@Kha I marked the corresponding methods as `protected`.
I currently can't stand `throw_error`, and I am optimistic about
server highlighting feature you are working on :)
@Kha This one required a bunch of manual fixes. The main issue is that
before we added the string interpolation feature, we created
`MessageData`s using `++` and coercions. For example, given
`(e : Expr)`, we would write
```
let msg : MessageData := "type: " ++ e
```
and rely on the coercions `String -> MessageData` and
`Expr -> MessageData`, and the instance `Append MessageData`.
However, heterogeneous operators "block" the expected type propagation downwards.
This kind of code is obsolete now since we can write a more compact
version using string interpolation
```
let msg := m!"type: {e}"
```
It preserves the location of the local declaration.
@Kha This tactic is going to be used to fix another hygiene related bug in
Lean3 :)
Here is small repro for the problem.
```
example (m n k : ℕ) (h : 0 + n = m) (h : k = m) : ... :=
begin
-- Here `h : k = m` is accessible.
rw [nat.zero_add] at *
-- `h : k = m` is not accessible anymore, and it is a name for
-- the simplified `h : n = m` which was inaccessible before.
end
```
