Bug: CppWinRTCopyWinMDToOutputDirectory: Outputs mismatch when merged WinMD name differs from RootNamespace

Version

2.0.220131.2

Summary

Problem

The CppWinRTCopyWinMDToOutputDirectory target has mismatched Inputs/Outputs:

• Inputs: @(_MdMergedOutput) — the merged WinMD (e.g. Contoso.Core.winmd)
• Outputs: $(CppWinRTProjectWinMD) — resolves to $(OutDir)$(RootNamespace).winmd (e.g. Contoso.App.winmd)
• Copy DestinationFiles: @(_MdMergedOutput->'$(OutDir)%(Filename)%(Extension)') — writes the correct file

When the merged WinMD filename differs from $(RootNamespace), the declared Output never matches the actual file written. MSBuild always considers the target out-of-date, causing cascading rebuilds in all downstream projects (.xbf copies, PRI regen, MSIX packaging, C# recompiles via CsWinRT).

This happens when a project's IDL files use a different root namespace than the project's RootNamespace property (e.g. IDL uses Contoso.Core but the project's RootNamespace is Contoso.App).

Fix

Change Outputs to a 1:1 transform matching the Copy task:

Outputs="@(_MdMergedOutput->'$(OutDir)%(Filename)%(Extension)')"

Also update FileWrites to match

Reproducible example

Expected behavior

No response

Actual behavior

No response

Additional comments

No response

Locate the build target that defines CppWinRTCopyWinMDToOutputDirectory and inspect its Inputs, Outputs, Copy destination, and FileWrites metadata. Align the declared output and FileWrites entries with the copied merged WinMD filename, then verify that repeated builds and downstream packaging no longer rebuild unnecessarily.