Failure to split a line exceeding the maximum width

[Jarcho]

The following code fails to format line formatted, but exceeded maximum width:

impl EarlyLintPass for NeedlessContinue {
    fn check_expr(&mut self, cx: &EarlyContext<'_>, expr: &Expr) {
        if let ExprKind::Loop(body, label, ..) | ExprKind::While(_, body, label) | ExprKind::ForLoop { body, label, .. } =
            &expr.kind
            && !in_external_macro(cx.sess, expr.span)
        {
            check_final_block_stmt(cx, body, label, expr.span.ctxt());
        }
    }
}

The line causing the error is the if let pattern (122 characters). Shortening the line by one character causes the same issue. Adding one character to the line causes it to be formatted correctly.

config:

max_width = 120
comment_width = 100
match_block_trailing_comma = true
wrap_comments = true
edition = "2021"
error_on_line_overflow = true
imports_granularity = "Module"
version = "Two"
ignore = ["tests/ui/crashes/ice-10912.rs"]

version: rustfmt 1.7.0-nightly (8337ba91 2024-06-12)

[ytmimi]

Thanks for the report! I think the issue here is that we're not taking the trailing = into account when rewriting the pattern. I think the issue is in rewrite_let

rustfmt/src/expr.rs

Lines 1852 to 1884 in 3ffd7d4

	fn rewrite_let(
	context: &RewriteContext<'_>,
	shape: Shape,
	pat: &ast::Pat,
	expr: &ast::Expr,
	) -> Option<String> {
	let mut result = "let ".to_owned();
	// TODO(ytmimi) comments could appear between `let` and the `pat`
	// 4 = "let ".len()
	let pat_shape = shape.offset_left(4)?;
	let pat_str = pat.rewrite(context, pat_shape)?;
	result.push_str(&pat_str);
	// TODO(ytmimi) comments could appear between `pat` and `=`
	result.push_str(" =");
	let comments_lo = context
	.snippet_provider
	.span_after(expr.span.with_lo(pat.span.hi()), "=");
	let comments_span = mk_sp(comments_lo, expr.span.lo());
	rewrite_assign_rhs_with_comments(
	context,
	result,
	expr,
	shape,
	&RhsAssignKind::Expr(&expr.kind, expr.span),
	RhsTactics::Default,
	comments_span,
	true,
	)
	}

and I thinks something like this would resolve the issue:

    if context.config.version() == Version::Two {
        // 2 for the length of " ="
        pat_shape = pat_shape.sub_width(2)?
    }

[CalebLItalien]

Can I be assigned to this issue? I haven't contributed to rust-lang before, so I'm looking for a good first issue.

[ytmimi]

@CalebLItalien I just assigned you. Just a tip, in the future you can comment @rustbot claim to assign yourself if you see an issue you'd like to work on!

[CalebLItalien]

Thanks for letting me know! I see that I can post questions I have on this issue here and to the Discord. Which would you recommend? @ytmimi

[ytmimi]

The rustfmt team doesn't use Discord that much these days. You can reach out here, though the best place to ask about rustfmt development related questions is the t-rustfmt channel on Zulip