[O] [PATCH] Fix alphabetic sorting for headlines, tags

[Sebastian Reuße]

* org.el (org-sort-entries): Use collated sorting.
(org-tags-sort-function): Use collated sorting.
(org-string-collate-greaterp): Add helper-function to use as defcustom
option, since there is no ‘string-collate-greaterp’ in Emacs.

* org-compat.el (org-string-collate-lessp): Add proxy to fall-back on
string-lessp when string-collate-lessp is missing (Emacs ≤ 24).

* test-org.el (test-org/string-collate-lessp): Add test.

‘org-sort-entries’ and ‘org-tags-sort-function’ advertise alphabetic
sorting, but actually sort based only on character code.  This
produces non-alphabetic orderings of strings in non-ASCII locales.

E. g., German Umlauts “Ä Ü Ö” are alphabetically sorted as if they
were “A U O”, whereas sorting based on character-code will place them
after “Z”, which is unexpected.
---
 lisp/org-compat.el       |  6 ++++++
 lisp/org.el              | 12 +++++++++---
 testing/lisp/test-org.el |  5 +++++
 3 files changed, 20 insertions(+), 3 deletions(-)

diff --git a/lisp/org-compat.el b/lisp/org-compat.el
index 2553286e1..acd5c3e1e 100644
--- a/lisp/org-compat.el
+++ b/lisp/org-compat.el
@@ -118,6 +118,12 @@ (defvar org-table1-hline-regexp)
              (push (expand-file-name file dir) files)))))
       (nconc result (nreverse files)))))
 
+;; `string-collate-lessp' is new in Emacs 25.
+(defalias 'org-string-collate-lessp
+  (if (fboundp 'string-collate-lessp)
+      'string-collate-lessp
+    'string-lessp))
+
 
 ;;; Obsolete aliases (remove them after the next major release).
 
diff --git a/lisp/org.el b/lisp/org.el
index 688e48bcc..fbbeea80f 100644
--- a/lisp/org.el
+++ b/lisp/org.el
@@ -3558,8 +3558,8 @@ (defcustom org-tags-sort-function nil
   :group 'org-tags
   :type '(choice
          (const :tag "No sorting" nil)
-         (const :tag "Alphabetical" string<)
-         (const :tag "Reverse alphabetical" string>)
+         (const :tag "Alphabetical" org-string-collate-lessp)
+         (const :tag "Reverse alphabetical" org-string-collate-greaterp)
          (function :tag "Custom function" nil)))
 
 (defvar org-tags-history nil
@@ -8803,7 +8803,7 @@ (defun org-sort-entries
             (t (error "Invalid sorting type `%c'" sorting-type))))
          nil
          (cond
-          ((= dcst ?a) 'string<)
+          ((= dcst ?a) 'org-string-collate-lessp)
           ((= dcst ?f)
            (or compare-func
                (and interactive?
@@ -8913,6 +8913,12 @@ (defun org-context-p (&rest contexts)
                    (org-in-item-p)))
       (goto-char pos))))
 
+;; Defined to provide a value for defcustom, since there is no
+;; string-collate-greaterp in Emacs.
+(defun org-string-collate-greaterp (s1 s2)
+  "Return non-nil if S1 is greater than S2 in collation order."
+  (not (org-string-collate-lessp s1 s2)))
+
 ;;;###autoload
 (defun org-run-like-in-org-mode (cmd)
   "Run a command, pretending that the current buffer is in Org mode.
diff --git a/testing/lisp/test-org.el b/testing/lisp/test-org.el
index cb21cda47..ec4535551 100644
--- a/testing/lisp/test-org.el
+++ b/testing/lisp/test-org.el
@@ -2927,6 +2927,11 @@
            (org-sort-entries nil ?a)
            (buffer-string)))))
 
+(ert-deftest test-org/string-collate-greaterp ()
+  "Test `org-string-collate-greaterp' specifications."
+  (should (org-string-collate-greaterp "def" "abc"))
+  (should-not (org-string-collate-greaterp "abc" "def")))
+
 (ert-deftest test-org/file-contents ()
   "Test `org-file-contents' specifications."
   ;; Open files.
-- 
2.16.1