[Xamarin.Android.Build.Tasks] downgrade d8/r8 warning messages to info

[jonathanpeppers]

Fixes: dotnet/maui#10901

Building a .NET MAUI project such as:

dotnet new maui
dotnet build -c Release -f net6.0-android -p:AndroidLinkMode=r8

Results in build warnings from R8 such as:

R8 : warning : Missing class androidx.window.extensions.WindowExtensions

In 92bc705, we already had attempted to silence warnings from R8 such as:

R8 : warning : Resource 'META-INF/MANIFEST.MF' already exists.

At the time, there was no option to hide warnings, now there is!

--map-diagnostics[:<type>] <from-level> <to-level>
    # Map diagnostics of <type> (default any) reported as
    # <from-level> to <to-level> where <from-level> and
    # <to-level> are one of 'info', 'warning', or 'error' and the
    # optional <type> is either the simple or fully qualified
    # Java type name of a diagnostic. If <type> is unspecified,
    # all diagnostics at <from-level> will be mapped.
    # Note that fatal compiler errors cannot be mapped.

We can pass:

--map-diagnostics warning info

Which can be done in existing apps via:

<AndroidD8ExtraArguments>--map-diagnostics warning info</AndroidD8ExtraArguments>
<AndroidR8ExtraArguments>--map-diagnostics warning info</AndroidR8ExtraArguments>

To solve this problem, let's create a new $(AndroidD8IgnoreWarnings) MSBuild property and make use of one we already have $(AndroidR8IgnoreWarnings):

<ItemGroup>
  <_AndroidD8MapDiagnostics Condition=" '$(AndroidD8IgnoreWarnings)' == 'true' " Include="warning" To="info" />
  <_AndroidR8MapDiagnostics Condition=" '$(AndroidR8IgnoreWarnings)' == 'true' " Include="warning" To="info" />
</ItemGroup>

We can then use these item groups to pass --map-diagnostics as appropriate. Developers can turn off either property to disable this behavior.

We can then remove the weird Regex code added in 92bc705. The existing tests from 92bc705 should also be sufficient for testing this change.

Now r8 emits:

Info: Missing class androidx.window.extensions.WindowExtensions (referenced from: androidx.window.extensions.layout.WindowLayoutComponent androidx.window.layout.SafeWindowLayoutComponentProvider$windowLayoutComponent$2.invoke())
Info: Resource 'META-INF/MANIFEST.MF' already exists.

And you don't get an MSBuild warning anymore.

[jonathanpeppers]

The one test failure looks unrelated:

dotnet run should succeed
Expected: True
But was:  False
...
[BT Error retrieving device SDK version. Please try again. [/Users/runner/work/1/a/TestRelease/12-15_23.39.44/temp/DotNetInstallAndRunTrueTruenet6.0-android/UnnamedProject.csproj]

[dellis1972]

Do we have a unit test which convers this to make sure the warnings are mapped to info?

[jonathanpeppers]

The test from 92bc705, it previously had build warnings like this when enabling multi-dex:

R8 : warning : Resource 'META-INF/MANIFEST.MF' already exists.

It asserts there are 0 warnings: https://github.com/xamarin/xamarin-android/blob/d4c2a5e2ba148ea1d63fdc7f8c984642e7b5b369/src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/BuildTest2.cs#L282

Now it should log a message instead:

Info: Resource 'META-INF/MANIFEST.MF' already exists.