environment: Add --user.

This change allows overriding the home directory of all filesystem mappings to
help hide the identity of the calling user in a container.

* doc/guix.texi (Invoking guix environment)[--container]: Mention --user.
[--user]: Add item.
* guix/scripts/environment.scm (show-help): Add --user.
(%options): Add --user.
(launch-environment/container) Add 'user' parameter.  Update doc.  Override
'user-mappings' using 'override-user-mappings'.  Consider override for chdir.
(mock-passwd, user-override-home, overrid-euser-dir): New procedures.
(guix-environment): Disallow --user without --container.  Provide user to
'launch-environment/container'.
* tests/guix-environment.sh: Add user test.

Signed-off-by: Ludovic Courtès <ludo@gnu.org>

1 files changed, 11 insertions, 0 deletions

diff --git a/tests/guix-environment-container.sh b/tests/guix-environment-container.sh
index df40ce03e0..a2da9a0773 100644
--- a/tests/guix-environment-container.sh
+++ b/tests/guix-environment-container.sh
@@ -109,6 +109,17 @@ rm $tmpdir/mounts
              -- guile -c "$linktest"
 )
 
+# Test that user can be mocked.
+usertest='(exit (and (string=? (getenv "HOME") "/home/foognu")
+                     (string=? (passwd:name (getpwuid 0)) "foognu")
+                     (file-exists? "/home/foognu/umock")))'
+touch "$tmpdir/umock"
+HOME="$tmpdir" guix environment --bootstrap --container --user=foognu \
+     --ad-hoc guile-bootstrap --pure \
+     --share="$tmpdir/umock" \
+     -- guile -c "$usertest"
+
+
 # Check the exit code.
 
 abnormal_exit_code="