Template pred is true for pred!(pred!(pred)) but not for value "true"

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On Sunday, 8 March 2015 at 20:36:34 UTC, anonymous wrote:
> I get an error on your code: "test.d(16): Error: static assert  
> (canBeAlias!(true)) is false". But when commenting out the 
> first assert (line 15), there's no error.

Hmm, I might have made a mistake reducing my actual code.

> Played around with it, and I think it's a bug in the compiler:
>
> ----
> /* The differently numbered 'canBeAliasN' are all the same. */
>
> enum true_ = true;
>
> enum canBeAlias1(T...) = is(typeof({alias _ = T[0];}));
> pragma(msg, canBeAlias1!true); /* "false" */
>
> enum canBeAlias2(T...) = is(typeof({alias _ = T[0];}));
> pragma(msg, canBeAlias2!true_); /* "true" */
>
> enum canBeAlias3(T...) = is(typeof({alias _ = T[0];}));
> pragma(msg, canBeAlias3!true, " ", canBeAlias3!true_); /* 
> "false false" */
>
> enum canBeAlias4(T...) = is(typeof({alias _ = T[0];}));
> pragma(msg, canBeAlias4!true_, " ", canBeAlias4!true); /* "true 
> true" */
> ----
>
> On their own, `canBeAlias!true` = false and `canBeAlias!true_` 
> = true. This makes sense, because `true_` is a symbol whereas 
> `true` is a value.
>
> But the two instantiations are apparently recognized as 
> equivalent. Whichever is instantiated first, its value is used 
> for the other instantiation, too. I think this behaviour is 
> wrong.

Yeah, definitely wrong.

template canBeAlias(T...)
if (T.length == 1)
{
	static if (is(typeof({alias _ = T[0];})))
	{
		enum canBeAlias = true;
	}
	else
	{
		enum canBeAlias = false;
	}
}

void main()
{
     pragma(msg, canBeAlias!canBeAlias); //prints "true"
     static assert(canBeAlias!(canBeAlias!canBeAlias)); //passes?!
     static assert(!canBeAlias!true); //Error: static 
assert(!true) is false
}

OR

void main()
{
     pragma(msg, canBeAlias!canBeAlias); //prints "true"
     static assert(!canBeAlias!true); //passes
     //Error: static assert (canBeAlias!(true)) is false
     static assert(canBeAlias!(canBeAlias!canBeAlias));
}

So it definitely does depend on which comes first. This is a 
weird bug...