Replace our homegrown ARRAY_SIZE() with Chrome's arraysize().

src/base/macros.h

Index: src/base/macros.h
diff --git a/src/base/macros.h b/src/base/macros.h
index 50828db57ff95420fe2ab386c8ed69dec197f56b..c8a140849dcf3e370c7e845929c25ebf3409ca0c 100644
--- a/src/base/macros.h
+++ b/src/base/macros.h
@@ -20,13 +20,74 @@
   (reinterpret_cast<intptr_t>(&(reinterpret_cast<type*>(4)->field)) - 4)
 
 
-// The expression ARRAY_SIZE(a) is a compile-time constant of type
-// size_t which represents the number of elements of the given
-// array. You should only use ARRAY_SIZE on statically allocated
-// arrays.
-#define ARRAY_SIZE(a)                                   \
-  ((sizeof(a) / sizeof(*(a))) /                         \
-  static_cast<size_t>(!(sizeof(a) % sizeof(*(a)))))
+// The arraysize(arr) macro returns the # of elements in an array arr.
+// The expression is a compile-time constant, and therefore can be
+// used in defining new arrays, for example.  If you use arraysize on
+// a pointer by mistake, you will get a compile-time error.
+//
+// One caveat is that arraysize() doesn't accept any array of an
+// anonymous type or a type defined inside a function.  In these rare
+// cases, you have to use the unsafe ARRAYSIZE_UNSAFE() macro below.  This is
+// due to a limitation in C++'s template system.  The limitation might
+// eventually be removed, but it hasn't happened yet.
+#define arraysize(array) (sizeof(ArraySizeHelper(array)))
+
+
+// This template function declaration is used in defining arraysize.
+// Note that the function doesn't need an implementation, as we only
+// use its type.
+template <typename T, size_t N>
+char (&ArraySizeHelper(T (&array)[N]))[N];
+
+
+#if V8_CC_GNU
+// That gcc wants both of these prototypes seems mysterious. VC, for
+// its part, can't decide which to use (another mystery). Matching of
+// template overloads: the final frontier.
+template <typename T, size_t N>
+char (&ArraySizeHelper(const T (&array)[N]))[N];
+#endif
+
+
+// ARRAYSIZE_UNSAFE performs essentially the same calculation as arraysize,
+// but can be used on anonymous types or types defined inside
+// functions.  It's less safe than arraysize as it accepts some
+// (although not all) pointers.  Therefore, you should use arraysize
+// whenever possible.
+//
+// The expression ARRAYSIZE_UNSAFE(a) is a compile-time constant of type
+// size_t.
+//
+// ARRAYSIZE_UNSAFE catches a few type errors.  If you see a compiler error
+//
+//   "warning: division by zero in ..."
+//
+// when using ARRAYSIZE_UNSAFE, you are (wrongfully) giving it a pointer.
+// You should only use ARRAYSIZE_UNSAFE on statically allocated arrays.
+//
+// The following comments are on the implementation details, and can
+// be ignored by the users.
+//
+// ARRAYSIZE_UNSAFE(arr) works by inspecting sizeof(arr) (the # of bytes in
+// the array) and sizeof(*(arr)) (the # of bytes in one array
+// element).  If the former is divisible by the latter, perhaps arr is
+// indeed an array, in which case the division result is the # of
+// elements in the array.  Otherwise, arr cannot possibly be an array,
+// and we generate a compiler error to prevent the code from
+// compiling.
+//
+// Since the size of bool is implementation-defined, we need to cast
+// !(sizeof(a) & sizeof(*(a))) to size_t in order to ensure the final
+// result has type size_t.
+//
+// This macro is not perfect as it wrongfully accepts certain
+// pointers, namely where the pointer size is divisible by the pointee
+// size.  Since all our code has to go through a 32-bit compiler,
+// where a pointer is 4 bytes, this means all pointers to a type whose
+// size is 3 or greater than 4 will be (righteously) rejected.
+#define ARRAYSIZE_UNSAFE(a)     \

[Yang, 2014/08/26 09:17:22]

Do we actually need this?

+  ((sizeof(a) / sizeof(*(a))) / \
+   static_cast<size_t>(!(sizeof(a) % sizeof(*(a)))))  // NOLINT
 
 
 // A macro to disallow the evil copy constructor and operator= functions