[rush] Setting to avoid manually configuring decoupledLocalDependencies across subspaces

[L-Qun]

Summary

Currently, our Monorepo contains numerous projects, and naturally, there are many projects that need to depend on other projects in the monorepo via version numbers rather than workspaces. As a result, business teams need to frequently modify the rush.json file.

The purpose of decoupledLocalDependencies is to encourage projects in the repository to depend on each other through workspaces, which is understandable. However, as the number of projects in the monorepo increases, this becomes a burden for everyone. Therefore, there is a need for a capability to disable the configuration of decoupledLocalDependencies.

How it was tested

1. Change the project's workspace dependencies to version-based dependencies.
2. Enable exemptDecoupledDependenciesBetweenSubspaces to true.
3. Run rush install without any errors.

[octogonz]

This is an O(n^2 * m) algorithm cost, where n is the # of projects in rush.json and m is the number of dependencies in package.json. Additionally the [... notation and projects.some( notation will allocate lots of short-lived GC objects. Since this code runs for many Rush commands, I think it could be a performance concern.

[octogonz]

If we automatically generate decoupledLocalDependencies for everything from devDependencies and dependencies, isn't that equivalent to disabling the policy entirely? Disabling the policy could be more cheaply accomplished by simply skipping the validation itself.

On the other hand, perhaps we DO want to enforce decoupledLocalDependencies for some kinds of relationships but not others. For example, maybe decoupledLocalDependencies should be enforced for dependencies within the same subspace, but not enforced for dependencies across subspaces? Or perhaps it is up to the library owner to declare whether they want decoupledLocalDependencies to be enforced for dependencies on that library? (Maybe that is what you are already doing here?) Making the policy more configurable/flexible in this way would be great, but the rules need to be clearly explained.

@L-Qun @jzhang026

[L-Qun]

@octogonz
I agree with your point of view. decoupledLocalDependencies can be declared within the subspace, and won't report errors for cross-subspace dependencies, but to achieve this goal, the following is required:

1. A rush.json at the subspace level is required.
2. Disable cross-subspace validation.

Given the current situation, the cost is relatively low, which allows us to quickly improve the user experience. Next, I think we can implement the solution we mentioned above to fully resolve this issue.

[octogonz]

  /**
   * Rush has a policy that normally requires Rush projects to specify `workspace:*` in package.json when depending
   * on other projects in the workspace, unless they are explicitly declared as `decoupledLocalDependencies`
   * in rush.json.  Enabling this experiment will remove that requirement for dependencies belonging to a different
   * subspace.  This is useful for large product groups who work in separate subspaces and generally prefer to consume
   * each other's packages via the NPM registry.
   */
  /*[LINE "HYPOTHETICAL"]*/ "exemptDecoupledDependenciesBetweenSubspaces": false

[octogonz]

I noticed that this message is still referring to the old terminology "cyclic dependency" which we later renamed to "decoupled local dependency":

console.log(
  Colorize.red(
    `"${rushProject.packageName}" depends on package "${name}" (${version}) which exists ` +
      'within the workspace but cannot be fulfilled with the specified version range. Either ' +
      'specify a valid version range, or add the package as a cyclic dependency.'
  )
);

Could you update that string to something like:

console.log(
  Colorize.red(
    `"${rushProject.packageName}" depends on package "${name}" (${version}) which belongs to ` +
      'the workspace but cannot be fulfilled with the specified version range. Either ' +
      'specify a valid version range, or add the package to "decoupledLocalDependencies" in rush.json.'
  )
);