rune 1.3.0

Converts Dart widget code strings into real Flutter widgets at runtime via AST interpretation.

Rune

Turn Dart widget-construction source strings into live Flutter widgets at runtime.

Rune parses a string of Dart widget syntax (e.g. Column(children: [Text('Hello')])), walks the resulting AST via the official analyzer package, and constructs real Flutter widgets through pre-registered builders.

No dart:mirrors. No eval. No runtime code execution. The widgets that come out are ordinary Flutter widgets: they compose, animate, and perform like hand-written code.

Why

Deliver UI from a server, a CMS, or a designer tool without shipping a new app binary. The source you pass to a RuneView can be edited, A/B-tested, or user-authored. Because Rune only interprets a constrained subset of Dart expression syntax (never executing arbitrary code), it's compatible with Apple App Store and Google Play store-review policies.

Features

• Runtime interpretation, not compilation. analyzer produces the AST; Rune walks it.
• Store-compliant. No dart:mirrors, no eval, no on-device code generation.
• Layered and open/closed. Adding a new widget is one builder file, one registration, one test, with no core change.
• Strict typing. Dart 3 sealed exceptions, pattern matching, final class, @immutable. dynamic is banned outside the parser boundary.
• Single runtime dependency besides Flutter: analyzer. All other integrations (responsive scaling, state management, routing, ...) live in separate bridge packages.
• Rich data binding. Free identifiers (userName), deep dot-path (user.profile.name), list/map indexing (items[0].title), and data-driven widget lists (for (final item in items) ...), all resolved against a Map<String, Object?> you supply.
• String interpolation. 'Hello, $name!' and 'Count: ${n}' substitute data-context values into literal strings.
• Named events. ElevatedButton(onPressed: "submit") routes taps through RuneView.onEvent(name, args) to the host app.
• Extensible. A RuneBridge package registers widget/value/constant/extension handlers with one registerInto(config) call. 10.w, size.half, and similar receiver-style property access go through PropertyResolver → ExtensionRegistry.
• Typed error surface. Every failure raises a RuneException subtype carrying the offending source substring plus a human-readable message. RuneView.fallback + onError make failures non-fatal.
• very_good_analysis-strict. The whole package passes the strict lint floor with zero ignores beyond two documented exceptions.

Install

dependencies:
  rune: ^1.3.0

The package is pre-publication; use a git: or path: dependency until a tagged pub.dev release lands. dart pub publish --dry-run currently reports 0 errors / 0 warnings.

Quickstart

import 'package:flutter/material.dart';
import 'package:rune/rune.dart';

void main() {
  runApp(
    MaterialApp(
      home: Scaffold(
        appBar: AppBar(title: const Text('Rune Demo')),
        body: RuneView(
          source: r"""
            Column(
              mainAxisAlignment: MainAxisAlignment.center,
              children: [
                Text('Hello, $userName!'),
                SizedBox(height: 8),
                Text('You have ${cart.itemCount} items.'),
                SizedBox(height: 16),
                for (final item in cart.items)
                  Card(
                    child: ListTile(
                      title: Text(item.title),
                      subtitle: Text(item.subtitle),
                    ),
                  ),
                ElevatedButton(
                  onPressed: 'checkout',
                  child: Text('Checkout'),
                ),
              ],
            )
          """,
          config: RuneConfig.defaults(),
          data: const {
            'userName': 'Ali',
            'cart': {
              'itemCount': 3,
              'items': [
                {'title': 'Mouse', 'subtitle': '\$19'},
                {'title': 'Keyboard', 'subtitle': '\$79'},
                {'title': 'Monitor', 'subtitle': '\$299'},
              ],
            },
          },
          onEvent: (name, [args]) => debugPrint('event: $name'),
          fallback: const Text('Failed to render.'),
          onError: (error, stack) => debugPrint('Rune error: $error'),
        ),
      ),
    ),
  );
}

A runnable version lives in example/.

Supported source syntax

Current release: v1.3.0. Dialogs (AlertDialog, SimpleDialog, Dialog), popup menus (PopupMenuButton, PopupMenuItem, PopupMenuDivider), SnackBar, and imperative bridges (showDialog, showModalBottomSheet, showSnackBar, Navigator.pop). Source can now drive modal UI without touching the host app.

Category	Elements
Widgets	Text, SizedBox, Container, Column, Row, Padding, Center, Stack, Expanded, Flexible, Card, Icon, ListView, AppBar, Scaffold, ElevatedButton, TextButton, IconButton, TextField, Switch, Checkbox, ListTile, Divider, Spacer, GestureDetector, InkWell, SingleChildScrollView, Wrap, AspectRatio, Positioned, Slider, Radio, CheckboxListTile, SwitchListTile, RadioListTile, AnimatedContainer, AnimatedOpacity, AnimatedPositioned, BottomNavigationBar, TabBar, Tab, DropdownButton, DropdownMenuItem, FloatingActionButton, Chip, ChoiceChip, FilterChip, Badge, CircularProgressIndicator, LinearProgressIndicator, Hero, AnimatedSwitcher, AnimatedCrossFade, AnimatedSize, GridView.count, GridView.extent, Drawer, SafeArea, Visibility, Opacity, ClipRRect, ClipOval, Tooltip, CustomScrollView, SliverList, SliverToBoxAdapter, SliverAppBar, SliverPadding, SliverFillRemaining, SliverGrid.count, SliverGrid.extent, FittedBox, ColoredBox, DecoratedBox, Offstage, Semantics, ConstrainedBox, LimitedBox, UnconstrainedBox, FractionallySizedBox, NavigationBar, NavigationRail, StatefulBuilder, RuneCompose, FutureBuilder, StreamBuilder, LayoutBuilder, OrientationBuilder, AlertDialog, SimpleDialog, SimpleDialogOption, Dialog, PopupMenuButton, PopupMenuItem, PopupMenuDivider
Value ctors	EdgeInsets.all/symmetric/only/fromLTRB/zero, Color(hex), TextStyle(...), BorderRadius.circular(n), BoxDecoration(...), Image.network(url), Image.asset(path), Duration(...), BottomNavigationBarItem(...), Transform.scale/.rotate, Transform.translate, Transform.flip, Offset(dx, dy), BoxConstraints(...), NavigationDestination(...), NavigationRailDestination(...), RuneComponent(...), TextEditingController(...), ScrollController(...), FocusNode(...), PageController(...), ListView.builder, GridView.countBuilder, GridView.extentBuilder, SliverList.builder, SliverGrid.countBuilder, SliverGrid.extentBuilder, SnackBar(...)
Constants	Colors.*, MainAxisAlignment.*, CrossAxisAlignment.*, MainAxisSize.*, TextAlign.*, TextOverflow.*, Alignment.*, BoxFit.*, StackFit.*, Axis.*, FontWeight.*, BoxShape.*, FlexFit.*, BottomNavigationBarType.*, CrossFadeState.*, Clip.*, DecorationPosition.*, ListTileControlAffinity.*, NavigationRailLabelType.*, Curves.linear/easeIn/easeOut/easeInOut/bounce*/elastic*/fastOutSlowIn, ~60 common Icons.*, ConnectionState.*, Orientation.*, SnackBarBehavior.*
Literals	int, double, bool, null, string, list [...], set/map {...}, adjacent string concat
Interpolation	'Hello $name', 'Count: ${n}' (expressions resolve against data + constants)
Identifiers	Bare name → data['name']; Type.member → data Map traversal OR constants registry
Deep data paths	user.profile.name, items[0].title, Colors.grey[200] (any depth of nested maps plus list/map/MaterialColor indexing)
Collections	[for (final item in items) Text(item.title)] (data-driven widget lists, nested for-elements, static + for elements interleaved)
Built-in properties	.length, .isEmpty, .isNotEmpty, .first, .last on lists; .length, .isEmpty, .isNotEmpty on strings; .length, .isEmpty, .isNotEmpty, .keys, .values on maps; .hasData/.data/.hasError/.error/.connectionState on AsyncSnapshot; .maxWidth/.minWidth/.maxHeight/.minHeight/.biggest/.smallest on BoxConstraints
Built-in methods	toString() (any); toUpperCase/toLowerCase/trim/contains/startsWith/endsWith/split/substring/replaceAll on strings; contains/indexOf/join on lists plus closure-accepting map/where/any/every/firstWhere/forEach/fold/reduce; containsKey/containsValue on maps; abs/round/floor/ceil/toInt/toDouble on num
Events	ElevatedButton(onPressed: 'submit', ...) → RuneView.onEvent('submit', [])
Property extensions	10.w, size.half (via RuneBridge packages registering handlers)
Operators	== != < <= > >= on num+num or String+String; && || (short-circuit); + - * / % on num; ! on bool; unary - on num
Conditionals	Ternary cond ? a : b; list-literal [if (cond) widget] / [if (cond) a else b] (both short-circuit the un-taken branch)
Stateful source	StatefulBuilder(initial: {...}, builder: (state) => ...) produces source-level state; state.key reads, state.key = value assigns, setState(() { ... }) wraps a batch of mutations. Optional initState / dispose / didUpdateWidget closures own the full mount / unmount / rebuild lifecycle; autoDisposeListenables: true disposes any ChangeNotifier entries automatically on unmount.
Components	RuneComponent(name: 'X', params: [...], body: (...) => ...) declares a reusable component; RuneCompose(components: [...], root: ...) groups declarations and the widget tree; components dispatch before widget/value registries.
Imperative bridges	showDialog(builder: ...), showModalBottomSheet(builder: ...), showSnackBar(snackBar), Navigator.pop(result?). All route through RuneContext.flutterContext.

Anything outside this surface raises a RuneException (parse, resolve, or unregistered-builder variant). The plans in docs/superpowers/plans/ enumerate the phases that built this set.

Architecture

A unidirectional pipeline:

RuneView (StatefulWidget)
  │
  ▼
RuneConfig
  ├─ WidgetRegistry        : Phase 1-2d widget builders
  ├─ ValueRegistry         : Phase 1-2c value ctors
  ├─ ConstantRegistry      : Colors, enums, Icons
  └─ ExtensionRegistry     : Phase 3a .w/.px/.half handlers
  (+ withBridges([...])    : RuneBridge-packaged third-party contributions)
  │
  ▼
RuneContext  (carries data, events, all four registries, optional Flutter BuildContext)
  │
  ▼
DartParser ─────────▶ AstCache (LRU)
  │
  ▼
ExpressionResolver (dispatcher on Expression AST subtype)
  ├─ LiteralResolver       : literals + adjacent-string concat
  ├─ IdentifierResolver    : SimpleIdentifier / PrefixedIdentifier (data-first, constants fallback)
  ├─ PropertyResolver      : PropertyAccess (Map-first for deep paths, extensions for scalars)
  ├─ InvocationResolver    : MethodInvocation / InstanceCreationExpression
  └─ (inline)              : ListLiteral + ForElement, SetOrMapLiteral, IndexExpression, StringInterpolation
                              │
                              ▼
                        Registered widget/value builder
                              │
                              ▼
                        Real Flutter Widget

Architecture invariants (imports flow only downward) are enforced by test/architecture/import_flow_test.dart.

Extending

Register a new widget

final class FooBarBuilder implements RuneWidgetBuilder {
  const FooBarBuilder();

  @override
  String get typeName => 'FooBar';

  @override
  Widget build(ResolvedArguments args, RuneContext ctx) {
    return FooBar(
      label: args.requirePositional<String>(0, source: 'FooBar'),
      isActive: args.getOr<bool>('isActive', false),
    );
  }
}

final config = RuneConfig.defaults()
  ..widgets.registerBuilder(const FooBarBuilder());

Register a new constant group

config.constants
  ..register('BrandTheme', 'primary', const Color(0xFF0088FF))
  ..register('BrandTheme', 'accent', const Color(0xFFFF6B35));

Source strings can then use Container(color: BrandTheme.primary, ...).

Register a property extension

config.extensions.register('pct', (target, ctx) {
  if (target is num) return target / 100;
  throw ArgumentError('Expected num for .pct');
});

Source strings can then use SizedBox(width: (50).pct * MediaQuery.of(...)), or, more realistically, a bridge that uses ctx.flutterContext to do proper responsive math.

Ship a reusable bundle as a bridge

final class BrandBridge implements RuneBridge {
  const BrandBridge();

  @override
  void registerInto(RuneConfig config) {
    config.widgets.registerBuilder(const BrandButtonBuilder());
    config.constants
      ..register('BrandTheme', 'primary', const Color(0xFF0088FF))
      ..register('BrandTheme', 'accent', const Color(0xFFFF6B35));
    config.extensions.register('spacing', (t, c) {
      if (t is num) return t * 8.0; // 8-pt grid
      throw ArgumentError('spacing expects num');
    });
  }
}

final config = RuneConfig.defaults()
    .withBridges(const [BrandBridge(), OtherBridge()]);

The RuneDefaults helper exposes the same surface internally: RuneDefaults.registerWidgets(registry) / registerValues / registerConstants / registerAll(config). Handy for custom configs that want only a subset of defaults.

A live working bridge ships at packages/rune_responsive_sizer: a ~70-line implementation that adds .w / .h / .sp / .dm responsive-sizing extensions. Use it as both a consumer (pair it with rune via path dep) and a reference for writing your own bridges.

Error handling

• RuneException is a sealed class with five variants:
  • ParseException: analyzer could not produce an AST.
  • ResolveException: a resolver encountered an unsupported shape or missing extension.
  • UnregisteredBuilderException: a type name has no matching builder (exposes typeName).
  • ArgumentException: a required builder argument was missing or of the wrong type.
  • BindingException: an identifier referenced a key that is not present in RuneDataContext.
• Every exception carries the offending source substring plus a human-readable message.
• RuneView catches all exceptions, calls the optional onError callback, then renders fallback. In debug builds with no fallback, Flutter's red-screen ErrorWidget is shown; in release builds the view silently collapses to an empty SizedBox.
• RuneEventDispatcher.dispatch is crash-safe: handler throws (including arity mismatches) are caught and debugPrint-logged; they never escape into the render pipeline.

Source-location diagnostics

Every RuneException carries an optional location field: a SourceSpan pointing into the RuneView.source where the error originates. When present, toString() renders a caret pointer beneath the one-line summary:

ResolveException: Unknown identifier "userNmae" (not present in RuneDataContext) (source: "userNmae")
  at line 2, column 9:
    Text(userNmae)
         ^^^^^^^^

Access the structured data programmatically for custom diagnostics UI:

RuneView(
  source: mySource,
  onError: (error, _) {
    if (error is RuneException) {
      final loc = error.location;
      if (loc != null) {
        debugPrint('Rune error at L${loc.line}:C${loc.column}: ${error.message}');
        debugPrint(loc.toPointerString());
      }
    }
  },
);

Locations are populated for parse errors (analyzer diagnostics with offsets), every resolver throw site (via the AST node's offset/length), and bubbled builder ArgumentExceptions (rewrapped at the invocation). They are null for defensive throw sites that have no user-visible offset (e.g., the wrapped-variable-had-no-initializer invariant check inside DartParser), so consumers should treat the field as optional.

Testing

flutter test
flutter analyze

Three hundred and seventy-two tests cover every resolver, every builder, every registry, the architecture invariants, and end-to-end RuneView renders for each phase. Main is kept green at all times; every commit passes both gates under very_good_analysis.

Example

See example/ for a runnable demo that exercises the full current feature set.

License

MIT. See LICENSE.