rust/compiler/rustc_ast
Matthias Krüger f8f67b2969
Rollup merge of #126883 - dtolnay:breakvalue, r=fmease
Parenthesize break values containing leading label

The AST pretty printer previously produced invalid syntax in the case of `break` expressions with a value that begins with a loop or block label.

```rust
macro_rules! expr {
    ($e:expr) => {
        $e
    };
}

fn main() {
    loop {
        break expr!('a: loop { break 'a 1; } + 1);
    };
}
```

`rustc -Zunpretty=expanded main.rs `:

```console
#![feature(prelude_import)]
#![no_std]
#[prelude_import]
use ::std::prelude::rust_2015::*;
#[macro_use]
extern crate std;
macro_rules! expr { ($e:expr) => { $e }; }

fn main() { loop { break 'a: loop { break 'a 1; } + 1; }; }
```

The expanded code is not valid Rust syntax. Printing invalid syntax is bad because it blocks `cargo expand` from being able to format the output as Rust syntax using rustfmt.

```console
error: parentheses are required around this expression to avoid confusion with a labeled break expression
 --> <anon>:9:26
  |
9 | fn main() { loop { break 'a: loop { break 'a 1; } + 1; }; }
  |                          ^^^^^^^^^^^^^^^^^^^^^^^^
  |
help: wrap the expression in parentheses
  |
9 | fn main() { loop { break ('a: loop { break 'a 1; }) + 1; }; }
  |                          +                        +
```

This PR updates the AST pretty-printer to insert parentheses around the value of a `break` expression as required to avoid this edge case.
2024-07-02 17:47:45 +02:00
..
src Rollup merge of #126883 - dtolnay:breakvalue, r=fmease 2024-07-02 17:47:45 +02:00
Cargo.toml Split rustc_type_ir to avoid rustc_ast from depending on it 2024-02-27 18:11:23 +00:00
README.md docs(rustc_ast): update crate descriptions 2021-11-02 21:11:17 -05:00

The rustc_ast crate contains those things concerned purely with syntax that is, the AST ("abstract syntax tree"), along with some definitions for tokens and token streams, data structures/traits for mutating ASTs, and shared definitions for other AST-related parts of the compiler (like the lexer and macro-expansion).

For more information about how these things work in rustc, see the rustc dev guide: