Austin,

Thanks for the helpful comments.  I redid the patch to take a list of
regexps.  That way users can banish different kinds of tags or simply
list the tags themselves.  I've responded to your comments in text below
the patch.

---
 emacs/notmuch.el |   26 +++++++++++++++++++++++++-
 1 file changed, 25 insertions(+), 1 deletion(-)

diff --git a/emacs/notmuch.el b/emacs/notmuch.el
index f9454d8..05aa114 100644
--- a/emacs/notmuch.el
+++ b/emacs/notmuch.el
@@ -775,6 +775,21 @@ non-authors is found, assume that all of the authors match."
 	  (overlay-put overlay 'isearch-open-invisible #'delete-overlay)))
       (insert padding))))
 
+  
+(defcustom notmuch-search-hide-tag-regexps '()
+  "List of regular expressionss specifying tags to hide in search view.
+
+Notmuch will hide any tags in search view that match the regexps
+specified in the list `notmuch-search-hide-tag-regexp`.  The
+match is case-insensitive.
+
+If you are not comfortable with regular expressions, a list of
+tag words will work, assuming those tags use only alphanumeric
+characters.  An empty list will disable hiding of tags in search
+view.  The list can be set via setq or the customize interface."
+  :type '(repeat  regexp)
+  :group 'notmuch-search)
+
 (defun notmuch-search-insert-field (field format-string result)
   (cond
    ((string-equal field "date")
@@ -793,7 +808,16 @@ non-authors is found, assume that all of the authors match."
     (notmuch-search-insert-authors format-string (plist-get result :authors)))
 
    ((string-equal field "tags")
-    (let ((tags-str (mapconcat 'identity (plist-get result :tags) " ")))
+    (let ((tags-str
+	   (mapconcat 'identity
+		      (let ((case-fold-search t))
+			(remove-if
+			 (lambda (tag)
+			   (find tag notmuch-search-hide-tag-regexps
+				 :test (lambda (tag regexp)
+					 (string-match regexp tag))))
+			 (plist-get result :tags)))
+		      " ")))
       (insert (propertize (format format-string tags-str)
 			  'face 'notmuch-tag-face))))))
 
-- 
1.7.10.4


Austin Clements <amdragon@MIT.EDU> writes:
> I like it.

Thanks.

[snip]

> I have no idea why, but Emacs typically uses "regexp" instead of
> "regex".

It probably has something to do with rhyming with 'sexp'. ;) It's good
to conform to the vernacular, so I fixed it.

>
>> +
>> +Leave blank to disable hiding of tags in search view.
>
> Saying "Leave blank" supposes that the user knows what the default
> value is.  How about "An empty string disables hiding of tags in
> search view."?

I'm now using a list, but yes, "an empty list" is a good way to describe
it.

>
> Even better, though, would be to use nil to indicate this, since "" is
> a perfectly valid regexp and matches everything.  In that case, this
> should say something like "If nil, no tags will be hidden in search
> view."

"An empty list" is nil, so I think this is covered by my changes.  If
you think the defcustom text could be clearer, I'd appreciate edits.

>
>> +Note: elisp regexes are case-insensitive"
>
> Likewise, "regexps".  Also, Elisp regexps are not, in general,
> case-insensitive.  If we want to control this, we should bind
> case-fold-search to nil around the string-match below and say
> something here like "Matching is case-insensitive."

Good point.

>
>> +  :type 'string
>
> Better would be 'regexp.  Or, '(choice (const :tag "None" nil) regexp)
> to allow nil or a regexp.

Changed to 'regexp.

[snip]

> It would be simpler and more robust to use remove-if here.  What about
> something like
>
>   (let ((tags-str
>          (mapconcat 'identity
>                     (if notmuch-search-hide-tag-regex
>                         (let ((case-fold-search t))
>                           (remove-if
>                            (apply-partially #'string-match
>                                             notmuch-search-hide-tag-regex)
>                            (plist-get result :tags)))
>                       (plist-get result :tags))
>                     " ")))

That's a good idea.  I adjusted the code to use remove-if, and it is
improved by the change.

Thanks,
James