[bug#50208] [PATCH] home-services: Add symlink-manager

[Andrew Tropin]

---
This patch is targeted against wip-guix-home branch.

It's not a part of any patch series to make sure it will get enough attention,
because it's most unpure part of the Guix Home and operates on user's files.

 gnu/home-services/symlink-manager.scm | 248 ++++++++++++++++++++++++++
 1 file changed, 248 insertions(+)
 create mode 100644 gnu/home-services/symlink-manager.scm

diff --git a/gnu/home-services/symlink-manager.scm 
b/gnu/home-services/symlink-manager.scm
new file mode 100644
index 0000000000..f13c9f4dbe
--- /dev/null
+++ b/gnu/home-services/symlink-manager.scm
@@ -0,0 +1,248 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2021 Andrew Tropin <andrew@trop.in>
+;;; Copyright © 2021 Xinglu Chen <public@yoctocell.xyz>
+;;;
+;;; This file is part of GNU Guix.
+;;;
+;;; GNU Guix is free software; you can redistribute it and/or modify it
+;;; under the terms of the GNU General Public License as published by
+;;; the Free Software Foundation; either version 3 of the License, or (at
+;;; your option) any later version.
+;;;
+;;; GNU Guix is distributed in the hope that it will be useful, but
+;;; WITHOUT ANY WARRANTY; without even the implied warranty of
+;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;;; GNU General Public License for more details.
+;;;
+;;; You should have received a copy of the GNU General Public License
+;;; along with GNU Guix.  If not, see <http://www.gnu.org/licenses/>.
+
+(define-module (gnu home-services symlink-manager)
+  #:use-module (gnu home-services)
+  #:use-module (guix gexp)
+
+  #:export (home-symlink-manager-service-type))
+
+;;; Comment:
+;;;
+;;; symlink-manager cares about configuration files: it backups files
+;;; created by user, removes symlinks and directories created by
+;;; previous generation, and creates new directories and symlinks to
+;;; configs according to content of files/ directory of current home
+;;; environment generation (created by home-files-service).
+;;;
+;;; Code:
+
+(define (update-symlinks-script)
+  (program-file
+   "update-symlinks"
+   #~(begin
+       (use-modules (ice-9 ftw)
+                   (ice-9 curried-definitions)
+                   (ice-9 match)
+                   (srfi srfi-1))
+       (define ((simplify-file-tree parent) file)
+         "Convert the result produced by `file-system-tree' to less
+verbose and more suitable for further processing format.
+
+Extract dir/file info from stat and compose a relative path to the
+root of the file tree.
+
+Sample output:
+
+((dir . \".\")
+ ((dir . \"config\")
+  ((dir . \"config/fontconfig\")
+   (file . \"config/fontconfig/fonts.conf\"))
+  ((dir . \"config/isync\")
+   (file . \"config/isync/mbsyncrc\"))))
+"
+        (match file
+          ((name stat) `(file . ,(string-append parent name)))
+          ((name stat children ...)
+           (cons `(dir . ,(string-append parent name))
+                 (map (simplify-file-tree
+                       (if (equal? name ".")
+                           ""
+                           (string-append parent name "/")))
+                      children)))))
+
+       (define ((file-tree-traverse preordering) node)
+        "Traverses the file tree in different orders, depending on PREORDERING.
+
+if PREORDERING is @code{#t} resulting list will contain folders before
+files located in those folders, otherwise folders will appear only
+after all nested items already listed."
+        (let ((prepend (lambda (a b) (append b a))))
+          (match node
+            (('file . path) (list node))
+            ((('dir . path) . rest)
+             ((if preordering append prepend)
+              (list (cons 'dir path))
+              (append-map (file-tree-traverse preordering) rest))))))
+
+       (use-modules (guix build utils))
+
+       (let* ((he-path (string-append (getenv "HOME") "/.guix-home"))
+              (new-he-tmp-path (string-append he-path ".new"))
+              (new-home (getenv "GUIX_NEW_HOME")))
+         (symlink new-home new-he-tmp-path)
+         (rename-file new-he-tmp-path he-path))
+
+       (let* ((config-home    (or (getenv "XDG_CONFIG_HOME")
+                                 (string-append (getenv "HOME") "/.config")))
+
+             (he-path (string-append (getenv "HOME") "/.guix-home"))
+              (new-he-tmp-path (string-append he-path ".new"))
+
+             (files-path (string-append he-path "/files"))
+             ;; Leading dot is required, because files itself is symlink and
+             ;; to make file-system-tree works it should be a directory.
+             (files-dir-path (string-append files-path "/."))
+             (new-files-path (string-append new-he-tmp-path "/files"))
+             (new-files-dir-path (string-append files-path "/."))
+
+             (home-path (getenv "HOME"))
+             (backup-dir (string-append home-path "/"
+                                        (number->string (current-time))
+                                        "-guix-home-legacy-configs-backup"))
+
+             (old-tree (if (file-exists? files-dir-path)
+                          ((simplify-file-tree "")
+                          (file-system-tree files-dir-path))
+                          #f))
+             (new-tree ((simplify-file-tree "")
+                        (file-system-tree new-files-dir-path)))
+
+             (get-source-path
+              (lambda (path)
+                (readlink (string-append files-path "/" path))))
+
+             (get-target-path
+              (lambda (path)
+                (string-append home-path "/." path)))
+
+             (get-backup-path
+              (lambda (path)
+                (string-append backup-dir "/." path)))
+
+             (directory?
+              (lambda (path)
+                (equal? (stat:type (stat path)) 'directory)))
+
+             (empty-directory?
+              (lambda (dir)
+                (equal? (scandir dir) '("." ".."))))
+
+             (symlink-to-store?
+              (lambda (path)
+                (and
+                 (equal? (stat:type (lstat path)) 'symlink)
+                 (store-file-name? (readlink path)))))
+
+             (backup-file
+              (lambda (path)
+                (mkdir-p backup-dir)
+                (format #t "Backing up ~a..." (get-target-path path))
+                (mkdir-p (dirname (get-backup-path path)))
+                (rename-file (get-target-path path) (get-backup-path path))
+                (display " done\n")))
+
+             (cleanup-symlinks
+              (lambda ()
+                (let ((to-delete ((file-tree-traverse #f) old-tree)))
+                  (display
+                   "Cleaning up symlinks from previous home-environment.\n\n")
+                  (map
+                   (match-lambda
+                     (('dir . ".")
+                      (display "Cleanup finished.\n\n"))
+
+                     (('dir . path)
+                      (if (and
+                           (file-exists? (get-target-path path))
+                           (directory? (get-target-path path))
+                           (empty-directory? (get-target-path path)))
+                          (begin
+                            (format #t "Removing ~a..."
+                                    (get-target-path path))
+                            (rmdir (get-target-path path))
+                            (display " done\n"))
+                          (format
+                           #t "Skipping ~a (not an empty directory)... done\n"
+                           (get-target-path path))))
+
+                     (('file . path)
+                      (when (file-exists? (get-target-path path))
+                        ;; DO NOT remove the file if it was modified
+                        ;; by user (not a symlink to the /gnu/store
+                        ;; anymore) it will be backed up later during
+                        ;; create-symlinks phase.
+                        (if (symlink-to-store? (get-target-path path))
+                            (begin
+                              (format #t "Removing ~a..." (get-target-path 
path))
+                              (delete-file (get-target-path path))
+                              (display " done\n"))
+                            (format
+                             #t
+                             "Skipping ~a (not a symlink to store)... done\n"
+                             (get-target-path path))))))
+                   to-delete))))
+
+             (create-symlinks
+              (lambda ()
+                (let ((to-create ((file-tree-traverse #t) new-tree)))
+                  (map
+                   (match-lambda
+                     (('dir . ".")
+                      (display
+                       "New symlinks to home-environment will be created 
soon.\n")
+                      (format
+                       #t "All conflicting files will go to ~a.\n\n" 
backup-dir))
+
+                     (('dir . path)
+                      (let ((target-path (get-target-path path)))
+                        (when (and (file-exists? target-path)
+                                   (not (directory? target-path)))
+                          (backup-file path))
+
+                        (if (file-exists? target-path)
+                            (format
+                             #t "Skipping   ~a (directory already exists)... 
done\n"
+                             target-path)
+                            (begin
+                              (format #t "Creating   ~a..." target-path)
+                              (mkdir target-path)
+                              (display " done\n")))))
+
+                     (('file . path)
+                      (when (file-exists? (get-target-path path))
+                        (backup-file path))
+                      (format #t "Symlinking ~a -> ~a..."
+                              (get-target-path path) (get-source-path path))
+                      (symlink (get-source-path path) (get-target-path path))
+                      (display " done\n")))
+                   to-create)))))
+
+        (when old-tree
+          (cleanup-symlinks))
+
+        (create-symlinks)
+
+        (display " done\nFinished updating symlinks.\n\n")))))
+
+
+(define (update-symlinks-gexp _)
+  #~(primitive-load #$(update-symlinks-script)))
+
+(define home-symlink-manager-service-type
+  (service-type (name 'home-symlink-manager)
+                (extensions
+                 (list
+                 (service-extension
+                  home-activation-service-type
+                   update-symlinks-gexp)))
+               (default-value #f)
+                (description "Provide an @code{update-symlinks}
+script, which create and remove symlinks on every activation.  If the
+target is occupied by a file created by user, back it up.")))
-- 
2.33.0

signature.asc
Description: PGP signature