1// Copyright 2023 The Go Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style
3// license that can be found in the LICENSE file.
4
5package gover
6
7import (
8	"bytes"
9	"strings"
10)
11
12var nl = []byte("\n")
13
14// GoModLookup takes go.mod or go.work content,
15// finds the first line in the file starting with the given key,
16// and returns the value associated with that key.
17//
18// Lookup should only be used with non-factored verbs
19// such as "go" and "toolchain", usually to find versions
20// or version-like strings.
21func GoModLookup(gomod []byte, key string) string {
22	for len(gomod) > 0 {
23		var line []byte
24		line, gomod, _ = bytes.Cut(gomod, nl)
25		line = bytes.TrimSpace(line)
26		if v, ok := parseKey(line, key); ok {
27			return v
28		}
29	}
30	return ""
31}
32
33func parseKey(line []byte, key string) (string, bool) {
34	if !strings.HasPrefix(string(line), key) {
35		return "", false
36	}
37	s := strings.TrimPrefix(string(line), key)
38	if len(s) == 0 || (s[0] != ' ' && s[0] != '\t') {
39		return "", false
40	}
41	s, _, _ = strings.Cut(s, "//") // strip comments
42	return strings.TrimSpace(s), true
43}
44