Improve speed of smie by disabling features

This PR disables the worst offenders of lookbacks that make opening
large files very slow.

More testing is needed to determine if this is a worthwhile tradeoff.
The main reason it is palatable is that it fixes
elixir-editors#463 and
indentation isn't as important as it once was because you can simply run
`elixir-format` (or `lsp-format-buffer`).

elixir-smie.el

@@ -99,10 +99,6 @@
       'ppss-comment-or-string-start
     (lambda (parse-data) (nth 8 parse-data))))
 
-(defun elixir-smie-looking-around (back at)
-  "Check if looking backwards at BACK and forward at AT."
-  (and (looking-at-p at) (looking-back back)))
-
 ;; Declare variable that we need from the smie package
 (defvar smie--parent)
 
@@ -261,35 +257,7 @@
 
 (defun elixir-smie--semi-ends-match ()
   "Return non-nil if the current line concludes a match block."
-  (when (not (eobp))
-    (save-excursion
-      ;; Warning: Recursion.
-      ;; This is easy though.
-
-      ;; 1. If we're at a blank line, move forward a character. This takes us to
-      ;;    the next line.
-      ;; 2. If we're not at the end of the buffer, call this function again.
-      ;;    (Otherwise, return nil.)
-
-      ;; The point here is that we want to treat blank lines as a single semi-
-      ;; colon when it comes to detecting the end of match statements. This could
-      ;; also be handled by a `while' expression or some other looping mechanism.
-      (cl-flet ((self-call ()
-                           (if (< (point) (point-max))
-                               (elixir-smie--semi-ends-match)
-                             nil)))
-        (cond
-         ((and (eolp) (bolp))
-          (forward-char)
-          (self-call))
-         ((looking-at elixir-smie--spaces-til-eol-regexp)
-          (forward-char)
-          (self-call))
-         ;; And if we're NOT on a blank line, move to the end of the line, and see
-         ;; if we're looking back at a block operator.
-         (t (move-end-of-line 1)
-            (and (looking-back elixir-smie--block-operator-regexp)
-                 (not (looking-back ".+fn.+")))))))))
+  nil)
 
 (defun elixir-smie--same-line-as-parent (parent-pos child-pos)
   "Return non-nil if CHILD-POS is on same line as PARENT-POS."
@@ -897,39 +865,12 @@
     (forward-line -1)
     (current-indentation)))
 
-;; Add the custom function to handle indentation inside heredoc to the
-;; smie-indent-functions list. The indentation function will only be
-;; process inside an elixir-mode.
-(defun elixir-smie--indent-inside-heredoc ()
-  "Handle indentation inside Elixir heredocs.
-
-Rules:
-  1. If the previous line is empty, indent as the basic indentation
-     at the beginning of the heredoc.
-  2. If the previous line is not empty, indent as the previous line."
-  (if (eq major-mode 'elixir-mode)
-      (if (elixir-smie--heredoc-at-current-point-p)
-          (let ((indent
-                 (save-excursion
-                   (when (re-search-backward "^\\(\s+\\)\\(@doc\\|@moduledoc\\|.*\\)\"\"\"" nil t)
-                     (string-width (match-string 1))))))
-	    (cond
-	     ((elixir-smie--previous-line-empty-p)
-	      (goto-char indent))
-	     ((and (not (save-excursion (looking-at "\"\"\"")))
-		   (not (elixir-smie--previous-line-empty-p)))
-	      (goto-char (elixir-smie--previous-line-indentation)))
-	     (indent
-	      (goto-char indent)))))))
-
 (defun elixir-smie-empty-string-p (string)
   "Return non-nil if STRING is null, blank or whitespace only."
   (or (null string)
       (string= string "")
       (if (string-match-p "^\s+$" string) t)))
 
-(add-to-list 'smie-indent-functions 'elixir-smie--indent-inside-heredoc)
-
 (provide 'elixir-smie)
 
 ;;; elixir-smie.el ends here