[FIRRTL] Fix type cast to look through type alias for type interfaces

[uenoku]

This fixes a bug that type_cast doesn't work well if a request type isTypeInterface.

[dtzSiFive]

Seems like good step forward, thanks! Let's keep in mind (as discussed, correct me if I have this wrong) that aliases won't appear to implement the interfaces their alias-ee does when non-FIRRTL code checks, so common infra or upstream code (FieldIDTypeInterface would be great example, probably not unrelated to why alias type always implements it?) will do wrong thing unless knows to use our FIRRTL check.. is there some way to somewhat generically handle this?

Looks like we don't use type interfaces presently really beyond our FieldIDTypeInterface, but it'd be good to not have this lurking as a problem.

Anyway this gets our own interface checks working, which is good, thanks!

[uenoku]

Let's keep in mind (as discussed, correct me if I have this wrong) that aliases won't appear to implement the interfaces their alias-ee does when non-FIRRTL code checks,

Yes, aliases doesn't inherit & implement interfaces of each alias-ee type. That being said currently BaseTypeAliasType implements FIeldIDInterface since BaseTypeAliasType is derived from a base type and base type is required to implement FieldIDInterface.

so common infra or upstream code (FieldIDTypeInterface would be great example, probably not unrelated to why alias type always implements it?) will do wrong thing unless knows to use our FIRRTL check.. is there some way to somewhat generically handle this?

No, currently not. Right now it's user responsibility to apply type_cast before passing types to utility (though currently base alias does implements FIeldIDInterface so there would be much less problem). To fix the issue entirely, I think we have to declare multiple type alias types which inherits primitive types and define type interfaces. I tried implementing that idea but there was still an issue with type interface and traits. It seems currently child type (alias type in our case) cannot automatically use interface implementation of interfaces so I gave up that implementation.

circt/include/circt/Dialect/FIRRTL/FIRRTLTypesImpl.td

Lines 47 to 55 in fa26d3f

	class TypeAliasType <string baseTypeName,
	list<Trait> traits,
	string storage = "AliasStorage<" # baseTypeName # "AliasType>">:
	FIRRTLImplType<baseTypeName # "Alias", [TypeAliasInterface] # traits,
	"::circt::firrtl::" # baseTypeName> {
	let summary = "type alias for " # baseTypeName;
	let parameters =
	(ins "ArrayAttr":$names, TypeParameter<"::circt::firrtl::" # baseTypeName,
	"An inner type">:$innerType);

circt/include/circt/Dialect/FIRRTL/FIRRTLTypesImpl.td

Lines 652 to 659 in fa26d3f

	// ----- Type definitions for Type Alias
	foreach i = [UIntImpl, SIntImpl, ClockTypeImpl, ResetTypeImpl, AsyncResetTypeImpl, AnalogTypeImpl, // Int
	BundleImpl, OpenBundleImpl, FVectorImpl, OpenVectorImpl, FEnumImpl, // Aggregates
	RefImpl, ListImpl, MapImpl, // Non-hardware
	/*BigIntImpl, StringImpl*/
	] in {
	def _#i#TypeAlias: TypeAliasType<i.typeName, []>;
	}