FlatBuffers 64 for C++ (#7935)

* First working hack of adding 64-bit. Don't judge :)

* Made vector_downward work on 64 bit types

* vector_downward uses size_t, added offset64 to reflection

* cleaned up adding offset64 in parser

* Add C++ testing skeleton for 64-bit

* working test for CreateVector64

* working >2 GiB buffers

* support for large strings

* simplified CreateString<> to just provide the offset type

* generalize CreateVector template

* update test_64.afb due to upstream format change

* Added Vector64 type, which is just an alias for vector ATM

* Switch to Offset64 for Vector64

* Update for reflection bfbs output change

* Starting to add support for vector64 type in C++

* made a generic CreateVector that can handle different offsets and vector types

* Support for 32-vector with 64-addressing

* Vector64 basic builder + tests working

* basic support for json vector64 support

* renamed fields in test_64bit.fbs to better reflect their use

* working C++ vector64 builder

* Apply --annotate-sparse-vector to 64-bit tests

* Enable Vector64 for --annotate-sparse-vectors

* Merged from upstream

* Add `near_string` field for testing 32-bit offsets alongside

* keep track of where the 32-bit and 64-bit regions are for flatbufferbuilder

* move template<> outside class body for GCC

* update run.sh to build and run tests

* basic assertion for adding 64-bit offset at the wrong time

* started to separate `FlatBufferBuilder` into two classes, 1 64-bit aware, the other not

* add test for nested flatbuffer vector64, fix bug in alignment of big vectors

* fixed CreateDirect method by iterating by Offset64 first

* internal refactoring of flatbufferbuilder

* block not supported languages in the parser from using 64-bit

* evolution tests for adding a vector64 field

* conformity tests for adding/removing offset64 attributes

* ensure test is for a big buffer

* add parser error tests for `offset64` and `vector64` attributes

* add missing static that GCC only complains about

* remove stdint-uintn.h header that gets automatically added

* move 64-bit CalculateOffset internal

* fixed return size of EndVector

* various fixes on windows

* add SizeT to vector_downward

* minimze range of size changes in vector and builder

* reworked how tracking if 64-offsets are added

* Add ReturnT to EndVector

* small cleanups

* remove need for second Array definition

* combine IndirectHelpers into one definition

* started support for vector of struct

* Support for 32/64-vectors of structs + Offset64

* small cleanups

* add verification for vector64

* add sized prefix for 64-bit buffers

* add fuzzer for 64-bit

* add example of adding many vectors using a wrapper table

* run the new -bfbs-gen-embed logic on the 64-bit tests

* remove run.sh and fix cmakelist issue

* fixed bazel rules

* fixed some PR comments

* add 64-bit tests to cmakelist

2 files changed, 13 insertions, 5 deletions

diff --git a/java/src/main/java/com/google/flatbuffers/reflection/BaseType.java b/java/src/main/java/com/google/flatbuffers/reflection/BaseType.java
index fc4574a7..ef6ba2d4 100644
--- a/java/src/main/java/com/google/flatbuffers/reflection/BaseType.java
+++ b/java/src/main/java/com/google/flatbuffers/reflection/BaseType.java
@@ -23,9 +23,10 @@ public final class BaseType {
   public static final byte Obj = 15;
   public static final byte Union = 16;
   public static final byte Array = 17;
-  public static final byte MaxBaseType = 18;
+  public static final byte Vector64 = 18;
+  public static final byte MaxBaseType = 19;
 
-  public static final String[] names = { "None", "UType", "Bool", "Byte", "UByte", "Short", "UShort", "Int", "UInt", "Long", "ULong", "Float", "Double", "String", "Vector", "Obj", "Union", "Array", "MaxBaseType", };
+  public static final String[] names = { "None", "UType", "Bool", "Byte", "UByte", "Short", "UShort", "Int", "UInt", "Long", "ULong", "Float", "Double", "String", "Vector", "Obj", "Union", "Array", "Vector64", "MaxBaseType", };
 
   public static String name(int e) { return names[e]; }
 }
diff --git a/java/src/main/java/com/google/flatbuffers/reflection/Field.java b/java/src/main/java/com/google/flatbuffers/reflection/Field.java
index cdaccc6b..9b7c2034 100644
--- a/java/src/main/java/com/google/flatbuffers/reflection/Field.java
+++ b/java/src/main/java/com/google/flatbuffers/reflection/Field.java
@@ -55,6 +55,10 @@ public final class Field extends Table {
    * Number of padding octets to always add after this field. Structs only.
    */
   public int padding() { int o = __offset(28); return o != 0 ? bb.getShort(o + bb_pos) & 0xFFFF : 0; }
+  /**
+   * If the field uses 64-bit offsets.
+   */
+  public boolean offset64() { int o = __offset(30); return o != 0 ? 0!=bb.get(o + bb_pos) : false; }
 
   public static int createField(FlatBufferBuilder builder,
       int nameOffset,
@@ -69,8 +73,9 @@ public final class Field extends Table {
       int attributesOffset,
       int documentationOffset,
       boolean optional,
-      int padding) {
-    builder.startTable(13);
+      int padding,
+      boolean offset64) {
+    builder.startTable(14);
     Field.addDefaultReal(builder, defaultReal);
     Field.addDefaultInteger(builder, defaultInteger);
     Field.addDocumentation(builder, documentationOffset);
@@ -80,6 +85,7 @@ public final class Field extends Table {
     Field.addPadding(builder, padding);
     Field.addOffset(builder, offset);
     Field.addId(builder, id);
+    Field.addOffset64(builder, offset64);
     Field.addOptional(builder, optional);
     Field.addKey(builder, key);
     Field.addRequired(builder, required);
@@ -87,7 +93,7 @@ public final class Field extends Table {
     return Field.endField(builder);
   }
 
-  public static void startField(FlatBufferBuilder builder) { builder.startTable(13); }
+  public static void startField(FlatBufferBuilder builder) { builder.startTable(14); }
   public static void addName(FlatBufferBuilder builder, int nameOffset) { builder.addOffset(nameOffset); builder.slot(0); }
   public static void addType(FlatBufferBuilder builder, int typeOffset) { builder.addOffset(1, typeOffset, 0); }
   public static void addId(FlatBufferBuilder builder, int id) { builder.addShort(2, (short) id, (short) 0); }
@@ -105,6 +111,7 @@ public final class Field extends Table {
   public static void startDocumentationVector(FlatBufferBuilder builder, int numElems) { builder.startVector(4, numElems, 4); }
   public static void addOptional(FlatBufferBuilder builder, boolean optional) { builder.addBoolean(11, optional, false); }
   public static void addPadding(FlatBufferBuilder builder, int padding) { builder.addShort(12, (short) padding, (short) 0); }
+  public static void addOffset64(FlatBufferBuilder builder, boolean offset64) { builder.addBoolean(13, offset64, false); }
   public static int endField(FlatBufferBuilder builder) {
     int o = builder.endTable();
     builder.required(o, 4);  // name