Given
```d
import std.range.primitives : isInputRange;
enum isDumb(Args...) = (Args.length == 2 && Args.length == 3);
void f(Args...)(Args args)
if (isDumb!(Args))
{
}
void g(Arg)(Arg arg)
if (isInputRange!(Arg))
{
}
@safe pure unittest
{
f(2, 3);
g(2);
}
```
`dmd` diagnoses the first level as
```
/home/per/f.d(18,6): Error: template `f.f` cannot deduce function
from argument types `!()(int, int)`, candidates are:
/home/per/f.d(6,6): `f(Args...)(Args args)`
with `Args = (int, int)`
must satisfy the following constraint:
` isDumb!Args`
/home/per/f.d(19,6): Error: template `f.g` cannot deduce function
from argument types `!()(int)`, candidates are:
/home/per/f.d(11,6): `g(Arg)(Arg arg)`
with `Arg = int`
must satisfy the following constraint:
` isInputRange!Arg
```
I'm certain I've seen dmd be able to diagnose which
sub-expression of `isDumb` and `isInputRange` that evaluated to
false. Did I just dream this or is there a way? If there is a way
does this improvement still reside in a dmd PR?
