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Are we still in the window of preview3 so that this can be backported to it?

🤖 Copilot Code Review — PR #126594

Holistic Assessment

Motivation: Justified. Runtime-async (runtime-async=on) is already enabled for libraries (src/libraries/Directory.Build.targets), NativeAOT System.Private.CoreLib, and test projects — CoreCLR's System.Private.CoreLib was the remaining gap. Closing that gap is the right thing to do.

Approach: The intent is correct but the latest commit (9865b9d, co-authored with @am11) introduced an unintended behavioral change. When the architecture-conditional PropertyGroup was deleted and the <Features> line was kept, it became part of the adjacent Configuration == Release PropertyGroup — restricting runtime-async=on to Release builds only. This is almost certainly unintentional.

Summary: ⚠️ Needs Changes. The core idea is sound, but the latest commit accidentally restricts runtime-async to Release configuration only, which is inconsistent with every other place the flag is set. Additionally, the NativeAOT SPCL still has the riscv64/loongarch64 exclusions that @am11 says are now resolved — creating an inconsistency between the two CoreLib projects.

Detailed Findings

❌ Configuration Restriction — runtime-async=on is now Release-only

The <Features>$(Features);runtime-async=on</Features> line now lives inside the Configuration == Release PropertyGroup (lines 86-89 of the current csproj):

<PropertyGroup Condition="'$(Configuration)' == 'Release'">
  <Optimize Condition="'$(Optimize)' == ''">true</Optimize>
  <Features>$(Features);runtime-async=on</Features>
</PropertyGroup>

This means Debug and Checked builds will NOT have runtime-async enabled for CoreCLR SPCL. This is inconsistent with:

This appears to be an unintended side effect of applying @am11's suggestion to delete the architecture-conditional PropertyGroup. The deletion removed the </PropertyGroup> that closed the Release group and the <PropertyGroup Condition="..."> that opened the feature group — merging the <Features> line into the Release block.

Fix: Move <Features> into its own unconditional PropertyGroup, or add it to the existing unconditional PropertyGroup that follows:

<PropertyGroup Condition="'$(Configuration)' == 'Release'">
  <Optimize Condition="'$(Optimize)' == ''">true</Optimize>
</PropertyGroup>

<PropertyGroup>
  <Features>$(Features);runtime-async=on</Features>
</PropertyGroup>

⚠️ NativeAOT SPCL Inconsistency — still has riscv64/loongarch64 exclusions

If the riscv64 and loongarch64 runtime-async support is indeed complete (per @am11's review comment citing merged PRs #125446 and #125114), then the same exclusion removal should also be applied to the NativeAOT SPCL at src/coreclr/nativeaot/System.Private.CoreLib/src/System.Private.CoreLib.csproj (lines 45-50), which still has:

<!-- Enable runtime async for Native AOT -->
<!-- RISC-V: https://github.com/dotnet/runtime/issues/124934 -->
<!-- LoongArch: https://github.com/dotnet/runtime/issues/124935 -->
<PropertyGroup Condition="'$(TargetArchitecture)' != 'riscv64' and '$(TargetArchitecture)' != 'loongarch64'">
  <Features>$(Features);runtime-async=on</Features>
</PropertyGroup>

Without updating NativeAOT SPCL, we end up with:

• CoreCLR SPCL: runtime-async on all architectures ✅
• NativeAOT SPCL: runtime-async on all except riscv64/loongarch64 ❌

Note: tracking issues #124934 and #124935 are still open with unchecked items (including NativeAOT support). If the architecture work is not fully complete for NativeAOT, this inconsistency may be intentional — but it should be explicitly noted. Either way, the CoreCLR SPCL change should be made consistently with the NativeAOT SPCL.

⚠️ Stale Approval — VSadov's LGTM was on commit 1

@VSadov approved on the initial commit (c096559) which had Mono and architecture exclusions. The code has changed substantially since then (Mono exclusion removed per @MichalStrehovsky's feedback, architecture exclusions removed per @am11's feedback, and the unintended Release-only restriction). The current code is meaningfully different from what was approved.

💡 PR Description — Stale

The PR description still shows the original PropertyGroup with RuntimeFlavor != 'Mono' and architecture exclusions, and lists "riscv64 excluded" / "loongarch64 excluded" / "Mono flavor excluded" as features. None of these reflect the current state of the code. Consider updating.

Generated by Copilot Code Review workflow for PR #126594

Generated by Code Review for issue #126594 · ◷

/ba-g failures are networking

/backport to release/11.0-preview3

Started backporting to release/11.0-preview3 (link to workflow run)