GODRIVER-3427 Add a global "omitempty" flag.

Author: qingyang-hu

bson/bsoncodec.go

@@ -88,6 +88,7 @@ type EncodeContext struct {
 	nilSliceAsEmpty         bool
 	nilByteSliceAsEmpty     bool
 	omitZeroStruct          bool
+	omitEmpty               bool
 	useJSONStructTags       bool
 }
 

bson/encoder.go

@@ -108,14 +108,21 @@ func (e *Encoder) NilByteSliceAsEmpty() {
 // TODO struct fields once the logic is updated to also inspect private struct fields.
 
 // OmitZeroStruct causes the Encoder to consider the zero value for a struct (e.g. MyStruct{})
-// as empty and omit it from the marshaled BSON when the "omitempty" struct tag option is set.
+// as empty and omit it from the marshaled BSON when the "omitempty" struct tag option is set
+// or the OmitEmpty() method is called.
 //
 // Note that the Encoder only examines exported struct fields when determining if a struct is the
 // zero value. It considers pointers to a zero struct value (e.g. &MyStruct{}) not empty.
 func (e *Encoder) OmitZeroStruct() {
 	e.ec.omitZeroStruct = true
 }
 
+// OmitEmpty causes the Encoder to omit empty values from the marshaled BSON as the "omitempty"
+// struct tag option is set.
+func (e *Encoder) OmitEmpty() {
+	e.ec.omitEmpty = true
+}
+
 // UseJSONStructTags causes the Encoder to fall back to using the "json" struct tag if a "bson"
 // struct tag is not specified.
 func (e *Encoder) UseJSONStructTags() {

bson/encoder_test.go

@@ -248,6 +248,19 @@ func TestEncoderConfiguration(t *testing.T) {
 			}{},
 			want: bsoncore.NewDocumentBuilder().Build(),
 		},
+		// Test that OmitZeroStruct omits empty structs from the marshaled document if
+		// OmitEmpty is also set.
+		{
+			description: "OmitEmpty",
+			configure: func(enc *Encoder) {
+				enc.OmitZeroStruct()
+				enc.OmitEmpty()
+			},
+			input: struct {
+				Zero zeroStruct
+			}{},
+			want: bsoncore.NewDocumentBuilder().Build(),
+		},
 		// Test that UseJSONStructTags causes the Encoder to fall back to "json" struct tags if
 		// "bson" struct tags are not available.
 		{

bson/struct_codec.go

@@ -118,6 +118,10 @@ func (sc *structCodec) EncodeValue(ec EncodeContext, vw ValueWriter, val reflect
 			}
 		}
 
+		if ec.omitEmpty {
+			desc.omitEmpty = true
+		}
+
 		desc.encoder, rv, err = lookupElementEncoder(ec, desc.encoder, rv)
 
 		if err != nil && !errors.Is(err, errInvalidValue) {

internal/integration/client_test.go

@@ -956,6 +956,19 @@ func TestClient_BSONOptions(t *testing.T) {
 			want:       &bson.D{},
 			wantRaw:    bson.Raw(bsoncore.NewDocumentBuilder().Build()),
 		},
+		{
+			name: "OmitEmpty",
+			bsonOpts: &options.BSONOptions{
+				OmitZeroStruct: true,
+				OmitEmpty:      true,
+			},
+			doc: struct {
+				X jsonTagsTest `bson:"x"`
+			}{},
+			decodeInto: func() interface{} { return &bson.D{} },
+			want:       &bson.D{},
+			wantRaw:    bson.Raw(bsoncore.NewDocumentBuilder().Build()),
+		},
 		{
 			name: "StringifyMapKeysWithFmt",
 			bsonOpts: &options.BSONOptions{

mongo/mongo.go

@@ -83,6 +83,9 @@ func getEncoder(
 		if opts.OmitZeroStruct {
 			enc.OmitZeroStruct()
 		}
+		if opts.OmitEmpty {
+			enc.OmitEmpty()
+		}
 		if opts.StringifyMapKeysWithFmt {
 			enc.StringifyMapKeysWithFmt()
 		}

mongo/options/clientoptions.go

@@ -182,9 +182,12 @@ type BSONOptions struct {
 
 	// OmitZeroStruct causes the driver to consider the zero value for a struct
 	// (e.g. MyStruct{}) as empty and omit it from the marshaled BSON when the
-	// "omitempty" struct tag option is set.
+	// "omitempty" struct tag option or the "OmitEmpty" field is set.
 	OmitZeroStruct bool
 
+	// OmitEmpty causes the driver to omit empty values from the marshaled BSON.
+	OmitEmpty bool
+
 	// StringifyMapKeysWithFmt causes the driver to convert Go map keys to BSON
 	// document field name strings using fmt.Sprint instead of the default
 	// string conversion logic.