Steps to reproduce the issue

$ spack install glib ^python@3: 

leads to

==> Error: ProcessError: Command exited with status 2:
'make' '-j8' 'install'

6 errors found in build log:
1590 /usr/bin/install -c -m 644 ./html/right.png
1591 /usr/bin/install -c -m 644 ./html/style.css
1592 /usr/bin/install -c -m 644 ./html/tools.html
1593 /usr/bin/install -c -m 644 ./html/up-insensitive.png
1594 /usr/bin/install -c -m 644 ./html/up.png
1595 ImportError: No module named site

which seems to be an error with the python path

Platform and user environment

Please report your OS here:

$ uname -a 
Darwin orca.llnl.gov 16.7.0 Darwin Kernel Version 16.7.0: Thu Jun 21 20:07:39 PDT 2018; root:xnu-3789.73.14~1/RELEASE_X86_64 x86_64

Additional information

The same thing happens for

$ spack install glib ^[email protected] 

$ spack install glib ^[email protected]

but not for the python default which is equivalent to

$ spack install glib ^[email protected]