MDEV-14609 XA Transction unable to ROLLBACK TO SAVEPOINT

The function trans_rollback_to_savepoint(), unlike trans_savepoint(),
did not allow xa_state=XA_ACTIVE, so an attempt to do ROLLBCK TO SAVEPOINT
inside an XA transaction incorrectly returned an error
"...command cannot be executed ... in the ACTIVE state...".

Partially merging a MySQL patch:
  7fb5c47390311d9b1b5367f97cb8fedd4102dd05
  This is WL#7193 (Decouple THD and st_transactions)...

The currently merged part includes these changes:
- Introducing st_xid_state::check_has_uncommitted_xa()
- Reusing it in both trans_rollback_to_savepoint() and trans_savepoint(),
  so now both allow XA_ACTIVE.

1 files changed, 24 insertions, 0 deletions

diff --git a/sql/sql_class.h b/sql/sql_class.h
index f4be996c9a9..e8f50f13ebc 100644
--- a/sql/sql_class.h
+++ b/sql/sql_class.h
@@ -991,6 +991,30 @@ typedef struct st_xid_state {
   bool in_thd;
   /* Error reported by the Resource Manager (RM) to the Transaction Manager. */
   uint rm_error;
+
+  /**
+    Check that XA transaction has an uncommitted work. Report an error
+    to the user in case when there is an uncommitted work for XA transaction.
+
+    @return  result of check
+      @retval  false  XA transaction is NOT in state IDLE, PREPARED
+                      or ROLLBACK_ONLY.
+      @retval  true   XA transaction is in state IDLE or PREPARED
+                      or ROLLBACK_ONLY.
+  */
+
+  bool check_has_uncommitted_xa() const
+  {
+    if (xa_state == XA_IDLE ||
+        xa_state == XA_PREPARED ||
+        xa_state == XA_ROLLBACK_ONLY)
+    {
+      my_error(ER_XAER_RMFAIL, MYF(0), xa_state_names[xa_state]);
+      return true;
+    }
+    return false;
+  }
+
 } XID_STATE;
 
 extern mysql_mutex_t LOCK_xid_cache;