Function get_func_expr

src/backend/utils/adt/ruleutils.c:10009–10100

* get_func_expr - Parse back a FuncExpr node */

 * get_func_expr			- Parse back a FuncExpr node
 */
static void
get_func_expr(FuncExpr *expr, deparse_context *context,
			  bool showimplicit)
{
	StringInfo	buf = context->buf;
	Oid			funcoid = expr->funcid;
	Oid			argtypes[FUNC_MAX_ARGS];
	int			nargs;
	List	   *argnames;
	bool		use_variadic;
	ListCell   *l;

	/*
	 * If the function call came from an implicit coercion, then just show the
	 * first argument --- unless caller wants to see implicit coercions.
	 */
	if (expr->funcformat == COERCE_IMPLICIT_CAST && !showimplicit)
	{
		get_rule_expr_paren((Node *) linitial(expr->args), context,
							false, (Node *) expr);
		return;
	}

	/*
	 * If the function call came from a cast, then show the first argument
	 * plus an explicit cast operation.
	 */
	if (expr->funcformat == COERCE_EXPLICIT_CAST ||
		expr->funcformat == COERCE_IMPLICIT_CAST)
	{
		Node	   *arg = linitial(expr->args);
		Oid			rettype = expr->funcresulttype;
		int32		coercedTypmod;

		/* Get the typmod if this is a length-coercion function */
		(void) exprIsLengthCoercion((Node *) expr, &coercedTypmod);

		get_coercion_expr(arg, context,
						  rettype, coercedTypmod,
						  (Node *) expr);

		return;
	}

	/*
	 * If the function was called using one of the SQL spec's random special
	 * syntaxes, try to reproduce that.  If we don't recognize the function,
	 * fall through.
	 */
	if (expr->funcformat == COERCE_SQL_SYNTAX)
	{
		if (get_func_sql_syntax(expr, context))
			return;
	}

	/*
	 * Normal function: display as proname(args).  First we need to extract
	 * the argument datatypes.