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reserved width for unsafe in match arm pattern #7097

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025c070
reserved width for unsafe in match arm pattern
AsthaMishra Sep 2, 2026
af652e0
test case added for other blocks and style edition gate added, test f…
AsthaMishra Sep 3, 2026
fe93837
more test cases added + fix added for empty blocks violating max_width
AsthaMishra Sep 5, 2026
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13 changes: 12 additions & 1 deletion src/matches.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -286,6 +286,15 @@ fn rewrite_match_arm(
.sub_width(7 + label_len, arm.span)?
.offset_left(pipe_offset, arm.span)?
}
ast::ExprKind::Block(block, None)
if is_unsafe_block(block)
Comment on lines +289 to +290

@ytmimi ytmimi Sep 9, 2026 •
edited by rustbot
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Is it ever possible to have an unsafe block with a label?

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@AsthaMishra AsthaMishra Sep 9, 2026

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'a: unsafe{ 5 } gives compile error - after 'a -> a loop or block is expected.

&& context.config.style_edition() >= StyleEdition::Edition2027 =>
{
// 12 = ` => unsafe {`
shape
.sub_width(12, arm.span)?
.offset_left(pipe_offset, arm.span)?
Comment on lines +293 to +296

@ytmimi ytmimi Sep 9, 2026 •
edited by rustbot
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If we know the block is empty, should we:

// 13 = ` => unsafe {}`
sub_width(13, arm.span)

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@AsthaMishra AsthaMishra Sep 9, 2026

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yes we can

}
_ => {
// 5 = ` => {`
shape
Expand Down Expand Up @@ -526,9 +535,11 @@ pub(crate) fn rewrite_match_body(
body_shape.width,
);

let enforce_empty_block_width =
is_empty_block && context.config.style_edition() >= StyleEdition::Edition2027;
match rewrite {
Ok(ref body_str)
if is_block
if (is_block && !enforce_empty_block_width)
|| (!body_str.contains('\n')
&& unicode_str_width(body_str) <= body_shape.width) =>
{
Expand Down
90 changes: 90 additions & 0 deletions tests/source/issue_6848_style_edition_2024.rs
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Original file line number Diff line number Diff line change
@@ -0,0 +1,90 @@
// rustfmt-style_edition: 2024
// rustfmt-max_width: 80

#![feature(gen_blocks, try_blocks)]

#[derive(Clone, Copy)]
enum ExampleTypeX {
VariantAlphaSampleXYZ,
VariantBetaXYZ,
VariantABCD,
VariantABCDE,
VariantABCDEF,
VariantABCDEFG,
VariantABCDEFGH,
VariantABCDEFGHI,
VariantABCDEFGHIJ,
VariantABCDEFGHIJK,
}

fn demo(lhs: ExampleTypeX, rhs: ExampleTypeX) {
//unsafe block
match (lhs, rhs) {
(
ExampleTypeX::VariantAlphaSampleXYZ,
ExampleTypeX::VariantBetaXYZ,
) => unsafe {
}
_ => {}
}

match (lhs, rhs) {
// 1 char below the max_width limit
(ExampleTypeX::VariantABCD, ExampleTypeX::VariantBetaXYZ) => unsafe {},
// everything properly fits on 1 line at exactly the max_width limit
(ExampleTypeX::VariantABCDE, ExampleTypeX::VariantBetaXYZ) => unsafe {},
// 1 char over the max_width limit
(ExampleTypeX::VariantABCDEF, ExampleTypeX::VariantBetaXYZ) => unsafe {},
(ExampleTypeX::VariantABCDEF, ExampleTypeX::VariantBetaXYZ) => unsafe { non_empty_block()},
(ExampleTypeX::VariantABCDEFGHIJKL, ExampleTypeX::VariantBetaXYZ) => unsafe { non_empty_block()},
(ExampleTypeX::VariantABCDEFGHIJKLMNO, ExampleTypeX::VariantBetaXYZ) => unsafe { non_empty_block()},
(ExampleTypeX::VariantABCDEFHGHI, ExampleTypeX::VariantBetaXYZ) => 'a: {},
_ => {}
}

// const block
match (lhs, rhs) {
// 1 char below the max_width limit
(ExampleTypeX::VariantABCDE, ExampleTypeX::VariantBetaXYZ) => const {},
// everything properly fits on 1 line at exactly the max_width limit
(ExampleTypeX::VariantABCDEF, ExampleTypeX::VariantBetaXYZ) => const {},
// 1 char over the max_width limit
(ExampleTypeX::VariantABCDEFG, ExampleTypeX::VariantBetaXYZ) => const {},
_ => {}
}

// async block
match (lhs, rhs) {
// 1 char below the max_width limit
(ExampleTypeX::VariantABCDE, ExampleTypeX::VariantBetaXYZ) => async {},
// everything properly fits on 1 line at exactly the max_width limit
(ExampleTypeX::VariantABCDEF, ExampleTypeX::VariantBetaXYZ) => async {},
// 1 char over the max_width limit
(ExampleTypeX::VariantABCDEFG, ExampleTypeX::VariantBetaXYZ) => async {},
_ => {}
}

// gen block
match (lhs, rhs) {
// 1 char below the max_width limit
(ExampleTypeX::VariantABCDEFG, ExampleTypeX::VariantBetaXYZ) => gen {},
// everything properly fits on 1 line at exactly the max_width limit
(ExampleTypeX::VariantABCDEFGH, ExampleTypeX::VariantBetaXYZ) => gen {},
// 1 char over the max_width limit
(ExampleTypeX::VariantABCDEFGHI, ExampleTypeX::VariantBetaXYZ) => gen {},
_ => {}
}

// try block
match (lhs, rhs) {
//1 char below the max_width limit
(ExampleTypeX::VariantABCDEFG, ExampleTypeX::VariantBetaXYZ) => try {},
// everything properly fits on 1 line at exactly the max_width limit
(ExampleTypeX::VariantABCDEFGH, ExampleTypeX::VariantBetaXYZ) => try {},
// 1 char over the max_width limit
(ExampleTypeX::VariantABCDEFGHI, ExampleTypeX::VariantBetaXYZ) => try {},
_ => {}
}
}

fn main() {}
90 changes: 90 additions & 0 deletions tests/source/issue_6848_style_edition_2027.rs
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Original file line number Diff line number Diff line change
@@ -0,0 +1,90 @@
// rustfmt-style_edition: 2027
// rustfmt-max_width: 80

#![feature(gen_blocks, try_blocks)]

#[derive(Clone, Copy)]
enum ExampleTypeX {
VariantAlphaSampleXYZ,
VariantBetaXYZ,
VariantABCD,
VariantABCDE,
VariantABCDEF,
VariantABCDEFG,
VariantABCDEFGH,
VariantABCDEFGHI,
VariantABCDEFGHIJ,
VariantABCDEFGHIJK,
}

fn demo(lhs: ExampleTypeX, rhs: ExampleTypeX) {
//unsafe block
match (lhs, rhs) {
(
ExampleTypeX::VariantAlphaSampleXYZ,
ExampleTypeX::VariantBetaXYZ,
) => unsafe {
}
_ => {}
}

match (lhs, rhs) {
// 1 char below the max_width limit
(ExampleTypeX::VariantABCD, ExampleTypeX::VariantBetaXYZ) => unsafe {},
// everything properly fits on 1 line at exactly the max_width limit
(ExampleTypeX::VariantABCDE, ExampleTypeX::VariantBetaXYZ) => unsafe {},
// 1 char over the max_width limit
(ExampleTypeX::VariantABCDEF, ExampleTypeX::VariantBetaXYZ) => unsafe {},
(ExampleTypeX::VariantABCDEF, ExampleTypeX::VariantBetaXYZ) => unsafe { non_empty_block()},
(ExampleTypeX::VariantABCDEFGHIJKL, ExampleTypeX::VariantBetaXYZ) => unsafe { non_empty_block()},
(ExampleTypeX::VariantABCDEFGHIJKLMNO, ExampleTypeX::VariantBetaXYZ) => unsafe { non_empty_block()},
(ExampleTypeX::VariantABCDEFHGHI, ExampleTypeX::VariantBetaXYZ) => 'a: {},
_ => {}
}

// const block
match (lhs, rhs) {
// 1 char below the max_width limit
(ExampleTypeX::VariantABCDE, ExampleTypeX::VariantBetaXYZ) => const {},
// everything properly fits on 1 line at exactly the max_width limit
(ExampleTypeX::VariantABCDEF, ExampleTypeX::VariantBetaXYZ) => const {},
// 1 char over the max_width limit
(ExampleTypeX::VariantABCDEFG, ExampleTypeX::VariantBetaXYZ) => const {},
_ => {}
}

// async block
match (lhs, rhs) {
// 1 char below the max_width limit
(ExampleTypeX::VariantABCDE, ExampleTypeX::VariantBetaXYZ) => async {},
// everything properly fits on 1 line at exactly the max_width limit
(ExampleTypeX::VariantABCDEF, ExampleTypeX::VariantBetaXYZ) => async {},
// 1 char over the max_width limit
(ExampleTypeX::VariantABCDEFG, ExampleTypeX::VariantBetaXYZ) => async {},
_ => {}
}

// gen block
match (lhs, rhs) {
// 1 char below the max_width limit
(ExampleTypeX::VariantABCDEFG, ExampleTypeX::VariantBetaXYZ) => gen {},
// everything properly fits on 1 line at exactly the max_width limit
(ExampleTypeX::VariantABCDEFGH, ExampleTypeX::VariantBetaXYZ) => gen {},
// 1 char over the max_width limit
(ExampleTypeX::VariantABCDEFGHI, ExampleTypeX::VariantBetaXYZ) => gen {},
_ => {}
}

// try block
match (lhs, rhs) {
//1 char below the max_width limit
(ExampleTypeX::VariantABCDEFG, ExampleTypeX::VariantBetaXYZ) => try {},
// everything properly fits on 1 line at exactly the max_width limit
(ExampleTypeX::VariantABCDEFGH, ExampleTypeX::VariantBetaXYZ) => try {},
// 1 char over the max_width limit
(ExampleTypeX::VariantABCDEFGHI, ExampleTypeX::VariantBetaXYZ) => try {},
_ => {}
}
}

fn main() {}
102 changes: 102 additions & 0 deletions tests/target/issue_6848_style_edition_2024.rs
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Original file line number Diff line number Diff line change
@@ -0,0 +1,102 @@
// rustfmt-style_edition: 2024
// rustfmt-max_width: 80

#![feature(gen_blocks, try_blocks)]

#[derive(Clone, Copy)]
enum ExampleTypeX {
VariantAlphaSampleXYZ,
VariantBetaXYZ,
VariantABCD,
VariantABCDE,
VariantABCDEF,
VariantABCDEFG,
VariantABCDEFGH,
VariantABCDEFGHI,
VariantABCDEFGHIJ,
VariantABCDEFGHIJK,
}

fn demo(lhs: ExampleTypeX, rhs: ExampleTypeX) {
//unsafe block
match (lhs, rhs) {
(ExampleTypeX::VariantAlphaSampleXYZ, ExampleTypeX::VariantBetaXYZ) => unsafe {
},
_ => {}
}

match (lhs, rhs) {
// 1 char below the max_width limit
(ExampleTypeX::VariantABCD, ExampleTypeX::VariantBetaXYZ) => unsafe {},
// everything properly fits on 1 line at exactly the max_width limit
(ExampleTypeX::VariantABCDE, ExampleTypeX::VariantBetaXYZ) => unsafe {},
// 1 char over the max_width limit
(ExampleTypeX::VariantABCDEF, ExampleTypeX::VariantBetaXYZ) => unsafe {},

@ytmimi ytmimi Sep 9, 2026 •
edited by rustbot
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I'm trying to understand why there's this inconsistency between the unsafe formatting and const, async, gen and try examples below.

Do we need to update the pattern matching for these other kinds of blocks in rewrite_match_arm?

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@AsthaMishra AsthaMishra Sep 9, 2026 •
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pattern matching seems correct we are doing same thing in expr.rs as well and for ast::ExprKind::Block unsafe cases are handled in if branch.

we are just missing pattern arm for unsafe block,

rustfmt/src/matches.rs

Lines 280 to 295 in 7bc6cd7

let pat_shape = match &arm.body.as_ref().unknown_error()?.kind {
ast::ExprKind::Block(_, Some(label)) => {
// Some block with a label ` => 'label: {`
// 7 = ` => : {`
let label_len = label.ident.as_str().len();
shape
.sub_width(7 + label_len, arm.span)?
.offset_left(pipe_offset, arm.span)?
}
_ => {
// 5 = ` => {`
shape
.sub_width(5, arm.span)?
.offset_left(pipe_offset, arm.span)?
}
};

lable block works, - ast::ExprKind::Block(_, Some(label))
const , async, gen and try - these works - default arm

(ExampleTypeX::VariantABCDEF, ExampleTypeX::VariantBetaXYZ) => unsafe {
non_empty_block()
},
(ExampleTypeX::VariantABCDEFGHIJKL, ExampleTypeX::VariantBetaXYZ) => unsafe {
non_empty_block()
},
(
ExampleTypeX::VariantABCDEFGHIJKLMNO,
ExampleTypeX::VariantBetaXYZ,
) => unsafe { non_empty_block() },
(ExampleTypeX::VariantABCDEFHGHI, ExampleTypeX::VariantBetaXYZ) => 'a: {}
_ => {}
}

// const block
match (lhs, rhs) {
// 1 char below the max_width limit
(ExampleTypeX::VariantABCDE, ExampleTypeX::VariantBetaXYZ) => const {},
// everything properly fits on 1 line at exactly the max_width limit
(ExampleTypeX::VariantABCDEF, ExampleTypeX::VariantBetaXYZ) => const {},
// 1 char over the max_width limit
(ExampleTypeX::VariantABCDEFG, ExampleTypeX::VariantBetaXYZ) => {
const {}
}
_ => {}
}

// async block
match (lhs, rhs) {
// 1 char below the max_width limit
(ExampleTypeX::VariantABCDE, ExampleTypeX::VariantBetaXYZ) => async {},
// everything properly fits on 1 line at exactly the max_width limit
(ExampleTypeX::VariantABCDEF, ExampleTypeX::VariantBetaXYZ) => async {},
// 1 char over the max_width limit
(ExampleTypeX::VariantABCDEFG, ExampleTypeX::VariantBetaXYZ) => {
async {}
}
_ => {}
}

// gen block
match (lhs, rhs) {
// 1 char below the max_width limit
(ExampleTypeX::VariantABCDEFG, ExampleTypeX::VariantBetaXYZ) => gen {},
// everything properly fits on 1 line at exactly the max_width limit
(ExampleTypeX::VariantABCDEFGH, ExampleTypeX::VariantBetaXYZ) => gen {},
// 1 char over the max_width limit
(ExampleTypeX::VariantABCDEFGHI, ExampleTypeX::VariantBetaXYZ) => {
gen {}
}
_ => {}
}

// try block
match (lhs, rhs) {
//1 char below the max_width limit
(ExampleTypeX::VariantABCDEFG, ExampleTypeX::VariantBetaXYZ) => try {},
// everything properly fits on 1 line at exactly the max_width limit
(ExampleTypeX::VariantABCDEFGH, ExampleTypeX::VariantBetaXYZ) => try {},
// 1 char over the max_width limit
(ExampleTypeX::VariantABCDEFGHI, ExampleTypeX::VariantBetaXYZ) => {
try {}
}
_ => {}
}
}

fn main() {}
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