Fix R8 Message processing to remove false positives. (#9298)

Context #7008 (comment)

When building with certain libraries we are seeing the following errors

4>  Invalid signature '(TT;)TV;' for method java.lang.Object kotlin.jvm.internal.PropertyReference1.get(java.lang.Object). (TaskId:792)
4>R8 : Validation error : A type variable is not in scope.
4>  Signature is ignored and will not be present in the output. (TaskId:792)
4>  Info in ...\.nuget\packages\xamarin.kotlin.stdlib\1.6.20.1\buildTransitive\monoandroid12.0\..\..\jar\org.jetbrains.kotlin.kotlin-stdlib-1.6.20.jar:kotlin/jvm/internal/PropertyReference0.class: (TaskId:792)
4>  Invalid signature '()TV;' for method java.lang.Object kotlin.jvm.internal.PropertyReference0.get(). (TaskId:792)
4>R8 : Validation error : A type variable is not in scope.
If you look carefully these are Info messages not errors. It turns out the call to base.LogEventsFromTextOutput (singleLine, messageImportance); is also including the default MSBuild error processing. This is mistaking this output for actual errors. So lets get around this by NOT calling base.LogEventsFromTextOutput (singleLine, messageImportance);.
So lets add a new meethod CheckForError which does the actual check. By default LogEventsFromTextOutput will call this and base.LogEventsFromTextOutput . However to R8 and D8 we override LogEventsFromTextOutput and only call CheckForError  and Log.LogMessage. This fixing this issue.

Add a unit test which covers the error case.

src/Xamarin.Android.Build.Tasks/Tasks/D8.cs

@@ -124,5 +124,13 @@ protected virtual CommandLineBuilder GetCommandLineBuilder ()
 
 			return cmd;
 		}
+
+		// Note: We do not want to call the base.LogEventsFromTextOutput as it will incorrectly identify
+		// Warnings and Info messages as errors.
+		protected override void LogEventsFromTextOutput (string singleLine, MessageImportance messageImportance)
+		{
+			CheckForError (singleLine);
+			Log.LogMessage (messageImportance, singleLine);
+		}
 	}
 }

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

@@ -213,11 +213,10 @@ protected void AppendTextToErrorText (string text)
 			errorText.AppendLine (text);
 		}
 
-		protected override void LogEventsFromTextOutput (string singleLine, MessageImportance messageImportance)
+		protected virtual void CheckForError (string singleLine)
 		{
 			errorLines.Add (singleLine);
-			base.LogEventsFromTextOutput (singleLine, messageImportance);  // not sure why/when we would skip this?
-
+
 			if (foundError) {
 				return;
 			}
@@ -229,6 +228,12 @@ protected override void LogEventsFromTextOutput (string singleLine, MessageImpor
 			}
 			foundError = foundError || match.Success || exceptionMatch.Success || customMatch;
 		}
+
+		protected override void LogEventsFromTextOutput (string singleLine, MessageImportance messageImportance)
+		{
+			CheckForError (singleLine);
+			base.LogEventsFromTextOutput (singleLine, messageImportance);
+		}
 	}
 }
 

src/Xamarin.Android.Build.Tasks/Tasks/R8.cs

@@ -142,6 +142,14 @@ protected override CommandLineBuilder GetCommandLineBuilder ()
 
 			return cmd;
 		}
+
+		// Note: We do not want to call the base.LogEventsFromTextOutput as it will incorrectly identify
+		// Warnings and Info messages as errors.
+		protected override void LogEventsFromTextOutput (string singleLine, MessageImportance messageImportance)
+		{
+			CheckForError (singleLine);
+			Log.LogMessage (messageImportance, singleLine);
+		}
 	}
 
 }

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

@@ -33,6 +33,29 @@ public void CheckProguardMappingFileExists ()
 			}
 		}
 
+		[Test]
+		public void CheckR8InfoMessagesToNotBreakTheBuild ()
+		{
+			var proj = new XamarinAndroidApplicationProject {
+				IsRelease = true,
+			};
+			proj.SetProperty (proj.ReleaseProperties, KnownProperties.AndroidLinkTool, "r8");
+			proj.SetProperty (proj.ReleaseProperties, "AndroidCreateProguardMappingFile", true);
+			var packages = proj.PackageReferences;
+			packages.Add (KnownPackages.Xamarin_KotlinX_Coroutines_Android);
+			proj.OtherBuildItems.Add (new BuildItem ("ProguardConfiguration", "proguard.cfg") {
+				TextContent = () => @"-keepattributes Signature
+-keep class kotlinx.coroutines.channels.** { *; }
+"
+			});
+
+			using (var b = CreateApkBuilder ()) {
+				string mappingFile = Path.Combine (Root, b.ProjectDirectory, proj.OutputPath, "mapping.txt");
+				Assert.IsTrue (b.Build (proj), "build should have succeeded.");
+				FileAssert.Exists (mappingFile, $"'{mappingFile}' should have been generated.");
+			}
+		}
+
 		[Test]
 		[NonParallelizable] // Commonly fails NuGet restore
 		public void CheckIncludedAssemblies ([Values (false, true)] bool usesAssemblyStores)

src/Xamarin.Android.Build.Tasks/Tests/Xamarin.ProjectTools/Android/KnownPackages.cs

@@ -157,6 +157,10 @@ public static class KnownPackages
 			Id = "Xamarin.Kotlin.Reflect",
 			Version = "1.9.10.2"
 		};
+		public static Package Xamarin_KotlinX_Coroutines_Android = new Package {
+			Id = "Xamarin.KotlinX.Coroutines.Android",
+			Version = "1.8.1.1"
+		};
 		public static Package Acr_UserDialogs = new Package {
 			Id = "Acr.UserDialogs",
 			Version = "8.0.1",