Try to detect file modification within the same second.

* buffer.h (struct buffer): New field modtime_size.
* buffer.c (reset_buffer): Initialize it.
* fileio.c (Finsert_file_contents, Fwrite_region): Set it.
(Fverify_visited_file_modtime): Check it.
(Fclear_visited_file_modtime, Fset_visited_file_modtime): Clear it.
(Fset_visited_file_modtime): Set (or clear) it.

1 files changed, 6 insertions, 0 deletions

diff --git a/src/buffer.h b/src/buffer.h
index 40f03daca90..fa3fc6dafb8 100644
--- a/src/buffer.h
+++ b/src/buffer.h
@@ -513,6 +513,12 @@ struct buffer
      0 means visited file modtime unknown; in no case complain
      about any mismatch on next save attempt.  */
   int modtime;
+  /* Size of the file when modtime was set.  This is used to detect the
+     case where the file grew while we were reading it, so the modtime
+     is still the same (since it's rounded up to seconds) but we're actually
+     not up-to-date.  -1 means the size is unknown.  Only meaningful if
+     modtime is actually set.  */
+  EMACS_INT modtime_size;
   /* The value of text->modiff at the last auto-save.  */
   int auto_save_modified;
   /* The value of text->modiff at the last display error.