[generator] Remove buggy annotation loose match (#886)

Fixes: #885

Context: 1e8f513
Context: 3f12cd2

Attempting to build the xamarin/xamarin-android repo with a
xamarin/Java.Interop between commits [1e8f513, 3f12cd2), exclusive
-- as commit 3f12cd2 partially reverted commit 1e8f513 -- would
result in a build failure during `make framework-assemblies`:

	# in xamarin-android…
	% make prepare && make all && make framework-assemblies
	…
	…/src/Mono.Android/Mono.Android.targets(247,5): error : CompatApi command: $HOME/.nuget/packages/microsoft.dotnet.apicompat/5.0.0-beta.20181.7/tools/net472/Microsoft.DotNet.ApiCompat.exe "…/bin/Debug/lib/xamarin.android/xbuild-frameworks/MonoAndroid/v4.4.87/Mono.Android.dll" -i "…/bin/Debug/lib/xamarin.android/xbuild-frameworks/MonoAndroid/v5.0" --allow-default-interface-methods --baseline "…/tests/api-compatibility/acceptable-breakages-v5.0.txt" --validate-baseline --exclude-attributes "…/tests/api-compatibility/api-compat-exclude-attributes.txt"
	…/src/Mono.Android/Mono.Android.targets(247,5): error : CheckApiCompatibility found nonacceptable Api breakages for ApiLevel: v5.0.
	…/src/Mono.Android/Mono.Android.targets(247,5): error : Compat issues with assembly Mono.Android:
	…/src/Mono.Android/Mono.Android.targets(247,5): error : CannotChangeAttribute : Attribute 'Android.Runtime.RequiresPermissionAttribute' on 'Android.Net.ConnectivityManager.GetNetworkInfo(Android.Net.ConnectivityType)' changed from '[RequiresPermissionAttribute("quot;android.permission.ACCESS_NETWORK_STATE&quot")]' in the contract to '[RequiresPermissionAttribute("quot;android.permission.ACCESS_NETWORK_STATE&quot")]' in the implementation.
	…/src/Mono.Android/Mono.Android.targets(247,5): error : CannotChangeAttribute : Attribute 'Android.Runtime.RequiresPermissionAttribute' on 'Android.OS.Vibrator.Vibrate(System.Int64[], System.Int32)' changed from '[RequiresPermissionAttribute("quot;android.permission.VIBRATE&quot")]' in the contract to '[RequiresPermissionAttribute("quot;android.permission.VIBRATE&quot")]' in the implementation.
	…/src/Mono.Android/Mono.Android.targets(247,5): error : Total Issues: 2

The cause of the error was twofold:

 1. The `annotations.zip` within `platform-tools/api/annotations.zip`
    for the Android SDK Platform-tools r30 package contained
    annotations in the `androidx.annotation` package, which commit
    1e8f513 added support for, and

 2. The [method finding code][0] responsible for associating the
    method declared within `annotations.zip` to the `IMethodBase`
    which was responsible for C# codegen was "too loose", and could
    add annotations to methods which shouldn't get them.

Consider this XML snippet from `android/os/annotations.xml` within
`annotations.zip`, for two overloads of `Vibrator.vibrate()`:

	<item name="android.os.Vibrator void vibrate(android.os.VibrationEffect)">
	  <annotation name="androidx.annotation.RequiresPermission">
	    <val name="value" val="&quot;android.permission.VIBRATE&quot;" />
	  </annotation>
	</item>
	<item name="android.os.Vibrator void vibrate(long)">
	  <annotation name="androidx.annotation.RequiresPermission">
	    <val name="value" val="&quot;android.permission.VIBRATE&quot;" />
	  </annotation>
	</item>


which corresponds to the C# bindings:


	partial class Vibrator {
	    public virtual void Vibrate (Android.OS.VibrationEffect vibe);
	    public virtual void Vibrate (long milliseconds);
	}

However, the `Vibrator.Vibrate(VibrationEffect)` overload wasn't
added until API-26.  When binding API-21, only
`Vibrator.Vibrate(long)` exists.  The [method finding code][0] only
checks for *number* of parameters, *not* parameter type, and thus
would add the annotation for `vibrate(VibrationEffect)` to
`vibrate(long)`, resulting in the generated C# binding:

	namespace Android.OS {
	    public abstract partial class Vibrator : Java.Lang.Object {
	        [global::Android.Runtime.RequiresPermission ("quot;android.permission.VIBRATE&quot")]
		[global::Android.Runtime.RequiresPermission ("quot;android.permission.VIBRATE&quot")]
	        public abstract void Vibrate (long milliseconds);
	    }
	}

i.e. `Vibrator.Vibrate(long)` had *two* `[RequiresPermission]`
attributes, *both* with the same value.

Fix the bug by updating
`ManagedTypeFinderGeneratorTypeSystem.GetMethod()` to try only a
strict method overload match.

Finally, "revert the partial revert" of 3f12cd2, and reintroduce
support for the `androidx.annotation` package for Annotations.

[0]: https://github.com/xamarin/java.interop/blob/c936d09aec8171fa99a37fd99dba253e41fec05d/tools/generator/ManagedTypeFinderGeneratorTypeSystem.cs#L113

Author: jpobst

src/Xamarin.Android.Tools.AnnotationSupport/Objects/AnnotationData.cs

@@ -7,13 +7,21 @@ namespace Xamarin.AndroidTools.AnnotationSupport
 {
 	public class AnnotationData : AnnotationObject
 	{
+		static readonly string[] Prefixes = new[] {
+			"android.support.annotation.",
+			"androidx.annotation.",
+		};
+
 		public AnnotationData (XElement e)
 		{
 			var a = e.Attribute ("name");
 			Name = a == null ? null : a.Value;
-			string predef = "android.support.annotation.";
-			if (Name.StartsWith (predef, StringComparison.Ordinal))
+			foreach (var predef in Prefixes) {
+				if (!Name.StartsWith (predef, StringComparison.Ordinal))
+					continue;
 				Name = Name.Substring (predef.Length);
+				break;
+			}
 			Values = e.Elements ("val").Select (c => new AnnotationValue (c)).ToArray ();
 		}
 

tools/generator/ManagedTypeFinderGeneratorTypeSystem.cs

@@ -119,27 +119,6 @@ public override IMethodBase GetMethod (IType iType, AnnotatedItem item)
 				m.Parameters.Count == item.Arguments.Length)
 				.ToArray ();
 
-			// First, try loose match.
-
-			MethodBase candidate = null;
-			bool overloaded = false;
-			foreach (var m in methods) {
-				if (overloaded)
-					break;
-				if (candidate != null) {
-					overloaded = true;
-					break;
-				} else
-					candidate = m;
-			}
-			if (!overloaded) {
-				if (candidate == null)
-					Errors.Add ("warning: method with matching argument count not found: " + t.FullName + " member: " + item.FormatMember ());
-				return candidate.Wrap ();
-			}
-
-			// Second, try strict match.
-
 			var argTypeLists = methods.Select (m => new { Method = m, Jni = m is Ctor ? ((Ctor) m).JniSignature : ((Method) m).JniSignature})
 			                          .Select (p => new { Method = p.Method, Arguments = p.Jni == null ? null : ParseJniMethodArgumentsSignature (p.Jni)})
 			                          .ToArray ();