Checking if a flag was passed to the compiler

[Seb]

On Thursday, 22 March 2018 at 12:02:40 UTC, Nicholas Wilson wrote:
> On Thursday, 22 March 2018 at 10:08:31 UTC, Nordlöw wrote:
>> Is there a way to check in code whether a specific flag, 
>> -dip1000 in my case, was passed to the compiler?
>
> Most command line arguments that are detectable set a version, 
> e.g. D_Coverage, unittest, assert,D_BetterC. I don't see 
> dip1000 in LDC's list of version statements.
>
> You could do a !__traits(compiles, { something forbidden by 
> dip1000} );

For reference and completeness, a simple example:

```d
void main()
{
     enum isDIP1000 = __traits(compiles, () @safe {
          int x;
          int* p;
          p = &x;
     });
     pragma(msg, isDIP1000);
}
```

normal: https://run.dlang.io/is/RID7vh
-dip1000: https://run.dlang.io/is/1yJfVQ

(this could of course be fancier)