Fix git-init in case master is not the default branch

This fix will patch the `git-init` such that if user doesn't provides revision then instead of taking `master` as the default branch we are doing the `symbolic-link` to the HEAD branch.

Signed-off-by: vinamra28 <[email protected]>

pkg/apis/resource/v1alpha1/git/git_resource_test.go

@@ -675,6 +675,44 @@ func TestGitResource_GetDownloadTaskModifier(t *testing.T) {
 				{Name: "NO_PROXY", Value: "no-proxy.git.com"},
 			},
 		},
+	}, {
+		desc: "Without Refspec and without revision",
+		gitResource: &git.Resource{
+			Name:       "git-resource",
+			Type:       resourcev1alpha1.PipelineResourceTypeGit,
+			URL:        "[email protected]:test/test.git",
+			Revision:   "",
+			Refspec:    "",
+			GitImage:   "override-with-git:latest",
+			Submodules: false,
+			Depth:      1,
+			SSLVerify:  true,
+			HTTPProxy:  "http-proxy.git.com",
+			HTTPSProxy: "https-proxy.git.com",
+			NOProxy:    "no-proxy.git.com",
+		},
+		want: corev1.Container{
+			Name:    "git-source-git-resource-twkr2",
+			Image:   "override-with-git:latest",
+			Command: []string{"/ko-app/git-init"},
+			Args: []string{
+				"-url",
+				"[email protected]:test/test.git",
+				"-revision",
+				"",
+				"-path",
+				"/test/test",
+				"-submodules=false",
+			},
+			WorkingDir: "/workspace",
+			Env: []corev1.EnvVar{
+				{Name: "TEKTON_RESOURCE_NAME", Value: "git-resource"},
+				{Name: "HOME", Value: pipeline.HomeDir},
+				{Name: "HTTP_PROXY", Value: "http-proxy.git.com"},
+				{Name: "HTTPS_PROXY", Value: "https-proxy.git.com"},
+				{Name: "NO_PROXY", Value: "no-proxy.git.com"},
+			},
+		},
 	}} {
 		t.Run(tc.desc, func(t *testing.T) {
 			ts := v1beta1.TaskSpec{}

pkg/git/git.go

@@ -65,7 +65,7 @@ func Fetch(logger *zap.SugaredLogger, spec FetchSpec) error {
 	}
 
 	if spec.Revision == "" {
-		spec.Revision = "master"
+		spec.Revision = "HEAD"
 	}
 	if spec.Path != "" {
 		if _, err := run(logger, "", "init", spec.Path); err != nil {
@@ -85,7 +85,13 @@ func Fetch(logger *zap.SugaredLogger, spec FetchSpec) error {
 		logger.Warnf("Failed to set http.sslVerify in git config: %s", err)
 		return err
 	}
-
+	if spec.Revision == "" {
+		spec.Revision = "HEAD"
+		if _, err := run(logger, "", "symbolic-ref", spec.Revision, "refs/remotes/origin/HEAD"); err != nil {
+			return err
+		}
+	}
+
 	fetchArgs := []string{"fetch"}
 	if spec.Submodules {
 		fetchArgs = append(fetchArgs, "--recurse-submodules=yes")