Function build_coercion_expression

src/backend/parser/parse_coerce.c:882–1045

* build_coercion_expression() * Construct an expression tree for applying a pg_cast entry. * * This is used for both type-coercion and length-coercion operations, * since there is no difference in terms of the calling convention. */

 * since there is no difference in terms of the calling convention.
 */
static Node *
build_coercion_expression(Node *node,
						  CoercionPathType pathtype,
						  Oid funcId,
						  Oid targetTypeId, int32 targetTypMod,
						  CoercionContext ccontext, CoercionForm cformat,
						  int location)
{
	int			nargs = 0;

	if (OidIsValid(funcId))
	{
		HeapTuple	tp;
		Form_pg_proc procstruct;

		tp = SearchSysCache1(PROCOID, ObjectIdGetDatum(funcId));
		if (!HeapTupleIsValid(tp))
			elog(ERROR, "cache lookup failed for function %u", funcId);
		procstruct = (Form_pg_proc) GETSTRUCT(tp);

		/*
		 * These Asserts essentially check that function is a legal coercion
		 * function.  We can't make the seemingly obvious tests on prorettype
		 * and proargtypes[0], even in the COERCION_PATH_FUNC case, because of
		 * various binary-compatibility cases.
		 */
		/* Assert(targetTypeId == procstruct->prorettype); */
		Assert(!procstruct->proretset);
		Assert(procstruct->prokind == PROKIND_FUNCTION);
		nargs = procstruct->pronargs;
		Assert(nargs >= 1 && nargs <= 3);
		/* Assert(procstruct->proargtypes.values[0] == exprType(node)); */
		Assert(nargs < 2 || procstruct->proargtypes.values[1] == INT4OID);
		Assert(nargs < 3 || procstruct->proargtypes.values[2] == BOOLOID);

		ReleaseSysCache(tp);
	}

	if (pathtype == COERCION_PATH_FUNC)
	{
		/* We build an ordinary FuncExpr with special arguments */
		FuncExpr   *fexpr;
		List	   *args;
		Const	   *cons;

		Assert(OidIsValid(funcId));

		args = list_make1(node);

		if (nargs >= 2)
		{
			/* Pass target typmod as an int4 constant */
			cons = makeConst(INT4OID,
							 -1,
							 InvalidOid,
							 sizeof(int32),
							 Int32GetDatum(targetTypMod),
							 false,