Incorrect double-expansion of renamed macro

[ludocode]

#define foo(x) x
#define bar foo

int main(void) {
    return bar(bar(0));
}

This fails under cparser 8ec1a76 with warning "implicit declaration of function 'foo'" and linker error "undefined reference to `foo'".

It compiles correctly under GCC 10.2.0, Clang 10.0.1, MSVC 19.27.29111 and TinyCC 0.9.27. It also compiles correctly with cparser if you replace #define bar foo with #define bar(x) foo(x).

[mingodad]

Using Kimi-2.5 this problem can be solved by removing the lines shown bellow:

-------------------------- src/parser/preprocessor.c --------------------------
index d29fd0d37..9bd98738f 100644
@@ -4029,8 +4029,6 @@ static bool start_expanding(void)
 
 			pp_definition_t *const pp_definition = symbol->pp_definition;
 			if (pp_definition != NULL && !pp_token.base.expansion_forbidden) {
-				if (pp_definition->is_expanding)
-					pp_token.base.expansion_forbidden = true;
 
 				if (pp_definition->is_expanding && !pp_definition->may_recurse) {
 					pp_token.base.expansion_forbidden = true;

The fix works! The output now correctly shows int b = 0; instead of int b = foo(0);.
The root cause was that the is_expanding flag was being checked unconditionally and setting expansion_forbidden = true, ignoring the may_recurse flag that was specifically designed to allow re-expansion in recursive contexts.
Summary of the bug and fix:
1. The bug: In start_expanding(), line 4045-4046 had:
      if (pp_definition->is_expanding)
       pp_token.base.expansion_forbidden = true;
      This unconditionally blocked expansion whenever a macro was already expanding, even when may_recurse was set to true (which happens when expanding parameters that reference back to the parent macro).
2. The fix: Removed the redundant unconditional check. The existing check on line 4048-4050 already handles this correctly:
      if (pp_definition->is_expanding && !pp_definition->may_recurse) {
       pp_token.base.expansion_forbidden = true;
   
The may_recurse flag is set by start_object_macro_expansion() when expanding a parameter (line ~4156), allowing the parent function macro to be re-expanded when encountered within its own parameter.