In C++, 'throw' must go to the correct handler.

In C, we may have several "setjmp" nested, and the "longjmp" will go
to the one given by the corresponding "jmp_buf". In C++, a "throw"
will always go to the inner "catch". So, the "catch" must check
whether it is the recipient of the "throw" and, if not, rethrow
the exception to the outer level.

ldo.c

@@ -57,10 +57,18 @@
 ** =======================================================
 */
 
+/* chained list of long jump buffers */
+typedef struct lua_longjmp {
+  struct lua_longjmp *previous;
+  jmp_buf b;
+  volatile TStatus status;  /* error code */
+} lua_longjmp;
+
+
 /*
 ** LUAI_THROW/LUAI_TRY define how Lua does exception handling. By
 ** default, Lua handles errors with exceptions when compiling as
-** C++ code, with _longjmp/_setjmp when asked to use them, and with
+** C++ code, with _longjmp/_setjmp when available (POSIX), and with
 ** longjmp/setjmp otherwise.
 */
 #if !defined(LUAI_THROW)				/* { */
@@ -69,38 +77,38 @@
 
 /* C++ exceptions */
 #define LUAI_THROW(L,c)		throw(c)
-#define LUAI_TRY(L,c,f,ud) \
-    try { (f)(L, ud); } catch(...) { if ((c)->status == 0) (c)->status = -1; }
-#define luai_jmpbuf		int  /* dummy field */
+
+static void LUAI_TRY (lua_State *L, lua_longjmp *c, Pfunc f, void *ud) {
+  try {
+    f(L, ud);  /* call function protected */
+  }
+  catch (lua_longjmp *c1) { /* Lua error */
+    if (c1 != c)  /* not the correct level? */
+      throw;  /* rethrow to upper level */
+  }
+  catch (...) {  /* non-Lua exception */
+    c->status = -1;  /* create some error code */
+  }
+}
+
 
 #elif defined(LUA_USE_POSIX)				/* }{ */
 
-/* in POSIX, try _longjmp/_setjmp (more efficient) */
+/* in POSIX, use _longjmp/_setjmp (more efficient) */
 #define LUAI_THROW(L,c)		_longjmp((c)->b, 1)
 #define LUAI_TRY(L,c,f,ud)	if (_setjmp((c)->b) == 0) ((f)(L, ud))
-#define luai_jmpbuf		jmp_buf
 
 #else							/* }{ */
 
 /* ISO C handling with long jumps */
 #define LUAI_THROW(L,c)		longjmp((c)->b, 1)
 #define LUAI_TRY(L,c,f,ud)	if (setjmp((c)->b) == 0) ((f)(L, ud))
-#define luai_jmpbuf		jmp_buf
 
 #endif							/* } */
 
 #endif							/* } */
 
 
-
-/* chain list of long jump buffers */
-struct lua_longjmp {
-  struct lua_longjmp *previous;
-  luai_jmpbuf b;
-  volatile TStatus status;  /* error code */
-};
-
-
 void luaD_seterrorobj (lua_State *L, TStatus errcode, StkId oldtop) {
   if (errcode == LUA_ERRMEM) {  /* memory error? */
     setsvalue2s(L, oldtop, G(L)->memerrmsg); /* reuse preregistered msg. */
@@ -151,7 +159,7 @@ l_noret luaD_throwbaselevel (lua_State *L, TStatus errcode) {
 
 TStatus luaD_rawrunprotected (lua_State *L, Pfunc f, void *ud) {
   l_uint32 oldnCcalls = L->nCcalls;
-  struct lua_longjmp lj;
+  lua_longjmp lj;
   lj.status = LUA_OK;
   lj.previous = L->errorJmp;  /* chain new error handler */
   L->errorJmp = &lj;