Add support for reference projections #2143

manodasanW · 2025-12-07T03:00:01Z

With this change, projection projects need CsWinRTGenerateReferenceProjection set to true. When this is set, a reference assembly and a forwarder assembly is generated (replaces the output DLL that gets built).
Components would distribute both these binaries and with project references they would just flow through.
On the final app project which consumes all the reference projection assemblies, cswinrt is triggered to generate a merged projection of all of them. The forwarders are also included in the output folder which means any references to the projection DLL are forwarded to the merged projection DLL.
In the reference projections, we exclude the entire ABI namespace. This was achieved via changes to codewriters based on detecting a reference projection is being generated. The changes here could have been more scoped if we just built only a reference assembly with ProduceOnlyReferenceAssembly which is possible but that relied on an assumption that if we generated sources which referenced ABI namespaces that aren't there that they will continue to build like they do today and also have more msbuild target changes to enable (seen here). So, to keep it straight forward, we do the equivalent in codewriters instead.

Copilot

Pull request overview

This PR adds support for reference projections in CsWinRT, enabling a new build configuration where projection projects can generate reference assemblies and forwarder assemblies, with a merged projection created at the final application level.

Key Changes:

Adds new CsWinRTGenerateReferenceProjection property and CSWINRT_REFERENCE_PROJECTION conditional compilation symbol
Introduces code generation modifications to exclude ABI namespace types when generating reference projections
Implements new generator tools (cswinrtprojectiongen and cswinrtimplgen) with supporting infrastructure

Reviewed changes

Copilot reviewed 45 out of 45 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
`src/cswinrt/settings.h`	Adds `reference_projection` boolean flag to settings
`src/cswinrt/main.cpp`	Implements command-line argument parsing and conditional ABI namespace generation
`src/cswinrt/code_writers.h`	Modifies code writers to conditionally generate `throw null` stubs and exclude ABI-related attributes
`src/cswinrt/strings/ComInteropHelpers.cs`	Wraps interop helper implementations with preprocessor directives
`src/cswinrt/strings/additions/*`	Conditionally excludes marshaller attributes for reference projections
`src/WinRT.Projection.Generator/*`	New projection generator tool for creating merged projections
`src/RunCsWinRTGeneratorTask/*`	New MSBuild tasks for running generator tools
`nuget/Microsoft.Windows.CsWinRT.targets`	Configures build properties and targets for reference projection support
`src/cswinrt.slnx`	Updates solution configuration
`src/Directory.Packages.props`	Updates Roslyn package versions

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src/WinRT.Projection.Generator/Generation/ProjectionGenerator.Generate.cs

nuget/Microsoft.Windows.CsWinRT.CsWinRTGen.targets

src/WinRT.Projection.Generator/Errors/WellKnownImplException.cs

src/WinRT.Projection.Generator/Errors/WellKnownImplExceptions.cs

…Generate.cs Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

src/WinRT.Impl.Generator/Generation/ImplGenerator.cs

src/WinRT.Projection.Generator/Generation/ProjectionGenerator.Emit.cs

src/WinRT.Projection.Generator/Generation/ProjectionGenerator.cs

src/WinRT.Projection.Generator/WinRT.Projection.Generator.csproj

src/cswinrt/code_writers.h

…microsoft/CsWinRT into manodasanw/referenceProjection2

Sergio0694 · 2025-12-08T18:46:13Z

...ngs/additions/Microsoft.UI.Xaml.Media.Animation/Microsoft.UI.Xaml.Media.Animation.KeyTime.cs

    [WindowsRuntimeMetadata("Microsoft.UI")]
    [WindowsRuntimeClassName("Windows.Foundation.IReference<Microsoft.UI.Xaml.Media.Animation.KeyTime>")]


All of these attributes should also be hidden from reference assemblies, right?

Technically we use these in cswinrtgen right?

Yes but I feel like we should still find a way to hide them. In theory both the metadata and the runtime class name can be derived at compile time anyway. We could check if a type is a projected type just by checking if the defining assembly is a projection assembly, and the runtime class name we can just compute in 'cswinrtgen' easily, we already have most of the logic for it anyway. That would allow us to just keep these attributes in the merged projection and hide them from here.

src/WinRT.Projection.Generator/Generation/ProjectionGenerator.Emit.cs

Sergio0694 · 2025-12-09T19:57:15Z

src/WinRT.Interop.Generator/References/InteropReferences.cs

+    /// </summary>
+    public AssemblyReference WinRTProjection => field ??= new AssemblyReference(
+        name: "WinRT.Projection"u8,
+        version: new Version(0, 0, 0, 0),


Thinking this should rather match the .dll version with WinRT.Interop.dll? You can copy the logic we use for that.

Technically we can, but I don't pass the project dll to the projection generator today and it is generated differently from WinRT.Interop due to it uses the CSharpCompilation to do so. We can technically pass a parameter for the version and then add a version attribute which is passed to the CSharpCompilation if we want, but does it add any benefit?

src/WinRT.Interop.Generator/Helpers/GuidGenerator.cs

… by making this only build reference assemblies and then removing the constructors that reference it.

…ing implementation assemblies other than for projection DLLs

Introduces IsWindowsRuntimeReferenceAssembly property to check for the WindowsRuntimeReferenceAssemblyAttribute. Adds related metadata names to WellKnownMetadataNames for attribute detection.

Refined logic for filtering and processing assemblies in Interop and Impl generators, clarified XML documentation, and added comments to explain handling of Windows Runtime projections and implementation assemblies. Improved method signatures and parameter documentation for better maintainability and clarity.

Copilot

Pull request overview

Copilot reviewed 63 out of 63 changed files in this pull request and generated 15 comments.

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src/WinRT.Projection.Generator/Errors/WellKnownImplExceptions.cs

src/WinRT.Interop.Generator/Generation/InteropGenerator.DebugRepro.cs

src/RunCsWinRTGeneratorTask/RunCsWinRTMergedProjectionGenerator.cs

src/Tests/UnitTest/TestModuleInitializer.cs

src/WinRT.Interop.Generator/Generation/InteropGenerator.Discover.cs

src/WinRT.Projection.Generator/Resolvers/PathAssemblyResolver.cs

src/WinRT.Projection.Generator/Generation/ProjectionGeneratorArgs.Parsing.cs

Corrected minor typos in comments to consistently refer to 'assembly paths' and 'output assembly path' for improved clarity.

azure-pipelines · 2026-01-19T00:40:43Z

There was an error handling pipeline event f7a99059-766f-4842-a682-03c3361647ac.

manodasanW added 7 commits December 5, 2025 00:30

Add support for reference assembly

1cbef0a

Add generator for generating merged projection

ea29f1a

Try to fix build

d39f0af

Fix AOT

99704d0

Cleanup workarounds

2e7c611

Move to handling more of the reference projection and simplify targets

5df75b2

Fix incremental build

b1c9e93

manodasanW requested review from Sergio0694 and Copilot December 7, 2025 03:00

Copilot AI reviewed Dec 7, 2025

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manodasanW and others added 2 commits December 6, 2025 19:02

Update src/WinRT.Projection.Generator/Generation/ProjectionGenerator.…

53700da

…Generate.cs Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Update nuget/Microsoft.Windows.CsWinRT.CsWinRTGen.targets

12fe8d5

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Sergio0694 requested changes Dec 7, 2025

View reviewed changes

manodasanW added 5 commits December 7, 2025 18:58

Fix typemap not being used.

856ed29

Fix unit tests and get merged projection working

6856f16

PR feedback

76a89d6

Remove forwarder not needed anymore

28bfd9c

Merge branch 'manodasanw/referenceProjection2' of https://github.com/…

0ca3060

…microsoft/CsWinRT into manodasanw/referenceProjection2

Sergio0694 reviewed Dec 8, 2025

View reviewed changes

manodasanW added 2 commits December 8, 2025 15:44

PR feedback

590d62a

Cleanup InternalsVisisbleTo

9b2ddb9

Sergio0694 reviewed Dec 9, 2025

View reviewed changes

manodasanW and others added 8 commits January 15, 2026 16:57

Add PR feedback to remove references to WindowsRuntimeObjectReference…

9c0cc3a

… by making this only build reference assemblies and then removing the constructors that reference it.

Fix indenting

b7199c0

Simplify

c0043d7

Merge branch 'staging/3.0' into manodasanw/referenceProjection2

be5053c

Fix types missing in TypeSpec table due to using ref assemblies by us…

88b23f2

…ing implementation assemblies other than for projection DLLs

Merge branch 'staging/3.0' into manodasanw/referenceProjection2

3aa2d38

Remove accidental commit

a075d9f

Add support for detecting Windows Runtime reference assemblies

7e70a33

Introduces IsWindowsRuntimeReferenceAssembly property to check for the WindowsRuntimeReferenceAssemblyAttribute. Adds related metadata names to WellKnownMetadataNames for attribute detection.

Sergio0694 and others added 2 commits January 17, 2026 14:58

Remove app dll as it is not used by task

24e89f8

manodasanW requested review from Sergio0694 and Copilot January 18, 2026 02:31

Copilot started reviewing on behalf of manodasanW January 18, 2026 02:31 View session

Copilot AI reviewed Jan 18, 2026

View reviewed changes

manodasanW and others added 4 commits January 17, 2026 19:14

PR feedback of typos

57513f5

Fix typos in comments for assembly path references

53ff35c

Corrected minor typos in comments to consistently refer to 'assembly paths' and 'output assembly path' for improved clarity.

Merge branch 'staging/3.0' into manodasanw/referenceProjection2

cf8f0b5

Fix merge

ac8101c

manodasanW and others added 4 commits January 18, 2026 17:03

Couple more fixes to merge

0d186e7

Fix comments

5a0b7f3

Fix comments

bd1378c

Merge branch 'staging/3.0' into manodasanw/referenceProjection2

5233b21

		[WindowsRuntimeMetadata("Microsoft.UI")]
		[WindowsRuntimeClassName("Windows.Foundation.IReference<Microsoft.UI.Xaml.Media.Animation.KeyTime>")]

Add support for reference projections #2143

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azure-pipelines bot commented Jan 19, 2026

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