[Xamarin.Android.Build.Tasks] skip proguard.txt files in !app (#8025)

Context: c537dd2
Context: dotnet/android-libraries#729
Context: xamarin/GooglePlayServicesComponents#774

A customer reported a build error such as:

	C:\Program Files\dotnet\packs\Microsoft.Android.Sdk.Windows\33.0.46\targets\Microsoft.Android.Sdk.AndroidLibraries.targets(77,5):
	error XACAAR7014: System.OutOfMemoryException: Exception of type 'System.OutOfMemoryException' was thrown.
	   at System.Text.StringBuilder.ToString()
	   at Xamarin.Android.Tasks.CreateAar.RunTask()
	   at Microsoft.Android.Build.Tasks.AndroidTask.Execute()

Somewhere within [`<CreateAar/>`][0]:

	if (ProguardConfigurationFiles != null) {
	    var sb = new StringBuilder ();
	    foreach (var file in ProguardConfigurationFiles) {
	        sb.AppendLine (File.ReadAllText (file.ItemSpec));
	    }
	    aar.AddEntry ("proguard.txt", sb.ToString (), Files.UTF8withoutBOM);
	}

The problem appears to be triggered by:

 1. Library project `Lib.csproj` which bind `.aar` files include the
    `proguard.txt` from the `.aar` into the output `Lib.aar`, as
    `Lib.aar!proguard.txt`.

 2. Library project `References.csproj` which has a `@(Reference)` to
    `Lib.csproj` will include the contents of `Lib.aar!proguard.txt`
    into `References.aar!proguard.txt`.  If `References.csproj` has a
    `@(PackageReference)` which has `AnotherLib.aar`, then
    `AnotherLib.aar!proguard.txt` will *also* be copied into
    `References.aar!proguard.txt`.
    (Repeat for all `@(Reference)` and `@(projectreference)`.)
    (Note combinatorial explosion in `proguard.txt` size…)

 3. App project `App.csproj` references (2), merging all the contents
    of all the `proguard.txt` files from all the `.aar` files into a
    single unified `proguard.txt` file.

If the project has lots of library projects or package references,
step (3) could OOM.  "Lots" of references, such as:

	ProguardConfigurationFiles=
	    ~\.nuget\packages\xamarin.androidx.versionedparcelable\1.1.1.15\buildTransitive\net6.0-android31.0\..\..\proguard\proguard.txt
	    ~\.nuget\packages\xamarin.androidx.lifecycle.runtime\2.5.1.1\buildTransitive\net6.0-android31.0\..\..\proguard\proguard.txt
	    ~\.nuget\packages\xamarin.androidx.core\1.9.0.1\buildTransitive\net6.0-android31.0\..\..\proguard\proguard.txt
	    ~\.nuget\packages\xamarin.androidx.savedstate\1.2.0.1\buildTransitive\net6.0-android31.0\..\..\proguard\proguard.txt
	    ~\.nuget\packages\xamarin.androidx.recyclerview\1.2.1.7\buildTransitive\net6.0-android31.0\..\..\proguard\proguard.txt
	    ~\.nuget\packages\xamarin.androidx.lifecycle.viewmodel\2.5.1.1\buildTransitive\net6.0-android31.0\..\..\proguard\proguard.txt
	    ~\.nuget\packages\xamarin.androidx.lifecycle.viewmodelsavedstate\2.5.1.1\buildTransitive\net6.0-android31.0\..\..\proguard\proguard.txt
	    ~\.nuget\packages\xamarin.androidx.fragment\1.5.3.1\buildTransitive\net6.0-android31.0\..\..\proguard\proguard.txt
	    ~\.nuget\packages\xamarin.androidx.vectordrawable.animated\1.1.0.14\buildTransitive\net6.0-android31.0\..\..\proguard\proguard.txt
	    ~\.nuget\packages\xamarin.androidx.transition\1.4.1.8\buildTransitive\net6.0-android31.0\..\..\proguard\proguard.txt
	    ~\.nuget\packages\xamarin.androidx.startup.startupruntime\1.1.1.2\buildTransitive\net6.0-android31.0\..\..\proguard\proguard.txt
	    ~\.nuget\packages\xamarin.androidx.lifecycle.process\2.5.1\buildTransitive\net6.0-android31.0\..\..\proguard\proguard.txt
	    ~\.nuget\packages\xamarin.androidx.coordinatorlayout\1.2.0.3\buildTransitive\net6.0-android31.0\..\..\proguard\proguard.txt
	    ~\.nuget\packages\xamarin.androidx.appcompat\1.5.1\buildTransitive\net6.0-android31.0\..\..\proguard\proguard.txt
	    ~\.nuget\packages\xamarin.google.android.material\1.7.0\buildTransitive\net6.0-android31.0\..\..\proguard\proguard.txt
	    ~\.nuget\packages\xamarin.androidx.window\1.0.0.10\buildTransitive\net6.0-android31.0\..\..\proguard\proguard.txt
	    ~\.nuget\packages\xamarin.androidx.navigation.common\2.5.2.1\buildTransitive\net6.0-android31.0\..\..\proguard\proguard.txt
	    ~\.nuget\packages\xamarin.androidx.navigation.ui\2.5.2.1\buildTransitive\net6.0-android31.0\..\..\proguard\proguard.txt
	    ~\.nuget\packages\xamarin.androidx.media\1.6.0.2\buildTransitive\net6.0-android31.0\..\..\proguard\proguard.txt
	    ..\path\to\projectreference\obj\Debug\lp\160\jl\proguard.txt
	    ..\path\to\projectreference\obj\Debug\lp\155\jl\proguard.txt
	    ..\path\to\projectreference\obj\Debug\lp\161\jl\proguard.txt
	    ..\path\to\projectreference\obj\Debug\lp\162\jl\proguard.txt
	    ..\path\to\projectreference\obj\Debug\lp\156\jl\proguard.txt
	    ..\path\to\projectreference\obj\Debug\lp\157\jl\proguard.txt
	    ..\path\to\projectreference\obj\Debug\lp\163\jl\proguard.txt
	    ..\path\to\projectreference\obj\Debug\lp\164\jl\proguard.txt
	    ..\path\to\projectreference\obj\Debug\lp\165\jl\proguard.txt
	    ..\path\to\projectreference\obj\Debug\lp\166\jl\proguard.txt
	    ..\path\to\projectreference\obj\Debug\lp\167\jl\proguard.txt
	    ..\path\to\projectreference\obj\Debug\lp\170\jl\proguard.txt
	    ..\path\to\projectreference\obj\Debug\lp\168\jl\proguard.txt
	    ..\path\to\projectreference\obj\Debug\lp\169\jl\proguard.txt
	    ..\path\to\projectreference\obj\Debug\lp\171\jl\proguard.txt
	    ..\path\to\projectreference\obj\Debug\lp\172\jl\proguard.txt
	    ..\path\to\projectreference\obj\Debug\lp\173\jl\proguard.txt
	    …

I believe this problem was partially introduced in c537dd2, but we
didn't notice until now.  The AndroidX NuGet packages also cause this
problem, but in a different way as seen in dotnet/android-libraries#729 and
xamarin/GooglePlayServicesComponents#774.

A solution here is that `<ResolveLibraryProjectImports/>` should
simply ignore `proguard.txt` files in class libraries.  They are only
actually needed in "app" projects where the `<R8/>` MSBuild task
would use them.

I could reproduce this in a test using an `.aar` from maven that
contains a `proguard.txt`:

  * <https://mvnrepository.com/artifact/androidx.core/core/1.10.0>

And then just assert the `proguard.txt` contents don't make it to
`MyClassLibrary.aar`.

Note: dotnet/android-libraries#729 and xamarin/GooglePlayServicesComponents#774
update the NuGet Packages so that `proguard.txt` files are only
added to `@(ProguardConfiguration)` when `$(AndroidApplication)`=True.
This should also help prevent the OOM scenario.

[0]: https://github.com/xamarin/xamarin-android/blob/c31f3eda63a16e412a39fa61eb0f885be3c5f543/src/Xamarin.Android.Build.Tasks/Tasks/CreateAar.cs#L108-L114

Author: jonathanpeppers

src/Xamarin.Android.Build.Tasks/Tasks/ResolveLibraryProjectImports.cs

@@ -44,6 +44,8 @@ public class ResolveLibraryProjectImports : AndroidTask
 		[Required]
 		public bool DesignTimeBuild { get; set; }
 
+		public bool AndroidApplication { get; set; }
+
 		[Output]
 		public ITaskItem [] Jars { get; set; }
 
@@ -442,7 +444,7 @@ void Extract (
 					resolvedAssetDirectories.Add (new TaskItem (Path.GetFullPath (assetsDir), new Dictionary<string, string> {
 						{ OriginalFile, aarFullPath },
 					}));
-				if (File.Exists (proguardFile)) {
+				if (AndroidApplication && File.Exists (proguardFile)) {
 					proguardConfigFiles.Add (new TaskItem (Path.GetFullPath (proguardFile), new Dictionary<string, string> {
 						{ OriginalFile, aarFullPath },
 					}));

src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/Utilities/AssertionExtensions.cs

@@ -54,6 +54,19 @@ public static void AssertTargetIsPartiallyBuilt (this BuildOutput output, string
 				Assert.IsTrue (output.IsTargetPartiallyBuilt (target), $"The target {target} should have been partially built.");
 		}
 
+		[DebuggerHidden]
+		public static void AssertEntryEquals (this ZipArchive zip, string zipPath, string archivePath, string expected)
+		{
+			zip.AssertContainsEntry (zipPath, archivePath);
+
+			var entry = zip.ReadEntry (archivePath);
+			using var stream = new MemoryStream ();
+			entry.Extract (stream);
+			stream.Position = 0;
+			using var reader = new StreamReader (stream);
+			Assert.AreEqual (expected, reader.ReadToEnd ().Trim ());
+		}
+
 		[DebuggerHidden]
 		public static void AssertContainsEntry (this ZipArchive zip, string zipPath, string archivePath)
 		{

src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/XASdkTests.cs

@@ -79,7 +79,7 @@ public void DotNetBuildLibrary (bool isRelease, bool duplicateAar, bool useDesig
 						BinaryContent = () => XamarinAndroidApplicationProject.icon_binary_mdpi,
 					},
 					new AndroidItem.ProguardConfiguration ("proguard.txt") {
-						TextContent = () => @"-ignorewarnings",
+						TextContent = () => "# LibraryC",
 					},
 				}
 			};
@@ -97,7 +97,7 @@ public void DotNetBuildLibrary (bool isRelease, bool duplicateAar, bool useDesig
 			FileAssert.Exists (aarPath);
 			using (var aar = ZipHelper.OpenZip (aarPath)) {
 				aar.AssertContainsEntry (aarPath, "assets/bar/bar.txt");
-				aar.AssertContainsEntry (aarPath, "proguard.txt");
+				aar.AssertEntryEquals (aarPath, "proguard.txt", "# LibraryC");
 			}
 
 			var libB = new XASdkProject (outputType: "Library") {
@@ -139,7 +139,7 @@ public Foo ()
 						TextContent = () => ResourceData.JavaSourceTestExtension,
 					},
 					new AndroidItem.ProguardConfiguration ("proguard.txt") {
-						TextContent = () => @"-ignorewarnings",
+						TextContent = () => "# LibraryB",
 					},
 				}
 			};
@@ -185,6 +185,8 @@ public Foo ()
 				aar.AssertContainsEntry (aarPath, $"libs/{projectJarHash}.jar");
 				aar.AssertContainsEntry (aarPath, "jni/arm64-v8a/libfoo.so");
 				aar.AssertContainsEntry (aarPath, "jni/x86/libfoo.so");
+				// proguard.txt from Library C should not flow to Library B and "double"
+				aar.AssertEntryEquals (aarPath, "proguard.txt", "# LibraryB");
 			}
 
 			// Check EmbeddedResource files do not exist

src/Xamarin.Android.Build.Tasks/Xamarin.Android.EmbeddedResource.targets

@@ -38,6 +38,7 @@ This file is used by all project types, including binding projects.
       Outputs="$(_AndroidStampDirectory)_ResolveLibraryProjectImports.stamp">
     <ResolveLibraryProjectImports
         ContinueOnError="$(DesignTimeBuild)"
+        AndroidApplication="$(AndroidApplication)"
         CacheFile="$(_AndroidLibraryProjectImportsCache)"
         DesignTimeBuild="$(DesignTimeBuild)"
         Assemblies="@(_MonoAndroidReferencePath);@(_MonoAndroidReferenceDependencyPaths)"