feat: Add Spark get_struct_field function

[WangGuangxin]

No description provided.

[netlify]

✅ Deploy Preview for meta-velox canceled.

Name	Link
🔨 Latest commit	437ea5c
🔍 Latest deploy log	https://app.netlify.com/sites/meta-velox/deploys/67a70042b667340009a30832

[jinchengchenghh]

Maybe you need to extend class FunctionCallToSpecialForm rather than SpecialForm, so as the implementation

[WangGuangxin]

I think there are different, one is for function register, the other is for function iteself

[rui-mo]

I'm wondering if we can implement the get_struct_field as a vector function then register it as a special form. What's the specific consideration here to implement it by extending SpecialForm?

[WangGuangxin]

@jinchengchenghh @rui-mo Comments addressed. Please help review this again when you are convenient

[rui-mo]

Thanks. Please also add documentation for this function.

[rui-mo]

I suppose we can move the checks inside constructSpecialForm and extract the constant value there. Some example in decimal round:

velox/velox/functions/sparksql/specialforms/DecimalRound.cpp

Lines 229 to 245 in 04bfdff

	VELOX_USER_CHECK_EQ(
	args[1]->type()->kind(),
	TypeKind::INTEGER,
	"The second argument of decimal_round should be of integer type.");
	auto constantExpr = std::dynamic_pointer_cast<exec::ConstantExpr>(args[1]);
	VELOX_USER_CHECK_NOT_NULL(
	constantExpr,
	"The second argument of decimal_round should be constant expression.");
	VELOX_USER_CHECK(
	constantExpr->value()->isConstantEncoding(),
	"The second argument of decimal_round should be wrapped in constant vector.");
	auto constantVector =
	constantExpr->value()->asUnchecked<ConstantVector<int32_t>>();
	VELOX_USER_CHECK(
	!constantVector->isNullAt(0),
	"The second argument of decimal_round is non-nullable.");
	scale = constantVector->valueAt(0);

[rui-mo]

I'm wondering if we can implement the get_struct_field as a vector function then register it as a special form. What's the specific consideration here to implement it by extending SpecialForm?