Flaky test: BuildTest.BuildInDesignTimeMode(True,NativeAOT) sporadic design-time build failure on Linux

[simonrozsival]

Summary

BuildTest.BuildInDesignTimeMode flakes in its (True, NativeAOT) parametrization on the public dotnet-android pipeline (dnceng-public def 333, Linux > Tests > MSBuild 1 / Xamarin.Android.Build.Tests - Linux BuildTest). The design-time build fails sporadically with a FailedBuildException (the MSBuild step itself fails, before any assert).

Test: src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/BuildTest.cs:762

Representative failure (build 1485678, BuildInDesignTimeMode(True,NativeAOT)):

Xamarin.ProjectTools.FailedBuildException : Build failure: App1.csproj
Build log recorded at .../TestRelease/06-29_11.57.07/temp/BuildInDesignTimeMode_True_NativeAOT/App1/build.log
  at Xamarin.ProjectTools.Builder.BuildInternal(...)

Occurrences — the flake (dnceng-public def 333, 2026‑06‑27 → 06‑30)

Low-frequency: 2 isolated single-config hits on unrelated PRs, same (True, NativeAOT) config each time:

Build	PR	Date	Config	Result
1484514	#11698	06‑27	(True,NativeAOT)	failed
1485678	#11772	06‑29	(True,NativeAOT)	failed

Both are the NativeAOT design-time build failing to produce App1.csproj. The error message points at a captured build.log (temp/BuildInDesignTimeMode_True_NativeAOT/App1/build.log) that should be pulled from the failed build's artifacts to find the underlying MSBuild error.

⚠️ Not part of this flake — a likely real regression on [release/11.0.1xx-preview6]

While scanning the window, BuildInDesignTimeMode also failed 24 times, but those are not flaky — they are the (True, MonoVM) parametrization failing consistently (every build) on PR #11765 "[release/11.0.1xx-preview6] Update dependencies from dotnet/dotnet":

Build	PR	Date	Config	Result
1484013	#11765	06‑27	(True,MonoVM) ×8	failed
1484578	#11765	06‑28	(True,MonoVM) ×8	failed
1485065	#11765	06‑29	(True,MonoVM) ×8	failed

A test that fails on every run of one PR in a different config than the flake is a real regression on that branch's dependency bump, not flakiness. This should be investigated by the owner of #11765 (the release/11.0.1xx-preview6 dependency flow) and is explicitly out of scope for this flaky-test issue.

Suggested actions

1. Pull build.log from temp/BuildInDesignTimeMode_True_NativeAOT/App1/ in builds 1484514 / 1485678 to identify the sporadic NativeAOT design-time build failure.
2. Separately, ping [release/11.0.1xx-preview6] Update dependencies from dotnet/dotnet #11765 about the consistent (True,MonoVM) design-time failure on release/11.0.1xx-preview6 — likely a real regression from the dependency update.