[PATCH v1] WIP: emacs: show: expand unread tags

[Matt Armstrong]

Expand unread messages by default in show mode.

Show mode now expands messages matching tags designated by
notmuch-show-unread-tags (in addition to those matching the search
query).  By default, this list is `("unread").  This way, one can still
tag and search for messages however one likes, but if the thread is
displayed those messages matching the search term OR unread are
expanded.

---

See id:qf54m70o7h5.fsf at marmstrong-linux.kir.corp.google.com for a
related discussion thread.

What happens today when notmuch-show does the query to show a thread, it
takes the user's query Q and constructs:

  thread:THREAD and Q

This changes the above to:

  thread:THREAD and ((Q) or (tag:unread))

I've found this to be a much better day to day experience for myself and
am interesting on iterating on this idea until it is can be
committed.  (settling on interface first, then testing)

As I explain in the thread noted above, I found the default notmuch
experience to be quite confusing, at least when processing "inbox" mail.

The problem is that my work experience is based on a large number of
mailing lists that cross post to each other, often initiated mid-thread.
I aggressively archive these threads as "unread", but sometimes a long
thread is cross-posted to my team mailing list, or to me directly.  If
these show up in my "team" or "me" tags, I want to have a clear
indication that I have yet to read the entire thread.  Expanding
"tag:unread" messages makes sense here.

It might make less sense if drilling down for those specific messages.
In that case I wonder if C-u RET (to toggle
notmuch-show-elide-non-matching-messages) is sufficient?
---
 emacs/notmuch-show.el | 59 +++++++++++++++++++++++++++++++++++++++++----------
 emacs/notmuch.el      |  4 ++++
 2 files changed, 52 insertions(+), 11 deletions(-)

diff --git a/emacs/notmuch-show.el b/emacs/notmuch-show.el
index 5a585f3..f20eec6 100644
--- a/emacs/notmuch-show.el
+++ b/emacs/notmuch-show.el
@@ -142,10 +142,21 @@ indentation."
 			notmuch-show-interactively-view-part)))
 
 (defcustom notmuch-show-only-matching-messages nil
-  "Only matching messages are shown by default."
+  "When non-nil only matching messages are shown.
+
+See `notmuch-search-show-thread'."
   :type 'boolean
   :group 'notmuch-show)
 
+(defcustom notmuch-show-unread-tags '("unread")
+  "A list of tags to expand by default in `notmuch-show-mode'.
+
+In addition to the search query, any messages that match one of
+the tags in the list are expanded.  Has no effect if
+`notmuch-show-only-matching-messages', which see."
+  :type '(repeat string)
+  :group 'notmuch-show)
+
 ;; By default, block all external images to prevent privacy leaks and
 ;; potential attacks.
 (defcustom notmuch-show-text/html-blocked-images "."
@@ -1258,6 +1269,24 @@ matched."
 	(message "No messages matched the query!")
 	nil))))
 
+(defun notmuch-show--query-or (a b)
+  "Form a query string \"(A) or (B)\".
+
+The args must be strings. If either is nil, returns the other."
+  (cond
+   ((null a) b)
+   ((null b) a)
+   (t (concat "(" a ") or (" b ")"))))
+
+(defun notmuch-show--query-and (a b)
+  "Form a query string \"(A) and (B)\".
+
+The args must be strings. If either is nil, returns the other."
+  (cond
+   ((null a) b)
+   ((null b) a)
+   (t (concat "(" a ") and (" b ")"))))
+
 (defun notmuch-show--build-buffer (&optional state)
   "Display messages matching the current buffer context.
 
@@ -1265,21 +1294,29 @@ Apply the previously saved STATE if supplied, otherwise show the
 first relevant message.
 
 If no messages match the query return NIL."
-  (let* ((basic-args (list notmuch-show-thread-id))
-	 (args (if notmuch-show-query-context
-		   (append (list "\'") basic-args
-			   (list "and (" notmuch-show-query-context ")\'"))
-		 (append (list "\'") basic-args (list "\'"))))
+  (let* ((unread (if notmuch-show-unread-tags
+		     (mapconcat
+		      '(lambda (tag) (concat "tag:" tag))
+		      notmuch-show-unread-tags
+		      " or ")))
+	 (basic-query (notmuch-show--query-or
+		       notmuch-show-thread-id unread))
+	 (context-query (if notmuch-show-query-context
+			    (notmuch-show--query-and
+			     notmuch-show-thread-id
+			     (notmuch-show--query-or
+			      notmuch-show-query-context
+			      unread))))
 	 (cli-args (cons "--exclude=false"
 			 (when notmuch-show-elide-non-matching-messages
 			   (list "--entire-thread=false"))))
-
-	 (forest (or (notmuch-query-get-threads (append cli-args args))
+	 (forest (or (and context-query
+			  (notmuch-query-get-threads
+			   (append cli-args (list "\'" context-query "\'"))))
 		     ;; If a query context reduced the number of
 		     ;; results to zero, try again without it.
-		     (and notmuch-show-query-context
-			  (notmuch-query-get-threads (append cli-args basic-args)))))
-
+		     (notmuch-query-get-threads
+		      (append cli-args (list "\'" basic-query "\'")))))
 	 ;; Must be reset every time we are going to start inserting
 	 ;; messages into the buffer.
 	 (notmuch-show-previous-subject ""))
diff --git a/emacs/notmuch.el b/emacs/notmuch.el
index 8e14692..7cc9e9e 100644
--- a/emacs/notmuch.el
+++ b/emacs/notmuch.el
@@ -480,6 +480,10 @@ no messages in the region then return nil."
 (defun notmuch-search-show-thread (&optional elide-toggle)
   "Display the currently selected thread.
 
+Messages in the thread matching the query, as well as any in
+`notmuch-show-unread-tags', are expanded.  The others are
+initially displayed collapsed.
+
 With a prefix argument, invert the default value of
 `notmuch-show-only-matching-messages' when displaying the
 thread."
-- 
2.8.0.rc3.226.g39d4020