lang/scala: fix comment continuation #1515

On Doom's modded newline-and-indent.

modules/config/default/config.el

@@ -117,7 +117,7 @@
     (sp-local-pair
      '(js2-mode typescript-mode rjsx-mode rust-mode c-mode c++-mode objc-mode
        csharp-mode java-mode php-mode css-mode scss-mode less-css-mode
-       stylus-mode)
+       stylus-mode scala-mode)
      "/*" "*/"
      :actions '(insert)
      :post-handlers '(("| " "SPC") ("|\n*/[i][d-2]" "RET") (+default-expand-doc-comment-block "*")))

modules/lang/scala/autoload.el

@@ -0,0 +1,35 @@
+;;; lang/scala/autoload.el -*- lexical-binding: t; -*-
+
+;;;###autoload
+(defun +scala-comment-indent-new-line (&rest _)
+  "Continue the commnt on the current line.
+
+Meant to be used for `scala-mode's `comment-line-break-function'."
+  (let* ((state (syntax-ppss))
+         (comment-start-pos (nth 8 state)))
+    (save-match-data
+      (cond ((and (integerp (nth 4 state))
+                  ;; Ensure that we're inside a scaladoc comment
+                  (string-match-p "^/\\*\\*?[^\\*]?"
+                                  (buffer-substring-no-properties
+                                   comment-start-pos
+                                   (min (+ comment-start-pos 4)
+                                        (point-max))))
+                  (progn
+                    (setq prev-line (buffer-substring-no-properties
+                                     (line-beginning-position 0)
+                                     (line-end-position 0)))
+                    (or (string-match "^\\s-*\\*" prev-line)
+                        (string-match "\\s-*/*" prev-line))))
+             (newline nil t)
+             (indent-according-to-mode)
+             (insert (make-string (max 0 (- (1- (match-end 0))
+                                            (match-beginning 0)))
+                                  ? )
+                     "*")
+             (scala-indent:indent-on-scaladoc-asterisk))
+            ((nth 4 state) ; for line comments
+             (call-interactively #'comment-indent-new-line))
+            (t
+             (newline nil t)
+             (indent-according-to-mode))))))

modules/lang/scala/config.el

@@ -1,7 +1,12 @@
 ;;; lang/scala/config.el -*- lexical-binding: t; -*-
 
 (after! scala-mode
-  (setq scala-indent:align-parameters t)
+  (setq scala-indent:align-parameters t
+        ;; indent block comments to first asterix, not second
+        scala-indent:use-javadoc-style t)
+
+  (setq-hook! 'scala-mode-hook comment-line-break-function #'+scala-comment-indent-new-line)
+
   (after! dtrt-indent
     (add-to-list 'dtrt-indent-hook-mapping-list '(scala-mode c/c++/java scala-indent:step))))