1 files changed, 47 insertions, 0 deletions
diff --git a/libgo/go/cmd/go/internal/modfile/gopkgin.go b/libgo/go/cmd/go/internal/modfile/gopkgin.go
new file mode 100644
index 00000000000..c94b3848a0e
--- /dev/null
+++ b/libgo/go/cmd/go/internal/modfile/gopkgin.go
@@ -0,0 +1,47 @@
+// Copyright 2018 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.
+
+// TODO: Figure out what gopkg.in should do.
+
+package modfile
+
+import "strings"
+
+// ParseGopkgIn splits gopkg.in import paths into their constituent parts
+func ParseGopkgIn(path string) (root, repo, major, subdir string, ok bool) {
+	if !strings.HasPrefix(path, "gopkg.in/") {
+		return
+	}
+	f := strings.Split(path, "/")
+	if len(f) >= 2 {
+		if elem, v, ok := dotV(f[1]); ok {
+			root = strings.Join(f[:2], "/")
+			repo = "github.com/go-" + elem + "/" + elem
+			major = v
+			subdir = strings.Join(f[2:], "/")
+			return root, repo, major, subdir, true
+		}
+	}
+	if len(f) >= 3 {
+		if elem, v, ok := dotV(f[2]); ok {
+			root = strings.Join(f[:3], "/")
+			repo = "github.com/" + f[1] + "/" + elem
+			major = v
+			subdir = strings.Join(f[3:], "/")
+			return root, repo, major, subdir, true
+		}
+	}
+	return
+}
+
+func dotV(name string) (elem, v string, ok bool) {
+	i := len(name) - 1
+	for i >= 0 && '0' <= name[i] && name[i] <= '9' {
+		i--
+	}
+	if i <= 2 || i+1 >= len(name) || name[i-1] != '.' || name[i] != 'v' || name[i+1] == '0' && len(name) != i+2 {
+		return "", "", false
+	}
+	return name[:i-1], name[i:], true
+}