Function exec_command_if

src/bin/psql/command.c:1639–1678

* \if -- beginning of an \if..\endif block * * is parsed as a boolean expression. Invalid expressions will emit a * warning and be treated as false. Statements that follow a false expression * will be parsed but ignored. Note that in the case where an \if statement * is itself within an inactive section of a block, then the entire inner * \if..\endif block will be parsed but

 * \if..\endif block will be parsed but ignored.
 */
static backslashResult
exec_command_if(PsqlScanState scan_state, ConditionalStack cstack,
				PQExpBuffer query_buf)
{
	if (conditional_active(cstack))
	{
		/*
		 * First, push a new active stack entry; this ensures that the lexer
		 * will perform variable substitution and backtick evaluation while
		 * scanning the expression.  (That should happen anyway, since we know
		 * we're in an active outer branch, but let's be sure.)
		 */
		conditional_stack_push(cstack, IFSTATE_TRUE);

		/* Remember current query state in case we need to restore later */
		save_query_text_state(scan_state, cstack, query_buf);

		/*
		 * Evaluate the expression; if it's false, change to inactive state.
		 */
		if (!is_true_boolean_expression(scan_state, "\\if expression"))
			conditional_stack_poke(cstack, IFSTATE_FALSE);
	}
	else
	{
		/*
		 * We're within an inactive outer branch, so this entire \if block
		 * will be ignored.  We don't want to evaluate the expression, so push
		 * the "ignored" stack state before scanning it.
		 */
		conditional_stack_push(cstack, IFSTATE_IGNORED);

		/* Remember current query state in case we need to restore later */
		save_query_text_state(scan_state, cstack, query_buf);

		ignore_boolean_expression(scan_state);
	}

	return PSQL_CMD_SKIP_LINE;
}

/*
 * \elif <expr> -- alternative branch in an \if..\endif block