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

From: Andrew Tropin <[email-masked]>
Date: Thu, 26 Aug 2021 09:39:38 +0300

---
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 <[email-masked]>
+;;; Copyright © 2021 Xinglu Chen <[email-masked]>
+;;;
+;;; 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