Fallow - Codebase Intelligence

Version updated for https://github.com/fallow-rs/fallow to version v2.65.0.

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Action Summary

Fallow is a static analysis tool for TypeScript and JavaScript codebases, designed to identify unused code, duplication, complexity issues, and architectural inconsistencies. It automates the process of detecting inefficiencies, reducing technical debt, and maintaining code quality without requiring configuration or a runtime environment. Additionally, it offers optional runtime insights to analyze production execution paths, making it a valuable tool for streamlining development and improving maintainability.

What’s Changed

Highlights

Two new framework integrations and four detection-accuracy fixes from external contributors. All five external issues filed since v2.64.0 are credited and closed.

Added

Lit and Web Components: registered classes are now credited as used

Classes registered through runtime side effects on module load are now credited even when no other file imports them by name.

Two patterns are recognized end-to-end:

  1. Lit @customElement('tag') decorator on a class, in named-import form (import { customElement } from 'lit/decorators.js'), aliased imports, namespace-call form (@decorators.customElement('tag')), and anonymous export default @customElement('x') class extends LitElement {}. The decorator binding is verified against lit/decorators.js / lit/decorators/custom-element.js before crediting, so a same-named decorator from any other module is intentionally ignored.
  2. customElements.define('tag', ClassRef) call expressions at any depth where the second argument is an Identifier.

Lit lifecycle methods (render, updated, connectedCallback, etc.) are heritage-scoped to LitElement / ReactiveElement subclasses via the new lit plugin. Native Custom Elements lifecycle members (connectedCallback, observedAttributes, adoptedCallback, etc.) are heritage-scoped allowlists for HTMLElement subclasses, so they work without a Lit dependency. Non-lifecycle methods on Web Component classes are still reported, so member-level dead code detection on the rest of the class is preserved.

schema.json shipped inside the npm package

Consumers can now point $schema at the bundled file:

{
  "$schema": "./node_modules/fallow/schema.json",
  ...
}

The published fallow package now contains schema.json, so editors get version-aligned autocomplete and validation with no network round-trip to raw.githubusercontent.com. The release workflow copies the file in before publishing, and CI asserts it is present in every published tarball so the package never silently loses it.

Thanks @ChrisJr404 for the patch and @OmerGronich for the report. (Closes #275)

Fixed

Angular signal queries and plural QueryList iteration are traced for unused-class-members

Six previously-missed Angular query patterns now feed the bound-member-access pipeline:

  • viewChild<T>(...), contentChild<T>(...) (singular signal factories)
  • viewChildren<T>(...), contentChildren<T>(...) (plural signal factories)
  • @ViewChildren ... readonly q?: QueryList<T>, @ContentChildren ... readonly q?: QueryList<T> (plural decorator queries)

Methods called via this.vc()?.method() and this.vcs().forEach(c => c.method()) (and the this.q?.forEach(...) decorator form) are now credited correctly. The pre-existing @ViewChild and @ContentChild paths continue to work unchanged.

Thanks @ChrisJr404 for the patch and @OmerGronich for the eight-pattern reproducer. (Closes #274)

vite.config.* default export reachable under --include-entry-exports

The vite plugin now contributes used_exports for vite.config.{ts,js,mts,mjs} (default), mirroring the existing vitest treatment. With --include-entry-exports the strict reachability check previously surfaced the default export even though Vite’s CLI consumes it.

Thanks @ChrisJr404 for the patch and @filipw01 for the report. (Fixes #282)

prisma.config.* recognized as an entry point

The prisma plugin now treats prisma.config.{ts,mts,cts,js,mjs,cjs} as an entry, so the Prisma 6 config file (and any imports it reaches) stays alive in the graph and does not surface as unused-file.

Thanks @ChrisJr404 for the patch and @FunctionDJ for the report. (Closes #281)

fallow migrate accepts JSONC trailing commas

Real-world JSONC files (tsconfig.json, .vscode/settings.json, and similar) routinely trail commas before } / ]. load_json_or_jsonc previously ran the input through comment-stripping and then handed the result to serde_json, which rejects trailing commas. A final byte-level pass now strips them only when the comment-stripped parse fails, leaves commas inside string literals untouched, and still rejects genuinely malformed input like {,} (the comma_follows_json_value predicate keeps malformed leading-commas reporting as parse errors).

Thanks @ChrisJr404 for the patch and @madflow for the report. (Closes #276)

Vue generic and Svelte generics script-tag attributes scan for type references

A type-only import whose only consumer was a generic constraint on the <script> tag was falsely flagged as unused_types because the constraint lives on the tag, not in the script body:

<script setup lang="ts" generic="T extends Test<boolean>">
import type { Test } from './types';
defineProps<{ items: T[] }>();
</script>

The SFC parser now appends an augmented-source probe that re-introduces the constraint to the parse so the imported type’s binding shows up as referenced and oxc_semantic no longer classifies it as unused. Affects Vue SFCs (generic="...") and Svelte 5 components (generics="...").

Full Changelog: https://github.com/fallow-rs/fallow/compare/v2.64.0...v2.65.0