Given code below:
import std.stdio;

struct Annotation {
    public int delegate(int) dg;
}

void main() {
	import std.traits;
	
	__traits(getAttributes, Cls)[0].dg(20).writeln;
}

@Annotation(delegate int(int d) {
    return d;
})
class Cls {

    void method() {

    }
}

Dmd will complain with following statement for the delegate passed in annotation:
src/app.d(13,13): Error: delegate app.__dgliteral6 is a nested function and cannot be accessed from D main.

GDC will just throw internal compiler exception:
src/app.d: In function ‘D main’:
src/app.d:20:2: internal compiler error: in get_frame_for_symbol, at d/d-codegen.cc:3981
  __traits(getAttributes, Cls)[0].dg(20).writeln;
  ^

LDC will not argue, and compile it flawlessly, and return 20 as expected.

So the question, is the dmd error correct behavior?
If so, how the delegate is nested, and what is context that it is nested in?

DMD version is: v2.072.1
LDC version is: v1.1.0 based on v2.071.2 and LLVM 3.8.1
GDC version is: 6.2.1 20161215

On Thursday, 29 December 2016 at 20:55:43 UTC, Alexandru Ermicioi wrote:
> Given code below:
> import std.stdio;
>
> struct Annotation {
>     public int delegate(int) dg;
> }
>
> void main() {
> 	import std.traits;
> 	
> 	__traits(getAttributes, Cls)[0].dg(20).writeln;
> }
>
> @Annotation(delegate int(int d) {
>     return d;
> })
> class Cls {
>
>     void method() {
>
>     }
> }
>
> Dmd will complain with following statement for the delegate passed in annotation:
> src/app.d(13,13): Error: delegate app.__dgliteral6 is a nested function and cannot be accessed from D main.
>
> GDC will just throw internal compiler exception:
> src/app.d: In function ‘D main’:
> src/app.d:20:2: internal compiler error: in get_frame_for_symbol, at d/d-codegen.cc:3981
>   __traits(getAttributes, Cls)[0].dg(20).writeln;
>   ^
>
> LDC will not argue, and compile it flawlessly, and return 20 as expected.
>
> So the question, is the dmd error correct behavior?
> If so, how the delegate is nested, and what is context that it is nested in?
>
> DMD version is: v2.072.1
> LDC version is: v1.1.0 based on v2.071.2 and LLVM 3.8.1
> GDC version is: 6.2.1 20161215

It's a delegate and not function.
Therefore it will get a frame-ptr regardless, without checking if it is needed or not, or if there is a frame to point to.
Since there is no frame to point to you get the error.
At least this is my guess.
Make the delegate a function and the error should disappear.

On Thursday, 29 December 2016 at 21:07:00 UTC, Stefan Koch wrote:
> It's a delegate and not function.
> Therefore it will get a frame-ptr regardless, without checking if it is needed or not, or if there is a frame to point to.
> Since there is no frame to point to you get the error.
> At least this is my guess.
> Make the delegate a function and the error should disappear.

Yep, making it a function, will eliminate the problem.
Though what I'm also curious is why on LDC it compiles and runs, while on DMD it does not?
Should it be registered as a bug on issues.dlang.org, or at ldc bug tracker?

On Thursday, 29 December 2016 at 21:19:18 UTC, Alexandru Ermicioi wrote:
> On Thursday, 29 December 2016 at 21:07:00 UTC, Stefan Koch wrote:
>> It's a delegate and not function.
>> Therefore it will get a frame-ptr regardless, without checking if it is needed or not, or if there is a frame to point to.
>> Since there is no frame to point to you get the error.
>> At least this is my guess.
>> Make the delegate a function and the error should disappear.
>
> Yep, making it a function, will eliminate the problem.
> Though what I'm also curious is why on LDC it compiles and runs, while on DMD it does not?
> Should it be registered as a bug on issues.dlang.org, or at ldc bug tracker?

ldc accepts invalid code there.
But it might be that dmd 2.071.2 did that as well.
If so It will be fixed as soon as ldc updates the front-end version.

On Thursday, 29 December 2016 at 21:29:47 UTC, Stefan Koch wrote:
> ldc accepts invalid code there.
> But it might be that dmd 2.071.2 did that as well.
> If so It will be fixed as soon as ldc updates the front-end version.

Nope, tried with dmd v2.071.2 and it gives same error as v2.072.1.
I think I'll add a bug report to ldc, about not emitting the error.

Thanks for help.