[Xamarin.Android.Tools.Bytecode] Honor Kotlin class visibility (#499)

The [Kotlin language][0] stores Kotlin-specific metadata within a
[`RuntimeVisibleAnnotation` bytecode attribute blob][1] with a type
name value of `Lkotlin/Metadata;`.  The annotation can contain the
following keys:

  * `k`: The kind of metadata annotation (required)
  * `mv`: The version of metadata (required)
  * `bv`: The version of the byte code (required)
  * `d1`: The encoded metadata (optional)
  * `d2`: Additional strings (optional)

Add support for a kind value of `Class`.

The `Class` metadata is encoded as an array of strings.

First we have to decode the `d1` data into bytes using a variety of
potential encodings.  Once we have bytes, they are formatted as:

  * First byte - Length of the string table
    * optional additional bytes to encode length of string table
  * Protobuf encoded string data table is next `length` bytes
  * Remaining bytes are Protobuf encoded data

The string data table provides an indexed lookup table used by the
Protobuf metadata to retrieve strings from one of:

  * Directly encoded in the string table
  * The string array contained in the `d2` field
  * A predefined hardcoded string

The Protobuf encoded data is relatively straightforward.  All fields
that would be strings are instead indexes into the string data table.
It provides metadata about the class itself and every
field/method/property/parameter/etc. for the class.

Once the Protobuf data is parsed, we can use this information to
influence the normal XML declarations that `class-parse` produces:

  * Respect the Kotlin class visibility: if the Kotlin metadata
    specifies visibility as `Kotlin-Private` or `Kotlin-Internal`,
    set e.g. `//class/@visibility` to `private`, which prevents the
    type from being emitted into the XML description.

  * Filter out non-bindable constructs: Kotlin has a lot of
    interesting non-Class constructs it uses `.class` files for.
    Since our code doesn't understand them yet they do not generate
    usable bindings for these constructs.  Until we have completed
    our support for these constructs we mark them as `private` so we
    do not attempt to bind them.

~~ Protobuf Generation ~~

`src/Xamarin.Android.Tools.Bytecode/Kotlin/KotlinProtobufDefinition.cs`
is generated by using [`protogen`][2], by providing Kotlin's
[protobuf schema][3] as input.

Note that `protogen` doesn't support `import`, so the input text
provided to `protogen` will need to replace:

	import "core/metadata/src/ext_options.proto";

with the contents of [`core/metadata/src/ext_options.proto`][4], and
replace

	import "core/metadata/src/metadata.proto";

with the contents of [`core/metadata/src/metadata.proto`][5].

The default `protogen` options were used to generate
`KotlinProtobufDefinition.cs`.

[0]: https://kotlinlang.org
[1]: https://docs.oracle.com/javase/specs/jvms/se7/html/jvms-4.html#jvms-4.7.16
[2]: https://protogen.marcgravell.com
[3]: https://github.com/JetBrains/kotlin/blob/master/core/metadata.jvm/src/jvm_metadata.proto
[4]: https://github.com/JetBrains/kotlin/blob/master/core/metadata/src/ext_options.proto
[5]: https://github.com/JetBrains/kotlin/blob/master/core/metadata/src/metadata.proto

Author: jpobst

ThirdPartyNotices.txt

@@ -0,0 +1,219 @@
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src/Xamarin.Android.Tools.Bytecode/ClassPath.cs

@@ -8,6 +8,7 @@
 using System.Xml.Linq;
 using System.Xml.XPath;
 using System.Text;
+using Xamarin.Android.Tools.Bytecode.Kotlin;
 
 namespace Xamarin.Android.Tools.Bytecode {
 
@@ -298,6 +299,9 @@ public XElement ToXElement ()
 			// This optional behavior is to bring compatibility with old behavior.
 			if (AutoRename)
 				FixUpParametersFromClasses ();
+
+			KotlinFixups.Fixup (classFiles);
+
 			var packagesDictionary = GetPackages ();
 			var api = new XElement ("api",
 					GetApiSource (),

src/Xamarin.Android.Tools.Bytecode/Kotlin/JvmNameResolver.cs

@@ -0,0 +1,99 @@
+using System;
+using System.Collections.Generic;
+using org.jetbrains.kotlin.metadata.jvm;
+
+namespace Xamarin.Android.Tools.Bytecode
+{
+	// https://github.com/JetBrains/kotlin/blob/master/core/metadata.jvm/src/org/jetbrains/kotlin/metadata/jvm/deserialization/JvmNameResolver.kt
+	class JvmNameResolver
+	{
+		readonly List<StringTableTypes.Record> records = new List<StringTableTypes.Record> ();
+		readonly List<string> strings;
+
+		public JvmNameResolver (StringTableTypes table, List<string> strings)
+		{
+			foreach (var t in table.Records)
+				for (var i = 0; i < t.Range; i++)
+					records.Add (t);
+
+			this.strings = strings;
+		}
+
+		public string GetString (int index)
+		{
+			var record = records [index];
+
+			string val;
+
+			// Get string from:
+			// - Embedded in string record table
+			// - Predefined string
+			// - Constant pool
+			if (!string.IsNullOrEmpty (record.String))
+				val = record.String;
+			else if (record.PredefinedIndex > 0)
+				val = predefined_strings [record.PredefinedIndex];
+			else
+				val = strings [index];
+
+			if (record.SubstringIndexs?.Length >= 2) {
+				var begin = record.SubstringIndexs [0];
+				var end = record.SubstringIndexs [1];
+
+				if (begin > 0 && begin <= end && end <= val.Length)
+					val = val.Substring (begin, end);
+			}
+
+			if (record.ReplaceChars?.Length >= 2) {
+				var from = (char) record.ReplaceChars [0];
+				var to = (char) record.ReplaceChars [1];
+
+				val = val.Replace (from, to);
+			}
+
+			if (record.operation == StringTableTypes.Record.Operation.InternalToClassId)
+				val = val.Replace ('$', '.');
+			else if (record.operation == StringTableTypes.Record.Operation.DescToClassId) {
+				if (val.Length >= 2)
+					val = val.Substring (1, val.Length - 1);
+
+				val = val.Replace ('$', '.');
+			}
+
+			return val;
+		}
+
+		static readonly string [] predefined_strings = new string [] {
+			"kotlin/Any",
+			"kotlin/Nothing",
+			"kotlin/Unit",
+			"kotlin/Throwable",
+			"kotlin/Number",
+
+			"kotlin/Byte", "kotlin/Double", "kotlin/Float", "kotlin/Int",
+			"kotlin/Long", "kotlin/Short", "kotlin/Boolean", "kotlin/Char",
+
+			"kotlin/CharSequence",
+			"kotlin/String",
+			"kotlin/Comparable",
+			"kotlin/Enum",
+
+			"kotlin/Array",
+			"kotlin/ByteArray", "kotlin/DoubleArray", "kotlin/FloatArray", "kotlin/IntArray",
+			"kotlin/LongArray", "kotlin/ShortArray", "kotlin/BooleanArray", "kotlin/CharArray",
+
+			"kotlin/Cloneable",
+			"kotlin/Annotation",
+
+			"kotlin/collections/Iterable", "kotlin/collections/MutableIterable",
+			"kotlin/collections/Collection", "kotlin/collections/MutableCollection",
+			"kotlin/collections/List", "kotlin/collections/MutableList",
+			"kotlin/collections/Set", "kotlin/collections/MutableSet",
+			"kotlin/collections/Map", "kotlin/collections/MutableMap",
+			"kotlin/collections/Map.Entry", "kotlin/collections/MutableMap.MutableEntry",
+
+			"kotlin/collections/Iterator", "kotlin/collections/MutableIterator",
+			"kotlin/collections/ListIterator", "kotlin/collections/MutableListIterator"
+		};
+	}
+}