New command: revert-buffer-with-fine-grain

* doc/emacs/files.texi (Reverting): Document the new command and the
new variable.

* etc/NEWS: Mention the new command and the new variable.

* lisp/files.el (revert-buffer-with-fine-grain): New command.  Revert
a buffer trying to be non-destructive, by using replace-buffer-contents.
(revert-buffer-insert-file-contents-delicately): New function, alternative
to revert-buffer-insert-file-contents-function--default-function.
(revert-buffer-with-fine-grain-max-seconds): New variable.  Passed as
argument MAX-SECS of replace-buffer-contents.

* test/lisp/files-tests.el (files-tests-lao files-tests-tzu): Helper
variables, taken from diffutils manual, to test reverting a buffer.
(files-tests-revert-buffer)
(files-tests-revert-buffer-with-fine-grain): New tests (bug#18).

1 files changed, 54 insertions, 0 deletions

diff --git a/test/lisp/files-tests.el b/test/lisp/files-tests.el
index b73eac28174..34777013c35 100644
--- a/test/lisp/files-tests.el
+++ b/test/lisp/files-tests.el
@@ -1377,5 +1377,59 @@ See <https://debbugs.gnu.org/36401>."
     (normal-mode)
     (should (eq major-mode 'mhtml-mode))))
 
+(defvar files-tests-lao "The Way that can be told of is not the eternal Way;
+The name that can be named is not the eternal name.
+The Nameless is the origin of Heaven and Earth;
+The Named is the mother of all things.
+Therefore let there always be non-being,
+  so we may see their subtlety,
+And let there always be being,
+  so we may see their outcome.
+The two are the same,
+But after they are produced,
+  they have different names.
+")
+
+(defvar files-tests-tzu "The Nameless is the origin of Heaven and Earth;
+The named is the mother of all things.
+
+Therefore let there always be non-being,
+  so we may see their subtlety,
+And let there always be being,
+  so we may see their outcome.
+The two are the same,
+But after they are produced,
+  they have different names.
+They both may be called deep and profound.
+Deeper and more profound,
+The door of all subtleties!
+")
+
+(ert-deftest files-tests-revert-buffer ()
+  "Test that revert-buffer is succesful."
+  (files-tests--with-temp-file temp-file-name
+    (with-temp-buffer
+      (insert files-tests-lao)
+      (write-file temp-file-name)
+      (erase-buffer)
+      (insert files-tests-tzu)
+      (revert-buffer t t t)
+      (should (compare-strings files-tests-lao nil nil
+                               (buffer-substring (point-min) (point-max))
+                               nil nil)))))
+
+(ert-deftest files-tests-revert-buffer-with-fine-grain ()
+  "Test that revert-buffer-with-fine-grain is successful."
+  (files-tests--with-temp-file temp-file-name
+    (with-temp-buffer
+      (insert files-tests-lao)
+      (write-file temp-file-name)
+      (erase-buffer)
+      (insert files-tests-tzu)
+      (should (revert-buffer-with-fine-grain t t))
+      (should (compare-strings files-tests-lao nil nil
+                               (buffer-substring (point-min) (point-max))
+                               nil nil)))))
+
 (provide 'files-tests)
 ;;; files-tests.el ends here