Implement a dry-run mode for isolationtester

This mode prints out the permutations that would be run by the given
spec file, in the same format used by the permutation lines in spec
files.  This helps in building new spec files.

Author: Alexander Shulgin, with some tweaks by me

src/test/isolation/isolationtester.c

@@ -35,6 +35,10 @@ static PGconn **conns = NULL;
 static const char **backend_pids = NULL;
 static int	nconns = 0;
 
+/* In dry run only output permutations to be run by the tester. */
+static int	dry_run = false;
+
+static void run_testspec(TestSpec *testspec);
 static void run_all_permutations(TestSpec * testspec);
 static void run_all_permutations_recurse(TestSpec * testspec, int nsteps,
 							 Step ** steps);
@@ -69,20 +73,46 @@ main(int argc, char **argv)
 	int			i;
 	PGresult   *res;
 	PQExpBufferData wait_query;
+	int opt;
+
+	while ((opt = getopt(argc, argv, "n")) != -1)
+	{
+		switch (opt)
+		{
+			case 'n':
+				dry_run = true;
+				break;
+			default:
+				fprintf(stderr, "Usage: isolationtester [-n] [CONNINFO]\n");
+				return EXIT_FAILURE;
+		}
+	}
 
 	/*
-	 * If the user supplies a parameter on the command line, use it as the
-	 * conninfo string; otherwise default to setting dbname=postgres and using
-	 * environment variables or defaults for all other connection parameters.
+	 * If the user supplies a non-option parameter on the command line, use it
+	 * as the conninfo string; otherwise default to setting dbname=postgres and
+	 * using environment variables or defaults for all other connection
+	 * parameters.
 	 */
-	if (argc > 1)
-		conninfo = argv[1];
+	if (argc > optind)
+		conninfo = argv[optind];
 	else
 		conninfo = "dbname = postgres";
 
 	/* Read the test spec from stdin */
 	spec_yyparse();
 	testspec = &parseresult;
+
+	/*
+	 * In dry-run mode, just print the permutations that would be run, and
+	 * exit.
+	 */
+	if (dry_run)
+	{
+		run_testspec(testspec);
+		return 0;
+	}
+
 	printf("Parsed test spec with %d sessions\n", testspec->nsessions);
 
 	/*
@@ -240,10 +270,7 @@ main(int argc, char **argv)
 	 * Run the permutations specified in the spec, or all if none were
 	 * explicitly specified.
 	 */
-	if (testspec->permutations)
-		run_named_permutations(testspec);
-	else
-		run_all_permutations(testspec);
+	run_testspec(testspec);
 
 	/* Clean up and exit */
 	for (i = 0; i < nconns; i++)
@@ -253,6 +280,19 @@ main(int argc, char **argv)
 
 static int *piles;
 
+/*
+ * Run the permutations specified in the spec, or all if none were
+ * explicitly specified.
+ */
+static void
+run_testspec(TestSpec *testspec)
+{
+	if (testspec->permutations)
+		run_named_permutations(testspec);
+	else
+		run_all_permutations(testspec);
+}
+
 /*
  * Run all permutations of the steps and sessions.
  */
@@ -437,6 +477,19 @@ run_permutation(TestSpec * testspec, int nsteps, Step ** steps)
 	int			i;
 	Step	   *waiting = NULL;
 
+	/*
+	 * In dry run mode, just display the permutation in the same format used by
+	 * spec files, and return.
+	 */
+	if (dry_run)
+	{
+		printf("permutation");
+		for (i = 0; i < nsteps; i++)
+			printf(" \"%s\"", steps[i]->name);
+		printf("\n");
+		return;
+	}
+
 	printf("\nstarting permutation:");
 	for (i = 0; i < nsteps; i++)
 		printf(" %s", steps[i]->name);
@@ -649,7 +702,7 @@ try_complete_step(Step *step, int flags)
 				}
 				/* Detail may contain xid values, so just show primary. */
 				step->errormsg = malloc(5 +
-										strlen(PQresultErrorField(res, PG_DIAG_SEVERITY)) + 
+										strlen(PQresultErrorField(res, PG_DIAG_SEVERITY)) +
 										strlen(PQresultErrorField(res,
 																  PG_DIAG_MESSAGE_PRIMARY)));
 				sprintf(step->errormsg, "%s:  %s",