allow override to REMOVE elements by using x-null

Signed-off-by: Nicolas De Loof <nicolas.deloof@gmail.com>

loader/loader.go

@@ -341,6 +341,9 @@ const extensions = "#extensions" // Using # prefix, we prevent risk to conflict
 func groupXFieldsIntoExtensions(dict map[string]interface{}) map[string]interface{} {
 	extras := map[string]interface{}{}
 	for key, value := range dict {
+		if key == extensions {
+			continue
+		}
 		if strings.HasPrefix(key, "x-") {
 			extras[key] = value
 			delete(dict, key)

loader/merge.go

@@ -86,6 +86,11 @@ func merge(configs []*types.Config) (*types.Config, error) {
 		if err != nil {
 			return base, errors.Wrapf(err, "cannot merge extensions from %s", override.Filename)
 		}
+
+		err = applyNullOverrides(base)
+		if err != nil {
+			return nil, err
+		}
 	}
 	return base, nil
 }

loader/merge_test.go

@@ -20,6 +20,7 @@ import (
 	"reflect"
 	"testing"
 
+	"github.com/compose-spec/compose-go/consts"
 	"github.com/imdario/mergo"
 
 	"github.com/compose-spec/compose-go/types"
@@ -1364,3 +1365,48 @@ func TestMergeExtraHosts(t *testing.T) {
 		},
 	)
 }
+
+func TestLoadWithNullOverride(t *testing.T) {
+	base := `
+name: test
+services:
+  foo:
+    build:
+      context: .
+      dockerfile: foo.Dockerfile
+`
+	override := `
+services:
+  foo:
+    image: foo
+    build: 
+      x-null:   # this will reset build section to nil
+`
+	configDetails := types.ConfigDetails{
+		Environment: map[string]string{},
+		ConfigFiles: []types.ConfigFile{
+			{Filename: "base.yml", Content: []byte(base)},
+			{Filename: "override.yml", Content: []byte(override)},
+		},
+	}
+	config, err := loadTestProject(configDetails)
+	assert.NilError(t, err)
+	assert.DeepEqual(t, &types.Project{
+		Name:       "test",
+		WorkingDir: "",
+		Services: []types.ServiceConfig{
+			{
+				Name:        "foo",
+				Image:       "foo",
+				Environment: types.MappingWithEquals{},
+				Scale:       1,
+			},
+		},
+		Networks:    types.Networks{},
+		Volumes:     types.Volumes{},
+		Secrets:     types.Secrets{},
+		Configs:     types.Configs{},
+		Extensions:  types.Extensions{},
+		Environment: map[string]string{consts.ComposeProjectName: "test"},
+	}, config)
+}

loader/null.go

@@ -0,0 +1,74 @@
+/*
+   Copyright 2020 The Compose Specification Authors.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+
+package loader
+
+import (
+	"fmt"
+	"reflect"
+
+	"github.com/sirupsen/logrus"
+)
+
+var null = reflect.ValueOf("x-null")
+
+func applyNullOverrides(i interface{}) error {
+	return _applyNullOverrides(reflect.ValueOf(i))
+}
+
+func _applyNullOverrides(val reflect.Value) error {
+	val = reflect.Indirect(val)
+	typ := val.Type()
+	if typ.Kind() != reflect.Struct {
+		return nil
+	}
+
+	for i := 0; i < typ.NumField(); i++ {
+		v := reflect.Indirect(val.Field(i))
+
+		name := typ.Field(i).Name
+		switch v.Kind() {
+		case reflect.Slice:
+			for i := 0; i < v.Len(); i++ {
+				err := _applyNullOverrides(v.Index(i))
+				if err != nil {
+					return err
+				}
+			}
+		case reflect.Struct:
+			// search for Extensions["x-null"]. If set, reset field
+			extensions := v.FieldByName("Extensions")
+			if extensions.IsValid() {
+				xNull := extensions.MapIndex(null)
+				if xNull.IsValid() {
+					logrus.Debugf("%s reset to null", name)
+					f := val.Field(i)
+					if !f.CanSet() {
+						return fmt.Errorf("can't override attribute %s", name)
+					}
+					// f.SetZero() requires go 1.20
+					f.Set(reflect.Zero(f.Type()))
+					continue
+				}
+			}
+			err := _applyNullOverrides(val.Field(i))
+			if err != nil {
+				return err
+			}
+		}
+	}
+	return nil
+}