No error/warning is shown when attempting to install two packages that will install into the same directory

[KotlinIsland]

Description

When two packages with the same source directory are installed at the same time pip doesn't show any error/warning or information what so ever.

Pip will clobber the two packages together into the same directory(sus 😳).

You know, if the target directory already exists I would consider that to be EXTREMELY sus and an error should be shown.

Expected behavior

Show an error stating "Cannot install this package because the installation directory already exists 😳."

pip version

21.3.1

Python version

N/A

OS

N/A

How to Reproduce

1. pip install python-gitlab
2. pip install gitlab

Output

pip clobbers the files from the new package into the existing directory, completely breaking the installation of the first package.

Code of Conduct

• I agree to follow the PSF Code of Conduct.

[pradyunsg]

Duplicate of #5030.