MetadataAggregator.GetGenerationHandle returns incorrect results for Guid heap handles

[tmat]

Description

guidSizes is incorrectly accumulated here:

https://github.com/dotnet/runtime/blob/main/src/libraries/System.Reflection.Metadata/src/System/Reflection/Metadata/Ecma335/MetadataAggregator.cs#L156

The size of GUID heap in aggregated metadata is the same as the size in the metadata delta where the GUID is used (unlike other heaps).

Regression?

No

Known Workarounds

See dotnet/metadata-tools#308

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[ericstj]

@tmat I see you have added a workaround. Are you aware of any downstream callers of this API (like Roslyn) who might be impacted by this?

Did you want to suggest a fix?

[tmat]

I see you have added a workaround. Are you aware of any downstream callers of this API (like Roslyn) who might be impacted by this?

I'm not aware of any. Not high priority to fix. Would be nice to remove the workaround.

Did you want to suggest a fix?

The line referenced above needs to be updated to no accumulate. Then some comments and tests need to be updated.
Should be easy to do.

[fabrimaz]

Hello, I am trying to read this thread and hope to understand it so that I could start contributing this as my first task.
I guess I will need a bit of guidance, though.
I am not sure if I got what the recently added workaround should be replaced with.

[fabrimaz]

Can you elaborate on The line referenced above needs to be updated to no accumulate.?
Do you mean something like guidSizes[r + 1] = deltaReaders[r].GetHeapSize(HeapIndex.Guid) / guidSize;?