REPL Trying to highlight erroneous position

[som-snytt]

Minimized code

Starting dotty REPL...
scala> def (

Output

Starting dotty REPL...
scala> def Trying to highlight erroneous position [4..21]. Input size: 5
(

Expectation

Good position for bad code.

Noticed at https://gitter.im/lampepfl/dotty?at=5f6eab495b75b305ddc6bde3

[izhangzhihao]

Confirm fixed in 3.0-M3:

scala> def (
1 |def (
  |    ^
  |    an identifier expected, but '(' found
1 |def (
  |     ^
  |     '=' expected, but eof found

[som-snytt]

Fixed in M1 by 3bb85e5

in updated extension syntax
#9845

[som-snytt]

Misc regression tests were added in #10007 but the bad pos issue needs a pos-checking test.