Return of the Strings

Fixes: dotnet#4415
Context: dotnet@ce2bc68

This commit partially reverts ce2bc68
in the sense that it restores the use of type names for Java-to-Managed
and Managed-to-Java type lookups for **Debug** builds only.

The reason for the change is that in order for the MVID and type token
based lookups to work we need two things:

  - for the MVID to remain unchanged in each mapped assembly
	- for the type token to remain unchanged in each mapped assembly

However, in incremental builds neither of the above requirements is
met **unless** the application is fully rebuilt and, thus, the typemaps
are regenerated from scratch, which obviously doesn't sit well with the
incremental nature of incremental builds :)

With MVID/token id maps, every change to any source code that's built
into a mapped assembly, may cause the assembly to change its MVID and
renaming of any type, removing or adding a type, will rearrange the type
definition table in the resulting assembly, thus changing the type token
ids (which are basically offsets into the type definition table in the
PE executable). This is what may cause an app to crash on the runtime
with an exception similar to:

    android.runtime.JavaProxyThrowable: System.NotSupportedException: Cannot create instance of type 'com.glmsoftware.OBDNowProto.SettingsFragmentCompat': no Java peer type found.
      at Java.Interop.JniPeerMembers+JniInstanceMethods..ctor (System.Type declaringType) [0x0004b] in <e3e4dfa992a7411b85acfe193481be3e>:0
      at Java.Interop.JniPeerMembers+JniInstanceMethods.GetConstructorsForType (System.Type declaringType) [0x00031] in <e3e4dfa992a7411b85acfe193481be3e>:0
      at Java.Interop.JniPeerMembers+JniInstanceMethods.StartCreateInstance (System.String constructorSignature, System.Type declaringType, Java.Interop.JniArgumentValue* parameters) [0x00038] in <e3e4dfa992a7411b85acfe193481be3e>:0
      at AndroidX.Preference.PreferenceFragmentCompat..ctor () [0x00034] in <005e3ae6340747e1aea6d08b095cf286>:0
      at com.glmsoftware.OBDNowProto.SettingsFragmentCompat..ctor () [0x00026] in <a8dbee4be1674aa08cce57b50f21e347>:0
      at com.glmsoftware.OBDNowProto.SettingsActivity.OnCreate (Android.OS.Bundle bundle) [0x00083] in <a8dbee4be1674aa08cce57b50f21e347>:0
      at Android.App.Activity.n_OnCreate_Landroid_os_Bundle_ (System.IntPtr jnienv, System.IntPtr native__this, System.IntPtr native_savedInstanceState) [0x00011] in <c56099afccf04721853684f376a89527>:0
        at (wrapper dynamic-method) Android.Runtime.DynamicMethodNameCounter.3(intptr,intptr,intptr)
        at crc64596a13587a898911.SettingsActivity.n_onCreate(Native Method)
        at crc64596a13587a898911.SettingsActivity.onCreate(SettingsActivity.java:40)
        at android.app.Activity.performCreate(Activity.java:7825)
        at android.app.Activity.performCreate(Activity.java:7814)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1306)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3245)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3409)
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83)
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2016)
        at android.os.Handler.dispatchMessage(Handler.java:107)
        at android.os.Looper.loop(Looper.java:214)
        at android.app.ActivityThread.main(ActivityThread.java:7356)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)

Thus, we need to revert the Debug builds to the variation of the old
string-based type name mapping. This commit implements it in a slightly
leaner form than it was implemented before
ce2bc68 landed in that only one copy of
each set of type names (Java and managed) is maintained in both memory
and on disk, at a tiny (sub millisecond) expense at the run time to fix
up pointers between the two tables.

src/Mono.Android/Android.Runtime/JNIEnv.cs

@@ -670,8 +670,9 @@ public static string GetClassNameFromInstance (IntPtr jobject)
 			}
 		}
 
-		[DllImport ("__Internal", CallingConvention = CallingConvention.Cdecl)]
-		static extern IntPtr monodroid_typemap_managed_to_java (byte[] mvid, int token);
+		// TODO: `type_name` is temporary, until https://github.com/mono/mono/issues/19377 is fixed
+		[MethodImplAttribute(MethodImplOptions.InternalCall)]
+		static extern unsafe IntPtr monodroid_typemap_managed_to_java (Type type, byte* mvid, string type_name);
 
 		internal static void LogTypemapTrace (StackTrace st)
 		{
@@ -685,19 +686,24 @@ internal static void LogTypemapTrace (StackTrace st)
 			}
 		}
 
-		internal static string TypemapManagedToJava (Type type)
+		internal static unsafe string TypemapManagedToJava (Type type)
 		{
 			if (mvid_bytes == null)
 				mvid_bytes = new byte[16];
 
-			Span<byte> mvid = new Span<byte>(mvid_bytes);
-			byte[] mvid_slow = null;
+			var mvid = new Span<byte>(mvid_bytes);
+			byte[] mvid_data = null;
 			if (!type.Module.ModuleVersionId.TryWriteBytes (mvid)) {
 				monodroid_log (LogLevel.Warn, LogCategories.Default, $"Failed to obtain module MVID using the fast method, falling back to the slow one");
-				mvid_slow = type.Module.ModuleVersionId.ToByteArray ();
+				mvid_data = type.Module.ModuleVersionId.ToByteArray ();
+			} else {
+				mvid_data = mvid_bytes;
 			}
 
-			IntPtr ret = monodroid_typemap_managed_to_java (mvid_slow == null ? mvid_bytes : mvid_slow, type.MetadataToken);
+			IntPtr ret;
+			fixed (byte* mvidptr = mvid_data) {
+				ret = monodroid_typemap_managed_to_java (type, mvidptr, type.FullName);
+			}
 
 			if (ret == IntPtr.Zero) {
 				if (LogTypemapMissStackTrace) {

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

@@ -402,7 +402,7 @@ void SaveResource (string resource, string filename, string destDir, Func<string
 		void WriteTypeMappings (List<TypeDefinition> types)
 		{
 			var tmg = new TypeMapGenerator ((string message) => Log.LogDebugMessage (message), SupportedAbis);
-			if (!tmg.Generate (SkipJniAddNativeMethodRegistrationAttributeScan, types, TypemapOutputDirectory, GenerateNativeAssembly, out ApplicationConfigTaskState appConfState))
+			if (!tmg.Generate (Debug, SkipJniAddNativeMethodRegistrationAttributeScan, types, TypemapOutputDirectory, GenerateNativeAssembly, out ApplicationConfigTaskState appConfState))
 				throw new XamarinAndroidException (4308, Properties.Resources.XA4308);
 			GeneratedBinaryTypeMaps = tmg.GeneratedBinaryTypeMaps.ToArray ();
 			BuildEngine4.RegisterTaskObject (ApplicationConfigTaskState.RegisterTaskObjectKey, appConfState, RegisteredTaskObjectLifetime.Build, allowEarlyCollection: false);

src/Xamarin.Android.Build.Tasks/Utilities/ARMNativeAssemblerTargetProvider.cs

@@ -14,6 +14,7 @@ class ARMNativeAssemblerTargetProvider : NativeAssemblerTargetProvider
 		public override string AbiName => Is64Bit ? ARMV8a : ARMV7a;
 		public override uint MapModulesAlignBits => Is64Bit ? 3u : 2u;
 		public override uint MapJavaAlignBits { get; } = 2;
+		public override uint DebugTypeMapAlignBits => Is64Bit ? 3u : 2u;
 
 		public ARMNativeAssemblerTargetProvider (bool is64Bit)
 		{

src/Xamarin.Android.Build.Tasks/Utilities/NativeAssemblerTargetProvider.cs

@@ -11,6 +11,7 @@ abstract class NativeAssemblerTargetProvider
 		public abstract string AbiName { get; }
 		public abstract uint MapModulesAlignBits { get; }
 		public abstract uint MapJavaAlignBits { get; }
+		public abstract uint DebugTypeMapAlignBits { get; }
 
 		public virtual string MapType <T> ()
 		{

src/Xamarin.Android.Build.Tasks/Utilities/NativeTypeMappingData.cs

@@ -6,16 +6,16 @@ namespace Xamarin.Android.Tasks
 {
 	class NativeTypeMappingData
 	{
-		public TypeMapGenerator.ModuleData[] Modules { get; }
+		public TypeMapGenerator.ModuleReleaseData[] Modules { get; }
 		public IDictionary<string, string> AssemblyNames { get; }
 		public string[] JavaTypeNames                    { get; }
-		public TypeMapGenerator.TypeMapEntry[] JavaTypes { get; }
+		public TypeMapGenerator.TypeMapReleaseEntry[] JavaTypes { get; }
 
 		public uint MapModuleCount { get; }
 		public uint JavaTypeCount  { get; }
 		public uint JavaNameWidth  { get; }
 
-		public NativeTypeMappingData (Action<string> logger, TypeMapGenerator.ModuleData[] modules, int javaNameWidth)
+		public NativeTypeMappingData (Action<string> logger, TypeMapGenerator.ModuleReleaseData[] modules, int javaNameWidth)
 		{
 			Modules = modules ?? throw new ArgumentNullException (nameof (modules));
 
@@ -24,19 +24,19 @@ public NativeTypeMappingData (Action<string> logger, TypeMapGenerator.ModuleData
 
 			AssemblyNames = new Dictionary<string, string> (StringComparer.Ordinal);
 
-			var tempJavaTypes = new Dictionary<string, TypeMapGenerator.TypeMapEntry> (StringComparer.Ordinal);
+			var tempJavaTypes = new Dictionary<string, TypeMapGenerator.TypeMapReleaseEntry> (StringComparer.Ordinal);
 			int managedStringCounter = 0;
 			var moduleComparer = new TypeMapGenerator.ModuleUUIDArrayComparer ();
 
-			foreach (TypeMapGenerator.ModuleData data in modules) {
+			foreach (TypeMapGenerator.ModuleReleaseData data in modules) {
 				data.AssemblyNameLabel = $"map_aname.{managedStringCounter++}";
 				AssemblyNames.Add (data.AssemblyNameLabel, data.AssemblyName);
 
 				int moduleIndex = Array.BinarySearch (modules, data, moduleComparer);
 				if (moduleIndex < 0)
 					throw new InvalidOperationException ($"Unable to map module with MVID {data.Mvid} to array index");
 
-				foreach (TypeMapGenerator.TypeMapEntry entry in data.Types) {
+				foreach (TypeMapGenerator.TypeMapReleaseEntry entry in data.Types) {
 					entry.ModuleIndex = moduleIndex;
 					if (tempJavaTypes.ContainsKey (entry.JavaName))
 						continue;
@@ -47,7 +47,7 @@ public NativeTypeMappingData (Action<string> logger, TypeMapGenerator.ModuleData
 			var javaNames = tempJavaTypes.Keys.ToArray ();
 			Array.Sort (javaNames, StringComparer.Ordinal);
 
-			var javaTypes = new TypeMapGenerator.TypeMapEntry[javaNames.Length];
+			var javaTypes = new TypeMapGenerator.TypeMapReleaseEntry[javaNames.Length];
 			for (int i = 0; i < javaNames.Length; i++) {
 				javaTypes[i] = tempJavaTypes[javaNames[i]];
 			}