GenAPI incorrectly generates collection-based interface implementation

[mthalman]

When targeting System.Collections.Immutable.1.7.1, GenAPI generates a class implementation which doesn't implement the interface that its member explicitly attempts to implement.

This illustrates the issue:

public sealed partial class ImmutableHashSet<T> : IEnumerable, ICollection
{
    bool Generic.ICollection<T>.IsReadOnly { get { throw null; } }
}

This results in a build error:

error CS0540: 'ImmutableHashSet<T>.ICollection<T>.IsReadOnly': containing type does not implement interface 'ICollection<T>'

You can see that the generated class doesn't implement any of the generic interfaces that it should:

public sealed class ImmutableHashSet<T> : IImmutableSet<T>, IReadOnlyCollection<T>, IEnumerable<T>, IEnumerable, IHashKeyCollection<T>, ICollection<T>, ISet<T>, ICollection, IStrongEnumerable<T, ImmutableHashSet<T>.Enumerator>

[mthalman]

There are other issues besides the list of interfaces the class implements as well.

It generates explicit Item, get_Item, and set_Item property interface implementations that shouldn't exist:

public partial struct ImmutableArray<T> : IEnumerable, IEquatable<ImmutableArray<T>>, IList, ICollection, IStructuralComparable, IStructuralEquatable
{
    T Generic.IList<T>.Item { get { throw null; } set { } }
    object IList.get_Item(int index) { throw null; }
    void IList.set_Item(int index, object value) { }
}

[mthalman]

@ViktorHofer - There are quite a few issues here in how the code is generated for these classes that implement collection interfaces. I had to give up making manual updates in SBRP because there were just too many. I'm going to wait until this is fixed in the tooling. You can see the progress I had made with updates to the generated code in this commit: mthalman/source-build-reference-packages@1448c8d

[mthalman]

cc @andriipatsula

[andriipatsula]

There is a duplicated issue #31484. And a PR: #31545 that solves the problem.

[mthalman]

@andriipatsula - The filtering out of interfaces is one thing. But what about the IList<T>.Item and IList.get_Item that I mention above?

[andriipatsula]

Viktor is OOF for the next week+. I saw these types of issues when symbol resolution fails. I'll try to debug tomorrow.
If I am not mistaken, there should be int Generic.IList<T>.this[int index] instead of Generic.IList<T>.*Item.

[MichaelSimons]

I have also encountered these issue while trying to cleanup net4* packages. I am encountering this on many packages which renders the tooling pretty useless for this exercise.

[andriipatsula]

T System.Collections.Immutable.ImmutableArray<T>.System.Collections.Generic.IList<T>.Item[System.Int32 index] { get; set; }

is a member that is present in the symbol metadata for the IList<T>, IList, IReadOnlyList<T> (etc.) interfaces. The SyntaxGenerator generates three members:

  T Generic.IList<T>.Item { get { throw null; } set { } }
  object IList.get_Item(int index) { throw null; }
  void IList.set_Item(int index, object value) { }

It appears to be a minor bug or a side effect, and filtering them out should be a simple task (see comment).

[andriipatsula]

There are next 4 members(indexers) in the ImmutableArray<T>:

/*1*/ public T this[int index] { get { throw null; } }
/*2*/ T System.Collections.Generic.IList<T>.this[int index] { get { throw null; } set { } }
/*3*/ T System.Collections.Generic.IReadOnlyList<T>.this[int index] { get { throw null; } }
/*4*/ object System.Collections.IList.this[int index] { get { throw null; } set { } }

The indexer №1 is generated correctly and indexers №2, №3, №4 - not.
https://learn.microsoft.com/en-us/dotnet/api/system.collections.generic.ilist-1.item?view=net-8.0#system-collections-generic-ilist-1-item(system-int32)
For some reason, the SyntaxGenerator does not generate the IList<T>.Item[Int32] property as an indexer (ExplicitInterfaceImplementation property).