[TrimmableTypeMap] Add JCW Java source generator

src/Microsoft.Android.Sdk.TrimmableTypeMap/Generator/JcwJavaSourceGenerator.cs

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+using System;
+using System.Collections.Generic;
+using System.IO;
+
+namespace Microsoft.Android.Sdk.TrimmableTypeMap;
+
+/// <summary>
+/// Generates JCW (Java Callable Wrapper) .java source files from scanned <see cref="JavaPeerInfo"/> records.
+/// Only processes ACW types (where <see cref="JavaPeerInfo.DoNotGenerateAcw"/> is false).
+/// </summary>
+/// <remarks>
+/// <para>Each generated .java file looks like this (pseudo-Java):</para>
+/// <code>
+/// package com.example;
+///
+/// public class MainActivity
+///     extends android.app.Activity
+///     implements
+///         mono.android.IGCUserPeer,
+///         android.view.View.OnClickListener
+/// {
+///     static {
+///         mono.android.Runtime.registerNatives (MainActivity.class);
+///     }
+///
+///     public MainActivity (android.content.Context p0)
+///     {
+///         super (p0);
+///         if (getClass () == MainActivity.class) nctor_0 (p0);
+///     }
+///     private native void nctor_0 (android.content.Context p0);
+///
+///     @Override
+///     public void onCreate (android.os.Bundle p0)
+///     {
+///         n_onCreate (p0);
+///     }
+///     public native void n_onCreate (android.os.Bundle p0);
+/// }
+/// </code>
+/// </remarks>
+sealed class JcwJavaSourceGenerator
+{
+	/// <summary>
+	/// Generates .java source files for all ACW types and writes them to the output directory.
+	/// Returns the list of generated file paths.
+	/// </summary>
+	public IReadOnlyList<string> Generate (IReadOnlyList<JavaPeerInfo> types, string outputDirectory)
+	{
+		if (types is null) {
+			throw new ArgumentNullException (nameof (types));
+		}
+		if (outputDirectory is null) {
+			throw new ArgumentNullException (nameof (outputDirectory));
+		}
+
+		var generatedFiles = new List<string> ();
+
+		foreach (var type in types) {
+			if (type.DoNotGenerateAcw || type.IsInterface) {
+				continue;
+			}
+
+			string filePath = GetOutputFilePath (type, outputDirectory);
+			string? dir = Path.GetDirectoryName (filePath);
+			if (dir != null) {
+				Directory.CreateDirectory (dir);
+			}
+
+			using var writer = new StreamWriter (filePath);
+			Generate (type, writer);
+			generatedFiles.Add (filePath);
+		}
+
+		return generatedFiles;
+	}
+
+	/// <summary>
+	/// Generates a single .java source file for the given type.
+	/// </summary>
+	internal void Generate (JavaPeerInfo type, TextWriter writer)
+	{
+		writer.NewLine = "\n";
+		WritePackageDeclaration (type, writer);
+		WriteClassDeclaration (type, writer);
+		WriteStaticInitializer (type, writer);
+		WriteConstructors (type, writer);
+		WriteMethods (type, writer);
+		WriteGCUserPeerMethods (writer);
+		WriteClassClose (writer);
+	}
+
+	static string GetOutputFilePath (JavaPeerInfo type, string outputDirectory)
+	{
+		JniSignatureHelper.ValidateJniName (type.JavaName);
+		string relativePath = type.JavaName + ".java";
+		return Path.Combine (outputDirectory, relativePath);
+	}
+
+	/// <summary>
+	/// Validates that the JNI name is well-formed: non-empty, each segment separated by '/'
+	/// contains only valid Java identifier characters (letters, digits, '_', '$').
+	/// This also prevents path traversal (e.g., ".." segments, rooted paths, backslashes).
+	/// </summary>
+	static void WritePackageDeclaration (JavaPeerInfo type, TextWriter writer)
+	{
+		string? package = JniSignatureHelper.GetJavaPackageName (type.JavaName);
+		if (package != null) {
+			writer.Write ("package ");
+			writer.Write (package);
+			writer.WriteLine (';');
+			writer.WriteLine ();
+		}
+	}
+
+	static void WriteClassDeclaration (JavaPeerInfo type, TextWriter writer)
+	{
+		string abstractModifier = type.IsAbstract && !type.IsInterface ? "abstract " : "";
+		string className = JniSignatureHelper.GetJavaSimpleName (type.JavaName);
+
+		writer.Write ($"public {abstractModifier}class {className}\n");
+
+		// extends clause
+		if (type.BaseJavaName != null) {
+			writer.WriteLine ($"\textends {JniSignatureHelper.JniNameToJavaName (type.BaseJavaName)}");
+		}
+
+		// implements clause — always includes IGCUserPeer, plus any implemented interfaces
+		writer.Write ("\timplements\n\t\tmono.android.IGCUserPeer");
+
+		foreach (var iface in type.ImplementedInterfaceJavaNames) {
+			writer.Write ($",\n\t\t{JniSignatureHelper.JniNameToJavaName (iface)}");
+		}
+
+		writer.WriteLine ();
+		writer.WriteLine ('{');
+	}
+
+	static void WriteStaticInitializer (JavaPeerInfo type, TextWriter writer)
+	{
+		string className = JniSignatureHelper.GetJavaSimpleName (type.JavaName);
+		writer.Write ($$"""
+	static {
+		mono.android.Runtime.registerNatives ({{className}}.class);
+	}
+
+
+""");
+	}
+
+	static void WriteConstructors (JavaPeerInfo type, TextWriter writer)
+	{
+		string simpleClassName = JniSignatureHelper.GetJavaSimpleName (type.JavaName);
+
+		foreach (var ctor in type.JavaConstructors) {
+			string parameters = FormatParameterList (ctor.Parameters);
+			string superArgs = ctor.SuperArgumentsString ?? FormatArgumentList (ctor.Parameters);
+			string args = FormatArgumentList (ctor.Parameters);
+
+			writer.Write ($$"""
+	public {{simpleClassName}} ({{parameters}})
+	{
+		super ({{superArgs}});
+		if (getClass () == {{simpleClassName}}.class) nctor_{{ctor.ConstructorIndex}} ({{args}});
+	}
+
+
+""");
+		}
+
+		// Write native constructor declarations
+		foreach (var ctor in type.JavaConstructors) {
+			string parameters = FormatParameterList (ctor.Parameters);
+			writer.WriteLine ($"\tprivate native void nctor_{ctor.ConstructorIndex} ({parameters});");
+		}
+
+		if (type.JavaConstructors.Count > 0) {
+			writer.WriteLine ();
+		}
+	}
+
+	static void WriteMethods (JavaPeerInfo type, TextWriter writer)
+	{
+		foreach (var method in type.MarshalMethods) {
+			if (method.IsConstructor) {
+				continue;
+			}
+
+			string javaReturnType = JniSignatureHelper.JniTypeToJava (method.JniReturnType);
+			bool isVoid = method.JniReturnType == "V";
+			string parameters = FormatParameterList (method.Parameters);
+			string args = FormatArgumentList (method.Parameters);
+			string returnPrefix = isVoid ? "" : "return ";
+
+			// throws clause for [Export] methods
+			string throwsClause = "";
+			if (method.ThrownNames != null && method.ThrownNames.Count > 0) {
+				throwsClause = $"\n\t\tthrows {string.Join (", ", method.ThrownNames)}";
+			}
+
+			if (method.Connector != null) {
+				writer.Write ($$"""
+
+	@Override
+	public {{javaReturnType}} {{method.JniName}} ({{parameters}}){{throwsClause}}
+	{
+		{{returnPrefix}}{{method.NativeCallbackName}} ({{args}});
+	}
+	public native {{javaReturnType}} {{method.NativeCallbackName}} ({{parameters}});
+
+""");
+			} else {
+				writer.Write ($$"""
+
+	public {{javaReturnType}} {{method.JniName}} ({{parameters}}){{throwsClause}}
+	{
+		{{returnPrefix}}{{method.NativeCallbackName}} ({{args}});
+	}
+	public native {{javaReturnType}} {{method.NativeCallbackName}} ({{parameters}});
+
+""");
+			}
+		}
+	}
+
+	static void WriteGCUserPeerMethods (TextWriter writer)
+	{
+		writer.Write ("""
+
+	private java.util.ArrayList refList;
+	public void monodroidAddReference (java.lang.Object obj)
+	{
+		if (refList == null)
+			refList = new java.util.ArrayList ();
+		refList.add (obj);
+	}
+
+	public void monodroidClearReferences ()
+	{
+		if (refList != null)
+			refList.clear ();
+	}
+
+""");
+	}
+
+	static void WriteClassClose (TextWriter writer)
+	{
+		writer.WriteLine ('}');
+	}
+
+	static string FormatParameterList (IReadOnlyList<JniParameterInfo> parameters)
+	{
+		if (parameters.Count == 0) {
+			return "";
+		}
+
+		var sb = new System.Text.StringBuilder ();
+		for (int i = 0; i < parameters.Count; i++) {
+			if (i > 0) {
+				sb.Append (", ");
+			}
+			sb.Append (JniSignatureHelper.JniTypeToJava (parameters [i].JniType));
+			sb.Append (" p");
+			sb.Append (i);
+		}
+		return sb.ToString ();
+	}
+
+	static string FormatArgumentList (IReadOnlyList<JniParameterInfo> parameters)
+	{
+		if (parameters.Count == 0) {
+			return "";
+		}
+
+		var sb = new System.Text.StringBuilder ();
+		for (int i = 0; i < parameters.Count; i++) {
+			if (i > 0) {
+				sb.Append (", ");
+			}
+			sb.Append ('p');
+			sb.Append (i);
+		}
+		return sb.ToString ();
+	}
+
+}