snapshot of https://github.com/mattermost/mattermost.git (master, 2026-09-16; blobs > 131072B omitted)

server/channels/utils/merge.go

@@ -0,0 +1,170 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package utils
+
+import (
+	"fmt"
+	"reflect"
+)
+
+// StructFieldFilter defines a callback function used to decide if a patch value should be applied.
+type StructFieldFilter func(structField reflect.StructField, base reflect.Value, patch reflect.Value) bool
+
+// MergeConfig allows for optional merge customizations.
+type MergeConfig struct {
+	StructFieldFilter StructFieldFilter
+}
+
+// Merge will return a new value of the same type as base and patch, recursively merging non-nil values from patch on top of base.
+//
+// Restrictions/guarantees:
+//   - base and patch must be the same type
+//   - base and patch will never be modified
+//   - values from patch are always selected when non-nil
+//   - structs are merged recursively
+//   - maps and slices are treated as pointers, and merged as a single value
+//
+// Note that callers need to cast the returned interface back into the original type:
+//
+//	func mergeTestStruct(base, patch *testStruct) (*testStruct, error) {
+//	    ret, err := merge(base, patch)
+//	    if err != nil {
+//	        return nil, err
+//	    }
+//
+//	    retTS := ret.(testStruct)
+//	    return &retTS, nil
+//	}
+func Merge[T any](base T, patch T, mergeConfig *MergeConfig) (T, error) {
+	commonType := reflect.TypeOf(base)
+	baseVal := reflect.ValueOf(base)
+	patchVal := reflect.ValueOf(patch)
+	ret := reflect.New(commonType)
+
+	val, ok := merge(baseVal, patchVal, mergeConfig)
+	if ok {
+		ret.Elem().Set(val)
+	}
+
+	r, ok := ret.Elem().Interface().(T)
+	if !ok {
+		return r, fmt.Errorf(
+			"Unexpected type of return element, expected %s, is %s",
+			commonType,
+			reflect.TypeOf(r),
+		)
+	}
+
+	return r, nil
+}
+
+// merge recursively merges patch into base and returns the new struct, ptr, slice/map, or value
+func merge(base, patch reflect.Value, mergeConfig *MergeConfig) (reflect.Value, bool) {
+	commonType := base.Type()
+
+	switch commonType.Kind() {
+	case reflect.Struct:
+		merged := reflect.New(commonType).Elem()
+		for i := range base.NumField() {
+			if !merged.Field(i).CanSet() {
+				continue
+			}
+			if mergeConfig != nil && mergeConfig.StructFieldFilter != nil {
+				if !mergeConfig.StructFieldFilter(commonType.Field(i), base.Field(i), patch.Field(i)) {
+					merged.Field(i).Set(base.Field(i))
+					continue
+				}
+			}
+			val, ok := merge(base.Field(i), patch.Field(i), mergeConfig)
+			if ok {
+				merged.Field(i).Set(val)
+			}
+		}
+		return merged, true
+
+	case reflect.Pointer:
+		mergedPtr := reflect.New(commonType.Elem())
+		if base.IsNil() && patch.IsNil() {
+			return mergedPtr, false
+		}
+
+		// clone reference values (if any)
+		if base.IsNil() {
+			val, _ := merge(patch.Elem(), patch.Elem(), mergeConfig)
+			mergedPtr.Elem().Set(val)
+		} else if patch.IsNil() {
+			val, _ := merge(base.Elem(), base.Elem(), mergeConfig)
+			mergedPtr.Elem().Set(val)
+		} else {
+			val, _ := merge(base.Elem(), patch.Elem(), mergeConfig)
+			mergedPtr.Elem().Set(val)
+		}
+		return mergedPtr, true
+
+	case reflect.Slice:
+		if base.IsNil() && patch.IsNil() {
+			return reflect.Zero(commonType), false
+		}
+		if !patch.IsNil() {
+			// use patch
+			merged := reflect.MakeSlice(commonType, 0, patch.Len())
+			for i := range patch.Len() {
+				// recursively merge patch with itself. This will clone reference values.
+				val, _ := merge(patch.Index(i), patch.Index(i), mergeConfig)
+				merged = reflect.Append(merged, val)
+			}
+			return merged, true
+		}
+		// use base
+		merged := reflect.MakeSlice(commonType, 0, base.Len())
+		for i := range base.Len() {
+			// recursively merge base with itself. This will clone reference values.
+			val, _ := merge(base.Index(i), base.Index(i), mergeConfig)
+			merged = reflect.Append(merged, val)
+		}
+		return merged, true
+
+	case reflect.Map:
+		// maps are merged according to these rules:
+		// - if patch is not nil, replace the base map completely
+		// - otherwise, keep the base map
+		// - reference values (eg. slice/ptr/map) will be cloned
+		if base.IsNil() && patch.IsNil() {
+			return reflect.Zero(commonType), false
+		}
+		merged := reflect.MakeMap(commonType)
+		mapPtr := base
+		if !patch.IsNil() {
+			mapPtr = patch
+		}
+		for _, key := range mapPtr.MapKeys() {
+			// clone reference values
+			val, ok := merge(mapPtr.MapIndex(key), mapPtr.MapIndex(key), mergeConfig)
+			if !ok {
+				val = reflect.New(mapPtr.MapIndex(key).Type()).Elem()
+			}
+			merged.SetMapIndex(key, val)
+		}
+		return merged, true
+
+	case reflect.Interface:
+		var val reflect.Value
+		if base.IsNil() && patch.IsNil() {
+			return reflect.Zero(commonType), false
+		}
+
+		// clone reference values (if any)
+		if base.IsNil() {
+			val, _ = merge(patch.Elem(), patch.Elem(), mergeConfig)
+		} else if patch.IsNil() {
+			val, _ = merge(base.Elem(), base.Elem(), mergeConfig)
+		} else {
+			val, _ = merge(base.Elem(), patch.Elem(), mergeConfig)
+		}
+		return val, true
+
+	default:
+		return patch, true
+	}
+}