[Issue 24265] ref delegate literal no longer implicitly converts to unannotated type

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=24265

Paul Backus <snarwin+bugzilla at gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|ref delegate no longer      |ref delegate literal no
                   |implicitly converts to      |longer implicitly converts
                   |unannotated type            |to unannotated type

--- Comment #6 from Paul Backus <snarwin+bugzilla at gmail.com> ---
The bug *is* related to dropping function attributes during implicit
conversion, and it only affects a delegate whose type is inferred from the type
of a delegate literal:

---
void test()
{
    int local;

    auto inferred = delegate ref int() => local;

    ref int fun() pure nothrow @nogc @safe;
    static assert(is(typeof(inferred) == typeof(&fun)));

    typeof(&fun) explicit = inferred;

    ref int f();
    typeof(&f) dg;

    dg = &fun; // ok
    dg = explicit; // ok
    dg = inferred; // error
}
---

Output:

---
bug.d(17): Error: cannot implicitly convert expression `inferred` of type `int
delegate() pure nothrow @nogc ref @safe` to `int delegate() ref`
---

Somehow, the compiler is ending up with two internal representations of the
"same" delegate type, and only one of them can implicitly convert to the
unannotated version.

--