Document behavior of collation on Cygwin

* test/automated/fns-tests.el (fns-tests-collate-sort): Mark as
expected failure on Cygwin.
* doc/lispref/strings.texi (Text Comparison): Document that
punctuation and whitespace are not ignored for sorting on Cygwin.

2 files changed, 7 insertions, 2 deletions

diff --git a/doc/lispref/strings.texi b/doc/lispref/strings.texi
index 143de82d9a..f8685d9312 100644
--- a/doc/lispref/strings.texi
+++ b/doc/lispref/strings.texi
@@ -584,8 +584,8 @@ determined by the lexicographic order of the characters contained in
 relations between these characters.  Usually, it is defined by the
 @var{locale} environment Emacs is running with.
 
-For example, punctuation and whitespace characters might be considered
-less significant for @ref{Sorting,,sorting}.
+For example, punctuation and whitespace characters might be ignored
+for sorting (@pxref{Sequence Functions}):
 
 @example
 @group
@@ -594,6 +594,9 @@ less significant for @ref{Sorting,,sorting}.
 @end group
 @end example
 
+This behavior is system-dependent; punctuation and whitespace are
+never ignored on Cygwin, regardless of locale.
+
 The optional argument @var{locale}, a string, overrides the setting of
 your current locale identifier for collation.  The value is system
 dependent; a @var{locale} @code{"en_US.UTF-8"} is applicable on POSIX
diff --git a/test/automated/fns-tests.el b/test/automated/fns-tests.el
index 7e9c1f1058..b5222db3ca 100644
--- a/test/automated/fns-tests.el
+++ b/test/automated/fns-tests.el
@@ -155,6 +155,8 @@
 	    (9 . "aaa") (9 . "zzz") (9 . "ppp") (9 . "fff")])))
 
 (ert-deftest fns-tests-collate-sort ()
+  ;; See https://lists.gnu.org/archive/html/emacs-devel/2015-10/msg02505.html.
+  :expected-result (if (eq system-type 'cygwin) :failed :passed)
   (skip-unless (fns-tests--collate-enabled-p))
 
   ;; Punctuation and whitespace characters are relevant for POSIX.