Add -U option

chibicc.h

@@ -101,6 +101,7 @@ Token *tokenize_file(char *filename);
 
 void init_macros(void);
 void define_macro(char *name, char *buf);
+void undef_macro(char *name);
 Token *preprocess(Token *tok);
 
 //

main.c

@@ -110,6 +110,16 @@ static void parse_args(int argc, char **argv) {
       continue;
     }
 
+    if (!strcmp(argv[i], "-U")) {
+      undef_macro(argv[++i]);
+      continue;
+    }
+
+    if (!strncmp(argv[i], "-U", 2)) {
+      undef_macro(argv[i] + 2);
+      continue;
+    }
+
     if (!strcmp(argv[i], "-cc1-input")) {
       base_file = argv[++i];
       continue;

preprocess.c

@@ -752,11 +752,8 @@ static Token *preprocess2(Token *tok) {
       tok = tok->next;
       if (tok->kind != TK_IDENT)
         error_tok(tok, "macro name must be an identifier");
-      char *name = strndup(tok->loc, tok->len);
+      undef_macro(strndup(tok->loc, tok->len));
       tok = skip_line(tok->next);
-
-      Macro *m = add_macro(name, true, NULL);
-      m->deleted = true;
       continue;
     }
 
@@ -836,6 +833,11 @@ void define_macro(char *name, char *buf) {
   add_macro(name, true, tok);
 }
 
+void undef_macro(char *name) {
+  Macro *m = add_macro(name, true, NULL);
+  m->deleted = true;
+}
+
 static Macro *add_builtin(char *name, macro_handler_fn *fn) {
   Macro *m = add_macro(name, true, NULL);
   m->handler = fn;

test/driver.sh

@@ -99,4 +99,8 @@ check -D
 echo foo | $chibicc -Dfoo=bar -E - | grep -q bar
 check -D
 
+# -U
+echo foo | $chibicc -Dfoo=bar -Ufoo -E - | grep -q foo
+check -U
+
 echo OK