'io.read' accepts multiple formats in a single string argument

liolib.c

@@ -1,5 +1,5 @@
 /*
-** $Id: liolib.c,v 2.152 2017/02/09 14:50:05 roberto Exp roberto $
+** $Id: liolib.c,v 2.153 2017/11/16 13:19:06 roberto Exp roberto $
 ** Standard I/O (and system) library
 ** See Copyright Notice in lua.h
 */
@@ -528,40 +528,44 @@ static int read_chars (lua_State *L, FILE *f, size_t n) {
 
 static int g_read (lua_State *L, FILE *f, int first) {
   int nargs = lua_gettop(L) - 1;
-  int success;
-  int n;
+  int nresults, success;
   clearerr(f);
   if (nargs == 0) {  /* no arguments? */
     success = read_line(L, f, 1);
-    n = first+1;  /* to return 1 result */
+    nresults = 1;
   }
-  else {  /* ensure stack space for all results and for auxlib's buffer */
-    luaL_checkstack(L, nargs+LUA_MINSTACK, "too many arguments");
+  else {
     success = 1;
-    for (n = first; nargs-- && success; n++) {
-      if (lua_type(L, n) == LUA_TNUMBER) {
-        size_t l = (size_t)luaL_checkinteger(L, n);
+    nresults = 0;
+    for (; nargs-- && success; first++) {
+      luaL_checkstack(L, LUA_MINSTACK, "too many arguments");
+      if (lua_type(L, first) == LUA_TNUMBER) {
+        size_t l = (size_t)luaL_checkinteger(L, first);
         success = (l == 0) ? test_eof(L, f) : read_chars(L, f, l);
+        nresults++;
       }
       else {
-        const char *p = luaL_checkstring(L, n);
+        const char *p = luaL_checkstring(L, first);
         if (*p == '*') p++;  /* skip optional '*' (for compatibility) */
-        switch (*p) {
-          case 'n':  /* number */
-            success = read_number(L, f);
-            break;
-          case 'l':  /* line */
-            success = read_line(L, f, 1);
-            break;
-          case 'L':  /* line with end-of-line */
-            success = read_line(L, f, 0);
-            break;
-          case 'a':  /* file */
-            read_all(L, f);  /* read entire file */
-            success = 1; /* always success */
-            break;
-          default:
-            return luaL_argerror(L, n, "invalid format");
+        for (; success && *p != '\0'; p++) {
+          nresults++;
+          switch (*p) {
+            case 'n':  /* number */
+              success = read_number(L, f);
+              break;
+            case 'l':  /* line */
+              success = read_line(L, f, 1);
+              break;
+            case 'L':  /* line with end-of-line */
+              success = read_line(L, f, 0);
+              break;
+            case 'a':  /* file */
+              read_all(L, f);  /* read entire file */
+              success = 1; /* always success */
+              break;
+            default:
+              return luaL_argerror(L, first, "invalid format");
+          }
         }
       }
     }
@@ -572,7 +576,7 @@ static int g_read (lua_State *L, FILE *f, int first) {
     lua_pop(L, 1);  /* remove last result */
     lua_pushnil(L);  /* push nil instead */
   }
-  return n - first;
+  return nresults;
 }