keep the trailing semicolon on loops that break with a value - #7072
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AsthaMishra wants to merge 2 commits into
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keep the trailing semicolon on loops that break with a value#7072AsthaMishra wants to merge 2 commits into
AsthaMishra wants to merge 2 commits into
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ytmimi
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Aug 25, 2026
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What about loops deeply nested inside other loops loops?
ytmimi
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Aug 25, 2026
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| /// Does this `loop` evaluate to something other than `()`? | ||
| /// | ||
| /// `loop { break v }` evaluates to `v`, so the trailing semicolon is what | ||
| /// discards that value. Removing it leaves a bare expression statement, | ||
| /// which rustc requires to be `()` | ||
| fn loop_breaks_with_value(expr: &ast::Expr) -> bool { | ||
| struct BreakWithValue(bool); | ||
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| impl<'ast> visit::Visitor<'ast> for BreakWithValue { | ||
| fn visit_expr(&mut self, ex: &'ast ast::Expr) { | ||
| match ex.kind { | ||
| ast::ExprKind::Break(_, Some(_)) => self.0 = true, | ||
| _ => { | ||
| visit::walk_expr(self, ex); | ||
| } | ||
| } | ||
| } | ||
| } | ||
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| let ast::ExprKind::Loop(ref block, ..) = expr.kind else { | ||
| return false; | ||
| }; | ||
| let mut finder = BreakWithValue(false); | ||
| visit::walk_block(&mut finder, block); | ||
| finder.0 | ||
| } |
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How does rustfmt know that v doesn't resolve to ()? Does it make a difference?
For example:
fn main() {
'a: loop {
break 'a some_callback_function_that_returns_empty_tuple()
};
'b: loop {
break 'b some_macro_that_evaluates_to_empty_tuple!()
};
}
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issue : semicolon_for_stmt grouped loop with for, while and discarded trailing semicolon. This is correct for for and while as they evaluate to () but loop can evaluate to some value. so when loop { break v } has the type of v and semicolon discarded then it becomes a bare expression statement, which rustc requires to be () . that's why we got compilation error.
Fix: check the loop body, if it breaks with value then keep the trailing semicolon else remove it as before.
Fixes : #7061