Function exprIsLengthCoercion

src/backend/nodes/nodeFuncs.c:523–588

* exprIsLengthCoercion * Detect whether an expression tree is an application of a datatype's * typmod-coercion function. Optionally extract the result's typmod. * * If coercedTypmod is not NULL, the typmod is stored there if the expression * is a length-coercion function, else -1 is stored there. * * Note that a combined type-and-length coercion will be treated as a * length coercion by

 * length coercion by this routine.
 */
bool
exprIsLengthCoercion(const Node *expr, int32 *coercedTypmod)
{
	if (coercedTypmod != NULL)
		*coercedTypmod = -1;	/* default result on failure */

	/*
	 * Scalar-type length coercions are FuncExprs, array-type length coercions
	 * are ArrayCoerceExprs
	 */
	if (expr && IsA(expr, FuncExpr))
	{
		const FuncExpr *func = (const FuncExpr *) expr;
		int			nargs;
		Const	   *second_arg;

		/*
		 * If it didn't come from a coercion context, reject.
		 */
		if (func->funcformat != COERCE_EXPLICIT_CAST &&
			func->funcformat != COERCE_IMPLICIT_CAST)
			return false;

		/*
		 * If it's not a two-argument or three-argument function with the
		 * second argument being an int4 constant, it can't have been created
		 * from a length coercion (it must be a type coercion, instead).
		 */
		nargs = list_length(func->args);
		if (nargs < 2 || nargs > 3)
			return false;

		second_arg = (Const *) lsecond(func->args);
		if (!IsA(second_arg, Const) ||
			second_arg->consttype != INT4OID ||
			second_arg->constisnull)
			return false;

		/*
		 * OK, it is indeed a length-coercion function.
		 */
		if (coercedTypmod != NULL)
			*coercedTypmod = DatumGetInt32(second_arg->constvalue);

		return true;
	}

	if (expr && IsA(expr, ArrayCoerceExpr))
	{
		const ArrayCoerceExpr *acoerce = (const ArrayCoerceExpr *) expr;

		/* It's not a length coercion unless there's a nondefault typmod */
		if (acoerce->resulttypmod < 0)
			return false;

		/*
		 * OK, it is indeed a length-coercion expression.
		 */