Merge pull request #2373 from take-cheeze/static_assert

Add macro `mrb_static_assert`.

include/mruby.h

@@ -429,6 +429,12 @@ void mrb_atexit(mrb_state *mrb, mrb_atexit_func func);
 #define mrb_assert_int_fit(t1,n,t2,max) ((void)0)
 #endif
 
+#if __STDC_VERSION__ >= 201112L
+#define mrb_static_assert(exp, str) _Static_assert(exp, str)
+#else
+#define mrb_static_assert(exp, str) mrb_assert(exp)
+#endif
+
 mrb_value mrb_format(mrb_state *mrb, const char *format, ...);
 
 #if defined(__cplusplus)

src/state.c

@@ -29,7 +29,7 @@ mrb_open_allocf(mrb_allocf f, void *ud)
   mrb_state *mrb;
 
 #ifdef MRB_NAN_BOXING
-  mrb_assert(sizeof(void*) == 4);
+  mrb_static_assert(sizeof(void*) == 4, "when using NaN boxing sizeof pointer must be 4 byte");
 #endif
 
   mrb = (mrb_state *)(f)(NULL, NULL, sizeof(mrb_state), ud);

src/string.c

@@ -2503,6 +2503,8 @@ mrb_init_string(mrb_state *mrb)
 {
   struct RClass *s;
 
+  mrb_static_assert(RSTRING_EMBED_LEN_MAX < (1 << 5), "pointer size too big for embedded string");
+
   s = mrb->string_class = mrb_define_class(mrb, "String", mrb->object_class);             /* 15.2.10 */
   MRB_SET_INSTANCE_TT(s, MRB_TT_STRING);