Use 'regexp-opt' in 'dired-omit-regexp'

In my benchmarking, for large dired buffers, using 'regexp-opt'
provides around a 3x speedup in omitting.

'regexp-opt' takes around 5 milliseconds, so to avoid slowing
down omitting in small dired buffers we cache the return value.

Since omitting is now 3x faster, increase 'dired-omit-size-limit'
by 3x.  Also, document 'dired-omit-size-limit' better.

* doc/misc/dired-x.texi (Omitting Variables): Document
'dired-omit-size-limit'.
* etc/NEWS: Announce increase of 'dired-omit-size-limit'.
* lisp/dired-x.el (dired-omit--extension-regexp-cache): Add.
(dired-omit-regexp): Use 'regexp-opt'.  (Bug#69775)
(dired-omit-size-limit): Increase and improve docs.

1 files changed, 9 insertions, 0 deletions

diff --git a/doc/misc/dired-x.texi b/doc/misc/dired-x.texi
index 4cad016a0f6..726b6653d0d 100644
--- a/doc/misc/dired-x.texi
+++ b/doc/misc/dired-x.texi
@@ -346,6 +346,15 @@ only match against the non-directory part of the file name.  Set it to
 match the file name relative to the buffer's top-level directory.
 @end defvar
 
+@defvar dired-omit-size-limit
+If non-@code{nil}, @code{dired-omit-mode} will be effectively disabled
+in directories whose listing has size (in bytes) larger than the value
+of this option.  Since omitting can be slow for very large directories,
+this avoids having to wait before seeing the directory.  This variable
+is ignored when @code{dired-omit-mode} is called interactively, such as
+by @code{C-x M-o}, so you can still enable omitting in the directory
+after the initial display.
+
 @cindex omitting additional files
 @defvar dired-omit-marker-char
 Temporary marker used by Dired to implement omitting.  Should never be used