This code

@deprecated void func() {}
void main() {}

results in this error:

q.d(1): Error: @identifier or @(ArgumentList) expected, not @deprecated
q.d(1): Error: valid attributes are @property, @safe, @trusted, @system, @disable

Notice that the list of valid @ attributes is missing @nogc (presumably, because it's new). Also, if the change for issue# 13388 doesn't get reverted, then @nothrow, @pure, and @return will need to be added to the list.

Ideally, I would think that the error message would treat the problem a bit like happens with a spelling error for variables, and ask if you meant "deprecated" instead of "@deprecated" - at least as long as @deprecated hasn't been declared as a UDA anyway - but if we're going to give a list of built-in attributes with @, the list should be correct and complete.