in match/optimize.go [226:274]
func flattenRepetition(r *syntax.Regexp) (bool, *syntax.Regexp) {
if r.Op != syntax.OpConcat {
// don't iterate sub-expressions if top-level is no OpConcat
return false, r
}
sub := r.Sub
inRepetition := false
if isConcatRepetition(r) {
sub = sub[:1]
inRepetition = true
// create flattened regex repetition multiplying count
// if nexted expression is also a repetition
if s := sub[0]; isConcatRepetition(s) {
count := len(s.Sub) * len(r.Sub)
return true, &syntax.Regexp{
Op: syntax.OpRepeat,
Sub: s.Sub[:1],
Min: count,
Max: count,
Flags: r.Flags | s.Flags,
}
}
}
// recursively check if we can flatten sub-expressions
changed := false
for i, s := range sub {
upd, tmp := flattenRepetition(s)
changed = changed || upd
sub[i] = tmp
}
if !changed {
return false, r
}
// fix up top-level repetition with modified one
tmp := *r
if inRepetition {
for i := range r.Sub {
tmp.Sub[i] = sub[0]
}
} else {
tmp.Sub = sub
}
return changed, &tmp
}