Parallelism within the package tree

It’s not clear how lerna parallelism works in regards to package dependency and the build order. For example, if I have the follow dependency tree (via devDependencies/dependencies):

packages/
  +--package1
  +   +--package3
  +   +--package2
  +--package2
  +   +--package4
  +--package3
  +   +--package4
  +--package4

When I run lerna run build, obviously package4 is built first, and package1 is built last, but then it’s not clear if package2 and package4 are build in parallel, or one after the other (even though they have no relation to each other.

Expected Behavior

Packages should be built in parallel as much as possible.

Current Behavior

Not sure. The docs aren’t clear on this.

Context

• How has this issue affected you? What are you trying to accomplish?
  • Faster build times

Your Environment

Executable	Version
lerna --version	3.11.1
npm --version	6.7.0
node --version	10.12.0

OS	Version
macOS Mohave	10.14.2

[evocateur]

Not directly, though both lerna exec and lerna run will execute their arguments with maximal topological concurrency.

Programmatically, all the bits are available as separate packages, so it wouldn’t be too hard to retrieve the same topologically batched package list that Lerna uses internally:

const { getPackages } = require('@lerna/project');
const batchPackages = require('@lerna/batch-packages');

(async () {
  const cwd = process.cwd();
  const pkgs = await getPackages(cwd);
  const batches = batchPackages(pkgs);

  for (const batch of batches) {
    // all packages in a batch are safe to operate on concurrently
    for (const pkg of batch) {
      console.log(pkg.name);
      console.log(pkg.location); // absolute path to leaf directory
    }
  }
}());

[evocateur]

@wbern That’s a separate issue, which I believe already exists (possibly in triplicate).