This capability seems to be dropped by SI-6186, and no mechanism could be used to replace it
I found the following remarks in its commit message:
Now we restore the broken balance by banning TypeTag from macro impls. This forces anyone to use AbsTypeTags, and if someone wants to check the input for presence of abstract types, it's possible to do that manually.
What does "the presence of abstract types" and "do that manually" mean? Can someone give me a concrete example on these?