Add static asserts to ensure that reflection API arrays are kept in sync (#5934)

* Add static asserts to ensure that reflection API arrays are kept in sync

* Move changes from generated file into source fbs file

* Rename enum value and regenerate reflection_generated.h

* Add comments to each entries of type sizes array

include/flatbuffers/reflection.h

@@ -46,7 +46,30 @@ inline bool IsLong(reflection::BaseType t) {
 // Size of a basic type, don't use with structs.
 inline size_t GetTypeSize(reflection::BaseType base_type) {
   // This needs to correspond to the BaseType enum.
-  static size_t sizes[] = { 0, 1, 1, 1, 1, 2, 2, 4, 4, 8, 8, 4, 8, 4, 4, 4, 4 };
+  static size_t sizes[] = {
+    0, // None
+    1, // UType
+    1, // Bool
+    1, // Byte
+    1, // UByte
+    2, // Short
+    2, // UShort
+    4, // Int
+    4, // UInt
+    8, // Long
+    8, // ULong
+    4, // Float
+    8, // Double
+    4, // String
+    4, // Vector
+    4, // Obj
+    4, // Union
+    0, // Array. Only used in structs. 0 was chosen to prevent out-of-bounds errors.
+
+    0  // MaxBaseType. This must be kept the last entry in this array.
+    };
+  static_assert(sizeof(sizes) / sizeof(size_t) == reflection::MaxBaseType + 1,
+                "Size of sizes[] array does not match the count of BaseType enum values.");
   return sizes[base_type];
 }
 

include/flatbuffers/reflection_generated.h

@@ -53,10 +53,11 @@ enum BaseType {
   Vector = 14,
   Obj = 15,
   Union = 16,
-  Array = 17
+  Array = 17,
+  MaxBaseType = 18
 };
 
-inline const BaseType (&EnumValuesBaseType())[18] {
+inline const BaseType (&EnumValuesBaseType())[19] {
   static const BaseType values[] = {
     None,
     UType,
@@ -75,13 +76,14 @@ inline const BaseType (&EnumValuesBaseType())[18] {
     Vector,
     Obj,
     Union,
-    Array
+    Array,
+    MaxBaseType
   };
   return values;
 }
 
 inline const char * const *EnumNamesBaseType() {
-  static const char * const names[19] = {
+  static const char * const names[20] = {
     "None",
     "UType",
     "Bool",
@@ -100,13 +102,14 @@ inline const char * const *EnumNamesBaseType() {
     "Obj",
     "Union",
     "Array",
+    "MaxBaseType",
     nullptr
   };
   return names;
 }
 
 inline const char *EnumNameBaseType(BaseType e) {
-  if (flatbuffers::IsOutRange(e, None, Array)) return "";
+  if (flatbuffers::IsOutRange(e, None, MaxBaseType)) return "";
   const size_t index = static_cast<size_t>(e);
   return EnumNamesBaseType()[index];
 }

reflection/reflection.fbs

@@ -24,12 +24,15 @@ enum BaseType : byte {
     Vector,
     Obj,     // Used for tables & structs.
     Union,
-    Array
+    Array,
+
+    // Add any new type above this value.
+    MaxBaseType
 }
 
 table Type {
     base_type:BaseType;
-    element:BaseType = None;  // Only if base_type == Vector 
+    element:BaseType = None;  // Only if base_type == Vector
                               // or base_type == Array.
     index:int = -1;  // If base_type == Object, index into "objects" below.
                      // If base_type == Union, UnionType, or integral derived