Fix broken collation-aware searches in SP-GiST text opclass.

spg_text_leaf_consistent() supposed that it should compare only
Min(querylen, entrylen) bytes of the two strings, and then deal with
any excess bytes in one string or the other by assuming the longer
string is greater if the prefixes are equal.  Quite aside from the
fact that that's just wrong in some locales (e.g., 'ch' is not less
than 'd' in cs_CZ), it also risked passing incomplete multibyte
characters to strcoll(), with ensuing bad results.

Instead, just pass the full strings to varstr_cmp, and let it decide
what to do about unequal-length strings.

Fortunately, this error doesn't imply any index corruption, it's just
that searches might return the wrong set of entries.

Per report from Emre Hasegeli, though this is not his patch.
Thanks to Peter Geoghegan for review and discussion.

This code was born broken, so back-patch to all supported branches.
In HEAD, I failed to resist the temptation to do a bit of cosmetic
cleanup/pgindent'ing on 710d90da1, too.

Discussion: https://postgr.es/m/CAE2gYzzb6K51VnTq5i5p52z+j9p2duEa-K1T3RrC_GQEynAKEg@mail.gmail.com

diff --git a/src/backend/access/spgist/spgtextproc.c b/src/backend/access/spgist/spgtextproc.c
index f7703cf134af3e05afbc0708d4d37d85e0411cf4..b42bf3eda21306a0a13c0f6a4010e2073d1a0557 100644 (file)
--- a/src/backend/access/spgist/spgtextproc.c
+++ b/src/backend/access/spgist/spgtextproc.c
@@ -603,22 +603,22 @@ spg_text_leaf_consistent(PG_FUNCTION_ARGS)
                        /* If asserts enabled, verify encoding of reconstructed string */
                        Assert(pg_verifymbstr(fullValue, fullLen, false));
 
-                       r = varstr_cmp(fullValue, Min(queryLen, fullLen),
-                                                  VARDATA_ANY(query), Min(queryLen, fullLen),
+                       r = varstr_cmp(fullValue, fullLen,
+                                                  VARDATA_ANY(query), queryLen,
                                                   PG_GET_COLLATION());
                }
                else
                {
                        /* Non-collation-aware comparison */
                        r = memcmp(fullValue, VARDATA_ANY(query), Min(queryLen, fullLen));
-               }
 
-               if (r == 0)
-               {
-                       if (queryLen > fullLen)
-                               r = -1;
-                       else if (queryLen < fullLen)
-                               r = 1;
+                       if (r == 0)
+                       {
+                               if (queryLen > fullLen)
+                                       r = -1;
+                               else if (queryLen < fullLen)
+                                       r = 1;
+                       }
                }
 
                switch (strategy)