[bug#39602] Generate font catalogues for the X server

[Ivan Kozlov]

Actually, I am sending this as a patch.

This should produce a "share/fontpath.d" directory in the profile which is a 
font catalogue as described in Xserver(1). Then the X server font path can be 
set to include this catalogue and it will find the installed fonts. This 
concerns all legacy X11 applications using the core fonts system, and most 
importantly xterm.

The hook ‘fonts-dir-file’ was originally added for this purpose as the comments 
can tell; you would include e. g. "share/fonts/X11/misc" from the profile in 
the font path, which is a union directory with symbolic links to fonts that 
want to install there and a fonts.dir file describing all of them. This has not 
been working for ages, since the X.org server stopped following symbolic links 
to font files for security reasons. It should be removed.

--- a/guix/profiles.scm 2020-01-01 13:03:15.579056969 +0300
+++ b/guix/profiles.scm 2020-02-14 19:52:51.979902836 +0300
@@ -1293,6 +1293,37 @@
                     `((type . profile-hook)
                       (hook . fonts-dir))))
 
+(define (fontpath-file manifest)
+  (define build
+    #~(begin
+       (use-modules (srfi srfi-1) (srfi srfi-26) (guix build utils))
+       (let* ((top-font-dirs (filter file-exists?
+                                     (map (cut string-append <>
+                                               "/share/fonts")
+                                          '#$(manifest-inputs manifest))))
+              (font-dirs (append-map (lambda (dir)
+                                       (find-files dir
+                                                   (lambda (file stat)
+                                                     (and (eq? 'directory 
(stat:type stat))
+                                                          (file-exists? 
(string-append file "/fonts.dir"))))
+                                                   #:directories? #t)) 
top-font-dirs))
+              (fonpath-dir (string-append #$output "/share/fontpath.d")))
+         (mkdir-p fontpath-dir)
+         (chdir fontpath-dir)
+         (for-each (lambda (dir pri)
+                     (symlink dir (string-append (basename dir) ":pri=" 
(number->string pri))))
+                   font-dirs
+                   (iota (length font-dirs) 1)))))
+  (gexp->derivation "fontpath.d" build
+                    #:modules '((guix build utils)
+                                (srfi srfi-1)
+                               (srfi srfi-26))
+                    #:local-build? #t
+                    #:substitutable? #f
+                    #:properties
+                    `((type . profile-hook)
+                      (hook . fontpath-dir))))
+
 (define (manual-database manifest)
   "Return a derivation that builds the manual page database (\"mandb\") for
 the entries in MANIFEST."
@@ -1430,6 +1461,7 @@
   (list info-dir-file
         manual-database
         fonts-dir-file
+       fontpath-file
         ghc-package-cache-file
         ca-certificate-bundle
         glib-schemas