Function: userlock--check-content-unchanged

userlock--check-content-unchanged is a byte-compiled function defined in userlock.el.gz.

Signature

(userlock--check-content-unchanged FILENAME)

Source Code

;; Defined in /usr/src/emacs/lisp/userlock.el.gz
(defun userlock--check-content-unchanged (filename)
  (with-demoted-errors "Unchanged content check: %S"
    ;; Even tho we receive `filename', we know that `filename' refers
    ;; to the current buffer's file.
    (cl-assert (or (null buffer-file-truename) ; temporary buffer
                   (equal (expand-file-name filename)
                          (expand-file-name buffer-file-truename))))
    ;; Note: rather than read the file and compare to the buffer, we could save
    ;; the buffer and compare to the file, but for encrypted data this
    ;; wouldn't work well (and would risk exposing the data).
    (save-restriction
      (widen)
      (let ((buf (current-buffer))
            (cs buffer-file-coding-system)
            (start (point-min))
            (end (point-max)))
        ;; FIXME: To avoid a slow `insert-file-contents' on large or
        ;; remote files, it'd be good to include file size in the
        ;; "visited-modtime" check.
        (when (with-temp-buffer
                (let ((coding-system-for-read cs)
                      (non-essential t))
                  (insert-file-contents filename))
                (when (= (buffer-size) (- end start)) ;Minor optimization.
                  (= 0 (let ((case-fold-search nil))
                         (compare-buffer-substrings
                          buf start end
                          (current-buffer) (point-min) (point-max))))))
          ;; We know that some buffer visits FILENAME, because our
          ;; caller (see lock_file) verified that.  Thus, we set the
          ;; modtime in that buffer, to cater to use case where the
          ;; file is about to be written to from some buffer that
          ;; doesn't visit any file, like a temporary buffer.
          (let ((buf (get-file-buffer (file-truename filename))))
            (when buf  ; If we cannot find the visiting buffer, punt.
              (with-current-buffer buf
                (set-visited-file-modtime))))
          'unchanged)))))