[BUG] npm link removes previously linked module

What / Why

Developing coupled packages linked with npm link is not optimal.

1. npm link breaks the linked package.
2. npm link removes others links. (regression from npm 6)

When

Developing/testing linked packages together

Where

• n/a

How

Current Behavior

• n/a

Steps to Reproduce

Preparing the environment

git clone https://github.com/yeoman/environment.git
cd environment
npm ci
npm link
cd ..
git clone https://github.com/yeoman/generator.git
cd generator
npm ci
npm link
cd ..
git clone https://github.com/yeoman/yeoman-test.git
cd yeoman-test
npm ci
npm link
cd ..

Reset the environment

cd environment
npm ci
cd ..
cd generator
npm ci
cd ..
cd yeoman-test
npm ci
cd ..

1. npm link breaks the linked package.

cd yeoman-test
npm link yeoman-generator
npm test

output:

Error: Cannot find module 'semver'
Require stack:
- /Users/mshima/git/reproduce/generator/lib/index.js
- /Users/mshima/git/reproduce/yeoman-test/test/helpers.js

Workaround go to generator folder and execute npm ci

2. npm link removes others links. (regression from npm 6)

cd yeoman-test
npm link yeoman-generator
ls -l node_modules/yeoman-*

output:

lrwxr-xr-x  1 mshima  staff  15  6 Mar 12:14 node_modules/yeoman-generator -> ../../generator

node_modules/yeoman-environment:
total 24
drwxr-xr-x   4 mshima  staff   128  6 Mar 12:14 cli
.
.
.

npm link yeoman-environment
ls -l node_modules/yeoman-*

output:

lrwxr-xr-x  1 mshima  staff  17  6 Mar 12:20 node_modules/yeoman-environment -> ../../environment

node_modules/yeoman-generator:
total 32
-rw-r--r--   1 mshima  staff  1292 26 Out  1985 LICENSE
drwxr-xr-x   5 mshima  staff   160  6 Mar 12:20 lib
.
.
.

Workaround: link both together npm link yeoman-generator yeoman-environment

ls -l node_modules/yeoman-*
lrwxr-xr-x  1 mshima  staff  17  6 Mar 12:20 node_modules/yeoman-environment -> ../../environment
lrwxr-xr-x  1 mshima  staff  15  6 Mar 12:22 node_modules/yeoman-generator -> ../../generator

Expected Behavior

1. should not break node_modules tree.
2. should not remove others manually linked modules.

Who

• n/a

References

• n/a

Start by reproducing the two failures with the provided environment, generator, and yeoman-test clone commands, then run npm link yeoman-generator and npm link yeoman-environment followed by npm test. Compare the linked and unlinked node_modules/yeoman-* entries. Done means linked packages retain their dependencies and linking one package does not remove another manual link.