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Jonathan Brouwer
8be4c463be
Parenthesize block-like expressions in index base of pretty printer The AST pretty printer produces invalid Rust when a block expression is the base of an index operation inside a macro expansion. This is a gap in the parenthesization fix from rust-lang/rust#119105 — the `FixupContext` approach handles statement position but not the case where a block-index is nested inside another expression. The following is a correct program: ```rust macro_rules! block_arr { () => {{ [0u8; 4] }}; } macro_rules! as_slice { () => {{ &block_arr!()[..] }}; } fn main() { let _: &[u8] = as_slice!(); } ``` But `rustc -Zunpretty=expanded` produces output that is not valid Rust, because the closing brace of `{ [0u8; 4] }` creates a statement boundary, causing the parser to treat `[..]` as a separate expression: ```rust fn main() { let _: &[u8] = { &{ [0u8; 4] }[..] }; } ``` ``` error: expected one of `.`, `;`, `?`, `}`, or an operator, found `[` ``` Fixed output after this change: ```rust fn main() { let _: &[u8] = { &({ [0u8; 4] })[..] }; } ``` Since `{ ... }[...]` never parses as indexing a block regardless of context, the fix unconditionally parenthesizes "complete" expressions (block, match, if, loop, etc.) when they appear as the base of an index operation.