Decoding ECMA-335 generic types

[raffaeler]

Hi, I am trying to follow the x-lang approach to write the interop for nodejs using N-API.
I am only doing experiments and started working on the xlang ecma library. I can currently dump signatures for properties and methods but had some difficulty in decoding generic types such as Task and others.
Can someone point me to an example of decoding generic types?

Thank you!

[DefaultRyan]

Generic type definitions are pretty straightforward. xlang's TypeDef provides a GenericParam() method that will return a pair of iterators for a range of its declared GenericParam entries. This is where you get the generic param names - the K and V in IMap`2<K, V>.

Next is referring to those generic params inside your definition. Still not too complicated. Sticking with our example, xlang will parse the method signature for bool IMap`2<K, V>.HasKey(K) and produce a MethodDefSig where the return type refers to ElementType::Boolean and holds a single parameter, a GenericTypeIndex holding an index of 0, which refers to the owning type's (IMap) first generic parameter K.

The trickier part is references and instantiations of generic types. In xlang, this is handled by GenericTypeInstSig - its GenericType() and GenericArgs() methods return what you'd expect, the generic type being instantiated and the type args supplied in that instantiation.

Sticking with the IMap example, the method signature for IMapView`2<K, V> IMap`2<K, V>.GetView() says the return type is a GenericTypeInstSig that refers to IMapView`2, with two generic args: a couple GenericTypeIndex with index of 0 and 1.

Here's a bigger, more complex example. StringMap has the method First() that returns IIterator`1<IKeyValuePair`2<string, string>>. In xlang, this method's return type gives you a GenericTypeInstSig that refers to IIterator`1, with one generic arg - which is itself a GenericTypeInstSig that refers to IKeyValuePair`2 with two generic args, both of which are ElementType::String.

Hope that helps.

[raffaeler]

Thank you @DefaultRyan
Generics on Types: I could easily get the definitions. I did not expect iterators but your suggestion immediately brought the solution.

GenericTypeIndex: I stole the visitor in the tools, so I already got the GenericTypeIndex to retrieve the generic type from the owning type.

GenericTypeInstSig: Still no luck. In the visitor I have a "auto && type" and the intellisense does not help me in understanding what is that. I did not find a way to get the generic types from there.

Generic Method: There is a last case where T Mul<T>(T tx, T ty) is defined. When I call method.Signature() it throws with "Unrecognized ELEMENT_TYPE encountered" and ElementType is MVar (0x1E).

Could you help me for the last two cases?
Thanks!

[kennykerr]

I suspect you're using the metadata reader to read .NET metadata. We've only tested with WinRT metadata, which is a subset of .NET metadata (ELEMENT_TYPE_MVAR is not used by WinRT).

Regarding IntelliSense, have you tried the xlang.meta.natvis visualizer?

[raffaeler]

Hi @kennykerr, yes, I am trying to read .NET netstandard class library since I already worked on interfacing in-process .net core with nodejs.
If this is not possible, I will have to rely on .NET itself in order to build a C++ set of descriptors of the ECMA metadata for the assemblies ... weird but I don't see other solutions.

With regards to the Intellisense:

• currently there is no data at all (it does not even show the tooltip
• I dropped the cppwinrt.natvis and cppwinrtvisualizer.dll into the Visualizers folder, but could not see any real improvement. Did I miss something?

Thanks

[kennykerr]

I don't object to adding support for .NET metadata if it doesn't require major changes. We'd be happy to review a PR. 😉

@Scottj1s may have some tips on how to get the visualizer working. We also have plans to publish some more content on that. It's just very new.

If this is not possible, I will have to rely on .NET itself in order to build a C++ set of descriptors of the ECMA metadata for the assemblies ... weird but I don't see other solutions.

It might be helpful to understand what you are trying to achieve here. Keep in mind that the WinRT subset is that which is well defined across an ABI boundary. The rest is not necessarily stable. We can also chat in person at the MVP summit next week (if you're coming).

[raffaeler]

Sure I am available to add that support ... it mostly depends how much I can get familiar with the code.

I will be in Redmond starting from this Fri, so yes, let's continue the discussion face to face :)

[Scottj1s]

Unlike pure natvis scripts, which can just be copied into the visualizer folder, the cppwinrtvisualizer.dll (and natvis) must be installed via VSIX. You can build that VSIX yourself from src\package\vsix, and install it. This might be useful if you're using VS 2019, which we haven't release support for yet (expect a simultaneous RTM).

[raffaeler]

Thank you @Scottj1s
I built all the solutions using cmake, but still can't see any vsix in the tree. Should I build it manually or what?

[kennykerr]

I think you only need this for metadata visualization:

https://github.com/Microsoft/xlang/blob/master/src/library/xlang.meta.natvis

[raffaeler]

Thank you @kennykerr. It works and I can finally start seeing something interesting

[raffaeler]

@kennykerr Supporting the MVar is not hard (is the same of Var) but I see no method to get the generic parameters specific of a method.
I don't remember if WinRT support generic methods whose generic parameter is specific of the method and not of the owning class.
Is this the case?

[DefaultRyan]

WinRT does not support generic methods. Ryan

[DefaultRyan]

Like Kenny said, we'd be happy with getting support for generic methods to the metadata reader library. It just hasn't been a priority for us because generic methods don't exist in the WinRT type system.

Did the visualizer assist with cracking open the GenericTypeInstSig helper?

[devhawk]

FYI, there are a few updates to meta_reader in the devhawk/RGM branch. That branch is likely orphaned but I can pull the meta_reader changes into a new branch and get them merged in

[raffaeler]

Thank you @devhawk while I see no changes in the MVar implementation, it would be great.
Please let me know as soon as you merge it :)

I hope to find the time to create a pull request before the upcoming MVP Summit, but definitely not sure.