Bug 24265 – ref delegate literal no longer implicitly converts to unannotated type

This worked fine on dmd 2.098 (my mainline LTS version) but ceased working some time between that and 2.105 (I don't feel like doing a bisect tonight): ``` void main() { ref int alol(); typeof(&alol) dg; int a; dg = delegate ref() { return a; }; dg() = 5; assert(a == 5); } ``` me@arsd:~/test$ dmd-2098 refdg me@arsd:~/test$ ./refdg # compiles and passes assert me@arsd:~/test$ dmd-master refdg refdg.d(5): Error: cannot implicitly convert expression `__dgliteral4` of type int delegate() pure nothrow @nogc ref @safe` to `int delegate() ref` refdg.d(5): Error: cannot implicitly convert expression `__dgliteral4` of type int delegate() pure nothrow @nogc ref @safe` to `int delegate() ref` Fails on the new dmd. If you write out all the attributes on the dg type: ``` void main() { ref int alol() @safe @nogc nothrow pure; typeof(&alol) dg; int a; dg = delegate ref() { return a; }; dg() = 5; assert(a == 5); } ``` Compiles and runs successfully on both old and new dmd.

Introduced by DMD PR 14142: https://issues.dlang.org/show_bug.cgi?id=24265 Looks like maybe this isn't a behavioral bug, but a bad error message: the actual problem is that `ref int delegate() return` does not convert to `ref int delegate()`, but the compiler does not print the `return` attribute when printing the delegate's type.

Oops, pasted the wrong link; the introducing PR is here: https://github.com/dlang/dmd/pull/14142

OK, yeah, I suspected it might have to do with the return thing, but weird that adding the explicit attributes made it work. I'm ok reclassifying this as a diagnostic bug. I'll at least add the keyword.

Looks like this only happens when the return attribute is inferred. --- void test() { int a; ref int f(); ref int g() return; ref int h() => a; // return inferred typeof(&f) dg; dg = &g; // line 9 dg = &h; // line 10 } --- Output: --- bug.d(9): Error: cannot implicitly convert expression `&g` of type `int delegate() ref return` to `int delegate() ref` bug.d(10): Error: cannot implicitly convert expression `&h` of type `int delegate() pure nothrow @nogc ref @safe` to `int delegate() ref` ---

Correction, it's not a diagnostic problem--the types are printed differently because they are actually considered different by the compiler. For example, this: --- void test() { int local; ref int explicit() pure nothrow @nogc @safe return; ref int inferred() pure nothrow @nogc @safe => local; static assert(is(typeof(&explicit) == typeof(&inferred))); } --- ...fails with the following output: --- bug.d(7): Error: static assert: `is(int delegate() pure nothrow @nogc ref return @safe == int delegate() pure nothrow @nogc ref @safe)` is false --- The return attribute is not printed because it is genuinely not being inferred, probably due to issue 22977.

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.

THIS ISSUE HAS BEEN MOVED TO GITHUB https://github.com/dlang/dmd/issues/18201 DO NOT COMMENT HERE ANYMORE, NOBODY WILL SEE IT, THIS ISSUE HAS BEEN MOVED TO GITHUB