is this a bug ? mixin template static function missing!

[Simen Kjærås]

On Friday, 10 August 2018 at 08:31:21 UTC, learnfirst1 wrote:
>
> #!/usr/bin/env rdmd
> import core.stdc.stdio;
>
> template G(size_t line = __LINE__, A...){
> 	int i = 3;
> 	static extern(C) pragma(crt_constructor) void init2(){
> 		printf("init: %d\n", line);
> 	}
> }
>
> pragma(crt_constructor) extern(C) void init1(){
>       printf("init from global\n");
> }
>
> struct A {
> 	mixin G!();
> }
>
> extern(C) void main(){
> 	mixin G!() g;
> 	printf("g.i=%d\n", g.i);
> 	g.init2(); // remove this can build, but g.init2 not get 
> called!
> }
>
> -----------------
>
> build error:
> Undefined symbols for architecture x86_64: 
> "__D4test4mainUZ1g5init2UNbNiZv", referenced from:

It is indeed. Reduced example:

template G(){
     extern(C) pragma(crt_constructor) void init(){}
}
void main(){
     mixin G!();
     init();
}

For nested functions, extern(C) is simply ignored[0]. Since 
pragma(crt_constructor) requires that the symbol it's applied to 
uses C linkage (and an error message to that effect is shown if 
you write pragma(crt_constructor) void fun() {} in module scope:
Error: function `fun` must be extern(C) for 
pragma(crt_constructor)

In addition, if you try to apply pragma(crt_constructor) to a 
nested function, you get this error message, showing further that 
nested functions can't be crt_constructors:
Error: unrecognized pragma(crt_constructor)

The correct behavior would be for the compiler to show the latter 
error message for a mixin'd function as well.

Filed a bug:
https://issues.dlang.org/show_bug.cgi?id=19153

--
   Simen

[0]: from https://dlang.org/spec/attribute.html#linkage:
Note that extern(C) can be provided for all types of 
declarations, including struct or class, even though there is no 
corresponding match on the C side. In that case, the attribute is 
ignored. This behavior applies for nested functions and nested 
variables as well.