Gnus: Improve subthread sorting;

 make subthread sorting customizable and add docs for it

* doc/misc/gnus.texi (Sorting the Summary Buffer): Document new defcustom
`gnus-subthread-sort-functions' and remove the obsolete documentation
of `gnus-sort-threads-recursively'.

* lisp/gnus/gnus-sum.el (gnus-subthread-sort-functions): New defcustom.
(gnus-sort-threads-recursively): Delete defcustom.
(gnus-sort-threads-recursive): Adapt accordingly.

* lisp/gnus/gnus-sum.el (gnus-sort-subthreads-recursive): New function.
(gnus-sort-threads-recursive): Use it.
(gnus-sort-threads): Unconditionally call `gnus-sort-threads-recursive'
again.  Now that determines how to sort subthreads.

4 files changed, 71 insertions, 18 deletions

diff --git a/doc/misc/ChangeLog b/doc/misc/ChangeLog
index b306ce5ba0a..9b45ac06f4c 100644
--- a/doc/misc/ChangeLog
+++ b/doc/misc/ChangeLog
@@ -1,4 +1,10 @@
-2013-07-29  David Engster <deng@randomsample.de>
+2013-07-30  Tassilo Horn  <tsdh@gnu.org>
+
+        * gnus.texi (Sorting the Summary Buffer): Document new defcustom
+        `gnus-subthread-sort-functions' and remove the obsolete documentation
+        of `gnus-sort-threads-recursively'.
+
+2013-07-29  David Engster  <deng@randomsample.de>
 
         * eieio.texi (top): Make clear that EIEIO is not a full CLOS
         implementation.
diff --git a/doc/misc/gnus.texi b/doc/misc/gnus.texi
index 5f9e0b9db28..808bd2b114b 100644
--- a/doc/misc/gnus.texi
+++ b/doc/misc/gnus.texi
@@ -7394,10 +7394,13 @@ say something like:
         gnus-thread-sort-by-score))
 @end lisp
 
-By default, threads are sorted recursively, that is, first the roots,
-then all subthreads, and so on.  If you feel more like sorting only
-the roots, so that inside a thread the original chronological order is
-retained, you can set @code{gnus-sort-threads-recursively} to nil.
+By default, threads including their subthreads are sorted according to
+the value of @code{gnus-thread-sort-functions}.  By customizing
+@code{gnus-subthread-sort-functions} you can define a custom sorting
+order for subthreads.  This allows for example to sort threads from
+high score to low score in the summary buffer, but to have subthreads
+still sorted chronologically from old to new without taking their
+score into account.
 
 @vindex gnus-thread-score-function
 The function in the @code{gnus-thread-score-function} variable (default
diff --git a/lisp/gnus/ChangeLog b/lisp/gnus/ChangeLog
index c32853a2a9f..4230d010a5d 100644
--- a/lisp/gnus/ChangeLog
+++ b/lisp/gnus/ChangeLog
@@ -1,3 +1,16 @@
+2013-07-30  Tassilo Horn  <tsdh@gnu.org>
+
+        * gnus-sum.el (gnus-subthread-sort-functions): New defcustom.
+        (gnus-sort-threads-recursively): Delete defcustom.
+        (gnus-sort-threads-recursive): Adapt accordingly.
+
+2013-07-30  Tassilo Horn  <tsdh@gnu.org>
+
+        * gnus-sum.el (gnus-sort-subthreads-recursive): New function.
+        (gnus-sort-threads-recursive): Use it.
+        (gnus-sort-threads): Unconditionally call `gnus-sort-threads-recursive'
+        again.  Now that determines how to sort subthreads.
+
 2013-07-26  Tassilo Horn  <tsdh@gnu.org>
 
         * gnus-sum.el (gnus-sort-threads-recursively): New defcustom.
diff --git a/lisp/gnus/gnus-sum.el b/lisp/gnus/gnus-sum.el
index 15cbb5a45e6..a7269baee74 100644
--- a/lisp/gnus/gnus-sum.el
+++ b/lisp/gnus/gnus-sum.el
@@ -847,14 +847,6 @@ controls how articles are sorted."
                           (function :tag "other"))
                   (boolean :tag "Reverse order"))))
 
-(defcustom gnus-sort-threads-recursively t
-  "If non-nil, `gnus-thread-sort-functions' are applied recursively.
-Setting this to nil allows sorting high-score, recent,
-etc. threads to the top of the summary buffer while still
-retaining chronological old to new sorting order inside threads."
-  :group 'gnus-summary-sort
-  :type 'boolean)
-
 (defcustom gnus-thread-sort-functions '(gnus-thread-sort-by-number)
   "*List of functions used for sorting threads in the summary buffer.
 By default, threads are sorted by article number.
@@ -880,7 +872,11 @@ and `gnus-thread-sort-by-total-score' (see
 `gnus-thread-score-function').
 
 When threading is turned off, the variable
-`gnus-article-sort-functions' controls how articles are sorted."
+`gnus-article-sort-functions' controls how articles are sorted.
+
+By default, threads and their subthreads are sorted according to
+the value of this variable.  To use a different sorting order for
+subthreads, customize `gnus-subthread-sort-functions'."
   :group 'gnus-summary-sort
   :type '(repeat
           (gnus-widget-reversible
@@ -897,6 +893,28 @@ When threading is turned off, the variable
                    (function :tag "other"))
            (boolean :tag "Reverse order"))))
 
+(defcustom gnus-subthread-sort-functions 'gnus-thread-sort-functions
+  "*List of functions used for sorting subthreads in the summary buffer.
+By default, subthreads are sorted the same as threads, i.e.,
+according to the value of `gnus-thread-sort-functions'."
+  :group 'gnus-summary-sort
+  :type '(choice
+          (const :tag "Sort subthreads like threads" gnus-thread-sort-functions)
+          (repeat
+           (gnus-widget-reversible
+            (choice (function-item gnus-thread-sort-by-number)
+                    (function-item gnus-thread-sort-by-author)
+                    (function-item gnus-thread-sort-by-recipient)
+                    (function-item gnus-thread-sort-by-subject)
+                    (function-item gnus-thread-sort-by-date)
+                    (function-item gnus-thread-sort-by-score)
+                    (function-item gnus-thread-sort-by-most-recent-number)
+                    (function-item gnus-thread-sort-by-most-recent-date)
+                    (function-item gnus-thread-sort-by-random)
+                    (function-item gnus-thread-sort-by-total-score)
+                    (function :tag "other"))
+            (boolean :tag "Reverse order")))))
+
 (defcustom gnus-thread-score-function '+
   "*Function used for calculating the total score of a thread.
 
@@ -4854,10 +4872,25 @@ If LINE, insert the rebuilt thread starting on line LINE."
             (gnus-delete-line)))))))
 
 (defun gnus-sort-threads-recursive (threads func)
+  ;; Responsible for sorting the root articles of threads.
+  (let ((subthread-sort-func (if (eq gnus-subthread-sort-functions
+                                     'gnus-thread-sort-functions)
+                                 func
+                               (gnus-make-sort-function
+                                gnus-subthread-sort-functions))))
+    (sort (mapcar (lambda (thread)
+                    (cons (car thread)
+                          (and (cdr thread)
+                               (gnus-sort-subthreads-recursive
+                                (cdr thread) subthread-sort-func))))
+                  threads) func)))
+
+(defun gnus-sort-subthreads-recursive (threads func)
+  ;; Responsible for sorting subthreads.
   (sort (mapcar (lambda (thread)
                   (cons (car thread)
                         (and (cdr thread)
-                             (gnus-sort-threads-recursive (cdr thread) func))))
+                             (gnus-sort-subthreads-recursive (cdr thread) func))))
                 threads) func))
 
 (defun gnus-sort-threads-loop (threads func)
@@ -4885,9 +4918,7 @@ If LINE, insert the rebuilt thread starting on line LINE."
         (condition-case nil
             (let ((max-lisp-eval-depth (max max-lisp-eval-depth 5000))
                   (sort-func (gnus-make-sort-function gnus-thread-sort-functions)))
-              (if gnus-sort-threads-recursively
-                  (gnus-sort-threads-recursive threads sort-func)
-                (sort threads sort-func)))
+              (gnus-sort-threads-recursive threads sort-func))
           ;; Even after binding max-lisp-eval-depth, the recursive
           ;; sorter might fail for very long threads.  In that case,
           ;; try using a (less well-tested) non-recursive sorter.