Document that `--ignore-installed` is dangerous
@@ -187,7 +187,11 @@ class InstallCommand(RequirementCommand):
'-I', '--ignore-installed',
dest='ignore_installed',
action='store_true',
- help='Ignore the installed packages (reinstalling instead).')
+ help='Ignore the installed packages, overwriting them. '
+ 'This can break your system if the existing package '
+ 'is of a different version or was installed '
+ 'with a different package manager!'
+ )
cmd_opts.add_option(cmdoptions.ignore_requires_python())
cmd_opts.add_option(cmdoptions.no_build_isolation())
