@Kha The hack I posted at Zulip didn't really work
```
macro x:ident : tactic => throw $ Lean.Macro.Exception.error x s!"unknown tactic '{x.getId}'"
```
For example, we would still get a weird error message at
```
theorem ex3 (x : Nat) : x = x → x = x :=
have x = x by foo (aaa bbb) -- The error would be at `bbb`
fun h => h
```
There were other minor issues that could be fixed, but this one was bad.
0a56057db1