Skip the apply_mutators phase when no mutators are configured

.nextchanges/bundles/skip-apply-mutators-without-mutators.md

@@ -0,0 +1 @@
+Skip the `apply_mutators` phase when no `python.mutators` are configured, so bundles that only load resources in Python no longer start a subprocess that loads every resource and returns it unchanged.

bundle/config/mutator/python/python_mutator.go

@@ -124,6 +124,13 @@ func getOpts(b *bundle.Bundle, phase phase) (opts, error) {
 		return opts{}, errors.New("experimental/pydabs is deprecated, use python instead (https://docs.databricks.com/dev-tools/bundles/python)")
 	}
 
+	// Without mutator functions there is nothing to mutate, so skip the subprocess that would load
+	// every resource and return it unchanged. load_resources still reports configuration errors.
+	if phase == PythonMutatorPhaseApplyMutators &&
+		len(b.Config.Python.Mutators) == 0 && len(experimental.Python.Mutators) == 0 {
+		return opts{}, nil
+	}
+
 	if experimentalPythonEnabled && pythonEnabled {
 		if !reflect.DeepEqual(experimental.Python, b.Config.Python) {
 			return opts{}, errors.New("'experimental/python' and 'python' configuration properties are mutually exclusive, use only 'python'")

bundle/config/mutator/python/python_mutator_test.go

@@ -406,6 +406,56 @@ func TestGetOps_empty(t *testing.T) {
 	assert.Equal(t, opts{enabled: false}, actual)
 }
 
+func TestGetOps_ApplyMutatorsWithoutMutators(t *testing.T) {
+	actual, err := getOpts(&bundle.Bundle{
+		Config: config.Root{
+			Python: config.Python{
+				VEnvPath: ".venv",
+				Resources: []string{
+					"resources:load_resources",
+				},
+			},
+		},
+	}, PythonMutatorPhaseApplyMutators)
+
+	assert.NoError(t, err)
+	assert.Equal(t, opts{enabled: false}, actual)
+}
+
+func TestGetOps_ApplyMutators(t *testing.T) {
+	actual, err := getOpts(&bundle.Bundle{
+		Config: config.Root{
+			Python: config.Python{
+				VEnvPath: ".venv",
+				Mutators: []string{
+					"mutators:add_email_notifications",
+				},
+			},
+		},
+	}, PythonMutatorPhaseApplyMutators)
+
+	assert.NoError(t, err)
+	assert.Equal(t, opts{venvPath: ".venv", enabled: true, loadLocations: true}, actual)
+}
+
+func TestGetOps_ApplyMutatorsExperimental(t *testing.T) {
+	actual, err := getOpts(&bundle.Bundle{
+		Config: config.Root{
+			Experimental: &config.Experimental{
+				Python: config.Python{
+					VEnvPath: ".venv",
+					Mutators: []string{
+						"mutators:add_email_notifications",
+					},
+				},
+			},
+		},
+	}, PythonMutatorPhaseApplyMutators)
+
+	assert.NoError(t, err)
+	assert.Equal(t, opts{venvPath: ".venv", enabled: true, loadLocations: true}, actual)
+}
+
 func TestApplyBackwardCompatibilityFixes(t *testing.T) {
 	b := &bundle.Bundle{
 		Config: config.Root{