Error out if no Dockerfiles are found

This should fix #1795; now, if no Dockerfiles are found in the workspace
then skaffold will error out. If no k8s manifests are found it will
error out (already implemented).

Author: Priya Wadhwa

pkg/skaffold/initializer/init.go

@@ -290,6 +290,9 @@ func generateSkaffoldPipeline(k Initializer, dockerfilePairs []dockerfilePair) (
 }
 
 func printAnalyzeJSON(out io.Writer, dockerfiles, images []string) error {
+	if len(dockerfiles) == 0 {
+		return errors.New("one or more valid Dockerfiles must be present to run skaffold; please provide at least one Dockerfile and try again")
+	}
 	a := struct {
 		Dockerfiles []string `json:"dockerfiles,omitempty"`
 		Images      []string `json:"images,omitempty"`

pkg/skaffold/initializer/init_test.go

@@ -28,6 +28,7 @@ func TestPrintAnalyzeJSON(t *testing.T) {
 		name        string
 		dockerfiles []string
 		images      []string
+		shouldErr   bool
 		expected    string
 	}{
 		{
@@ -37,25 +38,20 @@ func TestPrintAnalyzeJSON(t *testing.T) {
 			expected:    "{\"dockerfiles\":[\"Dockerfile\",\"Dockerfile_2\"],\"images\":[\"image1\",\"image2\"]}",
 		},
 		{
-			name:     "no dockerfile",
-			images:   []string{"image1", "image2"},
-			expected: "{\"images\":[\"image1\",\"image2\"]}",
+			name:      "no dockerfile",
+			images:    []string{"image1", "image2"},
+			shouldErr: true,
 		},
 		{
-			name:        "no images",
-			dockerfiles: []string{"Dockerfile", "Dockerfile_2"},
-			expected:    "{\"dockerfiles\":[\"Dockerfile\",\"Dockerfile_2\"]}",
-		},
-		{
-			name:     "no dockerfiles or images",
-			expected: "{}",
+			name:      "no dockerfiles or images",
+			shouldErr: true,
 		},
 	}
 	for _, test := range tests {
 		t.Run(test.name, func(t *testing.T) {
 			out := bytes.NewBuffer([]byte{})
 			err := printAnalyzeJSON(out, test.dockerfiles, test.images)
-			testutil.CheckErrorAndDeepEqual(t, false, err, test.expected, out.String())
+			testutil.CheckErrorAndDeepEqual(t, test.shouldErr, err, test.expected, out.String())
 		})
 	}
 }