[Mono] implement static virtual methods in interfaces support

[lambdageek]

Implement support for static interface methods (csharp design: dotnet/csharplang#4436)

Known issues for .NET 7

• Disabled runtime tests

  runtime/src/tests/issues.targets

  Lines 1532 to 1537 in 6f30425

  	<ExcludeList Include="$(XunitTestBinBase)/Loader/classloader/StaticVirtualMethods/InterfaceVariance/**">
  	<Issue>Static virtual methods are not yet implemented in the Mono runtime.</Issue>
  	</ExcludeList>
  	<ExcludeList Include="$(XunitTestBinBase)/Loader/classloader/StaticVirtualMethods/NegativeTestCases/**">
  	<Issue>Static virtual methods are not yet implemented in the Mono runtime.</Issue>
  	</ExcludeList>

  • Triage and create individual issues
  • GenericContext [mono] Fix static virtual calls to generic methods from gshared code #66739
  • InterfaceVariance
  • NegativeTestCases
• [mono] Default Interface Implementation of Static Virtual Methods #67540
• [iOS][tvOS] Generic math IntPtr SByte and Int16 test failures #61920
• [mini] gshared: Implement static virtual method constrained.ldftn in the JIT #61672
• support AOT with generic sharing [mono][aot] Static virtual interface methods do not work with generic sharing #54910
• generic sharing failure with contstrained.call [mono][fullaot] Calling static virtual method from a generic method leads to "Attempting to JIT" error #65002 and Use generic math in System.Numerics.Vectors (#60365) #60905
• [mini] gshared static virtual methods: asserts !sig->has_type_parameters #65394
• [mono] gshared calls to non-generic static virtual interface method throw BadImageFormatException: Method has no body #65384
• Generic math does not work in WASM AOT #60447

Work items completed in .net 6:

• metadata updates
  • allow virtual on static methods in interfaces (can borrow this and JIT from partydonk prototype)
  • implement implements-all-static-interface-methods-of relation
  • possibly implement a static vtable for MonoClass (partydonk just puts static methods into the instance vtable and also does matching by name)
• unconditionally enable JIT support
  • constrained.call
• unconditionally enable interpreter support
  • constrained.call
  • constrained.ldftn
• support for the RuntimeFeature flag System.Runtime.CompilerServices.RuntimeFeature.VirtualStaticsInInterfaces #49905 for statics in interfaces.

---

Related CoreCLR work items over at #50129

[lambdageek]

@vargaz I think we're probably going to need static vtables. The ecma spec addendum says the static interface methods are going to be in the methodimpl table. The partydonk prototype completely ignores that and does matching by name. But we should just add a PROP_STATIC_VTABLE to InfrequentDataKind and just write down the impls from the MethodImpl in there when setting up the class. It can be completely separate from instance vtable layout. What do you think?

[davidwrighton]

There is now a working implmentation of all of this for CoreCLR checked in. Tests are disabled for mono, but otherwise it should be ready for implementation work to begin in Mono.

[lambdageek]

Zoltan implemented the initial version in #53465

Notably generic sharing does not work correctly, so the AOT support isn't quite there yet.

[lambdageek]

Remaining work pushed back to .net 7

[lambdageek]

@tannergooding @stephentoub I think in general Mono is in good shape to use static virtual methods in libraries. There may be bugs, but the only remaining completely unimplemented functionality that I'm aware of is the constrained . ldftn opcode - ie &T.StaticMethod and creation of delegates from static virtual methods from inside another generic method.

[SamMonoRT]

@lambdageek @BrzVlad - There are a couple unchecked ones. Are these required for 7.0 or can this be moved to 8.0.0 ?

[BrzVlad]

Moving to 8.0 since only corner cases from runtime tests are left implementing