/in/foo.c:1:1: error: unknown type name 'def'
    1 | def fibonacci(n):
      | ^~~
/in/foo.c: In function 'fibonacci':
/in/foo.c:1:17: error: expected declaration specifiers before ':' token
    1 | def fibonacci(n):
      |                 ^
/in/foo.c:1:5: warning: type of 'n' defaults to 'int' [-Wimplicit-int]
    1 | def fibonacci(n):
      |     ^~~~~~~~~
/in/foo.c:27: warning: control reaches end of non-void function [-Wreturn-type]