Make rust-beginning-of-defun ignore comments and strings

Change rust-beginning-of-defun to keep searching when it stops in a
comment or a string.  Fixes #222.

Author: tromey

rust-mode-tests.el

@@ -1025,6 +1025,43 @@ All positions are position symbols found in `rust-test-positions-alist'."
    'beginning-of-fn3
    #'beginning-of-defun))
 
+(ert-deftest rust-beginning-of-defun-string-comment ()
+  (let (fn-1 fn-2 p-1 p-2)
+    (with-temp-buffer
+      (rust-mode)
+      (insert "fn test1() {
+  let s=r#\"
+fn test2();
+\"#;")
+      (setq p-1 (point))
+      (setq fn-1 (1+ p-1))
+      (insert "
+fn test3() {
+  /*
+fn test4();")
+      (setq p-2 (point))
+      (insert "\n*/\n}\n")
+      (setq fn-2 (point))
+      (insert "fn test5() { }")
+
+      (goto-char p-1)
+      (beginning-of-defun)
+      (should (eq (point) (point-min)))
+
+      (beginning-of-defun -2)
+      (should (eq (point) fn-2))
+
+      (goto-char p-2)
+      (beginning-of-defun)
+      (should (eq (point) fn-1))
+
+      (beginning-of-defun -1)
+      (should (eq (point) fn-2))
+
+      (goto-char (point-max))
+      (beginning-of-defun 2)
+      (should (eq (point) fn-1)))))
+
 (ert-deftest rust-end-of-defun-from-middle-of-fn ()
   (rust-test-motion
    rust-test-motion-string

rust-mode.el

@@ -1198,8 +1198,22 @@ This is written mainly to be used as `beginning-of-defun-function' for Rust.
 Don't move to the beginning of the line. `beginning-of-defun',
 which calls this, does that afterwards."
   (interactive "p")
-  (re-search-backward (concat "^\\(" rust-top-item-beg-re "\\)")
-                      nil 'move (or arg 1)))
+  (let* ((arg (or arg 1))
+	 (magnitude (abs arg))
+	 (sign (if (< arg 0) -1 1)))
+    ;; If moving forward, don't find the defun we might currently be
+    ;; on.
+    (when (< sign 0)
+      (end-of-line))
+    (catch 'done
+      (dotimes (_ magnitude)
+	;; Search until we find a match that is not in a string or comment.
+	(while (if (re-search-backward (concat "^\\(" rust-top-item-beg-re "\\)")
+				       nil 'move sign)
+		   (rust-in-str-or-cmnt)
+		 ;; Did not find it.
+		 (throw 'done nil)))))
+    t))
 
 (defun rust-end-of-defun ()
   "Move forward to the next end of defun.