MM-14441: restrict system admin config (#10477)

* tweak utils.Merge docs

* move merge_test to utils_test package for easier testing

* utils: support MergeConfig and StructFieldFilter

* constrain updating certain fields by the restricted system admin

utils/merge_test.go

@@ -1,11 +1,14 @@
-package utils
+package utils_test
 
 import (
 	"fmt"
+	"reflect"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
+
+	"github.com/mattermost/mattermost-server/utils"
 )
 
 // Test merging maps alone. This isolates the complexity of merging maps from merging maps recursively in
@@ -1156,6 +1159,38 @@ func TestMergeWithVeryComplexStruct(t *testing.T) {
 	})
 }
 
+func TestMergeWithStructFieldFilter(t *testing.T) {
+	t.Run("filter skips merging from patch", func(t *testing.T) {
+		t1 := evenSimpler{newBool(true), &evenSimpler2{newString("base")}}
+		t2 := evenSimpler{newBool(false), &evenSimpler2{newString("patch")}}
+		expected := evenSimpler{newBool(true), &evenSimpler2{newString("base")}}
+
+		merged, err := mergeEvenSimplerWithConfig(t1, t2, &utils.MergeConfig{
+			StructFieldFilter: func(structField reflect.StructField, base, patch reflect.Value) bool {
+				return false
+			},
+		})
+		require.NoError(t, err)
+
+		assert.Equal(t, expected, *merged)
+	})
+
+	t.Run("filter skips merging configured fields from patch", func(t *testing.T) {
+		t1 := evenSimpler{newBool(true), &evenSimpler2{newString("base")}}
+		t2 := evenSimpler{newBool(false), &evenSimpler2{newString("patch")}}
+		expected := evenSimpler{newBool(false), &evenSimpler2{newString("base")}}
+
+		merged, err := mergeEvenSimplerWithConfig(t1, t2, &utils.MergeConfig{
+			StructFieldFilter: func(structField reflect.StructField, base, patch reflect.Value) bool {
+				return structField.Name == "B"
+			},
+		})
+		require.NoError(t, err)
+
+		assert.Equal(t, expected, *merged)
+	})
+}
+
 type testStruct struct {
 	I        int
 	I8       int8
@@ -1504,11 +1539,10 @@ func setupStructs(t *testing.T) {
 		map[int]*string{1: newString("Another"), 2: newString("map of"), 3: newString("pointers, wow!")},
 		mergeStructEmbedBaseA, &mergeStructEmbedBaseB,
 	}
-
 }
 
 func mergeSimple(base, patch simple) (*simple, error) {
-	ret, err := Merge(base, patch)
+	ret, err := utils.Merge(base, patch, nil)
 	if err != nil {
 		return nil, err
 	}
@@ -1517,7 +1551,16 @@ func mergeSimple(base, patch simple) (*simple, error) {
 }
 
 func mergeEvenSimpler(base, patch evenSimpler) (*evenSimpler, error) {
-	ret, err := Merge(base, patch)
+	ret, err := utils.Merge(base, patch, nil)
+	if err != nil {
+		return nil, err
+	}
+	retTS := ret.(evenSimpler)
+	return &retTS, nil
+}
+
+func mergeEvenSimplerWithConfig(base, patch evenSimpler, mergeConfig *utils.MergeConfig) (*evenSimpler, error) {
+	ret, err := utils.Merge(base, patch, mergeConfig)
 	if err != nil {
 		return nil, err
 	}
@@ -1526,7 +1569,7 @@ func mergeEvenSimpler(base, patch evenSimpler) (*evenSimpler, error) {
 }
 
 func mergeSliceStruct(base, patch sliceStruct) (*sliceStruct, error) {
-	ret, err := Merge(base, patch)
+	ret, err := utils.Merge(base, patch, nil)
 	if err != nil {
 		return nil, err
 	}
@@ -1535,7 +1578,7 @@ func mergeSliceStruct(base, patch sliceStruct) (*sliceStruct, error) {
 }
 
 func mergeMapPtr(base, patch mapPtr) (*mapPtr, error) {
-	ret, err := Merge(base, patch)
+	ret, err := utils.Merge(base, patch, nil)
 	if err != nil {
 		return nil, err
 	}
@@ -1544,7 +1587,7 @@ func mergeMapPtr(base, patch mapPtr) (*mapPtr, error) {
 }
 
 func mergeMapPtrState(base, patch mapPtrState) (*mapPtrState, error) {
-	ret, err := Merge(base, patch)
+	ret, err := utils.Merge(base, patch, nil)
 	if err != nil {
 		return nil, err
 	}
@@ -1553,7 +1596,7 @@ func mergeMapPtrState(base, patch mapPtrState) (*mapPtrState, error) {
 }
 
 func mergeMapPtrState2(base, patch mapPtrState2) (*mapPtrState2, error) {
-	ret, err := Merge(base, patch)
+	ret, err := utils.Merge(base, patch, nil)
 	if err != nil {
 		return nil, err
 	}
@@ -1562,7 +1605,7 @@ func mergeMapPtrState2(base, patch mapPtrState2) (*mapPtrState2, error) {
 }
 
 func mergeTestStructs(base, patch testStruct) (*testStruct, error) {
-	ret, err := Merge(base, patch)
+	ret, err := utils.Merge(base, patch, nil)
 	if err != nil {
 		return nil, err
 	}
@@ -1571,7 +1614,7 @@ func mergeTestStructs(base, patch testStruct) (*testStruct, error) {
 }
 
 func mergeStringIntMap(base, patch map[string]int) (map[string]int, error) {
-	ret, err := Merge(base, patch)
+	ret, err := utils.Merge(base, patch, nil)
 	if err != nil {
 		return nil, err
 	}
@@ -1580,7 +1623,7 @@ func mergeStringIntMap(base, patch map[string]int) (map[string]int, error) {
 }
 
 func mergeStringPtrIntMap(base, patch map[string]*int) (map[string]*int, error) {
-	ret, err := Merge(base, patch)
+	ret, err := utils.Merge(base, patch, nil)
 	if err != nil {
 		return nil, err
 	}
@@ -1589,7 +1632,7 @@ func mergeStringPtrIntMap(base, patch map[string]*int) (map[string]*int, error)
 }
 
 func mergeStringSliceIntMap(base, patch map[string][]int) (map[string][]int, error) {
-	ret, err := Merge(base, patch)
+	ret, err := utils.Merge(base, patch, nil)
 	if err != nil {
 		return nil, err
 	}
@@ -1598,7 +1641,7 @@ func mergeStringSliceIntMap(base, patch map[string][]int) (map[string][]int, err
 }
 
 func mergeMapOfMap(base, patch map[string]map[string]*int) (map[string]map[string]*int, error) {
-	ret, err := Merge(base, patch)
+	ret, err := utils.Merge(base, patch, nil)
 	if err != nil {
 		return nil, err
 	}
@@ -1607,7 +1650,7 @@ func mergeMapOfMap(base, patch map[string]map[string]*int) (map[string]map[strin
 }
 
 func mergeInterfaceMap(base, patch map[string]interface{}) (map[string]interface{}, error) {
-	ret, err := Merge(base, patch)
+	ret, err := utils.Merge(base, patch, nil)
 	if err != nil {
 		return nil, err
 	}
@@ -1616,7 +1659,7 @@ func mergeInterfaceMap(base, patch map[string]interface{}) (map[string]interface
 }
 
 func mergeStringSlices(base, patch []string) ([]string, error) {
-	ret, err := Merge(base, patch)
+	ret, err := utils.Merge(base, patch, nil)
 	if err != nil {
 		return nil, err
 	}
@@ -1625,7 +1668,7 @@ func mergeStringSlices(base, patch []string) ([]string, error) {
 }
 
 func mergeTestStructsPtrs(base, patch *testStruct) (*testStruct, error) {
-	ret, err := Merge(base, patch)
+	ret, err := utils.Merge(base, patch, nil)
 	if err != nil {
 		return nil, err
 	}