1 files changed, 43 insertions, 0 deletions
diff --git a/src/cmd/go/internal/gover/gomod.go b/src/cmd/go/internal/gover/gomod.go
new file mode 100644
index 0000000..4a4ae53
--- /dev/null
+++ b/src/cmd/go/internal/gover/gomod.go
@@ -0,0 +1,43 @@
+// Copyright 2023 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package gover
+
+import (
+	"bytes"
+	"strings"
+)
+
+var nl = []byte("\n")
+
+// GoModLookup takes go.mod or go.work content,
+// finds the first line in the file starting with the given key,
+// and returns the value associated with that key.
+//
+// Lookup should only be used with non-factored verbs
+// such as "go" and "toolchain", usually to find versions
+// or version-like strings.
+func GoModLookup(gomod []byte, key string) string {
+	for len(gomod) > 0 {
+		var line []byte
+		line, gomod, _ = bytes.Cut(gomod, nl)
+		line = bytes.TrimSpace(line)
+		if v, ok := parseKey(line, key); ok {
+			return v
+		}
+	}
+	return ""
+}
+
+func parseKey(line []byte, key string) (string, bool) {
+	if !strings.HasPrefix(string(line), key) {
+		return "", false
+	}
+	s := strings.TrimPrefix(string(line), key)
+	if len(s) == 0 || (s[0] != ' ' && s[0] != '\t') {
+		return "", false
+	}
+	s, _, _ = strings.Cut(s, "//") // strip comments
+	return strings.TrimSpace(s), true
+}