farm-plugin-selective

Selective compilation plugin for FarmFE — conditionally include/exclude code at function, class, statement, and page level.

Install

npm install farm-plugin-selective

Dependencies: This plugin uses core-ast-ts internally for AST parsing. Installed automatically.

Concept

In a multi-app monorepo, different platforms (mobile, web, desktop) share code but also have platform-specific logic. This plugin lets you mark code with conditions so that only matching branches are compiled in — at function, class, variable, statement, and even page level.

Usage

import selective from 'farm-plugin-selective'

export default {
  plugins: [
    selective({
      conditions: {
        platform: 'mobile',
        features: ['premium', 'analytics'],
        debug: false,
      },
    }),
  ],
}

Or set conditions via environment variable:

SELECTIVE_CONDITIONS='{"platform":"mobile","features":["premium"]}' farm build

Or key=value format:

SELECTIVE_CONDITIONS='platform=mobile,features=premium|analytics,debug=false' farm build

API Surface

@selective('condition') — Function/Class/Variable level

Decorate a declaration to include it only when the condition matches.

@selective('platform:mobile')
function mobileLayout() { /* only in mobile builds */ }

@selective('feature:premium')
class PremiumDashboard { /* only when premium feature enabled */ }

@selective('!debug:true')
const API_URL = '/api'  /* excluded in debug builds */

When the condition doesn't match:

• Functions → empty stub function name() {}
• Classes → empty stub class name {}
• Variables → const name = undefined

$selective('condition', include, exclude?) — Expression level

const layout = $selective('platform:mobile', () => MobileLayout, () => WebLayout)
// → MobileLayout (when platform=mobile)
// → WebLayout (when platform!=mobile)

const color = $selective('feature:premium', () => 'gold')
// → 'gold' (when feature includes premium)
// → undefined (otherwise)

$selective.block('condition', () => { ... }) — Statement level

$selective.block('debug:true', () => {
  console.log('debug info')
  setupDevtools()
})
// → keeps the statements when debug=true
// → removes entirely when debug=false

@runtime — Compile-time code generator

A function decorated with @runtime executes at compile time. Its return value (a code string) replaces all call sites.

@runtime
function createHandler(env) {
  if (env.platform === 'mobile') {
    return `(url) => fetch('/m' + url)`
  }
  return `(url) => fetch('/api' + url)`
}

const handler = createHandler()
// → const handler = ((url) => fetch('/m' + url))  (when platform=mobile)

The function receives the current conditions object as its first argument, enabling condition-aware code generation.

Page-level selective compilation

selective({
  conditions: { platform: 'mobile' },
  pagePatterns: ['src/pages/**/*.vue', 'src/pages/**/*.tsx'],
})

When a page file contains @selective('condition') and the condition doesn't match, the entire page is replaced with an empty component stub. This means the page still exists in the route tree but renders nothing — no dead routes.

Custom empty page template:

selective({
  conditions: { platform: 'mobile' },
  pagePatterns: ['src/pages/**/*.vue'],
  emptyPageTemplate: (name, ext) => {
    if (ext === '.vue') return `<template><div></div></template>`
    return `export default function ${name}() { return null }`
  },
})

Condition Syntax

| Syntax | Meaning | |--------|---------| | platform:mobile | platform equals "mobile" | | !platform:mobile | platform is NOT "mobile" | | feature:premium,basic | feature is "premium" OR "basic" | | feature:* | feature key exists (any value) | | !feature:* | feature key does NOT exist | | platform:mobile && feature:premium | both conditions | | platform:mobile || platform:web | either condition |

HMR

When source files change, conditions are re-resolved and affected modules are re-transformed.

License

MIT