Fix error with merge composefile with networks…

cli/compose/loader/merge.go

@@ -61,7 +61,7 @@ func mergeServices(base, override []types.ServiceConfig) ([]types.ServiceConfig,
 	}
 	for name, overrideService := range overrideServices {
 		if baseService, ok := baseServices[name]; ok {
-			if err := mergo.Merge(&baseService, &overrideService, mergo.WithOverride, mergo.WithTransformers(specials)); err != nil {
+			if err := mergo.Merge(&baseService, &overrideService, mergo.WithAppendSlice, mergo.WithOverride, mergo.WithTransformers(specials)); err != nil {
 				return base, errors.Wrapf(err, "cannot merge service %s", name)
 			}
 			baseServices[name] = baseService
@@ -213,21 +213,21 @@ func mapByName(services []types.ServiceConfig) map[string]types.ServiceConfig {
 }
 
 func mergeVolumes(base, override map[string]types.VolumeConfig) (map[string]types.VolumeConfig, error) {
-	err := mergo.Map(&base, &override)
+	err := mergo.Map(&base, &override, mergo.WithOverride)
 	return base, err
 }
 
 func mergeNetworks(base, override map[string]types.NetworkConfig) (map[string]types.NetworkConfig, error) {
-	err := mergo.Map(&base, &override)
+	err := mergo.Map(&base, &override, mergo.WithOverride)
 	return base, err
 }
 
 func mergeSecrets(base, override map[string]types.SecretConfig) (map[string]types.SecretConfig, error) {
-	err := mergo.Map(&base, &override)
+	err := mergo.Map(&base, &override, mergo.WithOverride)
 	return base, err
 }
 
 func mergeConfigs(base, override map[string]types.ConfigObjConfig) (map[string]types.ConfigObjConfig, error) {
-	err := mergo.Map(&base, &override)
+	err := mergo.Map(&base, &override, mergo.WithOverride)
 	return base, err
 }

cli/compose/loader/merge_test.go

@@ -711,7 +711,7 @@ func TestLoadMultipleUlimits(t *testing.T) {
 	}
 }
 
-func TestLoadMultipleNetworks(t *testing.T) {
+func TestLoadMultipleServiceNetworks(t *testing.T) {
 	networkCases := []struct {
 		name            string
 		networkBase     map[string]interface{}
@@ -943,3 +943,74 @@ func TestLoadMultipleConfigs(t *testing.T) {
 		Configs:  map[string]types.ConfigObjConfig{},
 	}, config)
 }
+
+// Issue#972
+func TestLoadMultipleNetworks(t *testing.T) {
+	base := map[string]interface{}{
+		"version": "3.4",
+		"services": map[string]interface{}{
+			"foo": map[string]interface{}{
+				"image": "baz",
+			},
+		},
+		"volumes": map[string]interface{}{},
+		"networks": map[string]interface{}{
+			"hostnet": map[string]interface{}{
+				"driver": "overlay",
+				"ipam": map[string]interface{}{
+					"driver": "default",
+					"config": []interface{}{
+						map[string]interface{}{
+							"subnet": "10.0.0.0/20",
+						},
+					},
+				},
+			},
+		},
+		"secrets": map[string]interface{}{},
+		"configs": map[string]interface{}{},
+	}
+	override := map[string]interface{}{
+		"version":  "3.4",
+		"services": map[string]interface{}{},
+		"volumes":  map[string]interface{}{},
+		"networks": map[string]interface{}{
+			"hostnet": map[string]interface{}{
+				"external": map[string]interface{}{
+					"name": "host",
+				},
+			},
+		},
+		"secrets": map[string]interface{}{},
+		"configs": map[string]interface{}{},
+	}
+	configDetails := types.ConfigDetails{
+		ConfigFiles: []types.ConfigFile{
+			{Filename: "base.yml", Config: base},
+			{Filename: "override.yml", Config: override},
+		},
+	}
+	config, err := Load(configDetails)
+	assert.NilError(t, err)
+	assert.DeepEqual(t, &types.Config{
+		Filename: "base.yml",
+		Version:  "3.4",
+		Services: []types.ServiceConfig{
+			{
+				Name:        "foo",
+				Image:       "baz",
+				Environment: types.MappingWithEquals{},
+			}},
+		Networks: map[string]types.NetworkConfig{
+			"hostnet": {
+				Name: "host",
+				External: types.External{
+					External: true,
+				},
+			},
+		},
+		Volumes: map[string]types.VolumeConfig{},
+		Secrets: map[string]types.SecretConfig{},
+		Configs: map[string]types.ConfigObjConfig{},
+	}, config)
+}

vendor.conf

@@ -37,7 +37,7 @@ github.com/go-openapi/swag 1d0bd113de87027671077d3c71eb3ac5d7dbba72
 github.com/gregjones/httpcache c1f8028e62adb3d518b823a2f8e6a95c38bdd3aa
 github.com/grpc-ecosystem/grpc-gateway 1a03ca3bad1e1ebadaedd3abb76bc58d4ac8143b
 github.com/howeyc/gopass 3ca23474a7c7203e0a0a070fd33508f6efdb9b3d
-github.com/imdario/mergo ea74e0177b4df59af68c076af5008b427d00d40f
+github.com/imdario/mergo 9d5f1277e9a8ed20c3684bda8fde67c05628518c # v0.3.4
 github.com/inconshreveable/mousetrap 76626ae9c91c4f2a10f34cad8ce83ea42c93bb75
 github.com/juju/ratelimit 5b9ff866471762aa2ab2dced63c9fb6f53921342
 github.com/json-iterator/go 6240e1e7983a85228f7fd9c3e1b6932d46ec58e2