exec_eval_simple_expr() needs to do CommandCounterIncrement() not just

GetTransactionSnapshot() to ensure ActiveSnapshot advances properly.
Sigh.  Extend regression test so it reveals this error too.

3 files changed, 19 insertions, 1 deletions

diff --git a/src/pl/plpgsql/src/pl_exec.c b/src/pl/plpgsql/src/pl_exec.c
index f14b24056a..d81da83747 100644
--- a/src/pl/plpgsql/src/pl_exec.c
+++ b/src/pl/plpgsql/src/pl_exec.c
@@ -3631,7 +3631,7 @@ exec_eval_simple_expr(PLpgSQL_execstate *estate,
 
 	/*
 	 * We have to do some of the things SPI_execute_plan would do,
-	 * in particular adjust ActiveSnapshot if we are in a non-read-only
+	 * in particular advance the snapshot if we are in a non-read-only
 	 * function.  Without this, stable functions within the expression
 	 * would fail to see updates made so far by our own function.
 	 */
@@ -3644,7 +3644,11 @@ exec_eval_simple_expr(PLpgSQL_execstate *estate,
 
 		oldcontext = MemoryContextSwitchTo(econtext->ecxt_per_tuple_memory);
 		if (!estate->readonly_func)
+		{
+			CommandCounterIncrement();
 			ActiveSnapshot = CopySnapshot(GetTransactionSnapshot());
+		}
+
 		/*
 		 * Finally we can call the executor to evaluate the expression
 		 */
diff --git a/src/test/regress/expected/plpgsql.out b/src/test/regress/expected/plpgsql.out
index 1f11bbb75c..10df82cfc2 100644
--- a/src/test/regress/expected/plpgsql.out
+++ b/src/test/regress/expected/plpgsql.out
@@ -2089,5 +2089,17 @@ select sp_add_user('user2');
           -1
 (1 row)
 
+select sp_add_user('user3');
+ sp_add_user 
+-------------
+           3
+(1 row)
+
+select sp_add_user('user3');
+ sp_add_user 
+-------------
+          -1
+(1 row)
+
 drop function sp_add_user(text);
 drop function sp_id_user(text);
diff --git a/src/test/regress/sql/plpgsql.sql b/src/test/regress/sql/plpgsql.sql
index 48618b9508..62aa354347 100644
--- a/src/test/regress/sql/plpgsql.sql
+++ b/src/test/regress/sql/plpgsql.sql
@@ -1802,6 +1802,8 @@ end$$ language plpgsql;
 select sp_add_user('user1');
 select sp_add_user('user2');
 select sp_add_user('user2');
+select sp_add_user('user3');
+select sp_add_user('user3');
 
 drop function sp_add_user(text);
 drop function sp_id_user(text);