[build] Do not modify assemblies in the NuGet package cache

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

@@ -2300,6 +2300,79 @@ public void CheckLintResourceFileReferencesAreFixed ([Values (AndroidRuntime.Cor
 			}
 		}
 
+		[Test]
+		public void BuildDoesNotModifyNuGetPackageCache ()
+		{
+			var proj = new XamarinAndroidApplicationProject {
+				IsRelease = true,
+				GlobalPackagesFolder = Path.Combine (Root, TestName, "packages"),
+				Imports = {
+					new Import (() => "EnableMarshalMethodsForPostLink.targets") {
+						TextContent = () =>
+"""
+<Project>
+	<!-- Exercise the in-place post-link path without enabling marshal methods for later CoreCLR targets. -->
+	<Target Name="_EnableMarshalMethodsForPostLink"
+		BeforeTargets="_RunAfterILLinkAdditionalSteps"
+		Condition=" '$(TestEnableMarshalMethodsForPostLink)' == 'true' ">
+		<PropertyGroup>
+			<_AndroidUseMarshalMethods>true</_AndroidUseMarshalMethods>
+		</PropertyGroup>
+	</Target>
+</Project>
+"""
+					},
+				},
+				PackageReferences = {
+					new Package { Id = "Humanizer.Core", Version = "2.14.1" },
+					new Package { Id = "Humanizer.Core.es", Version = "2.14.1" },
+				},
+			};
+			proj.SetRuntime (AndroidRuntime.CoreCLR);
+			proj.SetProperty ("AndroidTypeMapImplementation", "llvm-ir");
+			proj.SetProperty (KnownProperties.PublishTrimmed, true.ToString ());
+			proj.MainActivity = proj.DefaultMainActivity
+				.Replace ("//${USINGS}", "using Humanizer;")
+				.Replace ("//${AFTER_ONCREATE}", "System.Console.WriteLine (System.DateTime.UtcNow.Humanize ());");
+
+			using var builder = CreateApkBuilder ();
+			var buildParameters = new [] { $"RestorePackagesPath={proj.GlobalPackagesFolder}" };
+			Assert.IsTrue (builder.Restore (proj, parameters: buildParameters), "Package restore should have succeeded.");
+			Assert.IsTrue (builder.Build (proj, doNotCleanupOnUpdate: true, saveProject: false, parameters: buildParameters),
+				"Initial build should have succeeded.");
+
+			var satelliteAssemblies = Directory.GetFiles (proj.GlobalPackagesFolder, "*.resources.dll", SearchOption.AllDirectories);
+			Assert.IsNotEmpty (satelliteAssemblies, "The NuGet package should contain satellite assemblies.");
+
+			var originalWriteTimes = new Dictionary<string, DateTime> ();
+			foreach (string assembly in satelliteAssemblies) {
+				File.SetLastWriteTimeUtc (assembly, new DateTime (2000, 1, 1, 0, 0, 0, DateTimeKind.Utc));
+				originalWriteTimes.Add (assembly, File.GetLastWriteTimeUtc (assembly));
+			}
+
+			var postLinkStamp = Path.Combine (Root, builder.ProjectDirectory, proj.IntermediateOutputPath, "stamp", "_AdditionalPostLinkerSteps.stamp");
+			FileAssert.Exists (postLinkStamp);
+			File.Delete (postLinkStamp);
+
+			// A package cache is immutable: deny write sharing and verify timestamps remain unchanged.
+			var packageLocks = satelliteAssemblies
+				.Select (assembly => File.Open (assembly, FileMode.Open, FileAccess.Read, FileShare.Read))
+				.ToList ();
+			try {
+				var postLinkParameters = buildParameters.Append ("TestEnableMarshalMethodsForPostLink=true").ToArray ();
+				Assert.IsTrue (builder.RunTarget (proj, "_PrepareAssemblies", doNotCleanupOnUpdate: true, saveProject: false, parameters: postLinkParameters),
+					"Preparing assemblies should have succeeded.");
+				FileAssert.Exists (postLinkStamp);
+				foreach (string assembly in satelliteAssemblies) {
+					Assert.AreEqual (originalWriteTimes [assembly], File.GetLastWriteTimeUtc (assembly), $"Build should not modify '{assembly}'.");
+				}
+			} finally {
+				foreach (var packageLock in packageLocks) {
+					packageLock.Dispose ();
+				}
+			}
+		}
+
 		[Test]
 		[TestCase (true, AndroidRuntime.CoreCLR)]
 		[TestCase (false, AndroidRuntime.CoreCLR)]

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

@@ -1472,8 +1472,10 @@ because xbuild doesn't support framework reference assemblies.
     Outputs="$(_AdditionalPostLinkerStepsFlag)">
   <MakeDir Directories="$(_AfterILLinkOutputDir)" Condition=" '$(_AndroidUseMarshalMethods)' != 'True' " />
   <ItemGroup>
-    <_AfterILLinkDestFiles Condition=" '$(_AndroidUseMarshalMethods)' != 'True' " Include="@(ResolvedAssemblies->'$(_AfterILLinkOutputDir)%(DestinationSubPath)')" />
-    <_AfterILLinkDestFiles Condition=" '$(_AndroidUseMarshalMethods)' == 'True' " Include="@(ResolvedAssemblies)" />
+    <_AfterILLinkSourceFiles Include="@(ResolvedAssemblies)"
+        Condition=" '$(_AndroidUseMarshalMethods)' != 'True' or !$([System.String]::Copy('%(ResolvedAssemblies.Filename)').ToLowerInvariant().EndsWith('.resources')) " />
+    <_AfterILLinkDestFiles Condition=" '$(_AndroidUseMarshalMethods)' != 'True' " Include="@(_AfterILLinkSourceFiles->'$(_AfterILLinkOutputDir)%(DestinationSubPath)')" />
+    <_AfterILLinkDestFiles Condition=" '$(_AndroidUseMarshalMethods)' == 'True' " Include="@(_AfterILLinkSourceFiles)" />
   </ItemGroup>
   <AssemblyModifierPipeline
       ApplicationJavaClass="$(AndroidApplicationJavaClass)"
@@ -1487,11 +1489,12 @@ because xbuild doesn't support framework reference assemblies.
       ReadSymbols="$(_AndroidLinkAssembliesReadSymbols)"
       ResolvedAssemblies="@(_AllResolvedAssemblies)"
       ResolvedUserAssemblies="@(ResolvedUserAssemblies)"
-      SourceFiles="@(ResolvedAssemblies)"
+      SourceFiles="@(_AfterILLinkSourceFiles)"
       TargetName="$(TargetName)">
   </AssemblyModifierPipeline>
   <Touch Files="$(_AdditionalPostLinkerStepsFlag)" AlwaysCreate="true" />
   <ItemGroup>
+    <_AfterILLinkSourceFiles Remove="@(_AfterILLinkSourceFiles)" />
     <_AfterILLinkDestFiles Remove="@(_AfterILLinkDestFiles)" />
   </ItemGroup>
   <ItemGroup Condition=" '$(_AndroidUseMarshalMethods)' != 'True' ">