Parenthesize break values containing leading label #126883

dtolnay · 2024-06-24T00:30:57Z

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.

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

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

rustc -Zunpretty=expanded main.rs :

#![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.

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.

rustbot · 2024-06-24T00:31:05Z

r? @fmease

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fmease

Thanks! Sorry for the delay.
r=me with nit addressed

compiler/rustc_ast/src/util/classify.rs

fmease · 2024-07-01T23:06:34Z

@bors rollup

dtolnay · 2024-07-02T00:22:32Z

@bors r=fmease

bors · 2024-07-02T00:22:34Z

📌 Commit 0698223 has been approved by fmease

It is now in the queue for this repository.

…iaskrgr Rollup of 10 pull requests Successful merges: - rust-lang#126883 (Parenthesize break values containing leading label) - rust-lang#127136 (Fix `FnMut::call_mut`/`Fn::call` shim for async closures that capture references) - rust-lang#127146 (Uplift fast rejection to new solver) - rust-lang#127152 (Bootstrap: Try renaming the file if removing fails) - rust-lang#127168 (Use the aligned size for alloca at args/ret when the pass mode is cast) - rust-lang#127203 (Fix import suggestion error when path segment failed not from starting) - rust-lang#127212 (Update books) - rust-lang#127224 (Make `FloatTy` checks exhaustive in pretty print) - rust-lang#127230 (chore: remove duplicate words) - rust-lang#127243 (Add test for adt_const_params) r? `@ghost` `@rustbot` modify labels: rollup

Add test of parenthesizing break value by AST pretty-printer

5f37433

rustbot assigned fmease Jun 24, 2024

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Jun 24, 2024

dtolnay force-pushed the breakvalue branch from 0d282f3 to eccfeca Compare June 24, 2024 00:35

fmease approved these changes Jul 1, 2024

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compiler/rustc_ast/src/util/classify.rs Outdated Show resolved Hide resolved

fmease added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Jul 1, 2024

Parenthesize break values containing leading label

0698223

dtolnay force-pushed the breakvalue branch from eccfeca to 0698223 Compare July 2, 2024 00:20

bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Jul 2, 2024

dtolnay mentioned this pull request Jul 2, 2024

Parenthesize break values containing leading label dtolnay/syn#1692

Merged

matthiaskrgr mentioned this pull request Jul 2, 2024

Rollup of 10 pull requests #127244

Merged

bors merged commit f8f67b2 into rust-lang:master Jul 2, 2024
6 checks passed

rustbot added this to the 1.81.0 milestone Jul 2, 2024

dtolnay deleted the breakvalue branch July 3, 2024 00:09

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Parenthesize break values containing leading label #126883

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