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

python/flatbuffers/reflection/BaseType.py

@@ -21,4 +21,5 @@ class BaseType(object):
     Obj = 15
     Union = 16
     Array = 17
-    MaxBaseType = 18
+    Vector64 = 18
+    MaxBaseType = 19

python/flatbuffers/reflection/Field.py

@@ -155,8 +155,16 @@ class Field(object):
             return self._tab.Get(flatbuffers.number_types.Uint16Flags, o + self._tab.Pos)
         return 0
 
+    # If the field uses 64-bit offsets.
+    # Field
+    def Offset64(self):
+        o = flatbuffers.number_types.UOffsetTFlags.py_type(self._tab.Offset(30))
+        if o != 0:
+            return bool(self._tab.Get(flatbuffers.number_types.BoolFlags, o + self._tab.Pos))
+        return False
+
 def FieldStart(builder):
-    builder.StartObject(13)
+    builder.StartObject(14)
 
 def Start(builder):
     FieldStart(builder)
@@ -251,6 +259,12 @@ def FieldAddPadding(builder, padding):
 def AddPadding(builder: flatbuffers.Builder, padding: int):
     FieldAddPadding(builder, padding)
 
+def FieldAddOffset64(builder, offset64):
+    builder.PrependBoolSlot(13, offset64, 0)
+
+def AddOffset64(builder: flatbuffers.Builder, offset64: bool):
+    FieldAddOffset64(builder, offset64)
+
 def FieldEnd(builder):
     return builder.EndObject()