* lisp/progmodes/js.el: Fix multiline declarations's indentation.

(js--declaration-keyword-re): New var.
(js--multi-line-declaration-indentation): New function.
(js--proper-indentation): Use it.

Fixes: debbugs:8576

1 files changed, 36 insertions, 1 deletions

diff --git a/lisp/progmodes/js.el b/lisp/progmodes/js.el
index 683b3927ae3..96e6039a8c2 100644
--- a/lisp/progmodes/js.el
+++ b/lisp/progmodes/js.el
@@ -1680,12 +1680,15 @@ This performs fontification according to `js--class-styles'."
      "each"))
   "Regexp matching keywords optionally followed by an opening brace.")
 
+(defconst js--declaration-keyword-re
+  (regexp-opt '("var" "let" "const") 'words)
+  "Regular expression matching variable declaration keywords.")
+
 (defconst js--indent-operator-re
   (concat "[-+*/%<>=&^|?:.]\\([^-+*/]\\|$\\)\\|"
           (js--regexp-opt-symbol '("in" "instanceof")))
   "Regexp matching operators that affect indentation of continued expressions.")
 
-
 (defun js--looking-at-operator-p ()
   "Return non-nil if point is on a JavaScript operator, other than a comma."
   (save-match-data
@@ -1764,6 +1767,37 @@ nil."
          (list (cons 'c js-comment-lineup-func))))
     (c-get-syntactic-indentation (list (cons symbol anchor)))))
 
+(defun js--multi-line-declaration-indentation ()
+  "Helper function for `js--proper-indentation'.
+Return the proper indentation of the current line if it belongs to a declaration
+statement spanning multiple lines; otherwise, return nil."
+  (let (at-opening-bracket)
+    (save-excursion
+      (back-to-indentation)
+      (when (not (looking-at js--declaration-keyword-re))
+        (when (looking-at js--indent-operator-re)
+          (goto-char (match-end 0)))
+        (while (and (not at-opening-bracket)
+                    (not (bobp))
+                    (let ((pos (point)))
+                      (save-excursion
+                        (js--backward-syntactic-ws)
+                        (or (eq (char-before) ?,)
+                            (and (not (eq (char-before) ?\;))
+                                 (prog2
+                                     (skip-chars-backward "[[:punct:]]")
+                                     (looking-at js--indent-operator-re)
+                                   (js--backward-syntactic-ws))
+                                 (not (eq (char-before) ?\;)))
+                            (and (>= pos (point-at-bol))
+                                 (<= pos (point-at-eol)))))))
+          (condition-case err
+              (backward-sexp)
+            (scan-error (setq at-opening-bracket t))))
+        (when (looking-at js--declaration-keyword-re)
+          (goto-char (match-end 0))
+          (1+ (current-column)))))))
+
 (defun js--proper-indentation (parse-status)
   "Return the proper indentation for the current line."
   (save-excursion
@@ -1772,6 +1806,7 @@ nil."
            (js--get-c-offset 'c (nth 8 parse-status)))
           ((nth 8 parse-status) 0) ; inside string
           ((js--ctrl-statement-indentation))
+          ((js--multi-line-declaration-indentation))
           ((eq (char-after) ?#) 0)
           ((save-excursion (js--beginning-of-macro)) 4)
           ((nth 1 parse-status)