Bug #12375190: UPDATEXML CRASHES ON SIMPLE INPUTS

The XPATH implementation was not handling correctly the XPATH 
production #19 
(http://www.w3.org/TR/1999/REC-xpath-19991116/#node-sets),
namely

PathExpr ::= | FilterExpr '/' RelativeLocationPath
                    | FilterExpr '//' RelativeLocationPath

It was lacking context for the RelativeLocationPath and it was just 
ignoring the second slash instead of treating it as a different axis 
specifier.
Fixed the above two problems and added a test case.

mysql-test/r/xml.result

@@ -1144,5 +1144,23 @@ SELECT UPDATEXML(CONVERT('' USING swe7), TRUNCATE('',1), 0);
 UPDATEXML(CONVERT('' USING swe7), TRUNCATE('',1), 0)
 NULL
 #
+# Bug#12375190: UPDATEXML CRASHES ON SIMPLE INPUTS
+#
+SELECT UPDATEXML('','(a)/a','');
+UPDATEXML('','(a)/a','')
+
+SELECT UPDATEXML('<a><a>x</a></a>','(a)/a','<b />');
+UPDATEXML('<a><a>x</a></a>','(a)/a','<b />')
+<a><b /></a>
+SELECT UPDATEXML('<a><c><a>x</a></c></a>','(a)/a','<b />');
+UPDATEXML('<a><c><a>x</a></c></a>','(a)/a','<b />')
+<a><c><a>x</a></c></a>
+SELECT UPDATEXML('<a><c><a>x</a></c></a>','(a)//a','<b />');
+UPDATEXML('<a><c><a>x</a></c></a>','(a)//a','<b />')
+<a><c><b /></c></a>
+SELECT ExtractValue('<a><a>aa</a><b>bb</b></a>','(a)/a|(a)/b');
+ExtractValue('<a><a>aa</a><b>bb</b></a>','(a)/a|(a)/b')
+aa bb
+#
 # End of 5.5 tests
 #

mysql-test/t/xml.test

@@ -664,6 +664,15 @@ SELECT ExtractValue(CONVERT('<\"', BINARY(10)), 1);
 SET NAMES latin1;
 SELECT UPDATEXML(CONVERT('' USING swe7), TRUNCATE('',1), 0);
 
+--echo #
+--echo # Bug#12375190: UPDATEXML CRASHES ON SIMPLE INPUTS
+--echo #
+SELECT UPDATEXML('','(a)/a','');
+SELECT UPDATEXML('<a><a>x</a></a>','(a)/a','<b />');
+SELECT UPDATEXML('<a><c><a>x</a></c></a>','(a)/a','<b />');
+SELECT UPDATEXML('<a><c><a>x</a></c></a>','(a)//a','<b />');
+SELECT ExtractValue('<a><a>aa</a><b>bb</b></a>','(a)/a|(a)/b');
+
 --echo #
 --echo # End of 5.5 tests
 --echo #

sql/item_xmlfunc.cc

@@ -1973,6 +1973,9 @@ static int my_xpath_parse_UnionExpr(MY_XPATH *xpath)
 static int
 my_xpath_parse_FilterExpr_opt_slashes_RelativeLocationPath(MY_XPATH *xpath)
 {
+  Item *context= xpath->context;
+  int rc;
+
   if (!my_xpath_parse_FilterExpr(xpath))
     return 0;
 
@@ -1986,8 +1989,22 @@ my_xpath_parse_FilterExpr_opt_slashes_RelativeLocationPath(MY_XPATH *xpath)
     return 0;
   }
 
-  my_xpath_parse_term(xpath, MY_XPATH_LEX_SLASH);
-  return my_xpath_parse_RelativeLocationPath(xpath);
+  /*
+    The context for the next relative path is the nodeset
+    returned by FilterExpr
+  */
+  xpath->context= xpath->item;
+
+  /* treat double slash (//) as /descendant-or-self::node()/ */
+  if (my_xpath_parse_term(xpath, MY_XPATH_LEX_SLASH))
+    xpath->context= new Item_nodeset_func_descendantbyname(xpath->context,
+                                                           "*", 1, xpath->pxml, 1);
+  rc= my_xpath_parse_RelativeLocationPath(xpath);
+
+  /* push back the context and restore the item */
+  xpath->item= xpath->context;
+  xpath->context= context;
+  return rc;
 }
 static int my_xpath_parse_PathExpr(MY_XPATH *xpath)
 {