Method replace

replacer.go:175–287

(input, empty string,
	treatUnknownAsEmpty, errOnEmpty, errOnUnknown bool,
	f ReplacementFunc,
)

}

func (r *Replacer) replace(input, empty string,
	treatUnknownAsEmpty, errOnEmpty, errOnUnknown bool,
	f ReplacementFunc,
) (string, error) {
	if !strings.Contains(input, string(phOpen)) && !strings.Contains(input, string(phClose)) {
		return input, nil
	}

	var sb strings.Builder

	// it is reasonable to assume that the output
	// will be approximately as long as the input
	sb.Grow(len(input))

	// iterate the input to find each placeholder
	var lastWriteCursor int

	// fail fast if too many placeholders are unclosed
	var unclosedCount int

scan:
	for i := 0; i < len(input); i++ {
		// check for escaped braces
		if i > 0 && input[i-1] == phEscape && (input[i] == phClose || input[i] == phOpen) {
			sb.WriteString(input[lastWriteCursor : i-1])
			lastWriteCursor = i
			continue
		}

		if input[i] != phOpen {
			continue
		}

		// our iterator is now on an unescaped open brace (start of placeholder)

		// too many unclosed placeholders in absolutely ridiculous input can be extremely slow (issue #4170)
		if unclosedCount > 100 {
			return "", fmt.Errorf("too many unclosed placeholders")
		}

		// find the end of the placeholder
		end := strings.Index(input[i:], string(phClose)) + i
		if end < i {
			unclosedCount++
			continue
		}

		// if necessary look for the first closing brace that is not escaped
		for end > 0 && end < len(input)-1 && input[end-1] == phEscape {
			nextEnd := strings.Index(input[end+1:], string(phClose))
			if nextEnd < 0 {
				unclosedCount++
				continue scan
			}
			end += nextEnd + 1
		}

		// write the substring from the last cursor to this point