Ability to run just the parts of the dependency graph which are ancestors to some project

[Nokel81]

Background:
I have a decently complex project graph (>250 projects) so my team is very cognizant of the build times during development. One thing that I think would help a lot would be a smarter nx run-many which could be used in conjunction with nx watch to do even less work.

Proposal:
Add the flag --inverted to run-many which inverts the graph and only runs the targets for the specified projects and those projects which depend on them.

Example:

nx watch -p "@my-scope/*" -- nx run-many --inverted -t "build,build:types" -p \$NX_PROJECT_NAME

Given a rough project graph similar to:

{
  "nodes": [
    "@my-scope/foo",
    "@my-scope/bar",
    "@my-scope/blat",
    "@my-scope/ding",
    "@my-scope/woot"
  ],
  "dependencies": {
    "@my-scope/foo": [
      "@my-scope/woot",
      "@my-scope/ding",
      "@my-scope/blat",
      "@my-scope/bar"
    ],
    "@my-scope/bar": [
      "@my-scope/woot",
      "@my-scope/ding",
      "@my-scope/blat"
    ],
    "@my-scope/blat": [
      "@my-scope/woot",
      "@my-scope/ding"
    ],
    "@my-scope/ding": [
      "@my-scope/woot"
    ],
    "@my-scope/woot": []
  }
}

Then if the package "@my-scope/woot" were to be changed then all packages get rebuilt, but if package "@my-scope/bar" were to be changed only "@my-scope/bar" and "@my-scope/foo" would have their targets run (modulo caching)

[jaysoo]

@Nokel81 What type of projects is your team developing? Trying to understand the use case here, as it sounds like you are rebuilding projects often, and this is a way to only rebuild what's affected?

What would the before and after look like for your team with and without this feature?

[Nokel81]

Yes this is part of a local build workflow. We are developing a large desktop application and use packages as a means of splitting the work.

With this feature we would hopefully massively speed up the development cycle by doing less work and by having more trust in our build system. Since we would want a change that affects the types of a package to cause the system to inform the developer which other packages need to updated.

[jaysoo]

Is there a reason you cannot run the build for all apps, and rely on caching to speed things up?