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Documentation Index

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Fallow is a syntactic analyzer: no TypeScript compiler, no type resolution. The trade-off is speed; the cost is that type-conditional dead code is not detectable.
The limitations below apply to specific patterns. Standard TypeScript projects with isolatedModules: true are unaffected by most of them.
Fallow parses source code as syntax trees using Oxc and uses oxc_semantic for scope-aware binding analysis. It does not invoke the TypeScript compiler or resolve type information. This trade-off is what makes fallow fast.Impact: Type-only imports (import type { Foo }) are handled correctly. Value imports used only as type annotations (e.g., import { Foo } followed by const x: Foo) are also tracked correctly via oxc_semantic reference counting. Conditional type exports or dead code behind generic interfaces would require actual type resolution to detect.Workaround: Set isolatedModules: true in tsconfig.json. esbuild, swc, and Vite already require this, so most modern projects have it. With isolatedModules, every import is either explicitly import type or a real value import, removing ambiguity.
tsconfig.json
{
  "compilerOptions": {
    "isolatedModules": true
  }
}
In Svelte components, export let declarations serve double duty: they define component props and regular exports. Fallow can’t distinguish between props (used by consumers via the template) and utility exports that may genuinely be unused.Impact: Some unused exports in .svelte files may not be reported.Workaround: No configuration workaround exists. Review Svelte component exports manually. Extract utility functions into separate .ts files where fallow can track them accurately.
This limitation is about export let prop detection only. Fallow does track template-visible imports since v2.15.0: component tags, directives (use:tooltip, v-focus-trap), expressions, $store subscriptions in Svelte, and v-on/v-bind object syntax in Vue are all correctly credited as used. See File types for details.
CSS and SCSS files are parsed with lightweight regex extraction rather than a full CSS parser. This covers the most common patterns but not the entire CSS specification.What’s tracked:
  • @import and @use statements
  • @forward rules
  • @apply and @tailwind directives (as Tailwind dependency usage)
  • @plugin directives (Tailwind v4 plugin sources, package or relative)
What’s not tracked:
  • composes: (CSS Modules composition)
  • :global() and :local() pseudo-selectors
  • Complex selector-based dependencies
Workaround: If fallow reports false positives for CSS files that use composes: or :global(), suppress them with ignorePatterns or inline comments.
.fallowrc.json
{
  "ignorePatterns": ["**/legacy-styles/**/*.css"]
}
Fallow tracks class member usage syntactically by looking for direct references in source code. In NestJS and other DI frameworks, abstract class methods may be invoked at runtime through the DI container without appearing as direct references.Impact: Abstract class methods and properties consumed via dependency injection may be reported as unused.Workaround: Disable unused-class-members for DI-heavy projects:
{
  "rules": {
    "unused-class-members": "off"
  }
}
If your package exports types for external consumers (e.g., ButtonProps, Config), fallow correctly reports them as unused within your project, because they are. No internal file imports them.Impact: Correct findings that are noisy for library authors.Workaround: Use ignoreExports to mark public API files:
.fallowrc.json
{
  "ignoreExports": [
    { "file": "src/index.ts", "exports": ["*"] },
    { "file": "src/types.ts", "exports": ["*"] }
  ]
}
Fallow’s built-in plugins parse config files (e.g., vite.config.ts, jest.config.js) using Oxc’s AST parser. This handles static objects, arrays, and defineConfig() wrappers, but it can’t evaluate arbitrary JavaScript.What’s handled:
  • Static object literals and arrays
  • defineConfig() / module.exports wrappers
  • String concatenation in simple cases
What’s not handled:
  • Computed property keys
  • Conditional expressions (process.env.NODE_ENV === 'production' ? ... : ...)
  • Nested factory functions
  • Dynamic require() with variables
Workaround: Add undetected entry points manually in your fallow config:
.fallowrc.json
{
  "entry": ["src/dynamic-entry.ts", "scripts/*.ts"]
}
React Native auto-linked native packages (installed via npx pod-install or auto-linking) aren’t detected as used by fallow. These packages may not have any explicit import in JavaScript code.Impact: Auto-linked packages like react-native-screens or react-native-gesture-handler may be reported as unused dependencies.Workaround: Add auto-linked packages to ignoreDependencies:
.fallowrc.json
{
  "ignoreDependencies": [
    "react-native-screens",
    "react-native-gesture-handler",
    "react-native-safe-area-context"
  ]
}
The fallow LSP server reports column positions as byte offsets rather than character offsets. For ASCII-only source files this makes no difference. For files with multi-byte characters (emoji, CJK, accented characters), the column number may be off by a few positions.Impact: Diagnostic squiggles in VS Code may be slightly misaligned on lines containing non-ASCII characters.Workaround: This is a cosmetic issue only. The line number and file path are always correct, so navigation still works. A fix is planned for a future release.

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See also

Inline suppression

Suppress individual false positives directly in source code.

Configuration

Full config file reference for ignorePatterns, ignoreExports, and rules.

Agent integration

How agents handle false positives via config and suppression.