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Skip checking COM objects on AOT #1662

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merged 2 commits into from
Jul 9, 2024
Merged

Skip checking COM objects on AOT #1662

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be4f586
Minor optimization in 'VtableEntries'
Sergio0694 Jul 4, 2024
fa86472
Minor tweak to 'IsRuntimeImplementedRCW'
Sergio0694 Jul 4, 2024
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14 changes: 10 additions & 4 deletions src/WinRT.Runtime/ComWrappersSupport.net5.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -572,6 +572,13 @@ static unsafe DefaultComWrappers()

private static unsafe bool IsRuntimeImplementedRCW(Type objType)
{
// Built-in COM interop isn't supported in AOT environments,
// so this method can only ever return false. Just inline it.
if (!RuntimeFeature.IsDynamicCodeCompiled)
{
return false;
}

Comment on lines +575 to +581
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How much does this really save? !IsDynamicCodeCompiled ==> built-in COM is not supported is a pretty major leap that might burn you in the future. What you'd want is Marshal.IsBuiltInComInteropSupported but such API doesn't exist.

This is basically assuming that IsDynamicCodeCompiled approximates IsNativeAot and that native AOT will never have built-in COM interop.

This approximation might be broken today if you put <PublishAot>true</PublishAot> and <BuiltInComInteropSupport>true</BuiltInComInteropSupport> to the project file and F5 launch the app (not Publish). In this configuration, RuntimeFeature.IsDynamicCodeCompiled is false, but built-in COM works. It is a terrible configuration to set, but it's possible.

Cc @jkoritzinsky @AaronRobinsonMSFT

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I would agree. I think adding some public check is possible. I also tend to agree with @MichalStrehovsky here, what is this actually saving in practice?

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This wasn't so much to save binary size per se, but rather to make the AOT-safe version of CsWinRT "stricter" and simpler. We have several parts of the code that we kept for backwards-compatibility (including built-in COM support), like being able to use old generated projections that are not fully trim-safe, etc.

Starting from .NET 8, we're saying that all that only applies to non-AOT scenarios. If you enable AOT, you also opt-in into the stricter mode, where we require you to only use updated projections everywhere (old projections wouldn't work with AOT anyway), and disable some more leftover features. Dropping built-in COM support entirely is part of that. We've added support for interop with generated COM interfaces starting with the .NET 8 TFM instead.

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The .NET 8 WinRT.Runtime (which implements generated COM interfaces) hasn't shipped though.

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Remember that AOT support hasn't shipped at all either, it's all experimental. We'll get there 🙂

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As long as we're in agreement that !RuntimeFeature.IsDynamicCodeCompiled doesn't imply built-in COM is disabled (neither today, nor in the future), consider this resolved.

bool isRcw = objType.IsCOMObject;
if (objType.IsGenericType)
{
Expand Down Expand Up @@ -692,10 +699,9 @@ public VtableEntries()
public VtableEntries(List<ComInterfaceEntry> entries, Type type)
{
Data = (ComInterfaceEntry*)RuntimeHelpers.AllocateTypeAssociatedMemory(type, sizeof(ComInterfaceEntry) * entries.Count);
for (int i = 0; i < entries.Count; i++)
{
Data[i] = entries[i];
}

CollectionsMarshal.AsSpan(entries).CopyTo(new Span<ComInterfaceEntry>(Data, entries.Count));

Count = entries.Count;
}
}
Expand Down