ||
| rfc-2632-const-trait-impl | ||
| rfc-3348-c-string-literals | ||