[BUG] Brace expansion with exactly 2 alternatives fails to match when 1, 3, or 4+ alternatives work correctly

[a244591052]

Summary

There appears to be a bug in the brace expansion logic when a pattern contains exactly 2 alternatives in braces {option1,option2}. Patterns with 1, 3, or 4+ alternatives work correctly, but patterns with exactly 2 alternatives fail to match even when the logic should succeed.

Reproduction Steps

package main

import (
    "fmt"
    "github.com/gobwas/glob"
)

func main() {
    input := "playground/daxing/generated/dev.yaml"
    
    // Test patterns with different numbers of brace alternatives
    testPatterns := []string{
        "{**/daxing}/**/*dev*.yaml",           // 1 option - WORKS
        "{**/daxing,daxing}/**/*dev*.yaml",    // 2 options - FAILS
        "{**/daxing,daxing,x}/**/*dev*.yaml",  // 3 options - WORKS  
        "{**/daxing,daxing,x,y}/**/*dev*.yaml", // 4 options - WORKS
    }
    
    for _, pattern := range testPatterns {
        g, _ := glob.Compile(pattern)
        result := g.Match(input)
        fmt.Printf("Pattern %s matches: %v\n", pattern, result)
    }
}

Expected Behavior

All patterns should return true since:

• **/daxing matches playground/daxing in the input path
• /**/*dev*.yaml matches /generated/dev.yaml portion

Actual Behavior

Pattern {**/daxing}/**/*dev*.yaml matches: true
Pattern {**/daxing,daxing}/**/*dev*.yaml matches: false  ← BUG
Pattern {**/daxing,daxing,x}/**/*dev*.yaml matches: true
Pattern {**/daxing,daxing,x,y}/**/*dev*.yaml matches: true

Analysis

The issue seems specific to brace expansions with exactly 2 alternatives. The pattern {**/daxing,daxing} should expand to two possibilities and match if either one matches, but this logic appears to fail.

Environment

• Go version: 1.24.1
• gobwas/glob version: v0.2.3

Workaround

Adding a dummy third option makes the pattern work:

"{**/daxing,daxing,dummy}/**/*dev*.yaml"  // Returns true