config/module: fix some issues where tag re-pulling didnt' work

config/module/get_git.go

@@ -17,10 +17,17 @@ func (g *GitGetter) Get(dst string, u *url.URL) error {
 	}
 
 	// Extract some query parameters we use
+	var tag string
 	q := u.Query()
-	tag := q.Get("tag")
+	if len(q) > 0 {
+		tag = q.Get("tag")
 		q.Del("tag")
+
+		// Copy the URL
+		var newU url.URL = *u
+		u = &newU
 		u.RawQuery = q.Encode()
+	}
 
 	// First: clone or update the repository
 	_, err := os.Stat(dst)
@@ -56,6 +63,11 @@ func (g *GitGetter) clone(dst string, u *url.URL) error {
 }
 
 func (g *GitGetter) update(dst string, u *url.URL) error {
+	// We have to be on a branch to pull
+	if err := g.checkout(dst, "master"); err != nil {
+		return err
+	}
+
 	cmd := exec.Command("git", "pull", "--ff-only")
 	cmd.Dir = dst
 	return getRunCommand(cmd)

config/module/get_git_test.go

@@ -83,4 +83,15 @@ func TestGitGetter_tag(t *testing.T) {
 	if _, err := os.Stat(mainPath); err != nil {
 		t.Fatalf("err: %s", err)
 	}
+
+	// Get again should work
+	if err := g.Get(dst, url); err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	// Verify the main file exists
+	mainPath = filepath.Join(dst, "main_tag1.tf")
+	if _, err := os.Stat(mainPath); err != nil {
+		t.Fatalf("err: %s", err)
+	}
 }