Defining struct in a loop gives confusing error message

[user202729]

for(int i=0; i<10; ++i){
    struct A{int x;}
    A f(A a, int y){ a.x+=i; return a; }
    A a;
    A b=f(a,1);
}

Error message:

        A b=f(a,1);
      ^
a.asy: 5.7: cannot cast 'A' to 'A'
success

Why is the f function not redefined anyway?

[johncbowman]

For the record, here's a more minimal example:

while(true) {
  struct A {
    int x;
  }
  A f(A a){ return a; }
  A a;
  a=f(a);
}