Support the PostgreSQL domain

[Leo-XM-Zeng]

Domain types are basically user defined aliases of existing types. This starts supporting columns of such domain types pg_duckdb. One interesting thing is that domain types can also contain constraints, e.g. "an int that is less than 10". This doesn't really matter for reading them though, their actual representation is still always the same as the underlying type. It also doesn't matter when doing operations on them, because Postgres already changes a domain type to its underlying representation automatically. So any constraints on the domain don't apply to a result of an operation (e.g. addition).

Fixes #514

[Leo-XM-Zeng]

I have simply merged and updated the project code. Could you please review it for me again? I have thought about some parts and made some adjustments. Although there might be some places where I didn't follow your way of adjustment completely.

[JelteF]

Thanks for continuing to update this. Left some final comments. After that this can be merged.

[JelteF]

A bunch of these functions can throw Postgres errors (like get_typtype and getBaseType). They all need to be wrapped in PostgresFunctionGuard. It's probably easiest to create a small wrapper function like this:

Suggested change

	Oid
	GetBaseDuckColumnType(Oid attribute_typoid) {
	std::lock_guard<std::recursive_mutex> lock(pgduckdb::GlobalProcessLock::GetLock());
	Oid typoid = attribute_typoid;
	if (get_typtype(attribute_typoid) == TYPTYPE_DOMAIN) {
	/* It is a domain type that needs to be reduced to its base type */
	typoid = getBaseType(attribute_typoid);
	} else if (type_is_array(attribute_typoid)) {
	Oid eltoid = get_base_element_type(attribute_typoid);
	if (OidIsValid(eltoid) && get_typtype(eltoid) == TYPTYPE_DOMAIN) {
	/* When the member type of an array is domain, you need to build a base array type */
	typoid = get_array_type(getBaseType(eltoid));
	}
	}
	return typoid;
	}
	static Oid
	GetBaseDuckColumnType_C(Oid attribute_typoid) {
	std::lock_guard<std::recursive_mutex> lock(pgduckdb::GlobalProcessLock::GetLock());
	Oid typoid = attribute_typoid;
	if (get_typtype(attribute_typoid) == TYPTYPE_DOMAIN) {
	/* It is a domain type that needs to be reduced to its base type */
	typoid = getBaseType(attribute_typoid);
	} else if (type_is_array(attribute_typoid)) {
	Oid eltoid = get_base_element_type(attribute_typoid);
	if (OidIsValid(eltoid) && get_typtype(eltoid) == TYPTYPE_DOMAIN) {
	/* When the member type of an array is domain, you need to build a base array type */
	typoid = get_array_type(getBaseType(eltoid));
	}
	}
	return typoid;
	}
	Oid
	GetBaseDuckColumnType(Oid attribute_type_oid) {
	return PostgresFunctionGuard(GetBaseDuckColumnType_C, attribute_type_oid);
	}

[Leo-XM-Zeng]

Ok, thank you very much for your guidance. I feel that the lock in the c function seems to have no effect at this time, so I try to remove it.

[JelteF]

Totally agreed.