key.s = seg.s
			}
			idx.segments[key] = append(idx.segments[key], pat)
		}
	}
}

// possiblyConflictingPatterns calls f on all patterns that might conflict with
// pat. If f returns a non-nil error, possiblyConflictingPatterns returns immediately
// with that error.
//
// To be correct, possiblyConflictingPatterns must include all patterns that
// might conflict. But it may also include patterns that cannot conflict.

		if pat.conflictsWith(p) {
			s = append(s, p.String())
		}
	}
	slices.Sort(s)
	return s
}

func indexConflicts(pat *pattern, idx *routingIndex) []string {
	var s []string
	idx.possiblyConflictingPatterns(pat, func(p *pattern) error {
		if pat.conflictsWith(p) {
			s = append(s, p.String())
		}
		return nil
	})
	slices.Sort(s)
	return slices.Compact(s)
}

		pat.loc = "unknown location"
	} else {
		pat.loc = fmt.Sprintf("%s:%d", file, line)
	}

	mux.mu.Lock()
	defer mux.mu.Unlock()
	// Check for conflict.
	if err := mux.index.possiblyConflictingPatterns(pat, func(pat2 *pattern) error {
		if pat.conflictsWith(pat2) {
			d := describeConflict(pat, pat2)
			return fmt.Errorf("pattern %q (registered at %s) conflicts with pattern %q (registered at %s):\n%s",