strcoll: Remove incorrect STRDIFF-based optimization (Bug 18589).

The optimization introduced in commit
f13c2a8dff2329c6692a80176262ceaaf8a6f74e, causes regressions in
sorting for languages that have digraphs that change sort order, like
cs_CZ which sorts ch between h and i.

My analysis shows the fast-forwarding optimization in STRCOLL advances
through a digraph while possibly stopping in the middle which results
in a subsequent skipping of the digraph and incorrect sorting. The
optimization is incorrect as implemented and because of that I'm
removing it for 2.23, and I will also commit this fix for 2.22 where
it was originally introduced.

This patch reverts the optimization, introduces a new bug-strcoll2.c
regression test that tests both cs_CZ.UTF-8 and da_DK.ISO-8859-1 and
ensures they sort one digraph each correctly. The optimization can't be
applied without regressing this test.

Checked on x86_64, bug-strcoll2.c fails without this patch and passes
after. This will also get a fix on 2.22 which has the same bug.

1 files changed, 1 insertions, 3 deletions

diff --git a/locale/C-collate.c b/locale/C-collate.c
index d7f3c550a5..06dfdfaad5 100644
--- a/locale/C-collate.c
+++ b/locale/C-collate.c
@@ -144,8 +144,6 @@ const struct __locale_data _nl_C_LC_COLLATE attribute_hidden =
     /* _NL_COLLATE_COLLSEQWC */
     { .string = (const char *) collseqwc },
     /* _NL_COLLATE_CODESET */
-    { .string = _nl_C_codeset },
-    /* _NL_COLLATE_ENCODING_TYPE */
-    { .word = __cet_8bit }
+    { .string = _nl_C_codeset }
   }
 };