Abort pgbench if script end is reached with an open pipeline

When a pipeline is opened with \startpipeline and not closed, pgbench
will either error on the next transaction with a "already in pipeline
mode" error or successfully end if this was the last transaction --
despite not sending anything that was piped in the pipeline.

Make it an error to reach end of script is reached while there's an
open pipeline.

Backpatch to 14, where pgbench got support for pipelines.

Author: Anthonin Bonnefoy <anthonin.bonnefoy@datadoghq.com>
Reported-by: Michael Paquier <michael@paquier.xyz>
Discussion: https://postgr.es/m/Za4IObZkDjrO4TcS@paquier.xyz

src/bin/pgbench/pgbench.c

@@ -3763,10 +3763,21 @@ advanceConnectionState(TState *thread, CState *st, StatsData *agg)
 			case CSTATE_START_COMMAND:
 				command = sql_script[st->use_file].commands[st->command];
 
-				/* Transition to script end processing if done */
+				/*
+				 * Transition to script end processing if done, but close up
+				 * shop if a pipeline is open at this point.
+				 */
 				if (command == NULL)
 				{
-					st->state = CSTATE_END_TX;
+					if (PQpipelineStatus(st->con) == PQ_PIPELINE_OFF)
+						st->state = CSTATE_END_TX;
+					else
+					{
+						pg_log_error("client %d aborted: end of script reached with pipeline open",
+									 st->id);
+						st->state = CSTATE_ABORTED;
+					}
+
 					break;
 				}
 

src/bin/pgbench/t/001_pgbench_with_server.pl

@@ -876,6 +876,34 @@ select 1 \gset f
 }
 	});
 
+# Try \startpipeline without \endpipeline in a single transaction
+$node->pgbench(
+	'-t 1 -n -M extended',
+	2,
+	[],
+	[qr{end of script reached with pipeline open}],
+	'error: call \startpipeline without \endpipeline in a single transaction',
+	{
+		'001_pgbench_pipeline_5' => q{
+-- startpipeline only with single transaction
+\startpipeline
+}
+	});
+
+# Try \startpipeline without \endpipeline
+$node->pgbench(
+	'-t 2 -n -M extended',
+	2,
+	[],
+	[qr{end of script reached with pipeline open}],
+	'error: call \startpipeline without \endpipeline',
+	{
+		'001_pgbench_pipeline_6' => q{
+-- startpipeline only
+\startpipeline
+}
+	});
+
 # Working \startpipeline in prepared query mode with serializable
 $node->pgbench(
 	'-c4 -t 10 -n -M prepared',