Fixed reflection.h not modifying certain table configurations.

It would write 64bits offsets instead of 32bit ones, and update
the vtable pointer before the fields were processed.

Change-Id: I0c0fa942bbd3b42839294f5653ba8fa048612624
Tested: on Linux.

include/flatbuffers/flatbuffers.h

@@ -356,7 +356,8 @@ public:
   void MutateOffset(uoffset_t i, const uint8_t *val) {
     assert(i < size());
     assert(sizeof(T) == sizeof(uoffset_t));
-    WriteScalar(data() + i, val - (Data() + i * sizeof(uoffset_t)));
+    WriteScalar(data() + i,
+                static_cast<uoffset_t>(val - (Data() + i * sizeof(uoffset_t))));
   }
 
   // Get a mutable pointer to tables/strings inside this vector.
@@ -1495,7 +1496,8 @@ class Table {
   bool SetPointer(voffset_t field, const uint8_t *val) {
     auto field_offset = GetOptionalFieldOffset(field);
     if (!field_offset) return false;
-    WriteScalar(data_ + field_offset, val - (data_ + field_offset));
+    WriteScalar(data_ + field_offset,
+                static_cast<uoffset_t>(val - (data_ + field_offset)));
     return true;
   }
 

src/reflection.cpp

@@ -204,16 +204,15 @@ class ResizeContext {
     if (DagCheck(table))
       return;  // Table already visited.
     auto vtable = table->GetVTable();
-    // Check if the vtable offset points beyond the insertion point.
-    Straddle<soffset_t, -1>(table, vtable, table);
-    // This direction shouldn't happen because vtables that sit before tables
-    // are always directly adjacent, but check just in case we ever change the
-    // way flatbuffers are built.
-    Straddle<soffset_t, -1>(vtable, table, table);
     // Early out: since all fields inside the table must point forwards in
     // memory, if the insertion point is before the table we can stop here.
     auto tableloc = reinterpret_cast<uint8_t *>(table);
-    if (startptr_ <= tableloc) return;
+    if (startptr_ <= tableloc) {
+      // Check if insertion point is between the table and a vtable that
+      // precedes it. This can't happen in current construction code, but check
+      // just in case we ever change the way flatbuffers are built.
+      Straddle<soffset_t, -1>(vtable, table, table);
+    } else {
       // Check each field.
       auto fielddefs = objectdef.fields();
       for (auto it = fielddefs->begin(); it != fielddefs->end(); ++it) {
@@ -271,6 +270,11 @@ class ResizeContext {
             assert(false);
         }
       }
+      // Check if the vtable offset points beyond the insertion point.
+      // Must do this last, since GetOptionalFieldOffset above still reads
+      // this value.
+      Straddle<soffset_t, -1>(table, vtable, table);
+    }
   }
 
   void operator=(const ResizeContext &rc);