Add noreturn support for MSVC, fix warnings

Adding the noreturn attribute for MSVC incurs additional warnings
for unreachable code. As we're only aiming to support the big three
compilers - all of which have attributes - we can fix unreachable
code warnings by just removing said code.

include/luaconf.h

@@ -210,6 +210,8 @@
 */
 #if defined(__GNUC__) || defined(__clang__)
 #define LUA_NORETURN __attribute__((noreturn))
+#elif defined(_MSC_VER)
+#define LUA_NORETURN __declspec(noreturn)
 #else
 #define LUA_NORETURN
 #endif

src/lapi.c

@@ -966,7 +966,6 @@ LUA_API int lua_error (lua_State *L) {
   api_checknelems(L, 1);
   luaG_errormsg(L);
   lua_unlock(L);
-  return 0;  /* to avoid warnings */
 }
 
 

src/ldebug.c

@@ -613,7 +613,7 @@ void luaG_aritherror (lua_State *L, const TValue *p1, const TValue *p2) {
 }
 
 
-int luaG_ordererror (lua_State *L, const TValue *p1, const TValue *p2) {
+void luaG_ordererror (lua_State *L, const TValue *p1, const TValue *p2) {
   const char *t1 = luaT_typenames[ttype(p1)];
   const char *t2 = luaT_typenames[ttype(p2)];
   if (t1[2] == t2[2])

src/ldebug.h

@@ -18,12 +18,12 @@
 #define resethookcount(L)	(L->hookcount = L->basehookcount)
 
 
-LUAI_FUNC void luaG_typeerror (lua_State *L, const TValue *o, const char *opname) LUA_NORETURN;
-LUAI_FUNC void luaG_concaterror (lua_State *L, StkId p1, StkId p2) LUA_NORETURN;
-LUAI_FUNC void luaG_aritherror (lua_State *L, const TValue *p1, const TValue *p2) LUA_NORETURN;
-LUAI_FUNC int luaG_ordererror (lua_State *L, const TValue *p1, const TValue *p2) LUA_NORETURN;
-LUAI_FUNC void luaG_runerror (lua_State *L, const char *fmt, ...) LUA_NORETURN;
-LUAI_FUNC void luaG_errormsg (lua_State *L) LUA_NORETURN;
+LUAI_FUNC LUA_NORETURN void luaG_typeerror (lua_State *L, const TValue *o, const char *opname);
+LUAI_FUNC LUA_NORETURN void luaG_concaterror (lua_State *L, StkId p1, StkId p2);
+LUAI_FUNC LUA_NORETURN void luaG_aritherror (lua_State *L, const TValue *p1, const TValue *p2);
+LUAI_FUNC LUA_NORETURN void luaG_ordererror (lua_State *L, const TValue *p1, const TValue *p2);
+LUAI_FUNC LUA_NORETURN void luaG_runerror (lua_State *L, const char *fmt, ...);
+LUAI_FUNC LUA_NORETURN void luaG_errormsg (lua_State *L);
 LUAI_FUNC int luaG_checkcode (const Proto *pt);
 LUAI_FUNC int luaG_checkopenop (Instruction i);
 

src/ldo.h

@@ -48,7 +48,7 @@ LUAI_FUNC void luaD_reallocCI (lua_State *L, int newsize);
 LUAI_FUNC void luaD_reallocstack (lua_State *L, int newsize);
 LUAI_FUNC void luaD_growstack (lua_State *L, int n);
 
-LUAI_FUNC void luaD_throw (lua_State *L, int errcode) LUA_NORETURN;
+LUAI_FUNC LUA_NORETURN void luaD_throw (lua_State *L, int errcode);
 LUAI_FUNC int luaD_rawrunprotected (lua_State *L, Pfunc f, void *ud);
 
 LUAI_FUNC void luaD_seterrorobj (lua_State *L, int errcode, StkId oldtop);

src/llex.h

@@ -73,8 +73,8 @@ LUAI_FUNC void luaX_setinput (lua_State *L, LexState *ls, ZIO *z,
 LUAI_FUNC TString *luaX_newstring (LexState *ls, const char *str, size_t l);
 LUAI_FUNC void luaX_next (LexState *ls);
 LUAI_FUNC void luaX_lookahead (LexState *ls);
-LUAI_FUNC void luaX_lexerror (LexState *ls, const char *msg, int token) LUA_NORETURN;
-LUAI_FUNC void luaX_syntaxerror (LexState *ls, const char *s) LUA_NORETURN;
+LUAI_FUNC LUA_NORETURN void luaX_lexerror (LexState *ls, const char *msg, int token);
+LUAI_FUNC LUA_NORETURN void luaX_syntaxerror (LexState *ls, const char *s);
 LUAI_FUNC const char *luaX_token2str (LexState *ls, int token);
 
 

src/lmem.c

@@ -65,7 +65,6 @@ void *luaM_growaux_ (lua_State *L, void *block, int *size, size_t size_elems,
 
 void *luaM_toobig (lua_State *L) {
   luaG_runerror(L, "memory allocation error: block too big");
-  return NULL;  /* to avoid warnings */
 }
 
 

src/ltable.c

@@ -154,7 +154,6 @@ static int findindex (lua_State *L, Table *t, StkId key) {
       else n = gnext(n);
     } while (n);
     luaG_runerror(L, "invalid key to " LUA_QL("next"));  /* key not found */
-    return 0;  /* to avoid warnings */
   }
 }
 

src/lvm.c

@@ -235,21 +235,21 @@ static int l_strcmp (const TString *ls, const TString *rs) {
 int luaV_lessthan (lua_State *L, const TValue *l, const TValue *r) {
   int res;
   if (ttype(l) != ttype(r))
-    return luaG_ordererror(L, l, r);
+    luaG_ordererror(L, l, r);
   else if (ttisnumber(l))
     return luai_numlt(nvalue(l), nvalue(r));
   else if (ttisstring(l))
     return l_strcmp(rawtsvalue(l), rawtsvalue(r)) < 0;
   else if ((res = call_orderTM(L, l, r, TM_LT)) != -1)
     return res;
-  return luaG_ordererror(L, l, r);
+  luaG_ordererror(L, l, r);
 }
 
 
 static int lessequal (lua_State *L, const TValue *l, const TValue *r) {
   int res;
   if (ttype(l) != ttype(r))
-    return luaG_ordererror(L, l, r);
+    luaG_ordererror(L, l, r);
   else if (ttisnumber(l))
     return luai_numle(nvalue(l), nvalue(r));
   else if (ttisstring(l))
@@ -258,7 +258,7 @@ static int lessequal (lua_State *L, const TValue *l, const TValue *r) {
     return res;
   else if ((res = call_orderTM(L, r, l, TM_LT)) != -1)  /* else try `lt' */
     return !res;
-  return luaG_ordererror(L, l, r);
+  luaG_ordererror(L, l, r);
 }