fix(dart): Deserialize maps with integral keys (#3285)

Author: brianquinlan

internal/sidekick/dart/annotate.go

@@ -833,7 +833,29 @@ func (annotate *annotateModel) decoder(typez api.Typez, typeid string, state *ap
 		typeName := annotate.resolveMessageName(state.MessageByID[typeid], true)
 		return fmt.Sprintf("%s.fromJson", typeName)
 	default:
-		panic("unknown type")
+		panic(fmt.Sprintf("unsupported type: %d", typez))
+	}
+}
+
+func (annotate *annotateModel) keyDecoder(typez api.Typez) string {
+	// JSON objects can only contain string keys so non-String types need to use specialized decoders.
+	// Supported key types are defined here:
+	// https://protobuf.dev/programming-guides/proto3/#maps
+	switch typez {
+	case api.STRING_TYPE:
+		return "decodeString"
+	case api.INT32_TYPE, // Integer types that can be decoded as Dart `int`.
+		api.FIXED32_TYPE,
+		api.SFIXED32_TYPE,
+		api.SINT32_TYPE,
+		api.UINT32_TYPE,
+		api.INT64_TYPE,
+		api.SINT64_TYPE,
+		api.SFIXED64_TYPE:
+		return "decodeIntKey"
+	default:
+		// TODO(https://github.com/googleapis/google-cloud-dart/issues/95): Support all key types.
+		panic(fmt.Sprintf("unsupported key type: %d", typez))
 	}
 }
 
@@ -867,8 +889,7 @@ func (annotate *annotateModel) createFromJsonLine(field *api.Field, state *api.A
 	case field.Map:
 		message := state.MessageByID[field.TypezID]
 		keyType := message.Fields[0].Typez
-		keyTypeID := message.Fields[0].TypezID
-		keyDecoder := annotate.decoder(keyType, keyTypeID, state)
+		keyDecoder := annotate.keyDecoder(keyType)
 		valueType := message.Fields[1].Typez
 		valueTypeID := message.Fields[1].TypezID
 		valueDecoder := annotate.decoder(valueType, valueTypeID, state)
@@ -880,7 +901,6 @@ func (annotate *annotateModel) createFromJsonLine(field *api.Field, state *api.A
 	}
 
 	decoder := annotate.decoder(field.Typez, field.TypezID, state)
-	// No decoding necessary.
 	return fmt.Sprintf("switch (%s) { null => %s, Object $1 => %s($1)}", data, defaultValue, decoder)
 }
 

internal/sidekick/dart/annotate_test.go

@@ -844,6 +844,21 @@ func TestCreateFromJsonLine(t *testing.T) {
 			},
 		},
 	}
+	mapInt32ToBytes := &api.Message{
+		Name:  "$Int32ToBytes",
+		ID:    "..$Int32ToBytes",
+		IsMap: true,
+		Fields: []*api.Field{
+			{
+				Name:  "key",
+				Typez: api.INT32_TYPE,
+			},
+			{
+				Name:  "value",
+				Typez: api.BYTES_TYPE,
+			},
+		},
+	}
 
 	for _, test := range []struct {
 		field *api.Field
@@ -993,11 +1008,18 @@ func TestCreateFromJsonLine(t *testing.T) {
 			&api.Field{Name: "message", JSONName: "message", Typez: api.MESSAGE_TYPE, TypezID: ".google.protobuf.Duration"},
 			"switch (json['message']) { null => null, Object $1 => Duration.fromJson($1)}",
 		},
+
+		// maps
 		{
-			// Map of bytes.
+			// string -> bytes
 			&api.Field{Name: "message", JSONName: "message", Map: true, Typez: api.MESSAGE_TYPE, TypezID: mapStringToBytes.ID},
 			"switch (json['message']) { null => {}, Map<String, Object?> $1 => {for (final e in $1.entries) decodeString(e.key): decodeBytes(e.value)}, _ => throw const FormatException('\"message\" is not an object') }",
 		},
+		{
+			// int32 -> bytes
+			&api.Field{Name: "message", JSONName: "message", Map: true, Typez: api.MESSAGE_TYPE, TypezID: mapInt32ToBytes.ID},
+			"switch (json['message']) { null => {}, Map<String, Object?> $1 => {for (final e in $1.entries) decodeIntKey(e.key): decodeBytes(e.value)}, _ => throw const FormatException('\"message\" is not an object') }",
+		},
 	} {
 		t.Run(test.field.Name, func(t *testing.T) {
 			message := &api.Message{
@@ -1006,7 +1028,10 @@ func TestCreateFromJsonLine(t *testing.T) {
 				Package: sample.Package,
 				Fields:  []*api.Field{test.field},
 			}
-			model := api.NewTestAPI([]*api.Message{message, secret, foreignMessage, mapStringToBytes}, []*api.Enum{enumState, foreignEnumState}, []*api.Service{})
+			model := api.NewTestAPI([]*api.Message{message,
+				secret, foreignMessage, mapStringToBytes, mapInt32ToBytes},
+				[]*api.Enum{enumState, foreignEnumState},
+				[]*api.Service{})
 			annotate := newAnnotateModel(model)
 			annotate.annotateModel(map[string]string{
 				"prefix:google.cloud.foo": "foo",