Make keys of notmuch-tag-formats regexps and use caching

This modifies `notmuch-tag-format-tag' to treat the keys of
`notmuch-tag-formats' as (anchored) regexps, rather than literal
strings.  This is clearly more flexible, as it allows for prefix
matching, defining a fallback format, etc.  This may cause compatibility
problems if people have customized `notmuch-tag-formats' to match tags
that contain regexp specials, but this seems unlikely.

Regular expression matching has quite a performance hit over string
lookup, so this also introduces a simple cache from exact tags to
formatted strings.  The number of unique tags is likely to be quite
small, so this cache should have a high hit rate.  In addition to
eliminating the regexp lookup in the common case, this cache stores
fully formatted tags, eliminating the repeated evaluation of potentially
expensive, user-specified formatting code.  This makes regexp lookup at
least as fast as assoc for unformatted tags (e.g., inbox) and *faster*
than the current code for formatted tags (e.g., unread):

                    inbox (usec)   unread (usec)
    assoc:              0.4            2.8
    regexp:             3.2            7.2
    regexp+caching:     0.4            0.4

(Though even at 7.2 usec, tag formatting is not our top bottleneck.)

This cache must be explicitly cleared to keep it coherent, so this adds
the appropriate clearing calls.

1 files changed, 1 insertions, 0 deletions

diff --git a/emacs/notmuch.el b/emacs/notmuch.el
index 9e39a76b..2e0b20eb 100644
--- a/emacs/notmuch.el
+++ b/emacs/notmuch.el
@@ -888,6 +888,7 @@ the configured default sort order."
     (set 'notmuch-search-oldest-first oldest-first)
     (set 'notmuch-search-target-thread target-thread)
     (set 'notmuch-search-target-line target-line)
+    (notmuch-tag-clear-cache)
     (let ((proc (get-buffer-process (current-buffer)))
 	  (inhibit-read-only t))
       (if proc