Does Checked C support safe function pointers in itype?

[secure-sw-dev-bot]

This issue was copied from checkedc/checkedc-clang#649

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Question: If Checked C supports safe function pointers in itype, then what is the correct syntax?

@Machiry and I have been trying to create a function pointer with itype.

As you can see from our example below the first two functions wild_func_ptr() and checkedc_func_ptr() will compile with no errors. When the itype is introduced in itype_func() and itype_ptr_func() the compiler will raise errors.

ityf.c:

int wild_func_ptr(int (*f)(int)) {
  return 0;
}
int checkedc_func_ptr(_Ptr<int (int)> f) {
  return 0;
}
// function pointer returning int
int itype_func(int (*f)(int) : itype(_Ptr<int (int)>)) {
  return 0;  
}
// function pointer that returns a pointer.
int itype_ptr_func(int *(*f)(int) : itype(_Ptr<_Ptr<int> (int)>)) {
  return 0; 
}

$ cclang -c ityf.c:

ityf.c:9:32: error: interface type only allowed for a pointer return type
int itype_func(int (*f)(int) : itype(_Ptr<int (int)>)) {
                               ^
ityf.c:13:43: error: mismatch between interface type '_Ptr<_Ptr<int> (int)>' and declared type 'int *'
int itype_ptr_func(int *(*f)(int) : itype(_Ptr<_Ptr<int> (int)>)) {
                                          ^
2 errors generated.

[secure-sw-dev-bot]

Comment from @Machiry:

btw, the following declaration checks out:

int itype_ptr_func(int *(*f)(int) : itype(_Ptr<int>))