ComInterfaceGenerator bugs when 2 interfaces inherit from the same interface

[m-celikba]

Description

Consider the following code:

    [GeneratedComInterface, Guid("427CE02F-515A-4338-BE30-F70DA3ADAEC1")]
    public unsafe partial interface IRoot 
    {
        void MyMethod0();
    }

    [GeneratedComInterface, Guid("1AEE856E-6501-43C8-843B-8210B57DFD27")]
    public unsafe partial interface ItfA : IRoot
    {
        void MyMethod1();
    }

    [GeneratedComInterface, Guid("3264857C-BB23-418D-9528-1E4226F2FEA4")]
    public unsafe partial interface ItfB : IRoot
    {
        void MyMethod2();
    }

when IRoot is defined int the same assembly it works.

However when it is defined in another assembly, I get:

 CSC : warning CS8785: Generator 'ComInterfaceGenerator' failed to generate source. It will not contribute to the output and compilation errors may occur as a result. Exception was of type 'ArgumentException' with message 'An item with the same key has already been added.'.

Detailed msbuild output:

CSC : warning CS8785: Generator 'ComInterfaceGenerator' failed to generate source. It will not contribute to the output and compilation errors may occur as a result. Exception was of type 'ArgumentException' with message 'An item with the same key has already been added.'.
1>    System.ArgumentException: An item with the same key has already been added.
1>    at System.ThrowHelper.ThrowArgumentException(ExceptionResource resource)
1>    at System.Collections.Generic.Dictionary`2.Insert(TKey key, TValue value, Boolean add)
1>    at Microsoft.Interop.ComInterfaceContext.GetContexts(ImmutableArray`1 data, CancellationToken _)
1>    at Microsoft.CodeAnalysis.TransformNode`2.UpdateStateTable(Builder builder, NodeStateTable`1 previousTable, CancellationToken cancellationToken)

Debugging this shows:

Reproduction Steps

see above

Expected behavior

no exception raised

Actual behavior

see description the following exception is raised System.ArgumentException: An item with the same key has already been added.

Regression?

No response

Known Workarounds

No response

Configuration

No response

Other information

No response

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[AaronRobinsonMSFT]

@jkoritzinsky @jtschuster This seems odd. The number of interfaces that require other implementations shouldn't matter. Actually is this one of the issues we talked about where the base interface is in another assembly?

[m-celikba]

@AaronRobinsonMSFT
If the base interface is in another assembly and only one interface inherits from it, it works.
If the base interface is in another assembly and more than one interface inherits from it, it fails with ArgumentException

[jkoritzinsky]

This is a real bug in the "different aseembly" limited support we added.

Basically, that loop is the only place we import the base interfaces into our view. We should change that to do a try-add instead of a throwing Add.

[m-celikba]

@jkoritzinsky I have a local fix. I'd like to move on locally with this fix.
I can build the generator project but have 2 problems: the assembly version numbers are messed up and I'm wondering what's the best way to override one of the runtime dll (in this case the generator dll) in my projects.
Where can I learn more about these ?

[jkoritzinsky]

There's no good mechanism to override a generator dll shipped with the sdk with a local one. You would have to add some custom MSBuild targets to remove the one provided by the SDK and add your own.