Granular target dependencies

[GeorgeTaveras1231]

Hi all,

I've been using nx for a few months and I've found myself wanting this feature multiple times.

Context

When defining targets with dependencies, nx assumes that a target depends on all of its dependencies

Example

package.json

In this package.json. There is only a single dependency that affects the build (build-dep)

{
  "dependencies": {
       "runtime-dep": "*"
   },
   "devDependencies": {
        "build-dep": "*",
        "test-dep": "*"
    }
}

nx.json

{
  targetsDefaults: {
    build: {
      dependsOn: [
        "^build" // The problem....It assumes that runtime-dep, and test-dep affect the build
      ]
    }
  }
}

Proposal

Support granular target dependencies

Example

nx.json

building on top of existing syntax

{
  targetsDefaults: {
    build: {
      dependsOn: [
        {
           projects: ["build-dep" /*, other build dependencies*/],
           target: "build"
        }
      ]
    }
  }
}

Benefits

1. More granular caching for targets will improve performance by reducing cache misses
2. Allow better job orchestration by allowing you to declare implicit dependencies of targets. (more in deep dive below)

Deep dive (implicit target dependency)

Scenario

Lets say you have a shared testing utility (cypress-test-util) that needs to be built but is referenced by shared global file

cypress.config.js

import myDefineConfig from 'cypress-test-util';

In each workspace you may reference this config from the root

project.json

{
  "targets": {
    "test.e2e": {
      "executor": "@nrwl/cypress:cypress",
      "options": {
        "cypressConfig": "./cypress.config.js",
        "testingType": "component",
        "spec": "{projectRoot}/_local_e2e_tests"
      }
    }
}

Current state

For each workspace you may need to add an implicit dependency on cypress-test-util so that it is built before test.e2e target is ran.

package.json

{
  "nx": {
    "implicitDependencies": ["cypress-test-util"]
  }
}

There are 2 problems with this

1. This is a lot of boilerplate to add to every project that has e2e tests (can possibly be mitigated with generators but some may rather avoid generators -- [like myself]).
2. Running other targets may trigger unnecessary targets in cypress-test-util to run -- the implicit dependency is only for the `test.e2e

With this proposal

With this proposal, you could define this implicit dependency on the targetDefaults

{
  targetsDefaults: {
    "test.e2e": {
      dependsOn: [
        "build",
        {
           projects: ["cypress-test-util"], // implicit dependency on cypress-test-util
           target: "build"
        }
      ]
    }
  }
}