v0.22.0

This release brings native Dart addons to Linux x64 with automatic runtime
downloads, and lets generic subclasses carry additional JavaScript payloads.

🐧 Build native addons on Linux

Use the same build API on Linux x64 and macOS arm64:

await buildPackage(
  library: File('lib/counter.dart').absolute.uri,
  output: Directory('npm-package'),
  packagesPath: File('.dart_tool/package_config.json').absolute.path,
  target: BuildTarget.native,
  metadata: {'name': '@scope/counter', 'version': '1.0.0'},
);

The first build downloads a precompiled runtime. Application authors need the
ordinary Dart SDK, without a C/C++ toolchain or Dart SDK sources. npm consumers
need only Node.js and the generated package; installation and import do not
perform runtime downloads.

Linux requires x64 and glibc 2.28 or later. /usr/bin/unzip is needed only
when downloading and extracting an uncached runtime. Cached runtimes support
offline builds; NAPI_RUNTIME_CACHE selects a custom cache, and
nativeRuntime still accepts a local bundle. Downloads and cached files are
verified against pinned hashes.

Each native package targets one platform. Automatic platform selection,
cross-compiling and musl distributions such as Alpine remain unsupported.
Both backends require Dart 3.13.5; native runtimes use ABI 15.

Native builds and offline use

🧩 Add payload parameters in subclasses

A subclass can now introduce independent generic parameters:

@NAPI()
class Box<T> {
  Box(this.value);
  T value;
}

@NAPI()
class Tagged<T, Meta> extends Box<T> {
  Tagged(super.value, this.metadata);
  Meta metadata;
}

const metadata = {source: 'cache'};
const box = new Tagged('value', metadata);
box instanceof Box;         // true
box.metadata === metadata;  // true

Parent and child views share the same JavaScript object. Generic subclasses can
also inherit selected non-generic classes, including resource classes. Each
ancestor parameter must still map to a distinct, non-nullable child parameter;
fixed, repeated or nested mappings remain unsupported.

Generic inheritance

Other improvements and fixes

• Private constant defaults can contain Dart type values such as String,
  List<int> and record types. These values stay inside Dart; Type is not a
  JavaScript-facing type. Function types and void remain unsupported inside
  inaccessible defaults.
• Preserve the canonical identity of constant defaults containing NaN on x64.

Constant defaults