Self-assignment of this has been cruelly outlawed

[som-snytt]

Compiler version

3.4.0-RC1-bin-SNAPSHOT-git-5454110

Minimized code

Welcome to Scala 3.4.0-RC1-bin-SNAPSHOT-git-5454110 (21, Java OpenJDK 64-Bit Server VM).
Type in expressions for evaluation. Or try :help.

scala> val this = this
-- [E040] Syntax Error: ------------------------------------------------------------------------------------------------
1 |val this = this
  |    ^
  |    an identifier expected, but 'this' found
  |
  | longer explanation available when compiling with `-explain`

scala>

Expectation

Don't disallow keywords which are patterns.

#12406

#18752

[Kordyjan]

I should probably classify this as a bug in the parser, but I feel this is a morally wrong thing to do.

[nicolasstucki]

Maybe the following message would be clearer

 an identifier expected, but 'this' keyword found

[Kordyjan]

Is this the only case where the pattern can start with something other than an identifier?

[bishabosha]

you can also have val 1 = 1, val true = true, val null = null