julia-mode: Improve paren indent perf

Replace julia-paren-indent with a version that uses the higher level
function backward-up-list to find any previous opening parentheses. This
function automatically skips balanced expressions like strings, as well
as comments.

On some test files the time to indent falls by more than 75% with this
change, even after increasing the threshold for paren lookback to 10k.

contrib/julia-mode.el

@@ -457,7 +457,7 @@ beginning of the buffer."
   (unless (eq (point) (point-min))
     (backward-char)))
 
-(defvar julia-max-paren-lookback 400
+(defvar julia-max-paren-lookback 10000
   "When indenting, don't look back more than this
 many characters to see if there are unclosed parens.
 
@@ -477,28 +477,14 @@ containing paren before point, so we can align succeeding code
 with it. Returns nil if we're not within nested parens."
   (save-excursion
     ;; Back up to previous line (beginning-of-line was already called)
-    (backward-char)
-    (let ((min-pos (max (- (point) julia-max-paren-lookback)
-                        (point-min)))
-          (open-count 0))
-      (while (and (> (point) min-pos)
-                  (not (plusp open-count)))
-
-        (when (looking-at (rx (any "[" "]" "(" ")")))
-          (unless (or (julia-in-string) (julia-in-comment))
-            (cond ((looking-at (rx (any "[" "(")))
-                   (incf open-count))
-                  ((looking-at (rx (any "]" ")")))
-                   (decf open-count)))))
-
-        (julia--safe-backward-char))
-
-      (if (plusp open-count)
-          (progn (forward-char 2)
-                 (while (looking-at (rx blank))
-                   (forward-char))
-                 (current-column))
-        nil))))
+    (let ((parser-state (syntax-ppss)))
+      (cond ((nth 3 parser-state) nil)       ;; strings
+            ((= (nth 0 parser-state) 0) nil) ;; top level
+            (t
+             (backward-up-list 1 t t)
+             (forward-char)
+             (skip-syntax-forward " ")
+             (current-column))))))
 
 (defun julia-prev-line-skip-blank-or-comment ()
   "Move point to beginning of previous line skipping blank lines
@@ -558,13 +544,10 @@ only comments."
   "Indent current line of julia code."
   (interactive)
   (let* ((point-offset (- (current-column) (current-indentation))))
-    (end-of-line)
     (indent-line-to
      (or
       ;; If we're inside an open paren, indent to line up arguments.
-      (save-excursion
-        (beginning-of-line)
-        (ignore-errors (julia-paren-indent)))
+      (julia-paren-indent)
       ;; indent due to hanging operators or a line ending in =
       (julia-indent-hanging)
       ;; Indent according to how many nested blocks we are in.