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

tests/evolution_test.cpp

@@ -80,7 +80,6 @@ void EvolutionTest(const std::string &tests_data_path) {
 #endif
 }
 
-
 void ConformTest() {
   const char ref[] = "table T { A:int; } enum E:byte { A }";
 
@@ -111,9 +110,41 @@ void ConformTest() {
   const char ref2[] = "enum E:byte { A } table T2 { f:E; } ";
   test_conform(ref2, "enum E:int32 { A } table T2 { df:byte; f:E; }",
                "field renamed to different type: T2.df (renamed from T2.f)");
+
+  // Check conformity for Offset64-related changes.
+  {
+    const char ref[] = "table T { a:[uint8]; b:string; }";
+
+    // Adding a 'vector64' changes the type.
+    test_conform(ref, "table T { a:[uint8] (vector64); b:string; }",
+                 "types differ for field: T.a");
+
+    // Adding a 'offset64' to the vector changes the type.
+    test_conform(ref, "table T { a:[uint8] (offset64); b:string; }",
+                 "offset types differ for field: T.a");
+
+    // Adding a 'offset64' to the string also changes the type.
+    test_conform(ref, "table T { a:[uint8]; b:string (offset64); }",
+                 "offset types differ for field: T.b");
+
+    // Now try the opposite direction of removing an attribute from an existing
+    // field.
+
+    // Removing a 'vector64' changes the type.
+    test_conform("table T { a:[uint8] (vector64); b:string; }", ref,
+                 "types differ for field: T.a");
+
+    // Removing a 'offset64' to the string also changes the type.
+    test_conform("table T { a:[uint8] (offset64); b:string; }", ref,
+                 "offset types differ for field: T.a");
+
+    // Remove a 'offset64' to the string also changes the type.
+    test_conform("table T { a:[uint8]; b:string (offset64); }", ref,
+                 "offset types differ for field: T.b");
+  }
 }
 
-void UnionDeprecationTest(const std::string& tests_data_path) {
+void UnionDeprecationTest(const std::string &tests_data_path) {
   const int NUM_VERSIONS = 2;
   std::string schemas[NUM_VERSIONS];
   std::string jsonfiles[NUM_VERSIONS];