fix(docker): provide workaround to save network name variable (#6080)

* fix/EE-1862/unable-to-stop-or-remove-stack workaround for var without default value in yaml file

* fix/EE-1862/unable-to-stop-or-remove-stack check yaml file

* fixed func and var names

* wrapper error and used bool for stringset

* UT case for createNetworkEnvFile

* UT case for %s=%s

* powerful StringSet

* wrapper error for extract network name

* wrapper all the return err

* store more env

* put to env file

* make default value None

api/exec/compose_stack_test.go

@@ -64,3 +64,57 @@ func Test_createEnvFile(t *testing.T) {
 		})
 	}
 }
+
+func Test_createNetworkEnvFile(t *testing.T) {
+	dir := t.TempDir()
+	buf := []byte(`
+version: '3.6'
+services:
+  nginx-example:
+    image: nginx:latest
+networks:
+  default:
+    name: ${test}
+    driver: bridge
+`)
+	if err := ioutil.WriteFile(path.Join(dir,
+		"docker-compose.yml"), buf, 0644); err != nil {
+		t.Fatalf("Failed to create yaml file: %s", err)
+	}
+
+	stackWithoutEnv := &portainer.Stack{
+		ProjectPath: dir,
+		EntryPoint:  "docker-compose.yml",
+		Env:         []portainer.Pair{},
+	}
+
+	if err := createNetworkEnvFile(stackWithoutEnv); err != nil {
+		t.Fatalf("Failed to create network env file: %s", err)
+	}
+
+	content, err := ioutil.ReadFile(path.Join(dir, ".env"))
+	if err != nil {
+		t.Fatalf("Failed to read network env file: %s", err)
+	}
+
+	assert.Equal(t, "test=None\n", string(content))
+
+	stackWithEnv := &portainer.Stack{
+		ProjectPath: dir,
+		EntryPoint:  "docker-compose.yml",
+		Env: []portainer.Pair{
+			{Name: "test", Value: "test-value"},
+		},
+	}
+
+	if err := createNetworkEnvFile(stackWithEnv); err != nil {
+		t.Fatalf("Failed to create network env file: %s", err)
+	}
+
+	content, err = ioutil.ReadFile(path.Join(dir, ".env"))
+	if err != nil {
+		t.Fatalf("Failed to read network env file: %s", err)
+	}
+
+	assert.Equal(t, "test=test-value\n", string(content))
+}