feat: support set null map entries for non-simple map values (#1782)

Previous impl assumed maps would be of type map[string]string. Although this is most of the map types this library uses some use more complex types. For these cases it is impossible to unset fields in patch requests until this fix. Reported internal

Ref: b/261221901

internal/gensupport/json.go

@@ -86,7 +86,12 @@ func schemaToMap(schema interface{}, mustInclude, useNull map[string]bool, useNu
 		if f.Type.Kind() == reflect.Map && useNullMaps[f.Name] != nil {
 			ms, ok := v.Interface().(map[string]string)
 			if !ok {
-				return nil, fmt.Errorf("field %q has keys in NullFields but is not a map[string]string", f.Name)
+				mi, err := initMapSlow(v, f.Name, useNullMaps)
+				if err != nil {
+					return nil, err
+				}
+				m[tag.apiName] = mi
+				continue
 			}
 			mi := map[string]interface{}{}
 			for k, v := range ms {
@@ -120,6 +125,25 @@ func schemaToMap(schema interface{}, mustInclude, useNull map[string]bool, useNu
 	return m, nil
 }
 
+// initMapSlow uses reflection to build up a map object. This is slower than
+// the default behavior so it should be used only as a fallback.
+func initMapSlow(rv reflect.Value, fieldName string, useNullMaps map[string]map[string]bool) (map[string]interface{}, error) {
+	mi := map[string]interface{}{}
+	iter := rv.MapRange()
+	for iter.Next() {
+		k, ok := iter.Key().Interface().(string)
+		if !ok {
+			return nil, fmt.Errorf("field %q has keys in NullFields but is not a map[string]any", fieldName)
+		}
+		v := iter.Value().Interface()
+		mi[k] = v
+	}
+	for k := range useNullMaps[fieldName] {
+		mi[k] = nil
+	}
+	return mi, nil
+}
+
 // formatAsString returns a string representation of v, dereferencing it first if possible.
 func formatAsString(v reflect.Value, kind reflect.Kind) string {
 	if kind == reflect.Ptr && !v.IsNil() {

internal/gensupport/json_test.go

@@ -12,6 +12,10 @@ import (
 	"google.golang.org/api/googleapi"
 )
 
+type CustomType struct {
+	Foo string `json:"foo,omitempty"`
+}
+
 type schema struct {
 	// Basic types
 	B    bool    `json:"b,omitempty"`
@@ -28,12 +32,13 @@ type schema struct {
 	PStr  *string  `json:"pstr,omitempty"`
 
 	// Other types
-	Int64s        googleapi.Int64s         `json:"i64s,omitempty"`
-	S             []int                    `json:"s,omitempty"`
-	M             map[string]string        `json:"m,omitempty"`
-	Any           interface{}              `json:"any,omitempty"`
-	Child         *child                   `json:"child,omitempty"`
-	MapToAnyArray map[string][]interface{} `json:"maptoanyarray,omitempty"`
+	Int64s          googleapi.Int64s         `json:"i64s,omitempty"`
+	S               []int                    `json:"s,omitempty"`
+	M               map[string]string        `json:"m,omitempty"`
+	Any             interface{}              `json:"any,omitempty"`
+	Child           *child                   `json:"child,omitempty"`
+	MapToAnyArray   map[string][]interface{} `json:"maptoanyarray,omitempty"`
+	MapToCustomType map[string]CustomType    `json:"maptocustomtype,omitempty"`
 
 	ForceSendFields []string `json:"-"`
 	NullFields      []string `json:"-"`
@@ -254,6 +259,15 @@ func TestMapField(t *testing.T) {
 			},
 			want: `{}`,
 		},
+		{
+			s: schema{
+				MapToCustomType: map[string]CustomType{
+					"a": {Foo: "foo"},
+				},
+				NullFields: []string{"MapToCustomType.b"},
+			},
+			want: `{"maptocustomtype": {"a": {"foo": "foo"}, "b": null}}`,
+		},
 	} {
 		checkMarshalJSON(t, tc)
 	}