Replace all uses of looking-back

 - it scans from the start of the buffer unless you give it a start
   position. In other words, it is hella slow in large files and in some
   suboptimal modes.

#100

cc-mode-expansions.el

@@ -101,7 +101,7 @@ This function captures identifiers composed of multiple
   (when (use-region-p)
     (when (> (point) (mark))
       (exchange-point-and-mark))
-    (while (looking-back "::")
+    (while (er/looking-back-exact "::")
       (backward-char 2)
       (skip-syntax-backward "_w"))
     (exchange-point-and-mark)

clojure-mode-expansions.el

@@ -39,19 +39,19 @@
   (interactive)
   (let ((word-regexp "\\(\\sw\\|-\\)"))
     (when (or (looking-at word-regexp)
-              (looking-back word-regexp))
+              (er/looking-back-on-line word-regexp))
       (while (looking-at word-regexp)
         (forward-char))
       (set-mark (point))
-      (while (looking-back word-regexp)
+      (while (er/looking-back-on-line word-regexp)
         (backward-char)))))
 
 (defun er/mark-clj-set-literal ()
   "Mark clj-set-literal presumes that point is outside the brackets.
 If point is inside the brackets, those will be marked first anyway."
   (interactive)
   (when (or (looking-at "#{")
-            (looking-back "#"))
+            (er/looking-back-exact "#"))
     (forward-char 1)
     (search-backward "#")
     (set-mark (point))
@@ -65,7 +65,7 @@ If point is inside the brackets, those will be marked first anyway."
 If point is inside the string, the quotes will be marked first anyway."
   (interactive)
   (when (or (looking-at "#\"")
-            (looking-back "#"))
+            (er/looking-back-exact "#"))
     (forward-char 1)
     (search-backward "#")
     (set-mark (point))
@@ -79,7 +79,7 @@ If point is inside the string, the quotes will be marked first anyway."
 If point is inside the parens, they will be marked first anyway."
   (interactive)
   (when (or (looking-at "#(")
-            (looking-back "#"))
+            (er/looking-back-exact "#"))
     (forward-char)
     (search-backward "#")
     (set-mark (point))

er-basic-expansions.el

@@ -31,21 +31,21 @@
   (interactive)
   (let ((word-regexp "\\sw"))
     (when (or (looking-at word-regexp)
-              (looking-back word-regexp))
+              (er/looking-back-on-line word-regexp))
       (skip-syntax-forward "w")
       (set-mark (point))
-      (while (looking-back word-regexp)
+      (while (er/looking-back-on-line word-regexp)
         (backward-char)))))
 
 (defun er/mark-symbol ()
   "Mark the entire symbol around or in front of point."
   (interactive)
   (let ((symbol-regexp "\\s_\\|\\sw"))
     (when (or (looking-at symbol-regexp)
-              (looking-back symbol-regexp))
+              (er/looking-back-on-line symbol-regexp))
       (skip-syntax-forward "_w")
       (set-mark (point))
-      (while (looking-back symbol-regexp)
+      (while (er/looking-back-on-line symbol-regexp)
         (backward-char)))))
 
 (defun er/mark-symbol-with-prefix ()
@@ -55,12 +55,12 @@
         (prefix-regexp "\\s'"))
     (when (or (looking-at prefix-regexp)
               (looking-at symbol-regexp)
-              (looking-back symbol-regexp))
+              (er/looking-back-on-line symbol-regexp))
       (skip-syntax-forward "'")
       (skip-syntax-forward "_w")
       (set-mark (point))
-      (while (or (looking-back symbol-regexp)
-                 (looking-back prefix-regexp))
+      (while (or (er/looking-back-on-line symbol-regexp)
+                 (er/looking-back-on-line prefix-regexp))
         (backward-char)))))
 
 ;; Mark method call
@@ -83,7 +83,7 @@ period and marks next symbol."
   (interactive)
   (let ((symbol-regexp "\\s_\\|\\sw\\|\\."))
     (when (or (looking-at symbol-regexp)
-              (looking-back symbol-regexp))
+              (er/looking-back-on-line symbol-regexp))
       (skip-syntax-backward "_w.")
       (set-mark (point))
       (while (looking-at symbol-regexp)
@@ -146,7 +146,7 @@ period and marks next symbol."
   (if (er--point-inside-string-p)
       (er--move-point-backward-out-of-string)
     (when (and (not (use-region-p))
-               (looking-back "\\s\""))
+               (er/looking-back-on-line "\\s\""))
       (backward-char)
       (er--move-point-backward-out-of-string)))
   (when (looking-at "\\s\"")
@@ -191,7 +191,7 @@ period and marks next symbol."
 (defun er/mark-outside-pairs ()
   "Mark pairs (as defined by the mode), including the pair chars."
   (interactive)
-  (if (looking-back "\\s)+\\=")
+  (if (er/looking-back-on-line "\\s)+\\=")
       (ignore-errors (backward-list 1))
     (skip-chars-forward er--space-str))
   (when (and (er--point-inside-pairs-p)

expand-region-core.el

@@ -264,6 +264,21 @@ remove the keymap depends on user input and KEEP-PRED:
         (when (derived-mode-p mode)
           (funcall add-fn))))))
 
+;; Some more performant version of `looking-back'
+
+(defun er/looking-back-on-line (regexp)
+  "Version of `looking-back' that only checks current line."
+  (looking-back regexp (line-beginning-position)))
+
+(defun er/looking-back-exact (s)
+  "Version of `looking-back' that only looks for exact matches, no regexp."
+  (string= s (buffer-substring (- (point) (length s))
+                               (point))))
+
+(defun er/looking-back-max (regexp count)
+  "Version of `looking-back' that only check COUNT chars back."
+  (looking-back regexp (max 1 (- (point) count))))
+
 (provide 'expand-region-core)
 
 ;;; expand-region-core.el ends here

html-mode-expansions.el

@@ -41,7 +41,7 @@ first anyway.  Does not support html-attributes with spaces
 around the equal sign or unquotes attributes atm."
   (interactive)
   (when (or (looking-at "\\(\\s_\\|\\sw\\)*=")
-            (looking-back "="))
+            (er/looking-back-exact "="))
     (search-backward " ")
     (forward-char 1)
     (set-mark (point))

js-mode-expansions.el

@@ -122,7 +122,7 @@
     (if (looking-at "\\s(")
         (forward-list)
       (forward-char)))
-  (when (looking-back "[\s\n]")
+  (when (er/looking-back-max "[\s\n]" 400)
     (search-backward-regexp "[^\s\n]")
     (forward-char))
   (exchange-point-and-mark))
@@ -133,7 +133,7 @@ If point is inside the value, that will be marked first anyway."
   (interactive)
   (when (or (looking-at "\"?\\(\\s_\\|\\sw\\| \\)*\":")
             (looking-at "\\(\\s_\\|\\sw\\)*:")
-            (looking-back ": ?"))
+            (er/looking-back-max ": ?" 2))
     (search-backward-regexp "[{,]")
     (forward-char)
     (search-forward-regexp "[^\s\n]")
@@ -144,7 +144,7 @@ If point is inside the value, that will be marked first anyway."
       (if (looking-at "\\s(")
           (forward-list)
         (forward-char)))
-    (when (looking-back "[\s\n]")
+    (when (er/looking-back-max "[\s\n]" 400)
       (search-backward-regexp "[^\s\n]")
       (forward-char))
     (exchange-point-and-mark)))

js2-mode-expansions.el

@@ -33,7 +33,7 @@
 
 (defun js2-mark-parent-statement ()
   (interactive)
-  (let* ((parent-statement (if (not (looking-back ";"))
+  (let* ((parent-statement (if (not (er/looking-back-exact ";"))
                                (js2-node-parent-stmt (js2-node-at-point))
                              (forward-char -1)
                              (js2-node-at-point)))

jsp-expansions.el

@@ -43,7 +43,7 @@
 If point is inside the brackets, they will be marked first anyway."
     (interactive)
       (when (or (looking-at "\\${")
-            (looking-back "\\$"))
+            (er/looking-back-exact "$"))
     (forward-char 1)
     (search-backward "\$")
     (set-mark (point))

nxml-mode-expansions.el

@@ -35,10 +35,10 @@
   (interactive)
   (cond ((looking-at "<")
          (nxml-mark-token-after))
-        ((looking-back ">")
+        ((er/looking-back-exact ">")
          (backward-char 1)
          (nxml-mark-token-after))
-        ((looking-back "<[^<>]*")
+        ((er/looking-back-max "<[^<>]*" 1000)
          (nxml-mark-token-after))))
 
 (defun er/mark-nxml-element ()
@@ -70,7 +70,8 @@
 (defun er/mark-nxml-attribute-string ()
   "Marks an attribute string."
   (interactive)
-  (when (looking-back "[\"']")
+  (when (or (er/looking-back-exact "\"")
+            (er/looking-back-exact "'"))
     (backward-char 1))
   ;; Using syntax highlighting is a hack, but I can't figure out how
   ;; to use nxml-mode functions to do it.

ruby-mode-expansions.el

@@ -169,7 +169,7 @@ Assumes that point is at the @ - if it is inside the word, that will
 be marked first anyway."
   (when (looking-at "@")
     (forward-char 1))
-  (when (looking-back "@")
+  (when (er/looking-back-exact "@")
     (er/mark-symbol)
     (forward-char -1)))