waste_lens

Catch wasted work in your Flutter app — dead widget rebuilds, redundant API calls, memory leaks, and memory pressure — surfaced live in-app and exportable as a report.

Many tools show you rebuilds/sec and FPS. waste_lens is different: it proves a rebuild produced identical output (dead) and that work was genuinely wasted — not just frequent.

waste_lens is a debug/profile tool. Everything is gated behind kDebugMode || kProfileMode; in release builds it compiles to a zero-overhead no-op — no timers, no listeners, an identical widget tree.

Install

dependencies:
  waste_lens: ^0.1.0

Quick start

Wrap your app once:

import 'package:waste_lens/waste_lens.dart';

void main() {
  runApp(
    WasteLens(
      config: WasteLensConfig(
        memory: true,
        leaks: true,
        rebuilds: true,
        overlay: true,
      ),
      child: const MyApp(),
    ),
  );
}

A draggable diagnostics bubble appears in debug/profile. Tap it for per-module tabs and live sparklines.

Modules

Dead rebuilds (the flagship)

A dead rebuild ran but produced identical output, so it was wasted.

• Tier A — churn (zero-config): hooks debugOnRebuildDirtyWidget and warns when a widget type rebuilds above churnThreshold within a window.
• Tier B — proven dead: wrap a subtree with a fingerprint of the inputs that should determine its output. If the fingerprint is unchanged across a rebuild, it was dead:

DeadRebuildProbe(
  label: 'PriceTag',
  fingerprint: () => [price, currency], // inputs that matter
  child: PriceTag(price: price, currency: currency),
);

The probe outlines the subtree in amber for a moment when it catches a dead rebuild — caught red-handed.

Memory

RSS sampling (every mode), image-cache pressure, and a best-effort VM-service allocation profiler:

final top = await WasteLens.snapshot(); // top allocating classes (debug)

Leaks

A thin wrapper over the official leak_tracker. Framework disposables are tracked automatically. For custom disposables, use the DisposeGuard mixin:

class SearchController with DisposeGuard {
  SearchController() {
    trackCreation();
  }
  void dispose() {
    trackDisposal();
    // release inner resources…
  }
}

Redundant API calls

Live in the companion package waste_lens_dio.

Optimization helpers

imageCacheTuner(maxBytes: 50 << 20); // cap decoded-image memory

class _MyState extends State<MyWidget> with AutoDisposeMixin<MyWidget> {
  late final controller =
      autoDispose(TextEditingController(), (c) => c.dispose());
}

Reports

final json = WasteLens.exportReport(); // aggregate snapshot for CI / bug reports

Release behaviour

Gate.enabled is a compile-time constant (kDebugMode || kProfileMode). In release every entry point short-circuits and the compiler tree-shakes the gated branches away.

Lints

Static companion: waste_lens_lints.

License

MIT.