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LintForge

Pluggable static analysis for Dart & Flutter — write custom lint rules as plain Dart classes.

Rule contracts, a registry, a multi-file runner, built-in unused_* rules, and a CLI —
so teams can enforce project-specific checks without writing a full analyzer plugin.

Why • Features • CLI • Rules • Custom Rules • Contributing

Why LintForge?

Adding a custom static check to a Dart or Flutter project usually means authoring a full analyzer plugin: a separate package, a plugin isolate, the analyzer plugin protocol, and a release cycle of its own. That is a lot of ceremony for "flag this one project-specific pattern."

LintForge is the lighter alternative — a framework that supplies the contracts, a rule registry, a single-file and multi-file runner, and a CLI, so a custom rule is just a plain Dart class that inspects a fully resolved AST and yields diagnostics. It ships with a growing set of built-in unused_* rules, and because it is itself a static-analysis package it holds itself to the same bar: it lints cleanly, follows Effective Dart, and never ships a rule it does not pass.

It is released under the MIT License and created by lezli01 at lezli01.is-a.dev. Contributions are welcome — see Contributing.

Features

Point LintForge at a package and it treats writing and running custom analysis as first-class, plain-Dart work:

Rules as plain Dart classes. Implement AnalyzerRule for file-local checks or MultiFileAnalyzerRule for cross-file ones, register it, and run — no analyzer-plugin package, protocol, or isolate to stand up.
Resolved AST, not text. Rules run over fully resolved package:analyzer compilation units, so they can follow types, inheritance, and references across files instead of grepping source.
Built-in unused-code rules. Ships unused_function, unused_class, and unused_source_file enabled by default, with a --rules flag to narrow the set.
Language-feature aware. The bundled rules account for extensions, extension types, mixins, records, patterns, cascades, tear-offs, operator overloads, super-parameter forwarding, noSuchMethod, dart:mirrors, conditional and deferred imports, and @pragma('vm:entry-point').
A standalone CLI. Installed once with dart pub global activate, the lintforge command analyzes lib/, bin/, and test/ of any project by default — no dev_dependency, no pubspec.yaml changes in the projects you lint — with --rules, --exclude, --list-rules, and sensible default excludes for generated files and build caches.
Reference-aware excludes. Excluded files (such as *.g.dart) are still parsed and resolved, so references from generated code keep hand-written declarations alive — they just never receive diagnostics themselves.
Containment-aware reporting. The three unused rules form a file → type → member hierarchy and suppress nested findings, so a dead artifact is reported once at the coarsest level instead of accruing per-declaration noise.

Installation

LintForge is a standalone command-line tool. Install it once and run it against any Dart or Flutter project — you do not add it to that project's pubspec.yaml:

dart pub global activate lintforge

This installs a lintforge executable into ~/.pub-cache/bin. Make sure that directory is on your PATH (see the pub global path setup). Re-run the same command to update; append a version to pin one:

dart pub global activate lintforge <version>

Writing custom rules? LintForge can also be consumed as a library so you can register your own AnalyzerRule / MultiFileAnalyzerRule classes and run them from a small entrypoint of your own — see Custom Rules.

CLI Usage

Run the analyzer against the current project:

lintforge [options] [paths...]

Example LintForge CLI output reporting unused_function, unused_class, and unused_source_file findings with file locations

When no paths are provided, LintForge inspects lib/, bin/, and test/.

Options:

--help, -h: print usage and exit.
--version: print the package version and exit.
--list-rules: print every registered rule with its id, severity, and description, then exit.
--rules <id,id,...>: run only the listed rule ids.
--exclude <glob>: exclude matching paths. Repeat for multiple patterns. Custom excludes are added on top of the built-in defaults.
--no-default-excludes: disable the built-in default exclude patterns. Use --exclude to list any patterns you still want excluded.
--color / --no-color: force colored output on or off. When omitted, color is auto-detected — enabled only for an interactive terminal, and disabled when the output is piped or redirected, when NO_COLOR is set, or when TERM=dumb. FORCE_COLOR forces it on. An explicit flag always wins over the environment.

By default, LintForge excludes generated files and tool/build caches that consumer projects almost never want to lint: *.g.dart, *.freezed.dart, **/.dart_tool/**, and **/build/**. The two directory patterns mirror the canonical Dart/Flutter ignore set, so running LintForge against a project root will not flag Flutter-generated registrants under .dart_tool/ or build artefacts under build/. Exclude patterns are matched against the file's basename, its path relative to the current working directory, and its absolute path; any match excludes the file. To opt out of the defaults entirely:

lintforge --no-default-excludes

List the rules shipped with LintForge — each entry shows the rule id, severity, and a one-line description, one rule per line:

lintforge --list-rules

Exit codes:

0: no diagnostics with Severity.error.
1: at least one error diagnostic was emitted.
64: command-line usage error.

Output

LintForge groups findings by file and lays them out in aligned severity line:col rule message columns, with any correction hint on a continuation line beneath the message. The report ends with a one-line summary — for example ✖ 3 issues found (1 error, 2 warnings) in 2 files, or ✓ No issues found for a clean run.

lib/unused_class_sample.dart
  warning  13:7   unused_class  The class "_Foo" is declared but never used.
                                ↳ Remove "_Foo" or reference it.
  warning  16:7   unused_class  The mixin "_Bar" is declared but never used.
                                ↳ Remove "_Bar" or reference it.

⚠ 2 issues found  (2 warnings)  in 1 file

When writing to an interactive terminal the report is colorized (severities in color, secondary detail dimmed, file headers bold) and left as plain text when piped or redirected, so captured output stays clean and diffable. Color follows the NO_COLOR / FORCE_COLOR conventions and can be forced either way with --color / --no-color.

While analysis runs, a live progress indicator (a spinner, a progress bar, and the file being resolved) is drawn to stderr whenever stderr is an interactive terminal, and erased before the results are printed — so it never pollutes the diagnostics written to stdout.

Excluded Files as Reference Sources

--exclude (and excludePaths in LintforgeOptions) suppresses diagnostic reporting for matched files. It does not remove them from analysis: the runner still discovers, parses, and resolves every excluded file through package:analyzer and feeds the resulting compilation unit into the multi-file reference and reachability graph. Excluded files participate in cross-file analysis as ordinary sources — they simply never receive diagnostics themselves and are not dispatched to single-file rules.

For example, with the default *.g.dart exclude in effect:

// lib/src/handlers.dart  (reportable)
String formatGreeting(String name) => 'Hi $name';

// lib/src/handlers.g.dart  (excluded — not reported on)
String greet(String name) => formatGreeting(name);

handlers.g.dart is excluded, so it can never be flagged. But the runner still resolves it, so the call to formatGreeting is recorded as a real reference: unused_function sees formatGreeting as used and does not flag it, even though its only caller lives in an excluded file.

Per built-in rule:

unused_function — references in excluded files count as uses of candidate declarations in the reportable set. Generated companions (*.g.dart, *.freezed.dart, …) that call into hand-written code legitimately keep those declarations alive without producing false positives.
unused_source_file — excluded files act as both edge sources and edge targets in the reachability graph: an excluded file's import / export / part directives can mark non-excluded files as reached, and a non-excluded file can reach an excluded one. Excluded files are never themselves reported as unused, regardless of whether anything in the analyzed set imports them.
unused_class — file-local. The rule only inspects references within the same compilation unit, so excluded-files-as-references has no effect beyond the standard "excluded files are never reported on" guarantee.

Built-In Rules

LintForge ships with the following rules enabled by default. To turn one off, pass --rules with a list that omits it.

`unused_function`

Id: unused_function
Default severity: warning
Dispatch: multi-file (registered via registerMultiFile); the rule sees every resolved compilation unit in the analyzed set on a single invocation and resolves references across files.

Flags function-shaped declarations that are never referenced anywhere in the analyzed file set:

top-level functions — private (name begins with _) unconditionally, and public when the file lives under a package's lib/src/ directory and is never referenced from outside it;
top-level getters and setters, with the same privacy + lib/src/ rule as top-level functions;
local function declarations inside another function or method body;
constructors on classes and enums (generative, named, factory, and redirecting forms);
instance and static methods on classes, mixins, enums, and extension types;
getters, setters, and operators declared on classes, mixins, enums, and extension types;
methods, static methods, getters, setters, and operators declared inside extension Foo on T {} blocks.

Direct calls, tear-offs, named-type references, constructor invocations and redirects, operator and index expressions, explicit member accesses, and setter writes all count as a use. The rule is feature-aware: it also follows Dart 3 object-pattern destructures (final Foo(:getter) = …), record literals and record patterns ((obj.getter,) / final (g,) = …), cascade sections (obj..foo()), and the implicit .call invocation on callable objects (instance() resolves to instance.call()), so members reached only through any of those forms are correctly counted as used. Super-parameter forwarding (Dart 2.17+, class B extends A { B({super.x}); }) counts as a use of the supertype constructor even though the AST has no super(...) call node — the rule reads the implicit super-constructor target off the resolved constructor element. The same applies to the synthetic default constructor inserted when a class declares no constructor of its own (class B extends A {} is a use of A.new). Parameterised-enum value declarations (enum Route { home('/'); const Route(this.path); final String path; }) implicitly invoke the enum's constructor at const-evaluation time, but the AST does not model that as an InstanceCreationExpression / ConstructorName. The rule reads the constructor target off EnumConstantDeclaration.constructorElement, so the enum's constructor counts as referenced once per declared value. Both the global reference set and the candidate set are projected through Element.baseElement before lookup, so members declared on a generic base class (class Box<T> { void put(T v) {} }) match call sites that resolve through a substituted view of the same declaration (IntBox().put(0) where IntBox extends Box<int>), and the same applies to factory constructors on generic sealed classes (Holder<int>.value(0)). Overrides of reachable supertype members are treated as uses: when a MethodDeclaration overrides an inherited supertype member that is either declared outside the analyzed unit set (dart:*, package:flutter, any package outside the run) or is itself in the global reference set, the override is exempt. No explicit @override annotation is required — a declaration that shadows a supertype member is an override whether or not it is annotated, and framework callbacks (State.createState, Widget.createElement, lifecycle hooks) are routinely written without it. The overridden member is resolved via the inheritance graph with a by-name fallback across the full extends / with / implements / on chain, so this applies uniformly to methods, operators, getters, and setters and covers framework callback overrides (State.build, Object.toString, operator ==, …) as well as in-repo abstract-base / concrete-subtype dispatch.

Deliberately not flagged:

the library's main function;
public top-level functions, getters, and setters declared outside lib/src/ (i.e. the package's public surface);
public instance/static methods, getters, setters, and operators of a public type (class, mixin, enum, extension type, or extension block) declared outside lib/src/ — these form the package's consumable public API surface, reachable by external consumers and exercised by tests, so "no references found in the analyzed set" cannot prove them unused. Private members, and members of private types, are still flagged;
declarations and members in the non-selected branch file of a conditional export or import (export 'stub.dart' if (dart.library.html) 'web.dart';) — the analyzer resolves each directive to a single branch per build target, but every if (…) configuration branch is a real reference, so members reachable only through a non-selected branch are exempt rather than flagged as dead;
external declarations of any shape;
declarations annotated with @pragma('vm:entry-point');
top-level functions, getters, and setters declared in a library that has part files (a sibling part could legitimately reference them, and the rule does not currently traverse part libraries);
every member and constructor of a class whose supertype chain (extends / with / implements) declares its own noSuchMethod — that override can service any selector at runtime, so members reached only through it have no static reference. The walk also recognises package:mocktail's Fake and Mock base classes by simple name, since the analyzed sources typically do not pull the mocktail library in as a resolved dependency;
every member and constructor declared in a library that imports dart:mirrors — reflection can invoke arbitrary members by name, so the rule conservatively skips the whole unit;
every declaration in a unit stamped with the de-facto generated-code marker // ignore_for_file: type=lint at the top of the file — Flutter's flutter gen-l10n writes this line into the synthetic L base class and every per-locale output-localization-file subclass it emits, and other build-time Dart codegen tools follow the same convention, so the rule treats the marker as a "this file is generated, do not flag" signal and skips every candidate collector for the unit;
members of a private, unreferenced class, mixin, enum, extension type, or extension — unused_class already flags the enclosing declaration, so re-flagging every member would just repeat the report;
every declaration in a file unused_source_file reports as unreachable — the whole file is already flagged, so listing each function inside it would just repeat the report (see Rule interaction).

`unused_class`

Id: unused_class
Default severity: warning

Flags file-local declarations whose names begin with _ that are never referenced within the same compilation unit:

class declarations (including abstract, base, final, sealed, and interface modifiers);
mixin declarations;
enum declarations;
extension type declarations.

Any reference to the declaration counts as a use, including type annotations, constructor invocations, extends/implements/with/on clauses, is/as checks, static-member access, enum-value access, and constructor or static tear-offs. The rule is Dart 3 feature-aware: it also follows Dart 3 object patterns (case _Foo() in a switch), record type annotations ((_Foo, int)), and exhaustive switch on a sealed supertype — so a private type referenced only through its subtypes' pattern arms is correctly treated as used.

Deliberately not flagged in this release:

public top-level classes, mixins, enums, and extension types;
class _Foo = A with B; typedef-style class declarations (ClassTypeAlias);
extension declarations (the non-type extension _Ext on T {} form);
declarations annotated with @pragma('vm:entry-point');
any private candidate declared in a library that imports dart:mirrors — reflection can name arbitrary types at runtime, so the rule conservatively skips the whole unit;
files belonging to libraries that have part files;
types declared in a file unused_source_file reports as unreachable — the whole file is already flagged, so re-flagging each type inside it would just repeat the report (see Rule interaction).

`unused_source_file`

Id: unused_source_file
Default severity: warning

A cross-file rule that flags Dart source files in the analyzed set that are never reached from any entry point. Reachability is computed by walking import, export, and part directives whose resolved URI lands inside the analyzed set; URIs that resolve to dart: libraries, package dependencies, or files excluded from the run are ignored. For conditional imports (import 'x' if (dart.library.io) 'y'), every if (...) configuration contributes a reachability edge regardless of the active platform — both alternatives stay reachable in a single analysis run. Deferred imports (import 'x' deferred as p) are followed identically to ordinary imports.

Entry points (always considered "reached") are:

files under bin/;
files under test/;
files that declare a top-level main function;
lib/<package>.dart and any other file sitting directly under lib/ (i.e. not nested inside a subdirectory such as lib/src/), which together form the package's public surface.

A non-entry-point file counts as "used" if it is reachable, directly or transitively, from an entry point via an import, export, or part directive — including every configuration of a conditional import and the target of a deferred import.

Deliberately not flagged in this release:

entry-point files themselves (files under bin/ or test/, files with a top-level main, and lib/*.dart files outside lib/src/);
any file reached, directly or transitively, by an import, export, or part directive from an entry point — including every configuration of a conditional import and the target of a deferred import;
generated-file basenames such as *.g.dart and *.freezed.dart, which are skipped defensively even if the runner's default excludes are turned off.

Rule interaction

The three "unused" rules form a containment hierarchy — a source file contains types, a type contains members:

unused_source_file   (whole file)
  └── unused_class    (whole type)
        └── unused_function   (member / constructor)

When a finding fires at an outer level, the levels nested inside it are suppressed rather than reported again, so a dead artifact is reported once at the coarsest level instead of accruing a pile of per-declaration warnings:

a file flagged by unused_source_file swallows any unused_class and unused_function findings inside it — the file is reported once, not once per declaration;
a private, unreferenced type flagged by unused_class swallows the unused_function findings for its members.

The two tiers are enforced in different places. The file tier keys off unused_source_file's emitted findings, so dropping unused_source_file from --rules lets the per-declaration findings inside those files through again. The type tier is computed inside unused_function itself (from whether the enclosing type is a private, unreferenced declaration), so it stays in effect whether or not unused_class is enabled.

Custom Rules

The standalone lintforge CLI runs the built-in rules. To run rules of your own, consume LintForge as a library instead: add it as a dev_dependency in the project you want to lint, implement AnalyzerRule, register it with a RuleRegistry, and pass the registry to AnalysisRunner from a small entrypoint you run with dart run:

import 'package:lintforge/lintforge.dart';

class MyRule extends AnalyzerRule {
  @override
  String get id => 'my_rule';

  @override
  String get description => 'Flags a project-specific pattern.';

  @override
  Severity get defaultSeverity => Severity.warning;

  @override
  Iterable<Diagnostic> analyze(AnalysisContext context) sync* {
    // Inspect context.unit and yield Diagnostic instances.
  }
}

Future<void> main() async {
  final registry = RuleRegistry()..register(MyRule());
  const options = LintforgeOptions.defaults();
  final runner = AnalysisRunner(registry: registry, options: options);

  final diagnostics = await runner.run();
  for (final diagnostic in diagnostics) {
    print(diagnostic);
  }
}

AnalyzerRule is dispatched once per file and remains the right contract for file-local checks: implementations see a single resolved compilation unit at a time and cannot observe sibling files.

For checks that must reason across files, implement MultiFileAnalyzerRule instead. A multi-file rule is invoked once per run with the full set of resolved compilation units, so it can build cross-file structures such as import graphs or symbol indices. Register multi-file rules with the same RuleRegistry used for AnalyzerRule implementations; the built-in unused_source_file rule is implemented this way. Existing AnalyzerRule implementations continue to work unchanged.

Sample Projects

The samples/ directory contains live, executable documentation of each built-in rule: one self-contained Dart/Flutter package per rule, plus an all_rules sample that exercises every built-in rule together. Each sample path-depends on this package and ships a README.md listing the exact positive (MUST be flagged) and negative (MUST NOT be flagged) cases for the rule it covers.

Sample	Exercises
`samples/unused_function/`	the `unused_function` rule
`samples/unused_class/`	the `unused_class` rule
`samples/unused_source_file/`	the `unused_source_file` multi-file rule
`samples/all_rules/`	every built-in rule together

Run any sample from the repository root, for example:

fvm dart pub get --directory samples/unused_function
fvm dart run lintforge samples/unused_function/lib

Development

LintForge is a pure-Dart package. This repository uses FVM to pin the SDK version. Install the configured SDK before working locally:

fvm install
fvm dart pub get

Before opening a pull request, run the same checks as CI:

fvm dart format .
fvm dart analyze --fatal-infos --fatal-warnings
fvm dart test --coverage=coverage
fvm dart pub publish --dry-run

Project Status

LintForge is pre-1.0.0. The framework — rule contracts, the registry, the single-file and multi-file runners, the CLI, and the built-in unused_function, unused_class, and unused_source_file rules — is working today and exercised by the sample projects under samples/. Public APIs may still change between minor versions while the framework matures, so pin a specific version with dart pub global activate lintforge <version> if you need repeatable behavior. Additional built-in rules, including broader unused-declaration detection and const suggestions, are planned.

Contributing

Contributions of every size are welcome — bug reports, docs, new rules, test cases, and features. LintForge is itself a static-analysis package, so it holds its own sources to the rules it ships; keeping that bar is part of the work. Start here:

Read the Contributing guide for development setup (FVM), the quality checks expected before a pull request, and the commit-message convention.
Be a good neighbor: this project follows a Code of Conduct.
Have a question or an idea? Open a Discussion.
Found a bug or want a rule? Open an issue.

Releases are automated with release-please, so pull requests use Conventional Commits titles. Details are in CONTRIBUTING.md.

Security

LintForge runs locally as a development dependency: it reads your source, resolves it with package:analyzer, and prints diagnostics. It performs no network access and never executes the code it analyzes, so its attack surface is small — but security reports are taken seriously. Please report suspected vulnerabilities privately via GitHub's private vulnerability reporting for this repository rather than a public issue. See SECURITY.md for details.