Added convenient create functions for Java/C#.

Bug: 15777857
Tested: on Linux and Windows.

Change-Id: I25db724349e2c801bb0e41137540507acd57cd03

docs/html/md__java_usage.html

@@ -77,7 +77,7 @@ Monster.addTest_type(fbb, (byte)1);
 Monster.addTest(fbb, mon2);
 Monster.addTest4(fbb, test4s);
 int mon = Monster.endMonster(fbb);
-</pre><p>As you can see, the Java code for tables does not use a convenient <code>createMonster</code> call like the C++ code. This is to create the buffer without using temporary object allocation.</p>
+</pre><p>For some simpler types, you can use a convenient <code>create</code> function call that allows you to construct tables in one function call. This example definition however contains an inline struct field, so we have to create the table manually. This is to create the buffer without using temporary object allocation.</p>
 <p>It's important to understand that fields that are structs are inline (like <code>Vec3</code> above), and MUST thus be created between the start and end calls of a table. Everything else (other tables, strings, vectors) MUST be created before the start of the table they are referenced in.</p>
 <p>Structs do have convenient methods that even have arguments for nested structs.</p>
 <p>As you can see, references to other objects (e.g. the string above) are simple ints, and thus do not have the type-safety of the Offset type in C++. Extra case must thus be taken that you set the right offset on the right field.</p>

docs/source/JavaUsage.md

@@ -75,9 +75,11 @@ Create a table with a struct contained therein:
     Monster.addTest4(fbb, test4s);
     int mon = Monster.endMonster(fbb);
 
-As you can see, the Java code for tables does not use a convenient
-`createMonster` call like the C++ code. This is to create the buffer without
-using temporary object allocation.
+For some simpler types, you can use a convenient `create` function call that
+allows you to construct tables in one function call. This example definition
+however contains an inline struct field, so we have to create the table
+manually.
+This is to create the buffer without using temporary object allocation.
 
 It's important to understand that fields that are structs are inline (like
 `Vec3` above), and MUST thus be created between the start and end calls of

src/idl_gen_general.cpp

@@ -10,7 +10,7 @@
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific GeneratorOptions::Language governing permissions and
+ * See the License for the specific language governing permissions and
  * limitations under the License.
  */
 
@@ -409,18 +409,71 @@ static void GenStruct(const LanguageParameters &lang, const Parser &parser,
     code += "    return builder.";
     code += FunctionStart(lang, 'O') + "ffset();\n  }\n";
   } else {
-    // Create a set of static methods that allow table construction,
+    // Generate a method that creates a table in one go. This is only possible
+    // when the table has no struct fields, since those have to be created
+    // inline, and there's no way to do so in Java.
+    bool has_no_struct_fields = true;
+    int num_fields = 0;
+    for (auto it = struct_def.fields.vec.begin();
+         it != struct_def.fields.vec.end(); ++it) {
+      auto &field = **it;
+      if (field.deprecated) continue;
+      if (IsStruct(field.value.type)) {
+        has_no_struct_fields = false;
+      } else {
+        num_fields++;
+      }
+    }
+    if (has_no_struct_fields && num_fields) {
+      // Generate a table constructor of the form:
+      // public static void createName(FlatBufferBuilder builder, args...)
+      code += "  public static void " + FunctionStart(lang, 'C') + "reate";
+      code += struct_def.name;
+      code += "(FlatBufferBuilder builder";
+      for (auto it = struct_def.fields.vec.begin();
+           it != struct_def.fields.vec.end(); ++it) {
+        auto &field = **it;
+        if (field.deprecated) continue;
+        code += ",\n      " + GenTypeBasic(lang, field.value.type) + " ";
+        code += field.name;
+        // Java doesn't have defaults, which means this method must always
+        // supply all arguments, and thus won't compile when fields are added.
+        if (lang.language != GeneratorOptions::kJava)
+          code += " = " + field.value.constant;
+      }
+      code += ") {\n    builder.";
+      code += FunctionStart(lang, 'S') + "tartObject(";
+      code += NumToString(struct_def.fields.vec.size()) + ");\n";
+      for (size_t size = struct_def.sortbysize ? sizeof(largest_scalar_t) : 1;
+           size;
+           size /= 2) {
+        for (auto it = struct_def.fields.vec.rbegin();
+             it != struct_def.fields.vec.rend(); ++it) {
+          auto &field = **it;
+          if (!field.deprecated &&
+              (!struct_def.sortbysize ||
+               size == SizeOf(field.value.type.base_type))) {
+            code += "    " + struct_def.name + ".";
+            code += FunctionStart(lang, 'A') + "dd";
+            code += MakeCamel(field.name) + "(builder, " + field.name + ");\n";
+          }
+        }
+      }
+      code += "    builder.";
+      code += FunctionStart(lang, 'E') + "ndObject();\n  }\n\n";
+    }
+    // Generate a set of static methods that allow table construction,
     // of the form:
     // public static void addName(FlatBufferBuilder builder, short name)
     // { builder.addShort(id, name, default); }
+    // Unlike the Create function, these always work.
     code += "  public static void " + FunctionStart(lang, 'S') + "tart";
     code += struct_def.name;
     code += "(FlatBufferBuilder builder) { builder.";
     code += FunctionStart(lang, 'S') + "tartObject(";
     code += NumToString(struct_def.fields.vec.size()) + "); }\n";
     for (auto it = struct_def.fields.vec.begin();
-         it != struct_def.fields.vec.end();
-         ++it) {
+         it != struct_def.fields.vec.end(); ++it) {
       auto &field = **it;
       if (field.deprecated) continue;
       code += "  public static void " + FunctionStart(lang, 'A') + "dd";