Related discussion: #372

Describe the feature you'd like to request

In a largeish monorepo, (150+ JS/TS projects), it's infeasible to build everything, even if just initially -- there are entire teams that never see sections of the monorepo, so why make their machines pay the cost of building / starting those apps?

Today, when doing turbo run <cmd>, it seems that <cmd> is run in every project that defines a <cmd> in package.json#scripts -- which is totally reasonable for small monorepos!

I would like the following behavior,
given a config:

{
  "turbo": {
    "baseBranch": "origin/main",
    "pipeline": {
      "start": { "dependsOn": ["^build"], "cache": false },
      "build": { "dependsOn": ["^build"] },
      "lint": {},
      "lint:fix": {},
    }
  },
}  

I would like the following to happen:

• when "starting an app for local development", currently: yarn turbo run start --scope='my-app' --include-dependencies
• build all the dependent projects in the monorepo (that have a build script)

What happens right now:

• in addition to the above all dependent projects are also "started" (even though I feel like I didn't tell them to?)

Describe the solution you'd like

maybe a --target='app-name' or --entry='app-name' instead of scope, that only runs the specified script in at the traget/entrypoint but first does the dependencies' build step (per the config).

so, `yarn turbo run start --target="app-name" would

1. run build in all dependencies
2. run start in app-name

Describe alternatives you've considered

I could try to re-work my scripts in my packages so that start means something else so this'd be a non-issue -- but that's a lot of work across a big monorepo that demands incremental changes 🙃
In small monorepos, it's reasonable to do have a "watch"-like behavior across all your packages (I assume that's what the dev pipeline refers to in the docs), and I can do that for the small open source monorepo I have here: NullVoxPopuli/limber#377 (there are like.. 5 packages).
but starting 30+ libraries in watch mode during development isn't a great option if app devs are going to stick to their apps.
For C.I., it's also important have the above requested behavior, because I'll need to run tests for a specific app and that app's dependencies need to be built in non-watch mode before the tests for the one app run.