rust/src/test/compile-fail/loop-break-value.rs
Geoffry Song 9d42549df4
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, `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 ^_^
2016-11-21 20:20:42 -08:00

102 lines
2.6 KiB
Rust

// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
#![feature(loop_break_value)]
#![feature(never_type)]
fn main() {
let val: ! = loop { break break; };
//~^ ERROR mismatched types
loop {
if true {
break "asdf";
} else {
break 123; //~ ERROR mismatched types
}
};
let _: i32 = loop {
break "asdf"; //~ ERROR mismatched types
};
let _: i32 = 'outer_loop: loop {
loop {
break 'outer_loop "nope"; //~ ERROR mismatched types
break "ok";
};
};
'while_loop: while true {
break;
break (); //~ ERROR `break` with value from a `while` loop
loop {
break 'while_loop 123;
//~^ ERROR `break` with value from a `while` loop
//~| ERROR mismatched types
break 456;
break 789;
};
}
'while_let_loop: while let Some(_) = Some(()) {
if break () { //~ ERROR `break` with value from a `while let` loop
break;
break None;
//~^ ERROR `break` with value from a `while let` loop
//~| ERROR mismatched types
}
loop {
break 'while_let_loop "nope";
//~^ ERROR `break` with value from a `while let` loop
//~| ERROR mismatched types
break 33;
};
}
'for_loop: for _ in &[1,2,3] {
break (); //~ ERROR `break` with value from a `for` loop
break [()];
//~^ ERROR `break` with value from a `for` loop
//~| ERROR mismatched types
loop {
break Some(3);
break 'for_loop Some(17);
//~^ ERROR `break` with value from a `for` loop
//~| ERROR mismatched types
};
}
let _: i32 = 'a: loop {
let _: () = 'b: loop {
break ('c: loop {
break;
break 'c 123; //~ ERROR mismatched types
});
break 'a 123;
};
};
loop {
break (break, break); //~ ERROR mismatched types
};
loop {
break;
break 2; //~ ERROR mismatched types
};
loop {
break 2;
break; //~ ERROR mismatched types
break 4;
};
}