parser: allow redefinition of builtin typedefs, but ignore them

The luajit behavior is that the builtins which are normally header
typedefs can be redefined without syntax error, but the resulting
definitions are ignored and the builtin type is always used. Do
the same thing to expand compatibility.

Fixes #40

src/parser.cc

@@ -1576,7 +1576,8 @@ static bool parse_array(lex_state &ls, std::size_t &ret, int &flags) {
  * below is described how it works:
  */
 static bool parse_type_ptr(
-    lex_state &ls, ast::c_type &tp, util::strbuf *fpname, bool needn
+    lex_state &ls, ast::c_type &tp, util::strbuf *fpname, bool needn,
+    bool tdef, bool &tdef_bltin
 ) {
     /* our input is the left-side qualified type; that means constructs such
      * as 'const int' or 'unsigned long int const'
@@ -1762,11 +1763,42 @@ static bool parse_type_ptr(
         if (!ls.param_maybe_name()) {
             return false;
         }
-        if (needn || (ls.t.token == TOK_NAME)) {
+        bool check_kw = (ls.t.token == TOK_NAME);
+        if (tdef) {
+            /* builtins can be "redefined", but the definitions
+             * are ignored, matching luajit fuzzy behavior
+             */
+            switch (ls.t.token) {
+                case TOK_int8_t:
+                case TOK_int16_t:
+                case TOK_int32_t:
+                case TOK_int64_t:
+                case TOK_uint8_t:
+                case TOK_uint16_t:
+                case TOK_uint32_t:
+                case TOK_uint64_t:
+                case TOK_uintptr_t:
+                case TOK_intptr_t:
+                case TOK_ptrdiff_t:
+                case TOK_ssize_t:
+                case TOK_size_t:
+                case TOK_va_list:
+                case TOK___builtin_va_list:
+                case TOK___gnuc_va_list:
+                case TOK_time_t:
+                case TOK_wchar_t:
+                    check_kw = true;
+                    tdef_bltin = true;
+                    break;
+                default:
+                    break;
+            }
+        }
+        if (needn || check_kw) {
             /* we're in a context where name can be provided, e.g. if
              * parsing a typedef or a prototype, this will be the name
              */
-            if (!check(ls, TOK_NAME)) {
+            if (!check_kw && !check(ls, TOK_NAME)) {
                 return false;
             }
             *fpname = ls.get_buf();
@@ -2255,7 +2287,10 @@ static bool parse_typebase(
 }
 
 static bool parse_type(lex_state &ls, ast::c_type &ret, util::strbuf *fpn) {
-    return (parse_typebase(ls, ret) && parse_type_ptr(ls, ret, fpn, false));
+    bool tdef_bltin = false;
+    return (parse_typebase(ls, ret) && parse_type_ptr(
+        ls, ret, fpn, false, false, tdef_bltin
+    ));
 }
 
 static ast::c_record const *parse_record(lex_state &ls, bool *newst) {
@@ -2344,7 +2379,8 @@ static ast::c_record const *parse_record(lex_state &ls, bool *newst) {
         do {
             util::strbuf fpn;
             auto tp = tpb.copy();
-            if (!parse_type_ptr(ls, tp, &fpn, false)) {
+            bool tdef_bltin = false;
+            if (!parse_type_ptr(ls, tp, &fpn, false, false, tdef_bltin)) {
                 return nullptr;
             }
             if (fpn[0] == '?') {
@@ -2556,7 +2592,8 @@ static bool parse_decl(lex_state &ls) {
             oldmode = ls.mode(PARSE_MODE_TYPEDEF);
         }
         auto tp = tpb.copy();
-        if (!parse_type_ptr(ls, tp, &dname, !first)) {
+        bool tdef_bltin = false;
+        if (!parse_type_ptr(ls, tp, &dname, !first, tdef, tdef_bltin)) {
             return false;
         }
         first = false;
@@ -2573,6 +2610,10 @@ static bool parse_decl(lex_state &ls) {
         if (tdef) {
             ls.mode(oldmode);
             if (dname[0] != '?') {
+                /* redefinition of builtin, skip */
+                if (tdef_bltin) {
+                    continue;
+                }
                 /* store if the name is non-empty, if it's empty there is no
                  * way to access the type and it'd be unique either way
                  */

tests/scalar.lua

@@ -71,6 +71,8 @@ ffi.cdef [[
     typedef unsigned long type2_t;
     typedef signed type3_t;
     typedef time_t type4_t;
+    /* redeclarations should be ignored */
+    typedef long time_t;
 ]]
 
 assert(ffi.cast("int", 150) == ffi.cast("type1_t", 150))