allow override by null

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

loader/loader.go

@@ -200,6 +200,8 @@ func Load(configDetails types.ConfigDetails, options ...func(*Options)) (*types.
 			configDetails.ConfigFiles[i] = file
 		}
 
+		configDict = markNullOverrides(configDict)
+
 		if !opts.SkipValidation {
 			if err := schema.Validate(configDict); err != nil {
 				return nil, err
@@ -333,6 +335,7 @@ func parseConfig(b []byte, opts *Options) (map[string]interface{}, error) {
 	if !opts.SkipInterpolation {
 		return interp.Interpolate(yml, *opts.Interpolate)
 	}
+
 	return yml, err
 }
 
@@ -341,6 +344,9 @@ 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 +1365,47 @@ 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: null # this should reset build section
+`
+	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 +1,83 @@
+/*
+   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"
+)
+
+func markNullOverrides(dict map[string]interface{}) map[string]interface{} {
+	for key, value := range dict {
+		if value == nil {
+			dict[key] = map[string]interface{}{
+				"x-null": true, // we use this as a marker for elements to be reset during merge
+			}
+		}
+		if d, ok := value.(map[string]interface{}); ok {
+			dict[key] = markNullOverrides(d)
+		}
+	}
+	return dict
+}
+
+var null = reflect.ValueOf("x-null")
+
+func applyNullOverrides(i interface{}) error {
+	val := reflect.ValueOf(i)
+	val = reflect.Indirect(val)
+	typ := val.Type()
+	fmt.Println(typ.Name())
+
+	fields := typ.NumField()
+	for i := 0; i < fields; 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).Interface())
+				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)
+					elem := val.Field(i).Elem()
+					if !elem.CanSet() {
+						return fmt.Errorf("can't override attribute %s", name)
+					}
+					elem.SetZero()
+					continue
+				}
+			}
+			err := applyNullOverrides(val.Field(i).Interface())
+			if err != nil {
+				return err
+			}
+		}
+	}
+	return nil
+}