environment: Add --link-profile.

This change is motivated by attempts to run programs (like GNU IceCat) within
containers.  The 'fontconfig' program, for example, is configured explicitly
to check ~/.guix-profile for additional fonts.

There were no existing container tests in 'tests/guix-environment.sh', but I
added one anyway for this change.

* doc/guix.texi (Invoking guix environment): Add '--link-profile'.
* guix/scripts/environment.scm (show-help): Add '--link-profile'.
(%options): Add 'link-profile' as '#\P', assigned to 'link-profile?'.
(link-environment): New procedure.
(launch-environment/container): Use it when 'link-profile?'.
[link-profile?]: New parameter.
(guix-environment): Leave when '--link-prof' but not '--container'.  Add
'#:link-profile?' argument to 'launch-environment/container' application.
* tests/guix-environment-container.sh: New '--link-profile' test.

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

1 files changed, 19 insertions, 2 deletions

diff --git a/doc/guix.texi b/doc/guix.texi
index 24db167618..826f924d22 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -46,7 +46,8 @@ Copyright @copyright{} 2017 Andy Wingo@*
 Copyright @copyright{} 2017, 2018 Arun Isaac@*
 Copyright @copyright{} 2017 nee@*
 Copyright @copyright{} 2018 Rutger Helling@*
-Copyright @copyright{} 2018 Oleg Pykhalov
+Copyright @copyright{} 2018 Oleg Pykhalov@*
+Copyright @copyright{} 2018 Mike Gerwitz
 
 Permission is granted to copy, distribute and/or modify this document
 under the terms of the GNU Free Documentation License, Version 1.3 or
@@ -1572,7 +1573,7 @@ To be able to use such full names for the TrueType fonts installed in
 your Guix profile, you need to extend the font path of the X server:
 
 @example
-xset +fp ~/.guix-profile/share/fonts/truetype
+xset +fp `readlink -f ~/.guix-profile/share/fonts/truetype`
 @end example
 
 @cindex @code{xlsfonts}
@@ -7296,6 +7297,22 @@ For containers, share the network namespace with the host system.
 Containers created without this flag only have access to the loopback
 device.
 
+@item --link-profile
+@itemx -P
+For containers, link the environment profile to
+@file{~/.guix-profile} within the container.  This is equivalent to
+running the command @command{ln -s $GUIX_ENVIRONMENT ~/.guix-profile}
+within the container.  Linking will fail and abort the environment if
+the directory already exists, which will certainly be the case if
+@command{guix environment} was invoked in the user's home directory.
+
+Certain packages are configured to look in
+@code{~/.guix-profile} for configuration files and data;@footnote{For
+example, the @code{fontconfig} package inspects
+@file{~/.guix-profile/share/fonts} for additional fonts.}
+@code{--link-profile} allows these programs to behave as expected within
+the environment.
+
 @item --expose=@var{source}[=@var{target}]
 For containers, expose the file system @var{source} from the host system
 as the read-only file system @var{target} within the container.  If