Various improvements to auto-narrow mode.

* lisp/files.el (auto-narrow-display-length): Improve docstring.
(auto-narrow-widen-automatically): Add 'undo' to the command list.
(auto-narrow-hook): New defcustom.
(auto-narrow-pre-command-function, auto-narrow-post-command-function):
Move initialization code.
(auto-narrow-mode): Do not make the 'auto-narrow-mode' permanent local
anymore.

* lisp/font-lock.el (turn-off-font-lock-mode): New convenience function.

* src/xdisp.c (set_vertical_scroll_bar): Fix typo.
(redisplay_window): Use the new convenience function.

* src/buffer.h (BUFFER_NEEDS_AUTO_NARROWING_P,
BUFFER_AUTO_NARROWED_NON_NARROWED_P): Two new convenience functions.

* src/window.c (Frecenter): Do not recenter auto-narrowed buffers that
are not actually narrowed.

* etc/NEWS: Improvement.

* doc/emacs/display.texi (Auto-Narrowing): Improvement.

1 files changed, 16 insertions, 0 deletions

diff --git a/src/buffer.h b/src/buffer.h
index 19faa844e02..84492737b0e 100644
--- a/src/buffer.h
+++ b/src/buffer.h
@@ -1120,12 +1120,28 @@ BUFFER_CHECK_INDIRECTION (struct buffer *b)
     }
 }
 
+/* Check the state of auto-narrowed buffers.  */
+
+INLINE bool
+BUFFER_NEEDS_AUTO_NARROWING_P (struct buffer *b)
+{
+  return EQ (BVAR (b, auto_narrow__narrowing_state), Qneeded);
+}
+
 INLINE bool
 BUFFER_AUTO_NARROWED_P (struct buffer *b)
 {
   return EQ (BVAR (b, auto_narrow__narrowing_state), Qauto);
 }
 
+INLINE bool
+BUFFER_AUTO_NARROWED_NON_NARROWED_P (struct buffer *b)
+{
+  return BUFFER_AUTO_NARROWED_P (b)
+    && BUF_BEG (b) == BUF_BEGV (b)
+    && BUF_Z (b) == BUF_ZV (b);
+}
+
 /* This structure holds the default values of the buffer-local variables
    that have special slots in each buffer.
    The default value occupies the same slot in this structure