emacs: show: mark tags changed since buffer loaded

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.

Since the formatting code matches regexps a user can match all deleted
tags with a ".*" in notmuch-tag-deleted-formats.  For example setting
notmuch-tag-deleted-formats to '((".*" nil)) tells notmuch not to show
deleted tags at all.

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.

4 files changed, 65 insertions, 39 deletions

diff --git a/emacs/notmuch-show.el b/emacs/notmuch-show.el
index 019f51d7..5492be42 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 3ae5e62f..07c260eb 100644
--- a/emacs/notmuch-tag.el
+++ b/emacs/notmuch-tag.el
@@ -193,45 +193,71 @@ This can be used with `notmuch-tag-format-image-data'."
   "Clear the internal cache of tag formats."
   (clrhash notmuch-tag--format-cache))
 
-(defun notmuch-tag-format-tag (tag)
-  "Format TAG by according to `notmuch-tag-formats'.
-
-Callers must ensure that the tag format cache has been recently cleared
-via `notmuch-tag-clear-cache' before using this function.  For example,
-it would be appropriate to clear the cache just prior to filling a
-buffer that uses formatted tags."
-
-  (let ((formatted (gethash tag notmuch-tag--format-cache 'missing)))
-    (when (eq formatted 'missing)
-      (let* ((formats
-	      (save-match-data
-		;; Don't use assoc-default since there's no way to
-		;; distinguish a missing key from a present key with a
-		;; null cdr:.
-		(assoc* tag notmuch-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 (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.
-		  (dolist (format (cdr formats) tag)
-		    (setq tag (eval format)))))))
-	(puthash tag formatted notmuch-tag--format-cache)))
-    formatted))
-
-(defun notmuch-tag-format-tags (tags &optional face)
+(defun notmuch-tag--get-formats (tag format-alist)
+  "Find the first item whose car regexp-matches TAG."
+  (save-match-data
+    ;; Don't use assoc-default since there's no way to distinguish a
+    ;; missing key from a present key with a null cdr.
+    (assoc* tag format-alist
+	    :test (lambda (tag key)
+		    (and (eq (string-match key tag) 0)
+			 (= (match-end 0) (length tag)))))))
+
+(defun notmuch-tag--do-format (tag formatted-tag formats)
+  "Apply a tag-formats entry to TAG."
+  (cond ((null formats)		;; - Tag not in `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, we must apply all the
+	 ;; formats.  TAG may be null so treat that as a special case.
+	 (let ((bare-tag tag)
+	       (tag (copy-sequence (or formatted-tag ""))))
+	   (dolist (format (cdr formats))
+	     (setq tag (eval format)))
+	   (if (and (null formatted-tag) (equal tag ""))
+	       nil
+	     tag)))))
+
+(defun notmuch-tag-format-tag (tags orig-tags tag)
+  "Format TAG according to `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* ((tag-state (cond ((not (member tag tags)) 'deleted)
+			  ((not (member tag orig-tags)) 'added)))
+	 (formatted-tag (gethash (cons tag tag-state) notmuch-tag--format-cache 'missing)))
+    (when (eq formatted-tag 'missing)
+      (let ((base (notmuch-tag--get-formats tag notmuch-tag-formats))
+	    (over (case tag-state
+		    (deleted (notmuch-tag--get-formats
+			      tag notmuch-tag-deleted-formats))
+		    (added (notmuch-tag--get-formats
+			    tag notmuch-tag-added-formats))
+		    (otherwise nil))))
+	(setq formatted-tag (notmuch-tag--do-format tag tag base))
+	(setq formatted-tag (notmuch-tag--do-format tag formatted-tag over))
+
+	(puthash (cons tag tag-state) formatted-tag notmuch-tag--format-cache)))
+    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-apply-face
      (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 c78d9de5..8bf2fbc5 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 2e0b20eb..59ad541e 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."