psql: complain if pg_dump custom-format is detected

Apparently, this is a very common mistake for users to make; it is
better to have it fail reasonably rather than throw potentially a large
number of errors.  Since we have a magic string at the start of the
file, we can detect the case easily and there's no other possible useful
behavior anyway.

Author: Craig Ringer

src/bin/psql/mainloop.c

@@ -175,6 +175,18 @@ MainLoop(FILE *source)
 		if (pset.lineno == 1 && pset.encoding == PG_UTF8 && strncmp(line, "\xef\xbb\xbf", 3) == 0)
 			memmove(line, line + 3, strlen(line + 3) + 1);
 
+		/* Detect attempts to run custom-format dumps as SQL scripts */
+		if (pset.lineno == 1 && !pset.cur_cmd_interactive &&
+			strncmp(line, "PGDMP", 5) == 0)
+		{
+			free(line);
+			puts(_("The input is a PostgreSQL custom-format dump.\n"
+				   "Use the pg_restore command-line client to restore this dump to a database.\n"));
+			fflush(stdout);
+			successResult = EXIT_FAILURE;
+			break;
+		}
+
 		/* nothing left on line? then ignore */
 		if (line[0] == '\0' && !psql_scan_in_quote(scan_state))
 		{