[Issue 21285] Delegate covariance broken between 2.092 and 2.094 (git master).

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=21285

hsteoh at quickfur.ath.cx changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |rejects-valid
             Status|RESOLVED                    |REOPENED
         Resolution|FIXED                       |---

--- Comment #5 from hsteoh at quickfur.ath.cx ---
The problem has not been completely fixed. Just a slight refactoring and it
fails again:

Code:
--------
int f(string s) { throw new Exception(""); }
void main()
{
    string path;
    int bank, preset;
    void delegate(string value)[string] aa = [
        "path": (string arg) {
            path = arg;
        },
        "bank": (string arg) {
            bank = f(arg);
        },
        "preset": (string arg) {
            preset = f(arg);
        },
    ];
}
--------

Compiler output:
--------
test.d(7): Error: cannot implicitly convert expression __lambda1 of type void
delegate(string arg) pure nothrow @nogc @safe to void delegate(string arg)
@system
--------

Oddly enough, replacing the `preset` line with `preset = 1;` makes the problem
go away. Somehow the number of elements in the AA initializer changes compiler
behaviour.

Expected behaviour: `pure nothrow @nogc @safe` ought to be covariant with
`@system`. And this covariance should not vary with unrelated factors such as
the number of elements in the AA initializer.

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