Msbuild: RAR cache dirty reason should be logged

[KirillOsenkov]

RAR should log the reason why the state file became dirty and why it chose to write it. It's hard to diagnose why the state file is written every time on empty rebuilds where nothing changes.

[KirillOsenkov]

State file being written triggers unnecessary rebuild of the _WriteAppConfigWithSupportedRuntime and _CopyAppConfigFile targets.

[rainersigwald]

State file being written triggers unnecessary rebuild of the _WriteAppConfigWithSupportedRuntime and _CopyAppConfigFile targets.

This is a separate bug, I think. The cache file should be an implementation detail of RAR and nothing else should even know about it.

[KirillOsenkov]

https://github.com/dotnet/sdk/blob/8cb31b0fd0bb5d36b9781442865f2e26cf6fbedc/src/Tasks/Microsoft.NET.Build.Tasks/targets/Microsoft.NET.GenerateSupportedRuntime.targets#L44

:) $(ResolveAssemblyReferencesStateFile) is treated as an input :)

[rainersigwald]

No, no: I believe you! But we should change that . . .

[KirillOsenkov]

Filed https://github.com/dotnet/sdk/issues/3131