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match lowering: consistently lower bindings deepest-first Currently when lowering match expressions to MIR, we do a funny little dance with the order of bindings. I attempt to explain it in the third commit: we handle refutable (i.e. needing a test) patterns differently than irrefutable ones. This leads to inconsistencies, as reported in https://github.com/rust-lang/rust/issues/120210. The reason we need a dance at all is for situations like: ```rust fn foo1(x: NonCopyStruct) { let y @ NonCopyStruct { copy_field: z } = x; // the above should turn into let z = x.copy_field; let y = x; } ``` Here the `y ```````@```````` binding will move out of `x`, so we need to copy the field first. I believe that the inconsistency came about when we fixed https://github.com/rust-lang/rust/issues/69971, and didn't notice that the fix didn't extend to refutable patterns. My guess then is that ordering bindings by "deepest-first, otherwise source order" is a sound choice. This PR implements that (at least I hope, match lowering is hard to follow 🥲). Fixes https://github.com/rust-lang/rust/issues/120210 r? ```````@oli-obk``````` since you merged the original fix to https://github.com/rust-lang/rust/issues/69971 cc ```````@matthewjasper``````` |
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