Remove /clr:pure from WPF C++/CLI projects

[vinnarayana-msft]

Description

MSVC 14.51 (VS 18.3) is removing support for /clr:pure when used with /clr:netcore. WPF is the only known consumer of /clr:pure. This PR migrates the two affected C++/CLI projects (DirectWriteForwarder.vcxproj and System.Printing.vcxproj) from /clr:pure to standard /clr:netcore (IJW mixed mode).

Changes:

• Changed CLRSupport and CompileAsManaged from pure to NetCore in both vcxproj files
• Updated Wpf.Cpp.props to remove the pure to NetCore conversion logic in ManagedCxx conditions
• Removed ijwhost.dll from packaging exclusions in both vcxproj files — mixed-mode assemblies require this .NET runtime bootstrap shim to load correctly
• Fixed ARM64 build break in intsafe_private_copy.h where _M_ARM64 was missing from an architecture detection #if condition (previously masked by _M_CEE_PURE)

Customer Impact

Without this fix, WPF will fail to build with MSVC 14.51+ (VS 18.3) since /clr:pure + /clr:netcore will no longer be a valid combination. This is a build-time breaking change from the MSVC toolset.

Regression

No. This is a proactive change to address an upcoming MSVC toolset deprecation. No existing behavior is regressed — the output DLLs function identically at runtime.

Testing

Test	Result
x64 build	✅ Pass
ARM64 build compilation	✅ Pass
WPF Gallery app run (x64)	✅ Pass

Risk

Low-Medium. The change is minimal (4 files) and surgical — it only affects the two C++/CLI projects in WPF. The runtime behavior of the DLLs is functionally equivalent; the difference is the compilation mode (pure MSIL → IJW mixed mode). The primary risk is potential performance impact from losing ahead-of-time MSIL compilation.

Microsoft Reviewers: Open in CodeFlow

[Copilot]

Pull request overview

Updates WPF’s C++/CLI build configuration to remove reliance on deprecated /clr:pure in favor of standard /clr:netcore (IJW mixed mode), aligning with upcoming MSVC toolset behavior and unblocking future builds.

Changes:

• Switched CLRSupport and CompileAsManaged from pure to NetCore for DirectWriteForwarder and System.Printing.
• Simplified Wpf.Cpp.props by removing the pure→NetCore remapping logic and updating ManagedCxx conditions.
• Fixed an ARM64 compilation break by extending architecture detection in intsafe_private_copy.h.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
src/Microsoft.DotNet.Wpf/src/System.Printing/System.Printing.vcxproj	Moves the project to /clr:netcore and allows ijwhost.dll to be packaged by removing the exclusion.
src/Microsoft.DotNet.Wpf/src/DirectWriteForwarder/DirectWriteForwarder.vcxproj	Moves the project to /clr:netcore and allows ijwhost.dll to be packaged by removing the exclusion.
src/Microsoft.DotNet.Wpf/src/DirectWriteForwarder/CPP/TrueTypeSubsetter/TtfDelta/intsafe_private_copy.h	Adds _M_ARM64 handling to prevent ARM64 build errors.
eng/WpfArcadeSdk/tools/Wpf.Cpp.props	Updates shared build logic to recognize CLRSupport=NetCore and removes the old pure remap.

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[miloush]

Can we have some link/reference to the deprecation of the combination?