[bug#62848] [PATCH] environment: Add --remote option and emacsclient-eshell backend.

[Antero Mejr]

* guix/scripts/environment.scm (launch-environment/eshell): New procedure.
(guix-environment*): Add logic for remote backend switching.
(%options): Add --remote and --list-remote-backends options.
(show-environment-options-help): Add help text for new options.
* guix/profiles.scm (load-profile)[getenv-proc, setenv-proc, unsetenv-proc]:
New optional keyword arguments.
(purify-environment)[unsetenv-proc]: New argument.
* doc/guix.texi(Invoking guix shell): Document --remote and
--list-remote-backends options.
---
"guix shell" doesn't support eshell due to eshell's quirks.
This change makes environments/profiles more network transparent to
support eshell, and maybe other remote environments in the future.

 doc/guix.texi                | 17 ++++++++
 guix/profiles.scm            | 30 ++++++++------
 guix/scripts/environment.scm | 80 ++++++++++++++++++++++++++++++++++--
 3 files changed, 112 insertions(+), 15 deletions(-)

diff --git a/doc/guix.texi b/doc/guix.texi
index adb1975935..f609e0c9b6 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -6245,6 +6245,23 @@ environment.
 @itemx -s @var{system}
 Attempt to build for @var{system}---e.g., @code{i686-linux}.
 
+@item --remote=@var{backend}[=@var{args}]
+Create an environment over a remote connection using @var{backend},
+optionally passing @var{args} to the backend.
+
+This option causes the @option{--container} option to be ignored.
+
+When @var{backend} is @code{emacsclient-eshell}, a new eshell buffer
+with the Guix environment will be opened.  An Emacs server must already
+be running, and the @code{emacsclient} program must be available.  Due
+to the way @code{eshell} handles commands, the @var{command} argument,
+if specified, will run in the initial @code{eshell} environment instead
+of the Guix @code{eshell} environment.
+
+@item --list-remote-backends
+Display the @var{backend} options for @code{guix shell --remote=BACKEND}
+and exit.
+
 @item --container
 @itemx -C
 @cindex container
diff --git a/guix/profiles.scm b/guix/profiles.scm
index 03333785f9..1bf6783eea 100644
--- a/guix/profiles.scm
+++ b/guix/profiles.scm
@@ -2062,10 +2062,10 @@ (define %precious-variables
   ;; Environment variables in the default 'load-profile' white list.
   '("HOME" "USER" "LOGNAME" "DISPLAY" "XAUTHORITY" "TERM" "TZ" "PAGER"))
 
-(define (purify-environment white-list white-list-regexps)
+(define (purify-environment white-list white-list-regexps unsetenv-proc)
   "Unset all environment variables except those that match the regexps in
 WHITE-LIST-REGEXPS and those listed in WHITE-LIST."
-  (for-each unsetenv
+  (for-each unsetenv-proc
             (remove (lambda (variable)
                       (or (member variable white-list)
                           (find (cut regexp-exec <> variable)
@@ -2077,23 +2077,29 @@ (define (purify-environment white-list 
white-list-regexps)
 (define* (load-profile profile
                        #:optional (manifest (profile-manifest profile))
                        #:key pure? (white-list-regexps '())
-                       (white-list %precious-variables))
+                       (white-list %precious-variables)
+                       (getenv-proc getenv) (setenv-proc setenv)
+                       (unsetenv-proc unsetenv))
   "Set the environment variables specified by MANIFEST for PROFILE.  When
 PURE? is #t, unset the variables in the current environment except those that
 match the regexps in WHITE-LIST-REGEXPS and those listed in WHITE-LIST.
 Otherwise, augment existing environment variables with additional search
-paths."
+paths.
+GETENV-PROC is a one-argument procedure that returns an env var value.
+SETENV-PROC is a two-argument procedure the sets environment variables.
+UNSETENV-PROC is a one-argument procedure that unsets environment variables.
+Change those procedures to load a profile over a remote connection."
   (when pure?
-    (purify-environment white-list white-list-regexps))
+    (purify-environment white-list white-list-regexps unsetenv-proc))
   (for-each (match-lambda
               ((($ <search-path-specification> variable _ separator) . value)
-               (let ((current (getenv variable)))
-                 (setenv variable
-                         (if (and current (not pure?))
-                             (if separator
-                                 (string-append value separator current)
-                                 value)
-                             value)))))
+               (let ((current (getenv-proc variable)))
+                 (setenv-proc variable
+                              (if (and current (not pure?))
+                                  (if separator
+                                      (string-append value separator current)
+                                      value)
+                                  value)))))
             (profile-search-paths profile manifest)))
 
 (define (profile-regexp profile)
diff --git a/guix/scripts/environment.scm b/guix/scripts/environment.scm
index ebfc05731c..7e67cf1d1d 100644
--- a/guix/scripts/environment.scm
+++ b/guix/scripts/environment.scm
@@ -53,6 +53,7 @@ (define-module (guix scripts environment)
   #:autoload   (gnu packages bootstrap) (bootstrap-executable %bootstrap-guile)
   #:autoload   (gnu packages package-management) (guix)
   #:use-module (ice-9 match)
+  #:use-module (ice-9 popen)
   #:autoload   (ice-9 rdelim) (read-line)
   #:use-module (ice-9 vlist)
   #:autoload   (web uri) (string->uri uri-scheme)
@@ -104,6 +105,13 @@ (define (show-environment-options-help)
   (display (G_ "
   -r, --root=FILE        make FILE a symlink to the result, and register it
                          as a garbage collector root"))
+  (display (G_ "
+      --remote=BACKEND[=ARGS]
+                        create environment over a remote connection by
+                        passing ARGS to BACKEND"))
+  (display (G_ "
+      --list-remote-backends
+                         list available remote backends and exit"))
   (display (G_ "
   -C, --container        run command within an isolated container"))
   (display (G_ "
@@ -283,6 +291,13 @@ (define %options
          (option '("bootstrap") #f #f
                  (lambda (opt name arg result)
                    (alist-cons 'bootstrap? #t result)))
+         (option '("remote") #t #f
+                 (lambda (opt name arg result)
+                   (alist-cons 'remote arg result)))
+         (option '("list-remote-backends") #f #f
+                 (lambda args
+                   (display "emacsclient-eshell\n")
+                   (exit 0)))
 
          (append %transformation-options
                  %standard-build-options
@@ -715,6 +730,50 @@ (define* (launch-environment/fork command profile manifest
            ((_ . status)
             status)))))
 
+(define* (launch-environment/eshell args command profile manifest
+                                    #:key pure? (white-list '()))
+  "Create an new eshell buffer with an environment containing PROFILE,
+with the search paths specified by MANIFEST.  When PURE?, pre-existing
+environment variables are cleared before setting the new ones, except those
+matching the regexps in WHITE-LIST."
+
+  (define (escape in)
+    (string-append "\"" (string-replace-substring in "\"" "\\\"") "\""))
+
+  (define* (ec cmd #:optional (check? #f))
+    (let* ((cmd (string-append "emacsclient " args " -e " (escape cmd)))
+           (port (open-input-pipe cmd))
+           (str (read-line port))
+           (code (status:exit-val (close-pipe port))))
+      (if (and check? (or (not (eqv? code 0)) (eof-object? str)))
+          (leave
+           (G_ "Emacs server connection failed. Is the server running?~%")))
+      str))
+
+  (let ((buf (ec "(buffer-name (eshell t))" #t)))
+    (define (ec-buf cmd)
+      (ec (string-append "(with-current-buffer " buf " " cmd ")")))
+
+    (load-profile
+     profile manifest #:pure? pure? #:white-list-regexps white-list
+     #:setenv-proc (lambda (var val)
+                     (ec-buf
+                      (if (string=? var "PATH")
+                          ;; TODO: TRAMP support?
+                          (string-append "(eshell-set-path " (escape val) ")")
+                          (string-append "(setenv " (escape var) " "
+                                         (escape val) ")"))))
+     #:unsetenv-proc (lambda (var)
+                       (ec-buf
+                        (string-append "(setenv " (escape var) ")"))))
+
+    (match command
+      ((program . args)
+       (ec-buf
+        (string-append
+         "(eshell-command "
+         (escape (string-append program " " (string-join args)))")"))))))
+
 (define* (launch-environment/container #:key command bash user user-mappings
                                        profile manifest link-profile? network?
                                        map-cwd? emulate-fhs? nesting?
@@ -1081,7 +1140,10 @@ (define (guix-environment* opts)
                            '("/bin/sh")
                            (list %default-shell))))
          (mappings   (pick-all opts 'file-system-mapping))
-         (white-list (pick-all opts 'inherit-regexp)))
+         (white-list (pick-all opts 'inherit-regexp))
+         (remote (match (string-split (assoc-ref opts 'remote) #\=)
+                   ((x) (cons x ""))
+                   ((x . y) (cons x (string-join y))))))
 
     (define store-needed?
       ;; Whether connecting to the daemon is needed.
@@ -1119,6 +1181,10 @@ (define-syntax-rule (with-store/maybe store exp ...)
       (when (pair? symlinks)
         (leave (G_ "'--symlink' cannot be used without '--container~%'"))))
 
+    (when (and remote (not (member (car remote) '("emacsclient-eshell"))))
+      (leave
+       (G_ "Invalid remote backend, see --list-remote-backends for 
options.~%'")))
+
     (with-store/maybe store
       (with-status-verbosity (assoc-ref opts 'verbosity)
         (define manifest-from-opts
@@ -1172,15 +1238,23 @@ (define manifest
 
                 (mwhen (assoc-ref opts 'check?)
                   (return
-                   (if container?
+                   (if (or container? remote)
                        (warning (G_ "'--check' is unnecessary \
-when using '--container'; doing nothing~%"))
+when using '--container' or '--remote'; doing nothing~%"))
                        (validate-child-shell-environment profile manifest))))
 
                 (cond
                  ((assoc-ref opts 'search-paths)
                   (show-search-paths profile manifest #:pure? pure?)
                   (return #t))
+                 (remote
+                  (match (car remote)
+                    ("emacsclient-eshell"
+                     (return
+                      (launch-environment/eshell (cdr remote)
+                                                 command profile manifest
+                                                 #:white-list white-list
+                                                 #:pure? pure?)))))
                  (container?
                   (let ((bash-binary
                          (if bootstrap?
-- 
2.39.2