Expand macros in the #if and #elif argument context

preprocess.c

@@ -20,6 +20,8 @@ struct CondIncl {
 static Macro *macros;
 static CondIncl *cond_incl;
 
+static Token *preprocess2(Token *tok);
+
 static bool is_hash(Token *tok) {
   return tok->at_bol && equal(tok, "#");
 }
@@ -113,6 +115,7 @@ static Token *copy_line(Token **rest, Token *tok) {
 static long eval_const_expr(Token **rest, Token *tok) {
   Token *start = tok;
   Token *expr = copy_line(rest, tok->next);
+  expr = preprocess2(expr);
 
   if (expr->kind == TK_EOF)
     error_tok(start, "no expression");

test/macro.c

@@ -128,6 +128,22 @@ int main() {
 
   if (0);
 
+#define M 5
+#if M
+  m = 5;
+#else
+  m = 6;
+#endif
+  assert(5, m, "m");
+
+#define M 5
+#if M-5
+  m = 6;
+#elif M
+  m = 5;
+#endif
+  assert(5, m, "m");
+
   printf("OK\n");
   return 0;
 }