Repository navigation
Incorrect "struct_variant_width cannot have a value that exceeds max_width" when using macros #7147
Description
Summary
Using struct_variant_width = 0 config option triggers an incorrect warning when encountering a macro.
Using this code:
macro_rules! m {
() => {};
}With config struct_variant_width =0, gives the following warning
`struct_variant_width` cannot have a value that exceeds `max_width`. `struct_variant_width` will be set to the same value as `max_width`
Potential Clause
Claude Opus 5.5 minimized this bug. It thinks the issue was introduced by PR #6651. The new adjust_max_width function will underflow if any of the width configs are smaller than the indenetation (permalink).
fn adjust_max_width(&mut self, delta: isize) {
// overflows whenever value < -delta
let adjust = |value: usize| (value as isize + delta) as usize;
// if `self.array_width = 0`, this will overflow for delta < 0
self.array_width.2 = adjust(self.array_width.2);
// <similar adjustments>
self.struct_variant_width.2 = adjust(self.struct_variant_width.2); // this is likely causing the issue
self.max_width.2 = adjust(self.max_width.2);
self.set_heuristics();
}This seems like a resonable theory, but I have not yet confirmed it.
If this theory is correct, claude suggests using usize::saturating_add_signed to avoid this underflow.
Meta
Version it worked on
This worked just fine on nightly-2026-09-16.
Version with regression
The problem occurs on rustfmt 1.11.0-nightly (75a75c3e0a 2026-09-26)
Activity
test(config): add regression test for `adjust_max_width` overflows
test(config): add regression test for `adjust_max_width` overflows
test(config): add regression test for `adjust_max_width` overflows
Auto merge of #163547 - jieyouxu:rustfmt-beta-backport, r=ytmimi