Types accepted in 'key in AA' expressions during speculative evaluation

[rainers]

Found this snippet in unit_threaded.assertions:

enum isLikeAssociativeArray(T, K) = is(typeof({
    if(K.init in T) { }
    if(K.init !in T) { }
}));

static assert(isLikeAssociativeArray!(string[string], string));
static assert(!isLikeAssociativeArray!(string[string], int));

This passes even though this fails:

void foo(T, K)()
{
    if(K.init in T) { } // Error: type `string[string]` is not an expression
}

void fooTK()
{
    foo!(string[string], string)();
}

It seems the error is only generated from the glue layer.