home: Add home-dotfiles-service.

* gnu/home/service/dotfiles.scm: New file;
* gnu/local.mk (GNU_SYSTEM_MODULES): Add it.
* po/guix/POTFILES.in: Add it.
* doc/guix.texi (Essential Home Services): Document it.

Change-Id: I6769169cfacefc3842faa5b31bee081c56c28743
Co-authored-by: Ludovic Courtès <ludo@gnu.org>

doc/guix.texi

@@ -44216,6 +44216,114 @@ to use alternative services to implement more advanced use cases like
 read-only home.  Feel free to experiment and share your results.
 @end defvar
 
+It is often the case that Guix Home users already have a setup for versioning
+their user configuration files (also known as @emph{dotfiles}) in a single
+directory, and some way of automatically deploy changes to their user home.
+
+The @code{home-dotfiles-service-type} from @code{(gnu home services dotfiles)}
+is designed to ease the way into using Guix Home for this kind of users,
+allowing them to point the service to their dotfiles directory, which must
+follow the layout suggested by
+@uref{https://www.gnu.org/software/stow/, GNU Stow},
+and have their dotfiles automatically deployed to their user home, without
+migrating them to Guix native configurations.
+
+The dotfiles directory layout is expected to be structured as follows. Please
+keep in mind that it is advisable to keep your dotfiles directories under
+version control, for example in the same repository where you'd track your
+Guix Home configuration.
+
+@example
+~$ tree -a ./dotfiles/
+dotfiles/
+├── git
+│   └── .gitconfig
+├── gpg
+│   └── .gnupg
+│       ├── gpg-agent.conf
+│       └── gpg.conf
+├── guile
+│   └── .guile
+├── guix
+│   └── .config
+│       └── guix
+│           └── channels.scm
+├── nix
+│   ├── .config
+│   │   └── nixpkgs
+│   │       └── config.nix
+│   └── .nix-channels
+├── tmux
+│   └── .tmux.conf
+└── vim
+    └── .vimrc
+
+13 directories, 10 files
+@end example
+
+For an informal specification please refer to the Stow manual
+(@pxref{Top,,, stow, Introduction}). A suitable configuration would then
+be:
+
+@lisp
+(home-environment
+  ;; @dots{}
+  (services
+    (service home-dotfiles-service-type
+             (home-dotfiles-configuration
+               (directories (list "./dotfiles"))))))
+@end lisp
+
+The expected home directory state would then be:
+
+@example
+.
+├── .config
+│   ├── guix
+│   │   └── channels.scm
+│   └── nixpkgs
+│       └── config.nix
+├── .gitconfig
+├── .gnupg
+│   ├── gpg-agent.conf
+│   └── gpg.conf
+├── .guile
+├── .nix-channels
+├── .tmux.conf
+└── .vimrc
+@end example
+
+@defvar home-dotfiles-service-type
+Return a service which is very similiar to @code{home-files-service-type}
+(and actually extends it), but designed to ease the way into using Guix
+Home for users that already track their dotfiles under some kind of version
+control.  This service allows users to point Guix Home to their dotfiles
+directory and have their files automatically deployed to their home directory
+just like Stow would, without migrating all of their dotfiles to Guix native
+configurations.
+@end defvar
+
+@deftp {Data Type} home-dotfiles-configuration
+Available @code{home-dotfiles-configuration} fields are:
+
+@table @asis
+@item @code{source-directory} (default: @code{(current-source-directory)})
+The path where dotfile directories are resolved. By default dotfile directories
+are resolved relative the source location where
+@code{home-dotfiles-configuration} appears.
+
+@item @code{directories} (type: list-of-strings)
+The list of dotfiles directories where @code{home-dotfiles-service-type} will
+look for application dotfiles.
+
+@item @code{exclude} (default: @code{'(".*~" ".*\\.swp" "\\.git" "\\.gitignore")})
+The list of file patterns @code{home-dotfiles-service-type} will exclude while
+visiting each one of the @code{directories}.
+
+@end table
+
+@end deftp
+
 @defvar home-xdg-configuration-files-service-type
 The service is very similar to @code{home-files-service-type} (and
 actually extends it), but used for defining files, which will go to

gnu/home/services/dotfiles.scm

@@ -0,0 +1,117 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2024 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2024 Giacomo Leidi <goodoldpaul@autistici.org>
+;;;
+;;; 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 dotfiles)
+  #:use-module (gnu home services)
+  #:use-module (gnu services)
+  #:autoload   (guix build utils) (find-files)
+  #:use-module (guix gexp)
+  #:use-module (guix records)
+  #:use-module ((guix utils) #:select (current-source-directory))
+  #:use-module (srfi srfi-1)
+  #:use-module (ice-9 ftw)
+  #:use-module (ice-9 regex)
+  #:export (home-dotfiles-service-type
+            home-dotfiles-configuration
+            home-dotfiles-configuration?
+            home-dotfiles-configuration-source-directory
+            home-dotfiles-configuration-directories
+            home-dotfiles-configuration-excluded))
+
+(define %home-dotfiles-excluded
+  '(".*~"
+    ".*\\.swp"
+    "\\.git"
+    "\\.gitignore"))
+
+(define-record-type* <home-dotfiles-configuration>
+  home-dotfiles-configuration make-home-dotfiles-configuration
+  home-dotfiles-configuration?
+  (source-directory  home-dotfiles-configuration-source-directory
+                     (default (current-source-directory))
+                     (innate))
+  (directories       home-dotfiles-configuration-directories       ;list of strings
+                     (default '()))
+  (excluded          home-dotfiles-configuration-excluded       ;list of strings
+                     (default %home-dotfiles-excluded)))
+
+(define (import-dotfiles directory files)
+  "Return a list of objects compatible with @code{home-files-service-type}'s
+value.  Each object is a pair where the first element is the relative path
+of a file and the second is a gexp representing the file content.  Objects are
+generated by recursively visiting DIRECTORY and mapping its contents to the
+user's home directory, excluding files that match any of the patterns in EXCLUDED."
+  (define (strip file)
+    (string-drop file (+ 1 (string-length directory))))
+
+  (define (format file)
+    ;; Remove from FILE characters that cannot be used in the store.
+    (string-append
+     "home-dotfiles-"
+     (string-map (lambda (chr)
+                   (if (and (char-set-contains? char-set:ascii chr)
+                            (char-set-contains? char-set:graphic chr)
+                            (not (memv chr '(#\. #\/ #\space))))
+                       chr
+                       #\-))
+                 file)))
+
+  (map (lambda (file)
+         (let ((stripped (strip file)))
+           (list stripped
+                 (local-file file (format stripped)
+                             #:recursive? #t))))
+       files))
+
+(define (home-dotfiles-configuration->files config)
+  "Return a list of objects compatible with @code{home-files-service-type}'s
+value, generated following GNU Stow's algorithm for each of the
+directories in CONFIG, excluding files that match any of the patterns configured."
+  (define excluded
+    (home-dotfiles-configuration-excluded config))
+  (define exclusion-rx
+    (make-regexp (string-append "^.*(" (string-join excluded "|") ")$")))
+
+  (define (directory-contents directory)
+    (find-files directory
+                (lambda (file stat)
+                  (not (regexp-exec exclusion-rx
+                                    (basename file))))))
+
+  (define (resolve directory)
+    ;; Resolve DIRECTORY relative to the 'source-directory' field of CONFIG.
+    (if (string-prefix? "/" directory)
+        directory
+        (in-vicinity (home-dotfiles-configuration-source-directory config)
+                     directory)))
+
+  (append-map (lambda (directory)
+                (let* ((directory (resolve directory))
+                       (contents  (directory-contents directory)))
+                  (import-dotfiles directory contents)))
+              (home-dotfiles-configuration-directories config)))
+
+(define-public home-dotfiles-service-type
+  (service-type (name 'home-dotfiles)
+                (extensions
+                 (list (service-extension home-files-service-type
+                                          home-dotfiles-configuration->files)))
+                (default-value (home-dotfiles-configuration))
+                (description "Files that will be put in the user's home directory
+following GNU Stow's algorithm, and further processed during activation.")))

gnu/local.mk

@@ -96,6 +96,7 @@ GNU_SYSTEM_MODULES =				\
   %D%/home/services.scm			\
   %D%/home/services/desktop.scm			\
   %D%/home/services/dict.scm			\
+  %D%/home/services/dotfiles.scm		\
   %D%/home/services/symlink-manager.scm		\
   %D%/home/services/fontutils.scm		\
   %D%/home/services/gnupg.scm			\

po/guix/POTFILES.in

@@ -14,6 +14,7 @@ gnu/services/samba.scm
 gnu/services/version-control.scm
 gnu/home/services.scm
 gnu/home/services/desktop.scm
+gnu/home/services/dotfiles.scm
 gnu/home/services/fontutils.scm
 gnu/home/services/gnupg.scm
 gnu/home/services/guix.scm