Current spec: "Type is the type being tested. It must be syntactically correct, but it need not be semantically correct.".

template foo()
{
    static assert(false); // 1
 
    void bar()
    {
        static assert(false); // 2
    }
}   

enum x = is(foo!());

----

The original test case compiles without errors.

If (1) is commented out:
Error: static assert  (false) is false

If (2) is commented out, there is no error.