context.go: Clean GOPATH with filepath.Clean() before returning

Removes artifacts such as trailing and repeated separators, directory
navigation symbols ('./' '../').

Also add a test case to ensure that repeated separators are handled
correctly (relevant for golang#1946).

Author: jpentland

context.go

@@ -302,7 +302,7 @@ func (c *Ctx) detectGOPATH(path string) (string, error) {
 			return "", errors.Wrap(err, "failed to detect GOPATH")
 		}
 		if isPrefix {
-			return gp, nil
+			return filepath.Clean(gp), nil
 		}
 	}
 	return "", errors.Errorf("%s is not within a known GOPATH/src", path)

context_test.go

@@ -524,10 +524,14 @@ func TestDetectGOPATH(t *testing.T) {
 	th.TempDir(filepath.Join("code", "src", "github.com", "username", "package"))
 	th.TempDir(filepath.Join("go", "src", "github.com", "username", "package"))
 	th.TempDir(filepath.Join("gotwo", "src", "github.com", "username", "package"))
+	th.TempDir(filepath.Join("gothree", "sep", "src", "github.com", "username", "package"))
+
+	sep := string(os.PathSeparator)
 
 	ctx := &Ctx{GOPATHs: []string{
 		th.Path("go"),
 		th.Path("gotwo"),
+		th.Path("gothree") + sep + sep + "sep",
 	}}
 
 	testcases := []struct {
@@ -538,6 +542,8 @@ func TestDetectGOPATH(t *testing.T) {
 		{th.Path("go"), th.Path(filepath.Join("go", "src", "github.com", "username", "package")), false},
 		{th.Path("go"), th.Path(filepath.Join("go", "src", "github.com", "username", "package")), false},
 		{th.Path("gotwo"), th.Path(filepath.Join("gotwo", "src", "github.com", "username", "package")), false},
+		{th.Path(filepath.Join("gothree", "sep")),
+			th.Path(filepath.Join("gothree", "sep", "src", "github.com", "username", "package")), false},
 		{"", th.Path(filepath.Join("code", "src", "github.com", "username", "package")), true},
 	}