fix: check for --image flag in build command

If the user provides an `--image` flag on the command line, it should be
used. This commit modifies the image resolving code to check whether or
not the image name was provided on the command line.

Fixes: knative#1125

Signed-off-by: Lance Ball <lball@redhat.com>

cmd/build.go

@@ -151,7 +151,7 @@ func runBuild(cmd *cobra.Command, _ []string, newClient ClientFactory) (err erro
 	}
 
 	// If the function does not yet have an image name and one was not provided on the command line
-	if function.Image == "" {
+	if function.Image == "" && config.Image == "" {
 		//  AND a --registry was not provided, then we need to
 		// prompt for a registry from which we can derive an image name.
 		if config.Registry == "" {
@@ -171,6 +171,7 @@ func runBuild(cmd *cobra.Command, _ []string, newClient ClientFactory) (err erro
 
 		// We have the registry, so let's use it to derive the function image name
 		config.Image = deriveImage(config.Image, config.Registry, config.Path)
+
 		function.Image = config.Image
 	}
 

cmd/build_test.go

@@ -14,6 +14,48 @@ import (
 	. "knative.dev/kn-plugin-func/testing"
 )
 
+// TestBuild_ImageFlag ensures that the image flag is used when specified.
+func TestBuild_ImageFlag(t *testing.T) {
+	var (
+		args    = []string{"--image", "docker.io/tigerteam/foo"}
+		builder = mock.NewBuilder()
+	)
+
+	root, cleanup := Mktemp(t)
+	defer cleanup()
+
+	// Write a func.yaml config which does not specify an image
+	funcYaml := `name: foo
+runtime: go
+builder: pack
+created: 2022-01-01T00:00:00+00:00
+`
+	if err := ioutil.WriteFile("func.yaml", []byte(funcYaml), 0600); err != nil {
+		t.Fatal(err)
+	}
+
+	// Create build command that will use a mock builder.
+	cmd := NewBuildCmd(NewClientFactory(func() *fn.Client {
+		return fn.New(fn.WithBuilder(builder))
+	}))
+
+	// Execute the command
+	cmd.SetArgs(args)
+	err := cmd.Execute()
+	if err != nil {
+		t.Fatal("Expected error")
+	}
+
+	// Now load the function and ensure that the image is set correctly.
+	f, err := fn.NewFunction(root)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if f.Image != "docker.io/tigerteam/foo" {
+		t.Fatalf("Expected image to be 'docker.io/tigerteam/foo', but got '%v'", f.Image)
+	}
+}
+
 // TestBuild_InvalidRegistry ensures that running build specifying the name of the
 // registry explicitly as an argument invokes the registry validation code.
 func TestBuild_InvalidRegistry(t *testing.T) {