Nullable java (#4455)

* add _Nullable Support for C++ interface

* generate @Nullable for Java generated code

.gitignore

@@ -5,6 +5,7 @@
 *.o.d
 *.class
 *.a
+*.swp
 *~
 *.vcxproj
 *.vcxproj.filters
@@ -43,6 +44,7 @@ flatsampletext.exe
 grpctest
 grpctest.exe
 snapshot.sh
+tags
 tests/go_gen
 tests/monsterdata_java_wire.mon
 tests/monsterdata_go_wire.mon

include/flatbuffers/idl.h

@@ -372,7 +372,7 @@ struct IDLOptions {
   bool generate_object_based_api;
   std::string cpp_object_api_pointer_type;
   std::string cpp_object_api_string_type;
-  bool clang_nullable;
+  bool gen_nullable;
   std::string object_prefix;
   std::string object_suffix;
   bool union_value_namespacing;
@@ -428,7 +428,7 @@ struct IDLOptions {
       generate_name_strings(false),
       generate_object_based_api(false),
       cpp_object_api_pointer_type("std::unique_ptr"),
-      clang_nullable(false),
+      gen_nullable(false),
       object_suffix("T"),
       union_value_namespacing(true),
       allow_non_utf8(false),

src/flatc.cpp

@@ -89,7 +89,7 @@ std::string FlatCompiler::GetUsageString(const char* program_name) const {
       "  --cpp-ptr-type T   Set object API pointer type (default std::unique_ptr)\n"
       "  --cpp-str-type T   Set object API string type (default std::string)\n"
       "                     T::c_str() and T::length() must be supported\n"
-      "  --clang-nullable   Add Clang _Nullable for C++ pointers.\n"
+      "  --gen-nullable     Add Clang _Nullable for C++ pointer. or @Nullable for Java\n"
       "  --object-prefix    Customise class prefix for C++ object-based API.\n"
       "  --object-suffix    Customise class suffix for C++ object-based API.\n"
       "                     Default value is \"T\"\n"
@@ -211,8 +211,8 @@ int FlatCompiler::Compile(int argc, const char** argv) {
       } else if (arg == "--cpp-str-type") {
         if (++argi >= argc) Error("missing type following" + arg, true);
         opts.cpp_object_api_string_type = argv[argi];
-      } else if (arg == "--clang-nullable") {
-        opts.clang_nullable = true;
+      } else if (arg == "--gen-nullable") {
+        opts.gen_nullable = true;
       } else if (arg == "--object-prefix") {
         if (++argi >= argc) Error("missing prefix following" + arg, true);
         opts.object_prefix = argv[argi];

src/idl_gen_cpp.cpp

@@ -127,7 +127,7 @@ class CppGenerator : public BaseGenerator {
     code_ += "#define " + include_guard;
     code_ += "";
 
-    if (parser_.opts.clang_nullable) {
+    if (parser_.opts.gen_nullable) {
       code_ += "#pragma clang system_header\n\n";
     }
 
@@ -433,7 +433,7 @@ class CppGenerator : public BaseGenerator {
   }
 
   std::string NullableExtension() {
-    return parser_.opts.clang_nullable ? " _Nullable " : "";
+    return parser_.opts.gen_nullable ? " _Nullable " : "";
   }
 
   static std::string NativeName(const std::string &name, const StructDef *sd, const IDLOptions & opts) {

src/idl_gen_general.cpp

@@ -70,6 +70,7 @@ struct LanguageParameters {
   std::string accessor_prefix_static;
   std::string optional_suffix;
   std::string includes;
+  std::string class_annotation;
   CommentConfig comment_config;
 };
 
@@ -99,8 +100,8 @@ const LanguageParameters& GetLangParams(IDLOptions::Language lang) {
       "",
       "",
       "",
-      "import java.nio.*;\nimport java.lang.*;\nimport java.util.*;\n"
-        "import com.google.flatbuffers.*;\n\n@SuppressWarnings(\"unused\")\n",
+      "import java.nio.*;\nimport java.lang.*;\nimport java.util.*;\nimport com.google.flatbuffers.*;\n",
+      "\n@SuppressWarnings(\"unused\")\n",
       {
         "/**",
         " *",
@@ -132,6 +133,7 @@ const LanguageParameters& GetLangParams(IDLOptions::Language lang) {
       "Table.",
       "?",
       "using global::System;\nusing global::FlatBuffers;\n\n",
+      "",
       {
         nullptr,
         "///",
@@ -220,7 +222,13 @@ class GeneralGenerator : public BaseGenerator {
       code += lang_.namespace_ident + namespace_name + lang_.namespace_begin;
       code += "\n\n";
     }
-    if (needs_includes) code += lang_.includes;
+    if (needs_includes) {
+      code += lang_.includes;
+      if (parser_.opts.gen_nullable) {
+        code += "\nimport javax.annotation.Nullable;\n";
+      }
+      code += lang_.class_annotation;
+    }
     code += classcode;
     if (!namespace_name.empty()) code += lang_.namespace_end;
     auto filename = NamespaceDir(ns) + defname + lang_.file_extension;
@@ -235,6 +243,12 @@ class GeneralGenerator : public BaseGenerator {
                                 : upper);
 }
 
+std::string GenNullableAnnotation(const Type& t) {
+  return lang_.language == IDLOptions::kJava 
+    && parser_.opts.gen_nullable 
+    && !IsScalar(DestinationType(t, true).base_type) ? " @Nullable ": "";
+}
+
 static bool IsEnum(const Type& type) {
   return type.enum_def != nullptr && IsInteger(type.base_type);
 }
@@ -869,7 +883,8 @@ void GenStruct(StructDef &struct_def, std::string *code_ptr) {
     std::string dest_mask = DestinationMask(field.value.type, true);
     std::string dest_cast = DestinationCast(field.value.type);
     std::string src_cast = SourceCast(field.value.type);
-    std::string method_start = "  public " + type_name_dest + optional + " " +
+    std::string method_start = "  public " + GenNullableAnnotation(field.value.type) +
+                               type_name_dest + optional + " " +
                                MakeCamel(field.name, lang_.first_camel_upper);
     std::string obj = lang_.language == IDLOptions::kCSharp
       ? "(new " + type_name + "())"