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Reserve width for const when formatting inline const blocks #7065

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Reserve width for const when formatting inline const blocks #7065

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226b319
reserve width for when formatting inline const blocks
AsthaMishra Aug 24, 2026
f6b8d36
formatting gated on style_edition 2027
AsthaMishra Aug 25, 2026
bd75704
Rename function `second_issue` to `removes_trailing_whitespace` for c…
AsthaMishra Aug 25, 2026
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6 changes: 6 additions & 0 deletions src/expr.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -186,6 +186,12 @@ pub(crate) fn format_expr(
// not the `ast::Block` node we're about to rewrite. To prevent dropping inner
// attributes call `rewrite_block` directly.
// See https://github.com/rust-lang/rustfmt/issues/6158
let shape = if context.config.style_edition() >= StyleEdition::Edition2027 {
// Shrink the shape by `"const ".len()` before rewriting the block
shape.offset_left(6, expr.span)?
} else {
shape
};
Comment on lines +189 to +194

@ytmimi ytmimi Aug 25, 2026 •
edited by rustbot
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Thanks for adding the gate. This looks right to me, but I want to confirm something first before moving forward. #7055 mentioned that unsafe blocks didn't have this problem. I'd like to understand why that's the case. Maybe there's something going on inside rewrite_block where the shape is properly updated?

There are also try, gen, and async blocks. Might be good to check that we're handling those correctly too.

View changes since the review

@AsthaMishra AsthaMishra Aug 25, 2026

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if there is unsafe , we get it in prefix - let prefix = block_prefix(context, block, shape)?; and in function rewrite_single_line_block result contains it

   let result = format!("{prefix}{label_str}{{ {expr_str} }}");
        if result.len() <= shape.width && !result.contains('\n') {
            return Ok(result);
        }

but for const - prefix is empty

@AsthaMishra AsthaMishra Aug 25, 2026 •
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try , async , and gen blocks pass their prefix into rewrite_single_line_block , so these works fine

rewrite_block(block, Some(&expr.attrs), opt_label, context, shape)?
}
_ => anon_const.rewrite_result(context, shape)?,
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29 changes: 29 additions & 0 deletions tests/source/issue-7055.rs
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@@ -0,0 +1,29 @@
// rustfmt-style_edition: 2027

struct S;

impl S {
const fn new(_: &str) -> Self {
S
}

fn go(&self) {}
}

fn main() {
const {
S::new(
"aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa",
)
}
.go();
}

fn removes_trailing_whitespace() {
const {
S::new(
"aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa",
)
}
.go();
}
Comment on lines +13 to +29

@ytmimi ytmimi Aug 24, 2026

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What's the difference between main and second_issue?

@astral4 astral4 Aug 25, 2026

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There's a space after S::new( in second_issue. #7055 should provide context

@ytmimi ytmimi Aug 25, 2026

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@astral4 thanks for pointing that out. @AsthaMishra the trailing whitespace isn't so obvious. Instead of naming it second_issue Maybe you could name the case something like removes_trailing_whitespace, which would make the intent clearer in my opinion.

25 changes: 25 additions & 0 deletions tests/target/issue-7055.rs
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@@ -0,0 +1,25 @@
// rustfmt-style_edition: 2027

struct S;

impl S {
const fn new(_: &str) -> Self {
S
}

fn go(&self) {}
}

fn main() {
const {
S::new("aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa")
}
.go();
}

fn removes_trailing_whitespace() {
const {
S::new("aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa")
}
.go();
}