resolve: fix label scopes #37360
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resolve: fix label scopes #37360
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@bors: r+ |
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📌 Commit dcdab2d has been approved by |
jseyfried
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nikomatsakis
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Marking for beta-accepted since this is a small, harmless-looking patch. It fixes an ICE (turns it back into a hard error). I could see a counter argument that such a change (since it is an error otherwise) doesn't merit a backport. What say you, @rust-lang/compiler ? |
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SGTM. |
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brson
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Nov 22, 2016
Implement the `loop_break_value` feature. This implements RFC 1624, tracking issue #37339. - `FnCtxt` (in typeck) gets a stack of `LoopCtxt`s, which store the currently deduced type of that loop, the desired type, and a list of break expressions currently seen. `loop` loops get a fresh type variable as their initial type (this logic is stolen from that for arrays). `while` loops get `()`. - `break {expr}` looks up the broken loop, and unifies the type of `expr` with the type of the loop. - `break` with no expr unifies the loop's type with `()`. - When building MIR, loops no longer construct a `()` value at termination of the loop; rather, the `break` expression assigns the result of the loop. - ~~I have also changed the loop scoping in MIR-building so that the test of a while loop is not considered to be part of that loop. This makes the rules consistent with #37360. The new loop scopes in typeck also follow this rule. That means that `loop { while (break) {} }` now terminates instead of looping forever. This is technically a breaking change.~~ - ~~On that note, expressions like `while break {}` and `if break {}` no longer parse because `{}` is interpreted as an expression argument to `break`. But no code except compiler test cases should do that anyway because it makes no sense.~~ - The RFC did not make it clear, but I chose to make `break ()` inside of a `while` loop illegal, just in case we wanted to do anything with that design space in the future. This is my first time dealing with this part of rustc so I'm sure there's plenty of problems to pick on here ^_^
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Fixes #37353 (turns an ICE back into an error).
r? @nrc