Imported From: https://issues.scala-lang.org/browse/SI-1828?orig=1
Reporter: @dragos

Anders Bach Nielsen [X] (nielsen) said:
This is a limitation of Emacs where the syntax choosen for Scala can not be handled by Emacs.
Let me try to explain the problem.
In Scala there are two kinds of comments, the single line // and the multiline /* / comments. However these comment are allowed to be nested so / /* **/ **/ is perfectly ok. If this was the only comment then it would not be a problem, however because // uses the same characters to indicate single line comment emacs goes bad :-/ If the single line comment should be ## or something that does not include a /, then emacs would be able to handle it.

So basically, this is a limitation in emacs itself and it cant be fixed as it is (or to my knowledge). Sorry

Suraj Acharya (surajacharya) said:
I was able to fix the reported problem by setting the nested comment flag only for '/* ... */' style comments. scala-mode.el needs the following changes :

@@ -142,10 +142,10 @@

;; comments
;; the `n' means that comments can be nested

• (modify-syntax-entry ?/ ". 124nb" scala-mode-syntax-table)

• (modify-syntax-entry ?/ ". 124b" scala-mode-syntax-table)
  (modify-syntax-entry ?* ". 23n" scala-mode-syntax-table)

• (modify-syntax-entry ?\n "> bn" scala-mode-syntax-table)
• (modify-syntax-entry ?\r "> bn" scala-mode-syntax-table))

• (modify-syntax-entry ?\n "> b" scala-mode-syntax-table)
• (modify-syntax-entry ?\r "> b" scala-mode-syntax-table))

;;; Mode

This allows nesting of '/* ... */' comments and only comments one line for '/////...' comments.

@SethTisue said:
emacs mode work continues at https://github.com/hvesalai/scala-mode2