[ShryukGrandhi]

Summary

Since npm 7, running npm link in a package directory no longer tells you where the global symlink went. npm 6 printed a line like /path/to/global/node_modules/pkg -> /path/to/project. This adds that line back.

Fixes #3177

Changes

• lib/commands/link.js: after the global reify in linkPkg, print <link path> -> <target> for each explicitly requested package (the current package, or each selected workspace). The line is skipped with --json, because the JSON summary already includes the path and the extra line would make the output invalid JSON.
• test/lib/commands/link.js: assert that the link line is printed for npm link with no args, and that nothing extra is printed with --json.

Example:

$ npm link
/usr/local/lib/node_modules/@my-package/cli -> /path/to/project

added 1 package in 1s

Testing

• node . run test -- test/lib/commands/link.js passes, with 100% coverage for lib/commands/link.js. The new assertion fails without the change to link.js.
• npx eslint lib/commands/link.js test/lib/commands/link.js is clean.
• Ran it by hand with a temporary global prefix (npm_config_prefix=<tmp> node . link) on a package with a bin field. The link line was printed, and the --json output still parses as JSON.