Using yarn and hoisting together causes yarn.lock to be ignored

If you try to use --npm-client=yarn and --hoist simultaneously, all your package’s yarn.lock files will be ignored because lerna uses npm instead of yarn for everything except the top-level hoisted dependencies.

Expected Behavior

When using yarn as the npm client, all installed dependencies should satisfy any yarn.lock files that are present.

Current Behavior

lerna invokes npm --global-style instead of yarn in each of the packages, causing the yarn.lock to be ignored.

Possible Solution

We could forbid the combination of hoisting and yarn, or at least warn that it will give surprising results.

A more complete solution would mangle the contents of yarn.lock in a way analogous to what lerna already does for package.json in order to preserve the intended semantics.

Steps to Reproduce (for bugs)

1. In any lerna project, run lerna bootstrap --hoist --npm-client=yarn
2. Observe the resulting processes via ps or pstree and see that lerna is running npm instead of yarn.

[MoOx]

Yarn will have a built in feature, called “workspaces” to offer a lerna like solution. More at https://github.com/yarnpkg/yarn/issues/3294

[evocateur]

If --hoist needs to do a leaf install (i.e., there are “unhoisted”, possibly conflicting deps in the tree), then it will use npm because yarn does not support --global-install, which avoids leaking transitive dependencies incorrectly.