[WIP Patch 4/7] emacs: show: mark tags changed since buffer loaded

[Mark Walters]

This allows (and requires) the original-tags to be passed along with
the current-tags to be passed to notmuch-tag-format-tags. This allows
the tag formatting to show added and deleted tags.By default a removed
tag is displayed with strike-through in red (if strike-through is not
available, eg on a terminal, inverse video is used instead) and an
added tag is displayed underlined in green.

If the caller does not wish to use the new feature it can pass
current-tags for both arguments and, at this point, we do exactly that
in the three callers of this function.

Note, we cannot tidily allow original-tags to be optional because we would
need to distinguish nil meaning "we are not specifying original-tags"
from nil meaning there were no original-tags (an empty list).

We use this in subsequent patches to make it clear when a message was
unread when you first loaded a show buffer (previously the unread tag
could be removed before a user realised that it had been unread).

The code adds into the existing tag formatting code. The user can
specify exactly how a tag should be displayed normally, when deleted,
or when added. For convenience an entry for the empty string in the
notmuch-tag-formats (and the corresponding notmuch-tag-deleted-formats
notmuch-tag-added-formats) is applied to all tags which do not have an
explicit match.

This means that a user can tell notmuch not to show deleted tags at
all by setting notmuch-tag-deleted-formats to
'(("" nil))
or not to show any deleted tags except "unread" by setting it to
'(("" nil)
  ("unread" (propertize tag 'face '(strike-through "red"))))

All the variables are customizable; however, more complicated cases
like changing the face depending on the type of display will require
custom lisp.

Currently this overrides notmuch-tag-deleted-formats for the tests
setting it to '(("" nil)) so that they get removed from the display
and, thus, all tests still pass.
---
 emacs/notmuch-show.el |    4 +-
 emacs/notmuch-tag.el  |   65 ++++++++++++++++++++++++++++++++++++++----------
 emacs/notmuch-tree.el |    2 +-
 emacs/notmuch.el      |    2 +-
 test/test-lib.el      |    5 ++++
 5 files changed, 60 insertions(+), 18 deletions(-)

diff --git a/emacs/notmuch-show.el b/emacs/notmuch-show.el
index 1ac80ca..1ce56f9 100644
--- a/emacs/notmuch-show.el
+++ b/emacs/notmuch-show.el
@@ -344,7 +344,7 @@ operation on the contents of the current buffer."
     (if (re-search-forward "(\\([^()]*\\))$" (line-end-position) t)
 	(let ((inhibit-read-only t))
 	  (replace-match (concat "("
-				 (notmuch-tag-format-tags tags)
+				 (notmuch-tag-format-tags tags tags)
 				 ")"))))))
 
 (defun notmuch-clean-address (address)
@@ -423,7 +423,7 @@ message at DEPTH in the current thread."
 	    " ("
 	    date
 	    ") ("
-	    (notmuch-tag-format-tags tags)
+	    (notmuch-tag-format-tags tags tags)
 	    ")\n")
     (overlay-put (make-overlay start (point)) 'face 'notmuch-message-summary-face)))
 
diff --git a/emacs/notmuch-tag.el b/emacs/notmuch-tag.el
index add60a3..812a0f4 100644
--- a/emacs/notmuch-tag.el
+++ b/emacs/notmuch-tag.el
@@ -192,36 +192,73 @@ This can be used with `notmuch-tag-format-image-data'."
   </g>
 </svg>")
 
-(defun notmuch-tag-format-tag (tag)
-  "Format TAG by looking into `notmuch-tag-formats'."
-  (let ((formatted (gethash tag notmuch-tag--format-cache 'missing)))
+(defun notmuch-tag-format-tag-by-state (tag formatted-tag tag-state)
+  "Format TAG by looking into the appropriate `notmuch-tag-formats`.
+
+Applies formats for TAG from the appropriate one of
+`notmuch-tag-formats`, `notmuch-tag-deleted-formats` and
+`notmuch-tag-added-formats` based on TAG-STATE to the partially
+formatted tag FORMATTED-TAG."
+  (let ((formatted (gethash (cons tag tag-state) notmuch-tag--format-cache 'missing)))
     (when (eq formatted 'missing)
-      (let* ((formats
+      (let* ((tag-formats (cond ((null tag-state) notmuch-tag-formats)
+				((eq 'deleted tag-state) notmuch-tag-deleted-formats)
+				((eq 'added tag-state) notmuch-tag-added-formats)))
+	     (formats
 	      (save-match-data
-		(assoc* tag notmuch-tag-formats
+		(assoc* tag tag-formats
 			:test (lambda (tag key)
 				(and (eq (string-match key tag) 0)
 				     (= (match-end 0) (length tag))))))))
 	(setq formatted
 	      (cond
-	       ((null formats)		;; - Tag not in `notmuch-tag-formats',
-		tag)			;;   the format is the tag itself.
+	       ((null formats)		;; - Tag not in `tag-formats',
+		formatted-tag)		;;   the format is the tag itself.
 	       ((null (cdr formats))	;; - Tag was deliberately hidden,
 		nil)			;;   no format must be returned
-	       (t			;; - Tag was found and has formats,
-		(let ((tag tag))	;;   we must apply all the formats.
+	       (t
+		;; Tag was found and has formats, we must apply all
+		;; the formats.  FORMATTED-TAG may be null so treat
+		;; that as a special case.
+		(let ((tag (or formatted-tag "")))
 		  (dolist (format (cdr formats) tag)
-		    (setq tag (eval format)))))))
-	(puthash tag formatted notmuch-tag--format-cache)))
+		    (setq tag (eval format)))
+		  (if (and (null formatted-tag)
+			   (equal tag ""))
+		      nil
+		    tag)))))
+	(puthash (cons tag tag-state) formatted notmuch-tag--format-cache)))
     formatted))
 
-(defun notmuch-tag-format-tags (tags &optional face)
+(defun notmuch-tag-format-tag (tags orig-tags tag)
+  "Format TAG by looking into `notmuch-tag-formats'.
+
+TAGS and ORIG-TAGS are lists of the current tags and the original
+tags; tags which have been deleted (i.e., are in ORIG-TAGS but
+are not in TAGS) are shown using formats from
+`notmuch-tag-deleted-formats'; tags which have been added (i.e.,
+are in TAGS but are not in ORIG-TAGS) are shown using formats
+from `notmuch-tag-added-formats' and tags which have not been
+changed (the normal case) are shown using formats from
+`notmuch-tag-formats'"
+  (let* ((formatted-tag (notmuch-tag-format-tag-by-state tag tag nil)))
+    (cond ((not (member tag tags))
+	   (notmuch-tag-format-tag-by-state tag formatted-tag 'deleted))
+	  ((not (member tag orig-tags))
+	   (notmuch-tag-format-tag-by-state tag formatted-tag 'added))
+	  (t
+	    formatted-tag))))
+
+(defun notmuch-tag-format-tags (tags orig-tags &optional face)
   "Return a string representing formatted TAGS."
-  (let ((face (or face 'notmuch-tag-face)))
+  (let ((face (or face 'notmuch-tag-face))
+	(all-tags (sort (delete-dups (append tags orig-tags nil)) #'string<)))
     (notmuch-combine-face-text-property-string
      (mapconcat #'identity
 		;; nil indicated that the tag was deliberately hidden
-		(delq nil (mapcar #'notmuch-tag-format-tag tags))
+		(delq nil (mapcar
+			   (apply-partially #'notmuch-tag-format-tag tags orig-tags)
+			   all-tags))
 		" ")
      face
      t)))
diff --git a/emacs/notmuch-tree.el b/emacs/notmuch-tree.el
index 4f2ac02..b37e2cd 100644
--- a/emacs/notmuch-tree.el
+++ b/emacs/notmuch-tree.el
@@ -704,7 +704,7 @@ unchanged ADDRESS if parsing fails."
 	    (face (if match
 		      'notmuch-tree-match-tag-face
 		    'notmuch-tree-no-match-tag-face)))
-	(format format-string (notmuch-tag-format-tags tags face)))))))
+	(format format-string (notmuch-tag-format-tags tags tags face)))))))
 
 (defun notmuch-tree-format-field-list (field-list msg)
   "Format fields of MSG according to FIELD-LIST and return string"
diff --git a/emacs/notmuch.el b/emacs/notmuch.el
index 0471750..1436e5a 100644
--- a/emacs/notmuch.el
+++ b/emacs/notmuch.el
@@ -754,7 +754,7 @@ non-authors is found, assume that all of the authors match."
 
    ((string-equal field "tags")
     (let ((tags (plist-get result :tags)))
-      (insert (format format-string (notmuch-tag-format-tags tags)))))))
+      (insert (format format-string (notmuch-tag-format-tags tags tags)))))))
 
 (defun notmuch-search-show-result (result &optional pos)
   "Insert RESULT at POS or the end of the buffer if POS is null."
diff --git a/test/test-lib.el b/test/test-lib.el
index 37fcb3d..437f83f 100644
--- a/test/test-lib.el
+++ b/test/test-lib.el
@@ -165,3 +165,8 @@ nothing."
 
      (t
       (notmuch-test-report-unexpected output expected)))))
+
+;; For historical reasons, we hide deleted tags by default in the test
+;; suite
+(setq notmuch-tag-deleted-formats
+      '((".*" nil)))
-- 
1.7.9.1