pg_upgrade: conditionally create cluster delete script

If users create tablespaces inside the old cluster directory, it is
impossible for the delete script to delete _only_ the old cluster files,
so don't create a script in that case, and issue a message to the user.

contrib/pg_upgrade/check.c

@@ -246,10 +246,17 @@ output_completion_banner(char *analyze_script_file_name,
 		"by pg_upgrade so, once you start the new server, consider running:\n"
 			   "    %s\n\n", analyze_script_file_name);
 
-	pg_log(PG_REPORT,
-		   "Running this script will delete the old cluster's data files:\n"
-		   "    %s\n",
-		   deletion_script_file_name);
+
+	if (deletion_script_file_name)
+		pg_log(PG_REPORT,
+			   "Running this script will delete the old cluster's data files:\n"
+			   "    %s\n",
+			   deletion_script_file_name);
+	else
+		pg_log(PG_REPORT,
+			   "Could not create a script to delete the old cluster's data\n"
+			   "files because user-defined tablespaces exist in the old cluster\n"
+			   "directory.  The old cluster's contents must be deleted manually.\n");
 }
 
 
@@ -584,14 +591,38 @@ create_script_for_old_cluster_deletion(char **deletion_script_file_name)
 {
 	FILE	   *script = NULL;
 	int			tblnum;
+	char		old_cluster_pgdata[MAXPGPATH];
 
 	*deletion_script_file_name = pg_malloc(MAXPGPATH);
 
-	prep_status("Creating script to delete old cluster");
-
 	snprintf(*deletion_script_file_name, MAXPGPATH, "delete_old_cluster.%s",
 			 SCRIPT_EXT);
 
+	/*
+	 *	Some users (oddly) create tablespaces inside the cluster data
+	 *	directory.  We can't create a proper old cluster delete script
+	 *	in that case.
+	 */
+	strlcpy(old_cluster_pgdata, old_cluster.pgdata, MAXPGPATH);
+	canonicalize_path(old_cluster_pgdata);
+	for (tblnum = 0; tblnum < os_info.num_old_tablespaces; tblnum++)
+	{
+		char		old_tablespace_dir[MAXPGPATH];
+		
+		strlcpy(old_tablespace_dir, os_info.old_tablespaces[tblnum], MAXPGPATH);
+		canonicalize_path(old_tablespace_dir);
+		if (path_is_prefix_of_path(old_cluster_pgdata, old_tablespace_dir))
+		{
+			/* Unlink file in case it is left over from a previous run. */
+			unlink(*deletion_script_file_name);
+			pg_free(*deletion_script_file_name);
+			*deletion_script_file_name = NULL;
+			return;
+		}
+	}
+
+	prep_status("Creating script to delete old cluster");
+
 	if ((script = fopen_priv(*deletion_script_file_name, "w")) == NULL)
 		pg_log(PG_FATAL, "Could not open file \"%s\": %s\n",
 			   *deletion_script_file_name, getErrorText(errno));