Allow to exclude specific tags from inheritance.

So far, the only way to select tags for inheritance was to
allow it for all tags, or to do a positive selection using
one of the more complex settings for
`org-use-tag-inheritance'.  It may actually be better to
allow inheritance for all but a few tags, which was difficult
to achieve with this methodology.

This patch introduces a new option,
`org-tags-exclude-from-inheritance' which allows to specify an
exclusion list for inherited tags.

ORGWEBPAGE/Changes.org

@@ -77,6 +77,18 @@
     If you prefer the old behavior of only showing the local
     tags, customize the variable =org-agenda-show-inherited-tags=.
 
+*** Exclude some tags from inheritance.
+
+    So far, the only way to select tags for inheritance was to
+    allow it for all tags, or to do a positive selection using
+    one of the more complex settings for
+    `org-use-tag-inheritance'.  It may actually be better to
+    allow inheritance for all but a few tags, which was difficult
+    to achieve with this methodology.
+
+    A new option, `org-tags-exclude-from-inheritance', allows to
+    specify an exclusion list for inherited tags.
+
 * Version 6.13
 
 ** Overview

doc/ChangeLog

@@ -1,3 +1,8 @@
+2008-11-27  Carsten Dominik  <carsten.dominik@gmail.com>
+
+	* org.texi (Tag inheritance): Refine the description of tag
+	inheritance.
+
 2008-11-25  Carsten Dominik  <carsten.dominik@gmail.com>
 
 	* org.texi (Project alist): Add info about the publishing sequence

doc/org.texi

@@ -3480,14 +3480,16 @@ level zero that surounds the entire file.
 
 @noindent
 To limit tag inheritance to specific tags, or to turn it off entirely, use
-the variable @code{org-use-tag-inheritance}.
+the variables @code{org-use-tag-inheritance} and
+@code{org-tags-exclude-from-inheritance}.
 
 When a headline matches during a tags search while tag inheritance is turned
-on, all the sublevels in the same tree will match as well@footnote{This is
-only true if the the search does not involve more complex tests including
-properties (@pxref{Property searches}).}.  The list of matches may then
-become very long.  If you only want to see the first tags match in a subtree,
-configure the variable @code{org-tags-match-list-sublevels}.
+on, all the sublevels in the same tree will (for a simple match form) match
+as well@footnote{This is only true if the the search does not involve more
+complex tests including properties (@pxref{Property searches}).}.  The list
+of matches may then become very long.  If you only want to see the first tags
+match in a subtree, configure the variable
+@code{org-tags-match-list-sublevels} (not recommended).
 
 @node Setting tags, Tag searches, Tag inheritance, Tags
 @section Setting tags

lisp/ChangeLog

@@ -1,5 +1,9 @@
 2008-11-27  Carsten Dominik  <carsten.dominik@gmail.com>
 
+	* org.el (org-tags-exclude-from-inheritance): New option.
+	(org-tag-inherit-p, org-remove-uniherited-tags): Respect
+	`org-tags-exclude-from-inheritance'.
+
 	* org-agenda.el (org-agenda-show-inherited-tags): New option.
 	(org-format-agenda-item): Add inherited tags to the agenda line
 	string, and make sure that properties are kept when downcasing the

lisp/org.el

@@ -1882,13 +1882,16 @@ the tags are again aligned to `org-tags-column'."
 (defcustom org-use-tag-inheritance t
   "Non-nil means, tags in levels apply also for sublevels.
 When nil, only the tags directly given in a specific line apply there.
-If this option is t, a match early-on in a tree can lead to a large
-number of matches in the subtree.  If you only want to see the first
-match in a tree during a search, check out the variable
-`org-tags-match-list-sublevels'.
-
 This may also be a list of tags that should be inherited, or a regexp that
-matches tags that should be inherited."
+matches tags that should be inherited.  Additional control is possible
+with the variable  `org-tags-exclude-from-inheritance' which gives an
+explicit list of tags to be excluded from inheritance., even if the value of
+`org-use-tag-inheritance' would select it for inheritance.
+
+If this option is t, a match early-on in a tree can lead to a large
+number of matches in the subtree when constructing the agenda or creating
+a sparse tree.  If you only want to see the first match in a tree during
+a search, check out the variable `org-tags-match-list-sublevels'."
   :group 'org-tags
   :type '(choice
 	  (const :tag "Not" nil)
@@ -1896,9 +1899,18 @@ matches tags that should be inherited."
 	  (repeat :tag "Specific tags" (string :tag "Tag"))
 	  (regexp :tag "Tags matched by regexp")))
 
+(defcustom org-tags-exclude-from-inheritance nil
+  "List of tags that should never be inherited.
+This is a way to exclude a few tags from inheritance.  For way to do
+the opposite, to actively allow inheritance for selected tags,
+see the variable `org-use-tag-inheritance'."
+  :group 'org-tags
+  :type '(repeat (string :tag "Tag")))
+
 (defun org-tag-inherit-p (tag)
   "Check if TAG is one that should be inherited."
   (cond
+   ((member tag org-tags-exclude-from-inheritance) nil)
    ((eq org-use-tag-inheritance t) t)
    ((not org-use-tag-inheritance) nil)
    ((stringp org-use-tag-inheritance)
@@ -1918,7 +1930,11 @@ inheritance off, you very likely want to turn this option on.
 
 As a special case, if the tag search is restricted to TODO items, the
 value of this variable is ignored and sublevels are always checked, to
-make sure all corresponding TODO items find their way into the list."
+make sure all corresponding TODO items find their way into the list.
+
+This variable is semi-obsolete and probably should always be true.  It
+is better to limit inheritance to certain tags using the variables
+`org-use-tag-inheritanc'e and `org-tags-exclude-from-inheritance'."
   :group 'org-tags
   :type 'boolean)
 
@@ -9101,15 +9117,22 @@ only lines with a TODO keyword are included in the output."
 (defun org-remove-uniherited-tags (tags)
   "Remove all tags that are not inherited from the list TAGS."
   (cond
-   ((eq org-use-tag-inheritance t) tags)
+   ((eq org-use-tag-inheritance t)
+    (if org-tags-exclude-from-inheritance
+	(org-delete-all org-tags-exclude-from-inheritance tags)
+      tags))
    ((not org-use-tag-inheritance) nil)
    ((stringp org-use-tag-inheritance)
     (delq nil (mapcar
-	       (lambda (x) (if (string-match org-use-tag-inheritance x) x nil))
+	       (lambda (x)
+		 (if (and (string-match org-use-tag-inheritance x)
+			  (not (member x org-tags-exclude-from-inheritance)))
+		     x nil))
 	       tags)))
    ((listp org-use-tag-inheritance)
     (delq nil (mapcar
-	       (lambda (x) (if (member x org-use-tag-inheritance) x nil))
+	       (lambda (x)
+		 (if (member x org-use-tag-inheritance) x nil))
 	       tags)))))
 
 (defvar todo-only) ;; dynamically scoped