[Issue 20389] New: __traits(isDisabled) with invalid template function

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=20389

          Issue ID: 20389
           Summary: __traits(isDisabled) with invalid template function
           Product: D
           Version: D2
          Hardware: x86
                OS: Windows
            Status: NEW
          Severity: enhancement
          Priority: P1
         Component: dmd
          Assignee: nobody at puremagic.com
          Reporter: john.michael.hall at gmail.com

If you @disable a templated function that is not valid and then try to call
__traits(isDisabled) on it with the template instantiated with something other
than a type, then you will get a message that the template instance does not
match the declaration. However, it does not tell you why. For instance, in the
code below, T should also be part of the template, but you can only find that
out if you actually call foo. 

@disable T[] foo(U)(T[] x, T rhs)
{
    return x ~ rhs;
}

unittest {
    static assert(__traits(isDisabled, foo!"~"));
}

I would reiterate that this seems to be related to using something other than a
type in the instantiation. If I try the code below, then it tells me that T is
an undefined identifier.

unittest {
    static assert(__traits(isDisabled, foo!(int)));
}

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