[shai-almog]

Closes the gaps a real-world Flutter port into Codename One ran into: language features the transpiler mishandled, runtime crashes, missing Flutter API, stubs that were too shallow, dart:* gaps, and weak diagnostics. A clean-room acceptance app, scripts/flutter-apps/club_hub, follows the same shape as that port: it pulls in async, collection, hive, http, markdown, source_span, stream_channel, string_scanner, table_calendar, web_socket_channel and more, 699 Dart files in all. It now transpiles and compiles with zero errors. field_notes and pet_adoption are still accepted.

What changed

Transpiler (maven/dart-transpiler)

• Generics:
  • type arguments are substituted from the receiver and the caller, for stub methods, named constructors, named factories and static generics
  • explicit type arguments are honoured on factories and on fold/map
  • covariant collection slots are cast
  • classes that are a Set, List or Iterable only through implements, beside a superclass, get live views, mixin forwarders and covariant-return pins
• Closures:
  • capture boxing covers every body emitter, parameters (block and arrow bodies) and cascades
  • local functions can call themselves
  • lambda parameter types are inferred from a generic context
  • tear-offs: constructors, sinks, raw-bound casts and typedef void adapters
  • an immediately invoked closure takes its return type from its own returns
  • a list literal of closures with no context is typed by their function shape
• Control flow:
  • a non-void body that ends in a Never call gets a closing throw
  • rethrow and guardless if-case count as leaving the method
• Constructors and lookup:
  • constructor redirects to named constructors
  • overrides that widen a type variable to its bound
  • top-level lookup is import-scoped
  • an async main waits for running async* bodies
• Strings: String.runes, and lone surrogates in literals are escaped.

Runtimes (maven/dart-runtime, maven/flutter-runtime)

• An isolate event loop for timers and microtasks.
• Lists record their element type, and dynamic downcasts are checked.
• Stream/StreamTransformer variance fixes, and typed File.openRead.
• Flutter API gaps closed: Matrix4's 16-argument constructor, generic TweenAnimationBuilder, AlignmentGeometry on Align/Stack/transitions, Scaffold.persistentFooterButtons, and a typed showDateRangePicker.

Tests

• Every fix has a behaviour case whose expect.txt comes from a real dart run; Flutter-only fixes have flutter-runtime unit tests.
• Behaviour cases this branch added are named for what they cover.
• Nothing in the tests or fixtures comes from the original app.

Verification

• install of dart-runtime, dart-transpiler and flutter-runtime with CN1_DART_TESTS_REQUIRED=1: 1,329 tests, 0 failures, 0 skipped, including 244 behaviour cases.
• Acceptance: club_hub, field_notes and pet_adoption all ACCEPTED.
• Other checks: EmbeddedStubDriftTest and FlutterProjectImporterTest (31) pass, and SpotBugs on build-engine reports 0 findings. The control-character, @author, @since, ASCII and copyright gates are clean.

Known limits

• Generic type arguments are not reified at runtime: whereType<Relay<int>>() keeps a Relay<String> that Dart would drop.
• async* bodies still run on their own thread; a CPS state-machine lowering is separate work.
• Function.apply with named arguments is unsupported.

🤖 Generated with Claude Code

[shai-almog]

Compared 210 screenshots: 210 matched.
Native Windows port (arm64 / Apple Silicon - Arm): full hellocodenameone screenshot suite rendered offscreen with Direct2D/DirectWrite, plus the real benchmarks (base64 native/CN1/SIMD, image createMask/applyMask/modifyAlpha/PNG/JPEG, NEON SIMD kernels). Compared against the in-repo baseline in scripts/windows/screenshots.

Benchmark Results

Detailed Performance Metrics

Metric	Duration
SIMD kernel backend	SSE2 (x64) / NEON (arm64) native kernels
SIMD int-add (64K x300)	java 48ms / native 3ms = 16.0x speedup
SIMD float-mul (64K x300)	java 49ms / native 3ms = 16.3x speedup
SIMD kernel correctness	PASS (native result == scalar reference)
Base64 native bridge	unavailable (CN1 + SIMD + image benchmarks only)
Base64 payload size	8192 bytes
Base64 benchmark iterations	6000
Base64 SIMD byte path	gated to scalar (CPU autovectorizes scalar; explicit SIMD not beneficial here)
Base64 CN1 encode	59.000 ms
Base64 CN1 decode	70.000 ms
Base64 SIMD encode	77.000 ms
Base64 encode ratio (SIMD/CN1)	1.305x (30.5% slower)
Base64 SIMD decode	73.000 ms
Base64 decode ratio (SIMD/CN1)	1.043x (4.3% slower)
Image encode benchmark iterations	100
Image createMask (SIMD off)	5.000 ms
Image createMask (SIMD on)	2.000 ms
Image createMask ratio (SIMD on/off)	0.400x (60.0% faster)
Image applyMask (SIMD off)	16.000 ms
Image applyMask (SIMD on)	20.000 ms
Image applyMask ratio (SIMD on/off)	1.250x (25.0% slower)
Image modifyAlpha (SIMD off)	17.000 ms
Image modifyAlpha (SIMD on)	13.000 ms
Image modifyAlpha ratio (SIMD on/off)	0.765x (23.5% faster)
Image modifyAlpha removeColor (SIMD off)	15.000 ms
Image modifyAlpha removeColor (SIMD on)	9.000 ms
Image modifyAlpha removeColor ratio (SIMD on/off)	0.600x (40.0% faster)

ParparVM vs HotSpot (JDK 25): Windows arm64

Runner CPU: ARMv8 (64-bit) Family 8 Model D49 Revision 0, MICROSOFT CORPORATION (baseline windows-arm64@armv8-64-bit-family-8-model-d49-microsoft-corporation)

Ratios are ParparVM / JDK 25: below 1.00x ParparVM is faster (time) or smaller (RAM). Median of 5 interleaved, paired rounds; every run's output was verified. A ratio more than 20% (time) / 25% (RAM) above its baseline in vm/selfhost/perf-baseline/ is a regression and fails; one that far below is an improvement, reported but not failed (a row whose calibration runs were noisier carries a wider tolerance), and for RAM the change must also exceed 0.05x in absolute terms. Both run unpinned on all of the runner's CPUs, with their own default thread counts.

Benchmark	Cores	Time	RAM	Status
hello (WinHelloMain)	4	1.06x (base 1.11x, -4.4%)	0.71x (base 0.75x, -6.0%)	ok
translator (self)	4	0.86x (base 0.84x, +2.8%)	0.47x (base 0.51x, -7.6%)	ok
intArithmetic	4	1.04x (base 1.04x, -0.1%)	0.06x (base 0.06x, +2.9%)	ok
longArithmetic	4	0.79x (base 0.80x, -0.0%)	0.06x (base 0.06x, +3.1%)	ok
mathTranscendental	4	0.70x (base 0.72x, -3.2%)	0.07x (base 0.06x, +1.7%)	ok
arraySequential	4	0.38x (base 0.46x, -16.2%)	0.39x (base 0.39x, +0.1%)	ok
arrayRandom	4	0.94x (base 0.94x, +0.0%)	0.23x (base 0.23x, +0.2%)	ok
objectAllocation	4	1.84x (base 1.82x, +0.9%)	0.40x (base 0.43x, -6.7%)	ok
valueEscape	4	0.76x (base 0.76x, +0.0%)	0.05x (base 0.05x, +3.5%)	ok
hashMapChurn	4	1.00x (base 0.98x, +1.1%)	0.12x (base 0.12x, +0.7%)	ok
stringBuilding	4	1.53x (base 1.43x, +7.1%)	0.27x (base 0.27x, -0.1%)	ok
recursion	4	1.46x (base 1.46x, -0.4%)	0.07x (base 0.07x, +1.2%)	ok
quicksort	4	1.01x (base 1.00x, +0.5%)	0.12x (base 0.12x, +0.6%)	ok

Result: no regression