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Inconsistent error when using bindings after @
#120210
Labels
C-bug
Category: This is a bug.
F-bindings_after_at
`#![feature(bindings_after_at)]`
T-compiler
Relevant to the compiler team, which will review and decide on the PR/issue.
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matthiaskrgr
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Feb 3, 2024
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 rust-lang#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 rust-lang#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 rust-lang#120210 r? `@oli-obk` since you merged the original fix to rust-lang#69971 cc `@matthewjasper`
matthiaskrgr
added a commit
to matthiaskrgr/rust
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Feb 3, 2024
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 rust-lang#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 rust-lang#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 rust-lang#120210 r? ``@oli-obk`` since you merged the original fix to rust-lang#69971 cc ``@matthewjasper``
matthiaskrgr
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Feb 5, 2024
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 rust-lang#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 rust-lang#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 rust-lang#120210 r? ```@oli-obk``` since you merged the original fix to rust-lang#69971 cc ```@matthewjasper```
matthiaskrgr
added a commit
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Feb 5, 2024
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 rust-lang#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 rust-lang#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 rust-lang#120210 r? ````@oli-obk```` since you merged the original fix to rust-lang#69971 cc ````@matthewjasper````
matthiaskrgr
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Feb 7, 2024
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 rust-lang#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 rust-lang#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 rust-lang#120210 r? `````@oli-obk````` since you merged the original fix to rust-lang#69971 cc `````@matthewjasper`````
matthiaskrgr
added a commit
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Feb 8, 2024
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 rust-lang#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 rust-lang#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 rust-lang#120210 r? ``````@oli-obk`````` since you merged the original fix to rust-lang#69971 cc ``````@matthewjasper``````
rust-timer
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Feb 8, 2024
Rollup merge of rust-lang#120214 - Nadrieril:fix-120210, r=pnkfelix 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 rust-lang#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 rust-lang#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 rust-lang#120210 r? ```````@oli-obk``````` since you merged the original fix to rust-lang#69971 cc ```````@matthewjasper```````
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Labels
C-bug
Category: This is a bug.
F-bindings_after_at
`#![feature(bindings_after_at)]`
T-compiler
Relevant to the compiler team, which will review and decide on the PR/issue.
In the following, the first case compiles (playground) and the second errors (playground). The only difference is adding a variant to the enum.
Error:
This is an extension to #69971. I discovered this while poking at the match lowering code. Essentially, #69971 was accidentally only fixed for the case of irrefutable patterns, since patterns that require a test go through a different code path.
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