[Xamarin.Android.Build.Tasks] Deploy changes to transitive reference …

…assembly dependencies (dotnet#4887)

Fixes: https://developercommunity.visualstudio.com/content/problem/1086457/index.html
Context: 8f2ae24
Context: https://dev.azure.com/devdiv/DevDiv/_workitems/edit/938468

If a Xamarin.Android app referenced a .NET Standard library that had
`$(ProduceReferenceAssembly)`=`true`, and that library in turn
referenced a second .NET Standard library, then changes to the second
library would not be deployed during incremental deployments in Visual
Studio unless the app project also directly referenced the second
library.

For additional context, note that as discussed in internal work item
938468, if a .NET Framework console application references a .NET
Standard library that has `$(ProduceReferenceAssembly)`=`true`, then
changes to the library are similarly missing in the running console app
after incremental builds in Visual Studio.

Although the problem in Xamarin.Android apps was similar to the .NET
Framework behavior, an important difference was that Xamarin.Android
apps did reflect changes correctly for libraries referenced directly by
the app.  Only transitive references caused trouble in Xamarin.Android.

The reason direct references worked was that Visual Studio always ran
Xamarin.Android's `Install` target on each incremental deployment, and
the `<ResolveAssemblies/>` task in that target correctly located the
up-to-date assemblies for direct references.

For example, for the included build test, the `<ResolveAssemblies/>`
task resolved the `Library1` reference to:

	C:\Source\xamarin-android\bin\TestDebug\temp\TransitiveDependencyProduceReferenceAssembly\Library1\bin\Debug\netstandard2.0\Library1.dll

In contrast, the `<ResolveAssemblies/>` task resolved the `Library2`
reference to:

	C:\Source\xamarin-android\bin\TestDebug\temp\TransitiveDependencyProduceReferenceAssembly\App\bin\Debug\Library2.dll

This was problematic because that copy of the library was left over from
the previous deployment.  In a sense, this was a circular reference: The
input for the current deployment was the output from the previous
deployment.

To fix this behavior, add the `@(ReferenceDependencyPaths)` items that
are found by the `<ResolveAssemblyReference/>` task to the
`@(FilteredAssemblies)` input.

For the included build test, this means the following additional item is
now included in `@(FilteredAssemblies)`:

	C:\Source\xamarin-android\bin\TestDebug\temp\TransitiveDependencyProduceReferenceAssembly\Library1\bin\Debug\netstandard2.0\Library2.dll

This path is then treated as a top-level reference in
`<ResolveAssemblies/>`, so the task no longer needs to try to resolve it
from elsewhere.

In theory, another way to fix the problem could be to change how
`<ResolveAssemblies/>` resolves transitive dependencies, but
`<ResolveAssemblies/>` is only used in the legacy build targets, so
adding more sophistication now would have limited value.

Other changes:

* The `BuildWithResolveAssembliesFailure` test using `packages.config`
  gets a slightly different error message due to the head project
  knowing about `Microsoft.Azure.EventHubs`. I think the new behavior
  is OK.
* `@(FilteredAssemblies)` can now have duplicates, so we need to use
  `->Distinct()`. Note that MSBuild preserves ordering:
  https://github.com/microsoft/msbuild/blob/9c2d922959e80ba72fefb7addec21ede227639c3/src/Build/Evaluation/Expander.cs#L2484-L2513

Co-authored-by: Jonathan Peppers <jonathan.peppers@gmail.com>

Co-authored-by: Jonathan Peppers <jonathan.peppers@gmail.com>

Documentation/release-notes/transitive-refasm.md

@@ -0,0 +1,8 @@
+#### Application and library build and deployment
+
+- [Developer Community 1086457](https://developercommunity.visualstudio.com/content/problem/1086457/index.html):
+  Changes to libraries referenced by the .NET Standard library in a default
+  Xamarin.Forms project were not reflected in the running app without a clean
+  rebuild.  More generally, this issue affected any library referenced
+  indirectly via a .NET Standard library that had the
+  `ProduceReferenceAssembly` MSBuild property set to `true`.

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

@@ -2743,7 +2743,7 @@ public void BuildWithResolveAssembliesFailure ([Values (true, false)] bool usePa
 					Assert.IsTrue (appBuilder.LastBuildOutput.ContainsText ($"{error} `Microsoft.Azure.EventHubs`, referenced by `MyLibrary`. Please add a NuGet package or assembly reference for `Microsoft.Azure.EventHubs`, or remove the reference to `MyLibrary`."),
 						$"Should recieve '{error}' regarding `Microsoft.Azure.EventHubs`!");
 				} else {
-					Assert.IsTrue (appBuilder.LastBuildOutput.ContainsText ($"{error} `Microsoft.Azure.Amqp`, referenced by `MyLibrary` > `Microsoft.Azure.EventHubs`. Please add a NuGet package or assembly reference for `Microsoft.Azure.Amqp`, or remove the reference to `MyLibrary`."),
+					Assert.IsTrue (appBuilder.LastBuildOutput.ContainsText ($"{error} `Microsoft.Azure.Amqp`, referenced by `Microsoft.Azure.EventHubs`. Please add a NuGet package or assembly reference for `Microsoft.Azure.Amqp`, or remove the reference to `Microsoft.Azure.EventHubs`"),
 						$"Should recieve '{error}' regarding `Microsoft.Azure.Amqp`!");
 				}
 				//Now add the PackageReference to the app to see a different error message

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

@@ -517,6 +517,68 @@ public void ProduceReferenceAssembly ()
 			}
 		}
 
+		[Test]
+		public void TransitiveDependencyProduceReferenceAssembly ()
+		{
+			var path = Path.Combine (Root, "temp", TestName);
+			var app = new XamarinAndroidApplicationProject {
+				ProjectName = "App",
+				Sources = {
+					new BuildItem.Source ("Class1.cs") {
+						TextContent = () => "public class Class1 : Library1.Class1 { }"
+					},
+				}
+			};
+			var lib1 = new DotNetStandard {
+				ProjectName = "Library1",
+				Sdk = "Microsoft.NET.Sdk",
+				TargetFramework = "netstandard2.0",
+				Sources = {
+					new BuildItem.Source ("Class1.cs") {
+						TextContent = () => "namespace Library1 { public class Class1 { } }"
+					},
+					new BuildItem.Source ("Class2.cs") {
+						TextContent = () => "namespace Library1 { public class Class2 : Library2.Class1 { } }"
+					}
+				}
+			};
+			lib1.SetProperty ("ProduceReferenceAssembly", "True");
+			var lib2 = new DotNetStandard {
+				ProjectName = "Library2",
+				Sdk = "Microsoft.NET.Sdk",
+				TargetFramework = "netstandard2.0",
+				Sources = {
+					new BuildItem.Source ("Class1.cs") {
+						TextContent = () => "namespace Library2 { public class Class1 { } }"
+					},
+				}
+			};
+			lib2.SetProperty ("ProduceReferenceAssembly", "True");
+			lib1.OtherBuildItems.Add (new BuildItem.ProjectReference ($"..\\{lib2.ProjectName}\\{lib2.ProjectName}.csproj", lib2.ProjectName, lib2.ProjectGuid));
+			app.References.Add (new BuildItem.ProjectReference ($"..\\{lib1.ProjectName}\\{lib1.ProjectName}.csproj", lib1.ProjectName, lib1.ProjectGuid));
+
+			using (var lib2Builder = CreateDllBuilder (Path.Combine (path, lib2.ProjectName), cleanupAfterSuccessfulBuild: false))
+			using (var lib1Builder = CreateDllBuilder (Path.Combine (path, lib1.ProjectName), cleanupAfterSuccessfulBuild: false))
+			using (var appBuilder = CreateApkBuilder (Path.Combine (path, app.ProjectName))) {
+				Assert.IsTrue (lib2Builder.Build (lib2), "first Library2 build should have succeeded.");
+				Assert.IsTrue (lib1Builder.Build (lib1), "first Library1 build should have succeeded.");
+				Assert.IsTrue (appBuilder.Build (app), "first app build should have succeeded.");
+
+				lib2.Sources.Add (new BuildItem.Source ("Class2.cs") {
+					TextContent = () => "namespace Library2 { public class Class2 { } }"
+				});
+
+				Assert.IsTrue (lib2Builder.Build (lib2, doNotCleanupOnUpdate: true), "second Library2 build should have succeeded.");
+				Assert.IsTrue (lib1Builder.Build (lib1, doNotCleanupOnUpdate: true, saveProject: false), "second Library1 build should have succeeded.");
+				appBuilder.Target = "SignAndroidPackage";
+				Assert.IsTrue (appBuilder.Build (app, doNotCleanupOnUpdate: true, saveProject: false), "app SignAndroidPackage build should have succeeded.");
+
+				var lib2Output = Path.Combine (path, lib2.ProjectName, "bin", "Debug", "netstandard2.0", $"{lib2.ProjectName}.dll");
+				var lib2InAppOutput = Path.Combine (path, app.ProjectName, app.IntermediateOutputPath, "android", "assets", $"{lib2.ProjectName}.dll");
+				FileAssert.AreEqual (lib2Output, lib2InAppOutput, "new Library2 should have been copied to app output directory");
+			}
+		}
+
 		[Test]
 		[Category ("dotnet")]
 		public void LinkAssembliesNoShrink ()

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

@@ -267,14 +267,18 @@ projects. .NET 5 projects will not import this file.
           Include="@(ReferenceCopyLocalPaths)"
           Condition="'%(ReferenceCopyLocalPaths.ResolvedFrom)' != 'ImplicitlyExpandDesignTimeFacades' And '%(ReferenceCopyLocalPaths.Extension)' == '.dll' And '%(ReferenceCopyLocalPaths.RelativeDir)' == '' And Exists('%(ReferenceCopyLocalPaths.Identity)') "
       />
+      <FilteredAssemblies
+          Include="@(_ReferenceDependencyPaths)"
+          Condition="'%(_ReferenceDependencyPaths.ResolvedFrom)' != 'ImplicitlyExpandDesignTimeFacades' And Exists('%(_ReferenceDependencyPaths.Identity)') "
+      />
       <FilteredAssemblies
           Include="@(_ReferencePath)"
           Condition="'%(ReferencePath.ResolvedFrom)' != 'ImplicitlyExpandDesignTimeFacades' And Exists('%(_ReferencePath.Identity)') "
       />
     </ItemGroup>
     <!-- Find all the assemblies this app requires -->
     <ResolveAssemblies
-        Assemblies="@(FilteredAssemblies)"
+        Assemblies="@(FilteredAssemblies->Distinct())"
         I18nAssemblies="$(MandroidI18n)"
         LinkMode="$(AndroidLinkMode)"
         ProjectFile="$(MSBuildProjectFullPath)"