trailing_semicolon = false changes the meaning of code, non-idempotent

[digama0]

The trailing_semicolon = false option, when run on this code:

fn foo() {}
fn main() {
    return;
    foo()
}

turns it into

fn foo() {}
fn main() {
    return
    foo()
}

which now runs foo() where it did not before, as a second run of rustfmt will make clearer:

fn foo() {}
fn main() {
    return foo()
}

Observed on rustfmt 1.5.3-nightly (065a1f5 2023-06-21).

[calebcartwright]

thanks for the report! tagging tracking issue: #3378

[calebcartwright]

@CosmicHorrorDev & @HarrisonHemstreet this is another one that should be a relatively quick fix if either of you are interested in working on it.

As discussed in chat don't feel obligated to work on any of these, we're just tagging things as they pop up if we think could be good opportunities for you.

I'm going to be a bit more lightweight in initial guidance on this one to give you more opportunity to poke around, so all I'll say for now is that you may want to start around here:

rustfmt/src/utils.rs

Lines 295 to 309 in 9386b32

	pub(crate) fn semicolon_for_stmt(context: &RewriteContext<'_>, stmt: &ast::Stmt) -> bool {
	match stmt.kind {
	ast::StmtKind::Semi(ref expr) => match expr.kind {
	ast::ExprKind::While(..) | ast::ExprKind::Loop(..) | ast::ExprKind::ForLoop(..) => {
	false
	}
	ast::ExprKind::Break(..) | ast::ExprKind::Continue(..) | ast::ExprKind::Ret(..) => {
	context.config.trailing_semicolon()
	}
	_ => true,
	},
	ast::StmtKind::Expr(..) => false,
	_ => true,
	}
	}

[CosmicHorrorDev]

I'm up for digging into it this weekend if @HarrisonHemstreet is fine with that