Revert a change accidentally included in an unrelated commit.

This partially reverts:

commit 76e3c115
Author: Vincent Pelletier <vincent@nexedi.com>
Date:   Mon Dec 10 16:40:48 2018 +0900

    Base: Fix isAncestryIndexable implementation.

as it accidentally carried over a totally unrelated (and unfinished)
change.

product/ZMySQLDA/db.py

@@ -354,20 +354,44 @@ class DB(TM):
         try:
             self.db.query(query)
         except OperationalError, m:
-            __traceback_info__ = (str(m), query)
-            if m[0] in hosed_connection and self._use_TM and allow_reconnect:
-                self._forceReconnection()
-                return self._query(query, allow_reconnect=False)
+            if m[0] in query_syntax_error:
+              raise OperationalError(m[0], '%s: %s' % (m[1], query))
             if m[0] in lock_error:
-                raise ConflictError
-            raise OperationalError
-        except ProgrammingError, exception:
-            __traceback_info__ = (str(exception), query)
-            # XXX sometimes, after a programming error, the database object
-            # gets fully broken and non-functional. So recover it by
-            # recreation.
+              raise ConflictError('%s: %s: %s' % (m[0], m[1], query))
+            if not allow_reconnect and self._use_TM or \
+              m[0] not in hosed_connection:
+                LOG('ZMySQLDA', ERROR, 'query failed: %s' % (query,))
+                raise
+            # Hm. maybe the db is hosed.  Let's restart it.
             self._forceReconnection()
-            raise ProgrammingError
+            self.db.query(query)
+        except ProgrammingError, exception:
+          LOG('ZMySQLDA', ERROR, 'query failed: %s' % (query,))
+          # XXX sometimes, after a programming error, the database object
+          # gets fully broken and non-functional. So recover it by
+          # recreation.
+          self._forceReconnection()
+          if exception[0] == ER.PARSE_ERROR:
+            # You have an error in your SQL syntax
+            # Replace MySQL brain dead error message with a more meaningful
+            # one. (MySQL only reports the SQL query *from* the error place,
+            # which strips important contextual information).
+            error_text = exception[1]
+            prefix, suffix = error_text.split("'", 1)
+            if prefix == "You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ":
+              sql, suffix = suffix.rsplit("'", 1)
+              try:
+                line_number = int(suffix.rsplit(' ', 1)[-1])
+              except TypeError:
+                pass
+              else:
+                reference_sql = query
+                split_reference_sql = reference_sql.split('\n')
+                candidate_sql = '\n'.join(split_reference_sql[line_number - 1:])
+                error_position = len(reference_sql) - len(candidate_sql) + candidate_sql.find(sql)
+                if error_position > -1:
+                  raise ProgrammingError(exception[0], "%s '%s' HERE '%s' %s" % (prefix, reference_sql[:error_position], reference_sql[error_position:], suffix))
+          raise exception
         return self.db.store_result()
 
     def query(self, query_string, max_rows=1000):