9d42549df4
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, `loop` loops no longer construct a `()` value at termination of the loop; rather, the `break` expression assigns the result of the loop. `while` loops are unchanged. - `break` respects contexts in which expressions may not end with braced blocks. That is, `while break { break-value } { while-body }` is illegal; this preserves backwards compatibility. - 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 ^_^
16 lines
564 B
Rust
16 lines
564 B
Rust
// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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fn main() {
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loop {
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break 123; //~ ERROR `break` with a value is experimental
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}
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}
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