add test of map with key with custom marshaler

Makefile

@@ -23,7 +23,8 @@ generate: root build
 		.root/src/$(PKG)/tests/data.go \
 		.root/src/$(PKG)/tests/omitempty.go \
 		.root/src/$(PKG)/tests/nothing.go \
-		.root/src/$(PKG)/tests/named_type.go
+		.root/src/$(PKG)/tests/named_type.go \
+		.root/src/$(PKG)/tests/custom_map_key_type.go
 
 	.root/bin/easyjson -all .root/src/$(PKG)/tests/data.go 
 	.root/bin/easyjson -all .root/src/$(PKG)/tests/nothing.go
@@ -33,6 +34,7 @@ generate: root build
 	.root/bin/easyjson -build_tags=use_easyjson .root/src/$(PKG)/benchmark/data.go
 	.root/bin/easyjson .root/src/$(PKG)/tests/nested_easy.go
 	.root/bin/easyjson .root/src/$(PKG)/tests/named_type.go
+	.root/bin/easyjson .root/src/$(PKG)/tests/custom_map_key_type.go
 
 test: generate root
 	go test \

tests/basic_test.go

@@ -38,6 +38,7 @@ var testCases = []struct {
 	{&IntsValue, IntsString},
 	{&mapStringStringValue, mapStringStringString},
 	{&namedTypeValue, namedTypeValueString},
+	{&customMapKeyTypeValue, customMapKeyTypeValueString},
 	{&mapMyIntStringValue, mapMyIntStringValueString},
 	{&mapIntStringValue, mapIntStringValueString},
 	{&mapInt32StringValue, mapInt32StringValueString},

tests/custom_map_key_type.go

@@ -0,0 +1,30 @@
+package tests
+
+import fmt "fmt"
+
+//easyjson:json
+type CustomMapKeyType struct {
+	Map map[customKeyType]int
+}
+
+type customKeyType [2]byte
+
+func (k customKeyType) MarshalJSON() ([]byte, error) {
+	return []byte(fmt.Sprintf(`"%02x"`, k)), nil
+}
+
+func (k *customKeyType) UnmarshalJSON(b []byte) error {
+	_, err := fmt.Sscanf(string(b), `"%02x%02x"`, &k[0], &k[1])
+	return err
+}
+
+var customMapKeyTypeValue CustomMapKeyType
+
+func init() {
+	customMapKeyTypeValue.Map = map[customKeyType]int{
+		customKeyType{0x01, 0x01}: 1,
+		customKeyType{0x02, 0x02}: 2,
+	}
+}
+
+var customMapKeyTypeValueString = `{"Map":{"0101":1,"0202":2}}`