cast to pure function stop work after upgrade

[Tejas]

On Monday, 14 June 2021 at 13:31:51 UTC, baby_tiger wrote:
> this used work for me, after upgrade I get this error.  how to 
> fix it ?
>
>
>     import std.traits;
>             enum LogLevel : ubyte {
>                     INFO = 0,
>                     WARN,
>                     ERROR,
>                     FATAL,
>             }
>
>
>     extern (C) string VFORMAT(LogLevel level, string file, 
> size_t line, char[] tmp, bool line_break, string tag, string 
> fmt, ...) @nogc nothrow {
>             return null;
>     }
>
>     template asPure(string P, alias Fn) if 
> (isFunctionPointer!(typeof(&Fn))) {
>             enum N = __traits(identifier, Fn);
>             enum string asPure = "private alias " ~ N ~ "_PURE 
> = " ~ typeof(&Fn).stringof ~ " pure;\n" ~ "__gshared immutable 
> " ~ N ~ "_PURE " ~ P ~"= cast(" ~ N ~ "_PURE) &" ~ N ~ " ;" ;
>     }
>     enum xx = asPure!("VFORMATP", VFORMAT);
>     mixin(xx);
>
> void main(){
>
> }
>
>
>      reinterpreting cast from `nothrow @nogc extern (C) 
> string(LogLevel level, string file, ulong line, char[] tmp, 
> bool line_break, string tag, string fmt, ...)*` to `pure 
> nothrow @nogc extern (C) string(LogLevel, string, ulong, 
> char[], bool, string, string, ...)*` is not supported in CTFE


It seems to not work at runtime either. Maybe they've made this 
behaviour illegal now? Hopefully someone answers.

```d

import std.traits;
import core.stdc.stdarg;
         enum LogLevel : ubyte {
                 INFO = 0,
                 WARN,
                 ERROR,
                 FATAL,
         }


extern (C) string VFORMAT(LogLevel level, string file, size_t 
line, char[] tmp, bool line_break, string tag, string fmt, ...) 
@nogc nothrow {
         return null;
}

extern (C) string function(LogLevel level, string file, size_t 
line, char[] tmp, bool line_break, string tag, string fmt, ...) 
@nogc nothrow pure fp;
void main(){
     fp = &VFORMAT; //fails
}
```