scripts: environment: Add --no-cwd.

* doc/guix.texi (Invoking guix environment): Add --no-cwd.
* guix/scripts/environment.scm (show-help, %options): Add --no-cwd.
(launch-environment/container): Add 'map-cwd?' param; only add mapping
for cwd if #t.  Only change to cwd within container if #t, otherwise
home.
(guix-environment): Error if --no-cwd without --container.  Provide
'(not no-cwd?)' to launch-environment/container as 'map-cwd?'.
* tests/guix-environment.sh: Add test for no-cwd.

Co-authored-by: Mike Gerwitz <mtg@gnu.org>

doc/guix.texi

@@ -4657,6 +4657,14 @@ While this will limit the leaking of user identity through home paths
 and each of the user fields, this is only one useful component of a
 broader privacy/anonymity solution---not one in and of itself.
 
+@item --no-cwd
+For containers, the default behavior is to share the current working
+directory with the isolated container and immediately change to that
+directory within the container.  If this is undesirable, @code{--no-cwd}
+will cause the current working directory to @emph{not} be automatically
+shared and will change to the user's home directory within the container
+instead.  See also @code{--user}.
+
 @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

guix/scripts/environment.scm

@@ -161,6 +161,10 @@ (define (show-help)
   -u, --user=USER        instead of copying the name and home of the current
                          user into an isolated container, use the name USER
                          with home directory /home/USER"))
+  (display (G_ "
+      --no-cwd           do not share current working directory with an
+                         isolated container"))
+
   (display (G_ "
       --share=SPEC       for containers, share writable host file system
                          according to SPEC"))
@@ -269,6 +273,9 @@ (define %options
                  (lambda (opt name arg result)
                    (alist-cons 'user arg
                                (alist-delete 'user result eq?))))
+         (option '("no-cwd") #f #f
+                 (lambda (opt name arg result)
+                   (alist-cons 'no-cwd? #t result)))
          (option '("share") #t #f
                  (lambda (opt name arg result)
                    (alist-cons 'file-system-mapping
@@ -444,7 +451,8 @@ (define* (launch-environment/fork command profile manifest
            ((_ . status) status)))))
 
 (define* (launch-environment/container #:key command bash user user-mappings
-                                       profile manifest link-profile? network?)
+                                       profile manifest link-profile? network?
+                                       map-cwd?)
   "Run COMMAND within a container that features the software in PROFILE.
 Environment variables are set according to the search paths of MANIFEST.
 The global shell is BASH, a file name for a GNU Bash binary in the
@@ -483,11 +491,13 @@ (define* (launch-environment/container #:key command bash user user-mappings
               (override-user-mappings
                user home
                (append user-mappings
-                       ;; Current working directory.
+                       ;; Share current working directory, unless asked not to.
+                       (if map-cwd?
                            (list (file-system-mapping
                                   (source cwd)
                                   (target cwd)
-                              (writable? #t)))))
+                                  (writable? #t)))
+                           '())))
               ;; When in Rome, do as Nix build.cc does: Automagically
               ;; map common network configuration files.
               (if network?
@@ -537,8 +547,10 @@ (define* (launch-environment/container #:key command bash user user-mappings
             (write-group groups)
 
             ;; For convenience, start in the user's current working
-            ;; directory rather than the root directory.
-            (chdir (override-user-dir user home cwd))
+            ;; directory or, if unmapped, the home directory.
+            (chdir (if map-cwd?
+                       (override-user-dir user home cwd)
+                       home-dir))
 
             (primitive-exit/status
              ;; A container's environment is already purified, so no need to
@@ -665,6 +677,7 @@ (define (guix-environment . args)
            (container? (assoc-ref opts 'container?))
            (link-prof? (assoc-ref opts 'link-profile?))
            (network?   (assoc-ref opts 'network?))
+           (no-cwd?    (assoc-ref opts 'no-cwd?))
            (user       (assoc-ref opts 'user))
            (bootstrap? (assoc-ref opts 'bootstrap?))
            (system     (assoc-ref opts 'system))
@@ -685,6 +698,9 @@ (define (guix-environment . args)
         (leave (G_ "'--link-profile' cannot be used without '--container'~%")))
       (when (and (not container?) user)
         (leave (G_ "'--user' cannot be used without '--container'~%")))
+      (when (and (not container?) no-cwd?)
+        (leave (G_ "--no-cwd cannot be used without --container~%")))
+
 
       (with-store store
         (with-status-verbosity (assoc-ref opts 'verbosity)
@@ -741,7 +757,9 @@ (define manifest
                                                     #:profile profile
                                                     #:manifest manifest
                                                     #:link-profile? link-prof?
-                                                    #:network? network?)))
+                                                    #:network? network?
+                                                    #:map-cwd? (not no-cwd?))))
+
                    (else
                     (return
                      (exit/status

tests/guix-environment.sh

@@ -84,6 +84,14 @@ echo "(use-modules (guix profiles) (gnu packages bootstrap))
 guix environment --bootstrap --manifest=$tmpdir/manifest.scm --pure \
      -- "$SHELL" -c 'test -f "$GUIX_ENVIRONMENT/bin/guile"'
 
+# if not sharing CWD, chdir home
+(
+  cd "$tmpdir" \
+    && guix environment --bootstrap --container --no-cwd --user=foo  \
+            --ad-hoc guile-bootstrap --pure \
+            -- /bin/sh -c 'test $(pwd) == "/home/foo" -a ! -d '"$tmpdir"
+)
+
 # Make sure '-r' works as expected.
 rm -f "$gcroot"
 expected="`guix environment --bootstrap --ad-hoc guile-bootstrap \