Occurs compilation error in overload with extern(Windows)

[kntroh]

dmd 2.091.0 passes this code, but ldc 1.20.1 occurs an compilation error:

extern (Windows) {
    // test.d(7): Error: Function type does not match previously declared function with the same mangled name: func1
    // test.d(7):        Previous IR type: void (i32)
    // test.d(7):        New IR type:      void (i8*)
    void func1(ptrdiff_t);
    void func1(void*);
}

func1 is included in another object file, Can be linked and run with dmd.

$ cat func1.d
extern (Windows) void func1(ptrdiff_t t) {
    import core.stdc.stdio;
    printf("%d\n", t);
}
$ dmd func1.d -c
$ cat test.d
extern (Windows) {
    void func1(ptrdiff_t);
    void func1(void*);
}
void main() {
    func1(null);
    func1(0);
}
$ dmd func1.obj -run test.d
0
0
$

I don't know which is correct, dmd or ldc. Should this be an incorrect code?

I found this problem while compiling dwt. This code:

 LRESULT SendMessageW(HWND, UINT, WPARAM, LPARAM);
 LRESULT SendMessageW(HWND, UINT, WPARAM, void*);
 LRESULT SendMessageW(HWND, UINT, void*, LPARAM);
 LRESULT SendMessageW(HWND, UINT, void*, void*);

dwt can be used without any problems with dmd.

[JohanEngelen]

Try compiling this code and look at compiler output:

extern (Windows) {
    void func1(ptrdiff_t);
    pragma(msg, func1.mangleof);
    void func2(void*);
    pragma(msg, func2.mangleof);
}

Outputs:

func1
func2

In other words: the function arguments are not part of the function name in the executable (C-style mangling). This means that the executable does not distinguish between calls to your void func1(ptrdiff_t) and void func1(void*), both point to the same function. Multiple functions with the same name but different argument types are of course very dangerous, so I think LDC is correct here in rejecting the code.

[kntroh]

Multiple functions with the same name but different argument types are of course very dangerous, so I think LDC is correct here in rejecting the code.

I think so too. Is this omission of the dlang specification?

[kinke]

Ideally, this would be a frontend error, clearly stating that there's no such thing as overloads for C functions. But because people tend to re-declare external C[++] structs in different modules/libraries, the current DMD behavior is sadly expected, see #2782.

[kntroh]

I looked at the behavior of dmd, I think it is bug (of spec or compiler).
It is completely wrong that this code can be compiled:

extern (C) {
    void func(int);
    void func(double, double);
    void func(char[42]);
}

I'll report to dmd.

[kntroh]

I reported it: https://issues.dlang.org/show_bug.cgi?id=20672