[BUG] npm set does not respect -g flag in 7.20.0 onwards

[billyjanitsch]

Is there an existing issue for this?

• I have searched the existing issues

Current Behavior

npm set -g foo bar

In npm < 7.20.0, this writes foo=bar to the global npm config file (/usr/local/etc/npmrc).

In npm >= 7.20.0, the -g flag is not respected and foo=bar is written to the user npm config file (~/.npmrc).

Expected Behavior

The -g flag should result in a modification to the global config, not the user config.

Steps To Reproduce

1. Run npm set -g foo bar.
2. Run npm get.
3. Note that foo has been set in the user config rather than the global config.

Environment

• OS: macOS 10.15.7
• Node: 14.17.3
• npm: 7.20.0

[billyjanitsch]

This bug was introduced in #3471.

There's some logic there that's supposed to set the value of the new -L flag based on -g, but it appears to not be working correctly.

That PR seems to have updated all of the tests for --global to instead use --location=global, so they didn't catch this regression. Perhaps at least one test should be added back to verify that --global continues to work?