[TrimmableTypeMap] Add JCW Java source generator

[simonrozsival]

Part of #10799

Summary

Adds JCW (Java Callable Wrapper) Java source code generation for TypeMap proxy types.

Changes

• JcwJavaSourceGenerator: generates .java source files for each ACW proxy type
  • Java class with extends/implements declarations
  • Constructor generation with super calls
  • Native method stubs for UCO wrappers
  • Uses $$"""...""" raw string literals for clean Java template output

Tests

• Comprehensive tests for all JCW generation scenarios (basic types, abstract types, constructors, inheritance)

Stacked PRs:

1. PR [TrimmableTypeMap] Add TypeMap proxy groundwork with CreateInstance #10808 — Proxy groundwork with CreateInstance
2. PR [TrimmableTypeMap] Add UCO wrappers, RegisterNatives, and IAndroidCallableWrapper #10831 — UCO wrappers + RegisterNatives
3. PR [TrimmableTypeMap] Add JCW Java source generator #10830 ← this PR — JCW Java Source Generation

[Copilot]

Pull request overview

Adds a new JCW (Java Callable Wrapper) Java source generator to the Microsoft.Android.Sdk.TrimmableTypeMap pipeline, intended to emit .java stubs from scanned JavaPeerInfo records, along with a new xUnit test suite covering generation scenarios.

Changes:

• Introduces JcwJavaSourceGenerator to emit package/class declarations, constructors, marshal method wrappers, and native declarations.
• Adds JcwJavaSourceGeneratorTests validating output formatting and key generation behaviors (constructors, methods, throws clauses, filtering).
• Implements JNI-to-Java name/type conversion helpers used by the generator and tests.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 7 comments.

File	Description
src/Microsoft.Android.Sdk.TrimmableTypeMap/Generator/JcwJavaSourceGenerator.cs	New generator responsible for producing JCW .java source files from JavaPeerInfo.
tests/Microsoft.Android.Sdk.TrimmableTypeMap.Tests/Generator/JcwJavaSourceGeneratorTests.cs	New unit tests validating the generated Java output and conversion helpers.

[Copilot]

The generator mixes explicit \n (e.g., writer.Write(..."\n")) with TextWriter.WriteLine(), which uses writer.NewLine (platform-dependent). This can yield inconsistent line endings and makes the output non-deterministic across OSes. Consider using WriteLine() consistently after setting writer.NewLine = "\n", or consistently writing \n everywhere.

[Copilot]

This assertion hard-codes \n line endings, but StringWriter/TextWriter.WriteLine() will use Environment.NewLine by default (e.g., \r\n on Windows). To keep the test cross-platform, normalize line endings (e.g., replace \r\n with \n) or assert using Assert.StartsWith($"package my.app;{Environment.NewLine}", java).

[Copilot]

Avoid using the null-forgiving operator (!) for nullable handling. Path.GetDirectoryName(...) can be asserted non-null (or checked) instead, which keeps the test consistent with the repo's nullable practices.

Suggested change

	var testAssemblyDir = Path.GetDirectoryName (typeof (JcwJavaSourceGeneratorTests).Assembly.Location)!;
	var testAssemblyDir = Path.GetDirectoryName (typeof (JcwJavaSourceGeneratorTests).Assembly.Location);
	Assert.NotNull (testAssemblyDir);

[Copilot]

JcwJavaSourceGenerator is declared without an access modifier (internal), but the test project instantiates it directly. There is no InternalsVisibleTo for Microsoft.Android.Sdk.TrimmableTypeMap.Tests, so this will make the tests (and any external caller) unable to access the type. Consider making the generator public, or add an InternalsVisibleTo attribute for the test assembly if you want to keep the API internal.

Suggested change

	sealed class JcwJavaSourceGenerator
	public sealed class JcwJavaSourceGenerator

[Copilot]

Generate(IReadOnlyList<JavaPeerInfo> ...) only filters on DoNotGenerateAcw, but the scanner can return interface peers (JavaPeerInfo.IsInterface=true). Generating a class stub for an interface will produce invalid Java. Align the filtering with ModelBuilder (skip interfaces, and possibly only generate for actual ACW types).

Suggested change

	if (type.DoNotGenerateAcw) {
	if (type.DoNotGenerateAcw || type.IsInterface) {

[Copilot]

The generated Java methods always include @Override. This will cause Java compilation failures for methods that do not actually override a supertype method (notably [Export] methods, which have Connector == null and are new methods on the stub). Consider omitting @Override entirely, or only emitting it when you can prove the method overrides something.

[Copilot]

GetOutputFilePath uses type.JavaName directly to build a relative path. Since JavaName ultimately comes from user-controlled [Register] strings, a malicious value containing .. or rooted paths could write files outside outputDirectory (path traversal). Validate/sanitize JavaName (e.g., reject .., drive roots, and invalid path chars) and ensure the final Path.GetFullPath stays under outputDirectory.

Suggested change

	// JNI name uses '/' as separator and '$' for nested types
	// e.g., "com/example/MainActivity" → "com/example/MainActivity.java"
	// Nested types: "com/example/Outer$Inner" → "com/example/Outer$Inner.java" (same file convention)
	string relativePath = type.JavaName + ".java";
	return Path.Combine (outputDirectory, relativePath);
	if (type.JavaName is null) {
	throw new InvalidOperationException ("JavaName cannot be null when generating JCW source.");
	}
	string javaName = type.JavaName;
	// Basic validation to prevent path traversal and rooted paths.
	// JavaName is expected to be a JNI-style class name (e.g., "com/example/MainActivity").
	if (javaName.Length == 0) {
	throw new InvalidOperationException ("JavaName cannot be empty when generating JCW source.");
	}
	// Disallow parent-directory traversal.
	if (javaName.Contains ("..", StringComparison.Ordinal)) {
	throw new InvalidOperationException ($"JavaName '{javaName}' is invalid: must not contain \"..\".");
	}
	// Disallow rooted or drive-qualified paths.
	if (Path.IsPathRooted (javaName)) {
	throw new InvalidOperationException ($"JavaName '{javaName}' is invalid: must not be a rooted path.");
	}
	// Disallow backslashes and drive separators (e.g., 'C:foo').
	if (javaName.IndexOfAny (new [] { '\\', ':' }) >= 0) {
	throw new InvalidOperationException ($"JavaName '{javaName}' is invalid: contains illegal path characters.");
	}
	// Disallow any other invalid path characters (excluding '/' which is valid in JNI names).
	char [] invalidPathChars = Path.GetInvalidPathChars ();
	for (int i = 0; i < javaName.Length; i++) {
	char c = javaName [i];
	if (c == '/') {
	continue;
	}
	if (Array.IndexOf (invalidPathChars, c) >= 0) {
	throw new InvalidOperationException ($"JavaName '{javaName}' is invalid: contains illegal path characters.");
	}
	}
	string fullOutputDir = Path.GetFullPath (outputDirectory);
	// JNI name uses '/' as separator and '$' for nested types
	// e.g., "com/example/MainActivity" → "com/example/MainActivity.java"
	// Nested types: "com/example/Outer$Inner" → "com/example/Outer$Inner.java" (same file convention)
	string relativePath = javaName + ".java";
	string combinedPath = Path.Combine (fullOutputDir, relativePath);
	string fullPath = Path.GetFullPath (combinedPath);
	// Ensure the resulting path stays within the output directory.
	if (!fullPath.StartsWith (fullOutputDir, StringComparison.OrdinalIgnoreCase)) {
	throw new InvalidOperationException ($"JavaName '{javaName}' is invalid: resulting path is outside the output directory.");
	}
	if (fullPath.Length > fullOutputDir.Length) {
	char separator = fullPath [fullOutputDir.Length];
	if (separator != Path.DirectorySeparatorChar && separator != Path.AltDirectorySeparatorChar) {
	throw new InvalidOperationException ($"JavaName '{javaName}' is invalid: resulting path is outside the output directory.");
	}
	}
	return fullPath;