This feature support to jail Spack inside a chroot (see #5193 approach 3 for details).
This allows to find potential missing depends_on calls.

It introduces the commands:

./spack isolate --build-environment path/to/jail/dir --tarball path/to/tarball
To create a jail for Spack and mount bind /dev, /sys and /proc to be available inside the jail.

./spack isolate --remove-environment
To unmount the mounted /dev, /sys and /proc directories.

./spack isolate --cli
To start a shell inside the jail.

To create a bootstrap environment it is possible to use an already generated tarball from OpenStack or by using mkosi. A restriction is, that the root directory of the tarball must be a directory which contains the distribution.

Because the mount bind process requires root rights, there are currently three approaches to solve this issue.

1. By being root user.
2. By register the /dev, /sys and /proc directories into fstab via the --permanent option, when building the jail with --build-environment. This operation requires to be root.
3. By starting a daemon via ./spack isolate --start-daemon. This allows every user to mount bind /dev, /sys and /proc to the desired location.
4. If someone knows a better method I'm happy to change the current one.