environment: Set 'GUIX_ENVIRONMENT' to the profile.

* guix/scripts/environment.scm (create-environment): Set
'GUIX_ENVIRONMENT' to PROFILE.
* tests/guix-environment.sh: Test it.
* doc/guix.texi (Invoking guix environment): Document it.

doc/guix.texi

@@ -5456,7 +5456,8 @@ details on Bash start-up files.}.
 
 @vindex GUIX_ENVIRONMENT
 @command{guix environment} defines the @code{GUIX_ENVIRONMENT}
-variable in the shell it spawns.  This allows users to, say, define a
+variable in the shell it spawns; its value is the file name of the
+profile of this environment.  This allows users to, say, define a
 specific prompt for development environments in their @file{.bashrc}
 (@pxref{Bash Startup Files,,, bash, The GNU Bash Reference Manual}):
 
@@ -5467,6 +5468,13 @@ then
 fi
 @end example
 
+@noindent
+... or to browse the profile:
+
+@example
+$ ls "$GUIX_ENVIRONMENT/bin"
+@end example
+
 Additionally, more than one package may be specified, in which case the
 union of the inputs for the given packages are used.  For example, the
 command below spawns a shell where all of the dependencies of both Guile

guix/scripts/environment.scm

@@ -90,8 +90,9 @@ existing enviroment variables with additional search paths."
             (evaluate-profile-search-paths profile paths))
 
   ;; Give users a way to know that they're in 'guix environment', so they can
-  ;; adjust 'PS1' accordingly, for instance.
-  (setenv "GUIX_ENVIRONMENT" "t"))
+  ;; adjust 'PS1' accordingly, for instance.  Set it to PROFILE so users can
+  ;; conveniently access its contents.
+  (setenv "GUIX_ENVIRONMENT" profile))
 
 (define (show-search-paths profile search-paths pure?)
   "Display SEARCH-PATHS applied to PROFILE.  When PURE? is #t, do not augment

tests/guix-environment.sh

@@ -57,6 +57,10 @@ else
     test $? = 42
 fi
 
+# Make sure 'GUIX_ENVIRONMENT' points to the profile.
+guix environment --bootstrap --ad-hoc guile-bootstrap --pure \
+     -- "$SHELL" -c 'test -f "$GUIX_ENVIRONMENT/bin/guile"'
+
 case "`uname -m`" in
     x86_64)
 	# On x86_64, we should be able to create a 32-bit environment.