[Xamarin.Android.Build.Tasks] only warn about failed deletion of temp dirs

[jonathanpeppers]

Context: https://build.azdo.io/3575078
Context: https://build.azdo.io/3574952

Our CI builds have been hitting random failures such as:

(_UpdateAndroidResgen target) ->
error XARDF7024: System.IO.IOException: The directory is not empty.
error XARDF7024:
error XARDF7024:    at System.IO.Directory.DeleteHelper(String fullPath, String userPath, Boolean recursive, Boolean throwOnTopLevelDirectoryNotFound, WIN32_FIND_DATA& data)
error XARDF7024:    at System.IO.Directory.Delete(String fullPath, String userPath, Boolean recursive, Boolean checkHost)
error XARDF7024:    at Xamarin.Android.Tasks.RemoveDirFixed.RunTask()

Or in another target:

(_CreateBaseApk target) ->
error XARDF7024: System.IO.IOException: The directory is not empty.
error XARDF7024:
error XARDF7024:    at System.IO.Directory.DeleteHelper(String fullPath, String userPath, Boolean recursive, Boolean throwOnTopLevelDirectoryNotFound, WIN32_FIND_DATA& data)
error XARDF7024:    at System.IO.Directory.Delete(String fullPath, String userPath, Boolean recursive, Boolean checkHost)
error XARDF7024:    at Xamarin.Android.Tasks.RemoveDirFixed.RunTask()

In both of these places, we have the pattern:

<CreateTemporaryDirectory>
  <Output TaskParameter="TemporaryDirectory" PropertyName="AaptTemporaryDirectory" />
</CreateTemporaryDirectory>
<!-- Then later on -->
<RemoveDirFixed Directories="$(AaptTemporaryDirectory)" />

The temporary directory is created in C# via:

TemporaryDirectory = Path.Combine (Path.GetTempPath (), Path.GetRandomFileName ());
Directory.CreateDirectory (TemporaryDirectory);

I think a solution here is to make the <RemoveDirFixed/> call set to
ContinueOnError="WarnAndContinue". I don't think we need to fail
the overall build in these scenarios.

The user is going to have leftover files in %TEMP%, and I don't
think there is much we can do. Changing this from a build error to a
warning is a general improvement if we are unable to delete the
directory. The error code will also be preserved.

I don't know if this will help our users at all, but should help our CI.

[jpobst]

I agree that we should do this fix, but I think we should also look and see if something changed recently that has caused this to start happening. Presumably something is still holding these files open that previously was not.

[jonathanpeppers]

@jpobst the only thing that would hold these directories open is aapt2.exe, and I don't see that process hanging around:

https://dev.azure.com/DevDiv/DevDiv/_build/results?buildId=3574952&view=logs&j=035e6729-702a-53d4-bea9-761745a9f552&t=c612f891-5417-5f54-1118-32301bb7e92f&l=63

I have no explanation, unless you have an idea.

We haven't changed aapt2, except for this PR that isn't merged yet: #4190

Maybe its PR builds could break other PRs running on the same machine?

[jonathanpeppers]

This PR is nearly green, but we get a network issue:

System.Net.WebException : Error: SecureChannelFailure (Remote prematurely closed connection.)
----> System.IO.IOException : Remote prematurely closed connection.

I'm going to merge, as it seems to help the Windows side.

[brendanzagaeski]

Draft release note

Although this issue hasn't been reported by users, I'll plan to include a tiny note for it just to be thorough.

Here's what I'm thinking:

  * [GitHub PR 4444](https://github.com/xamarin/xamarin-android/pull/4444):
    *System.IO.IOException: The directory is not empty* could sometimes prevent
    the `RemoveDirFixed` task from removing temporary build directories.  The
    task now produces a warning instead, allowing the build to complete
    successfully.

To suggest something different or to recommend excluding it from the release notes, feel free to reply in this PR or add a Documentation/release-notes/4444.md file with the new suggestion. Thanks in advance!