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Posted on Edited on Originally published at vznjs.github.io

Every task has a key

#javascript #monorepo #devtools #opensource

A task you don't cache still has a key. Change a code generator's env,
and the cached build after it runs again.

import { defineProject } from '@vzn/vx/config'

export default defineProject({
  tasks: {
    codegen: {
      exec: {
        command: 'mkdir -p gen && echo "export const api = \"$API_URL\"" > gen/api.ts',
        env: { passThrough: ['API_URL'] },
      },
      inputs: { files: ['schema.json', '.env.local'], env: ['API_URL'] },
    },
    build: {
      dependsOn: ['codegen'],
      exec: { command: 'mkdir -p dist && cat gen/api.ts > dist/app.js' },
      inputs: { files: ['src/**'] },
      cache: { outputs: { files: ['dist/**'] } },
    },
  },
})
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$ API_URL=https://a.example vx run packages/e#build
  cache     local 1✓ 1∅

$ API_URL=https://b.example vx run packages/e#build
  cache     local 1∅ 1↑
$ cat packages/e/dist/app.js
export const api = https://b.example

$ vx why packages/e#build
  verdict    cache key changed: upstream packages/e#codegen
  what changed (1 component, 3 unchanged):
    changed upstream  packages/e#codegen  35dfe1115aedc6d6 → a7a53dc4d9e0bde9
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codegen never caches (∅), but its key goes into build's key. A
new API_URL builds again instead of restoring a dist/ made for the
old one.

Demo workspace · vx 69617eb · 2026-10-23

diagram

Inputs live on the task

inputs sits on the task, next to exec. It sets the key whether the
task caches or not, as in Turbo and Nx. cache holds only outputs
and inputStability.

A task with a command and no inputs has no key. vx won't guess one.
Every task after it runs again and saves nothing:

$ vx run packages/e#build      # codegen without inputs
  cache     local 1∅ · 1 not saved
$ vx run packages/e#build
  cache     local 1∅ · 1 not saved
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A missing input costs a re-run, never a wrong cache hit. Every rule is
on the Caching page.

A gitignored file can still be an input

.env.local is gitignored. Editing it still changes the key:

$ echo "TOKEN=2" > packages/e/.env.local
$ vx run packages/e#build
  cache     local 1∅ 1↑
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vx reads tracked files' hashes from git. A path you name outright
(.env.local), or a glob whose fixed part git ignores (gen/**), is
read from disk. A broad glob like src/** still skips ignored files,
and node_modules is never walked.

--affected sees only what git sees, as in Nx. An ignored file never
picks a task by itself, but the key still changes when the task runs.

The full key, part by part: Caching. More at
vznjs.github.io/vx.

Originally published on the vx blog. vx is open-source (MIT) task orchestration with a build cache: vznjs.github.io/vx · GitHub.

Written with AI assistance.

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