tom_reflection_generator

> Part of the Tom Framework reflection toolkit. Derived from the > reflectable package by the Dart team > (google/reflectable.dart, > "Copyright (c) 2015, Dart", BSD-3-Clause); Tom-specific refactoring, fixes and > enhancements © 2024–2026 Peter Nicolai Alexis Kyaw, released under the same > BSD-3-Clause terms. See LICENSE and NOTICE.

The code generator for engine 1 of the Tom reflection toolkit. It reads the @reflector annotations produced with tom_reflection and emits the *.reflection.dart files that hold the precomputed, capability-gated mirror data.

It ships two interchangeable surfaces over one generation pipeline:

• a build_runner builder for the usual dart run build_runner build flow, and
• a standalone reflectiongenerator CLI (built on tom_build_base v2) that

also nests under buildkit as buildkit :reflectiongenerator.

Overview

tom_reflection keeps generated code small by gating it behind capabilities. This package is the tool that does the gating: it runs the Dart analyzer over your sources, finds classes annotated with a Reflection subclass, reads the capabilities that reflector declares, and writes exactly the mirror data those capabilities require into a sibling *.reflection.dart file. Your app then calls the generated initializeReflection() once and reflects at runtime.

   your sources                 tom_reflection_generator              output
@myReflector class Foo  ──►  analyze → read capabilities → emit  ──►  foo.reflection.dart
                             (builder  OR  reflectiongenerator CLI)

Both surfaces share the same analyzer infrastructure (StandaloneLibraryResolver, FileId) and the same generation core, so the builder and the CLI produce byte-identical output for the same input. The package was extracted from tom_build_tools; the CLI was rebuilt on the tom_build_base v2 tool framework so it gains standard arg parsing, --help/--version and buildkit nesting for free.

Installation

The generator is a development-time dependency — your shipped package depends only on tom_reflection.

dev_dependencies:
  build_runner: ^2.4.0
  tom_reflection_generator: ^1.1.1

Or:

dart pub add --dev build_runner tom_reflection_generator

SDK: Dart ^3.10.4. Pulls in analyzer ^8, build ^4, tom_analyzer_shared (summary cache), tom_build_base (v2 tool framework) and tom_reflection.

Features

Surface	Entry point	Use it for
build_runner builder	reflectionGenerator(BuilderOptions) ( tom_reflection_generator:reflection_generator )	The standard generate-on-build workflow.
Standalone CLI	binary reflectiongenerator / dart run tom_reflection_generator	One-off and CI generation, scriptable.
Buildkit-nested CLI	buildkit :reflectiongenerator	Workspace-wide generation across many projects.
Programmatic API	package:tom_reflection_generator/tom_reflection_generator.dart	Embedding the pipeline in your own tool.

Other features: analyzer summary caching for dependencies (faster repeat runs), capability-gated output, configurable output extension, and a --useAllCapabilities escape hatch that ignores the declared capabilities and emits full metadata.

Quick start

As a build_runner builder

Add build.yaml to the package that has the annotated classes:

targets:
  $default:
    builders:
      tom_reflection_generator:reflection_generator:
        generate_for:
          - lib/**.dart
          - example/**.dart

Then:

dart run build_runner build
# writes lib/<file>.reflection.dart next to each annotated source

The builder is auto_apply: dependents and build_to: source, so any package that depends on tom_reflection_generator gets the builder and the generated files land in the source tree (committable).

As the standalone CLI

# Generate for a single entry point
reflectiongenerator lib/main.dart

# Treat a directory as recursive
reflectiongenerator --all lib/

# Build mode: drive generation from build.yaml generate_for patterns
reflectiongenerator build

# Explicit globs in build mode
reflectiongenerator build "lib/**.dart" "test/**_test.dart"

# Self-describe (version + build timestamp, see Versioning below)
reflectiongenerator version

dart run tom_reflection_generator <args> is equivalent before the binary is compiled.

Configuration

build.yaml (build_runner / CLI build mode)

The builder maps .dart → .reflection.dart and is configured by the standard generate_for glob list shown above.

buildkit.yaml (nested / traversal mode)

In nested or traversal mode the generator reads a tom_reflection_generator: section from each project's buildkit.yaml:

tom_reflection_generator:
  generate_for:
    - lib/**/*.dart
  package: tom_reflection          # reflector package whose annotations trigger generation
  extension: .reflection.dart      # output file extension
  use_all_capabilities: false      # emit only declared capabilities

Target-resolution precedence (per project, in nested/traversal mode):

1. If buildkit.yaml has a tom_reflection_generator: section, its generate_for patterns are used. 2. Otherwise the generator falls back to the project's build.yaml generate_for patterns. 3. If neither is present, the project is skipped.

CLI options

Tool-specific options (framework options like --verbose/-v, --help/-h, --version, --nested and project-traversal flags are contributed by tom_build_base):

Option	Description
--all	Process directory targets recursively.
--package	Reflection package whose annotations trigger generation (default tom_reflection ). No -p — -p is the standard --project traversal flag.
--extension, -e	Output file extension (default .reflection.dart).
--config, -c	build.yaml path for the build-mode fallback (default build.yaml).
--useAllCapabilities	Emit full metadata regardless of declared capabilities.
--no-cache	Disable analyzer summary caching for dependencies.
--rebuild-cache	Force regeneration of all cached summaries.
--show-cache-status	List which packages have cached summaries, then stop.
--cache-only <package>	Restrict summary caching to the given package(s) (repeatable).

> Summary caching: caching speeds up repeat runs by reusing analyzer > summaries of unchanged dependencies (via tom_analyzer_shared). If a run in a > compiled/AOT environment misbehaves on summary discovery, --no-cache is the > reliable fallback while still producing correct output.

Versioning

buildkit.yaml declares a versioner block so the compiled binary always embeds the current version, build number, git commit and build timestamp:

versioner:
  variable-prefix: reflectionGen   # → generated class ReflectionGenVersionInfo

The :v stage runs before :comp, regenerating lib/src/version.versioner.dart, so reflectiongenerator version reports the exact build it was compiled from.

Programmatic usage

Embed the pipeline in your own tool:

import 'package:tom_reflection_generator/tom_reflection_generator.dart';

Future<void> main() async {
  final resolver = await StandaloneLibraryResolver.create('path/to/project');

  final generator = GeneratorImplementation();
  final inputId = FileId('my_package', 'lib/main.dart');
  final outputId = inputId.changeExtension('.reflection.dart');
  final library = await resolver.libraryFor(inputId);
  final visibleLibraries = await resolver.libraries;

  final source = await generator.buildMirrorLibrary(
    resolver,
    inputId,
    outputId,
    library,
    visibleLibraries.cast(),
    true,        // formatted
    const [],    // extra suppress-warnings
  );
  // Write `source` to outputId.
}

For the buildkit-nestable tool surface, import the v2 library instead:

import 'package:tom_reflection_generator/reflection_generator_v2.dart';
// exposes reflectionGeneratorTool and ReflectionGeneratorExecutor

Architecture

package:tom_reflection_generator/
├── reflection_generator.dart   build_runner builder:
│   ├── ReflectionGenerator (implements Builder)
│   └── reflectionGenerator(BuilderOptions) factory
├── reflection_generator_v2.dart  tom_build_base v2 tool surface:
│   ├── reflectionGeneratorTool (ToolDefinition, single-command)
│   └── ReflectionGeneratorExecutor (CommandExecutor)
├── src/generation/             shared generation core (capability gating)
└── src/reflection_generator/   analyzer infra: StandaloneLibraryResolver, FileId

bin/tom_reflection_generator.dart  → ToolRunner(reflectionGeneratorTool)  → `reflectiongenerator`

Both surfaces converge on the same generation core, which is why builder and CLI output match byte-for-byte. The CLI's single-command tool routes a --nested invocation to ReflectionGeneratorExecutor.executeWithoutTraversal, and a traversal invocation to execute per project.

Key types

Type	Responsibility
ReflectionGenerator	The build_runner Builder : maps .dart → .reflection.dart .
reflectionGenerator(BuilderOptions)	Builder factory referenced from build.yaml.
reflectionGeneratorTool	tom_build_base ToolDefinition (single-command) — the CLI surface and its options/help.
ReflectionGeneratorExecutor	CommandExecutor that runs the generation per target / nested invocation.
StandaloneLibraryResolver	Analyzer-backed resolver that loads libraries outside a build_runner context.
FileId	Package-relative file identity (changeExtension, etc.).
GeneratorImplementation	The generation core (buildMirrorLibrary).

Ecosystem

tom_reflection            runtime mirror library — defines the annotations & capabilities
      ▲ reads its annotations
tom_reflection_generator  THIS PACKAGE — emits *.reflection.dart
      │ builds on
      ├── tom_build_base        v2 tool framework (CLI, nesting, version flags)
      └── tom_analyzer_shared   analyzer summary cache (shared with tom_d4rt_generator)
      ▲ exercised end-to-end by
tom_reflection_test       fixture suite (input + committed expected output)

This is the engine-1 generator. The build-time structural engine (tom_reflector) is a separate technology with its own generator emitting *.r.dart — see the repo README.

Further documentation

• Usage guide: doc/reflection_generator.md
• CLI reference: doc/reflectiongenerator_user_reference.md
• Implementation notes: doc/reflection_generator_implementation.md
• Analyzer summary caching: doc/analyzer_summary_integration.md
• Test status: doc/reflection_test_result.md
• Runtime library it generates for: ../tom_reflection/README.md
• Capability gating in action: reflection_capability_sample

Status

• Version: 1.1.1 (published to pub.dev).
• SDK: Dart ^3.10.4; analyzer ^8.
• Surfaces: build_runner builder + reflectiongenerator CLI (standalone

and buildkit :reflectiongenerator). - Verification: output validated against the tom_reflection_test fixture suite, where CLI output matches the build_runner-generated reference.

License

BSD-3-Clause. Derived from the reflectable package by the Dart team (google/reflectable.dart, "Copyright (c) 2015, Dart") — retaining the upstream copyright alongside Tom's modifications (© 2024–2026 Peter Nicolai Alexis Kyaw), released under the same BSD-3-Clause terms. See LICENSE and NOTICE.