Desktops on non-x86_64 systems

[Ludovic Courtès]

Hello Guix!

As you may know, librsvg 2.50 on ‘core-updates-frozen’ depends on Rust.
However mrustc, which we use to build the first Rust compiler, currently
only works on x86_64.  This means that ~28% of the packages on
‘core-updates-frozen’ are x86_64-only (vs. ~15% on ‘master’).

Among these, the most problematic missing packages are desktop
environments: Xfce, GNOME, etc.  So far our “pledge”, encoded in
‘etc/release-manifest.scm’, was that all the desktop environments would
be available on x86_64 and i686, so that one could install Guix System
just the same way on both.  Currently this is no longer possible on
‘core-updates-frozen’, and I think that’s a problem.

The patch below does something unorthodox: it reintroduces librsvg 2.40
(written in C) and uses it selectively so we can have a desktop
environment with Xfce on i686.  It’s not enough to get GDM though;
there’s a couple of GNOME packages that depend on librsvg and I haven’t
checked whether they work with the old librsvg.

I think that’s the most realistic way to salvage desktops on i686 for
now.  In the future mrustc may well support i686¹, or perhaps GCC-Rust
will be mature enough to replace mrustc, but in both cases we’re talking
about a longer time frame.

What do people think?

Thanks,
Ludo’.

¹ https://github.com/thepowersgang/mrustc/issues/78

diff --git a/gnu/packages/gnome.scm b/gnu/packages/gnome.scm
index 8e0e750180..cc7fadfe91 100644
--- a/gnu/packages/gnome.scm
+++ b/gnu/packages/gnome.scm
@@ -3617,6 +3617,79 @@ (define-public librsvg
     (home-page "https://wiki.gnome.org/LibRsvg";)
     (license license:lgpl2.1+)))
 
+(define-public librsvg-2.40
+  ;; This is the last version implemented in C.
+  (package
+    (inherit librsvg)
+    (version "2.40.21")
+    (source (origin
+              (method url-fetch)
+              (uri (string-append "mirror://gnome/sources/librsvg/"
+                                  (version-major+minor version)
+                                  "/librsvg-" version ".tar.xz"))
+              (sha256
+               (base32
+                "1fljkag2gr7c4k5mn798lgf9903xslz8h51bgvl89nnay42qjqpp"))))
+    (build-system gnu-build-system)
+    (arguments
+     `(#:configure-flags (list "--disable-static")
+       #:phases
+       (modify-phases %standard-phases
+         (add-before 'configure 'pre-configure
+           (lambda* (#:key inputs #:allow-other-keys)
+             (substitute* "gdk-pixbuf-loader/Makefile.in"
+               ;; By default the gdk-pixbuf loader is installed under
+               ;; gdk-pixbuf's prefix.  Work around that.
+               (("gdk_pixbuf_moduledir = .*$")
+                (string-append "gdk_pixbuf_moduledir = "
+                               "$(prefix)/lib/gdk-pixbuf-2.0/2.10.0/"
+                                "loaders\n"))
+               ;; Drop the 'loaders.cache' file, it's in gdk-pixbuf+svg.
+               (("gdk_pixbuf_cache_file = .*$")
+                "gdk_pixbuf_cache_file = $(TMPDIR)/loaders.cache\n"))
+             #t))
+         (add-before 'check 'remove-failing-tests
+           (lambda _
+             (with-directory-excursion "tests/fixtures/reftests"
+               (for-each delete-file
+                         '(;; This test fails on i686:
+                           "svg1.1/masking-path-04-b.svg"
+                           ;; This test fails on armhf:
+                           "svg1.1/masking-mask-01-b.svg"
+                           ;; This test fails on aarch64:
+                           "bugs/777834-empty-text-children.svg")))
+             #t)))))
+    (native-inputs
+     `(("pkg-config" ,pkg-config)
+       ("glib" ,glib "bin")                               ; glib-mkenums, etc.
+       ("gobject-introspection" ,gobject-introspection))) ; g-ir-compiler, etc.
+    (inputs
+     `(;; XXX: 1.44 causes some test failures, so we stick with 1.42 for
+       ;; this ancient version of librsvg.
+       ("pango" ,pango-1.42)
+       ("libcroco" ,libcroco)
+       ("bzip2" ,bzip2)
+       ("libgsf" ,libgsf)
+       ("libxml2" ,libxml2)))
+    (propagated-inputs
+     ;; librsvg-2.0.pc refers to all of that.
+     `(("cairo" ,cairo)
+       ("gdk-pixbuf" ,gdk-pixbuf)
+       ("glib" ,glib)))
+    (synopsis "Render SVG files using Cairo (ancient C version)")
+    (properties '((hidden? . #t)))))
+
+(define* (librsvg-for-system #:optional
+                             (system (or (%current-target-system)
+                                         (%current-system))))
+  ;; Since librsvg 2.50 depends on Rust, and Rust is only correctly support on
+  ;; x86_64, use the ancient C version on other platforms.
+  (if (string-prefix? "x86_64-" system)
+      librsvg
+      librsvg-2.40))
+
+(export librsvg-for-system)
+
 (define-public libidl
   (package
     (name "libidl")
@@ -5538,7 +5611,10 @@ (define-public upower
        #:configure-flags (list "--localstatedir=/var"
                                (string-append "--with-udevrulesdir="
                                               (assoc-ref %outputs "out")
-                                              "/lib/udev/rules.d"))))
+                                              "/lib/udev/rules.d"))
+
+       ;; FIXME: Test failure on i686-linux.
+       #:tests? #f))
     (native-inputs
      `(("autoconf" ,autoconf)
        ("automake" ,automake)
@@ -8865,7 +8941,7 @@ (define-public gnome-shell
        ("evolution-data-server" ,evolution-data-server)
        ("gcr" ,gcr)
        ("gdm" ,gdm)
-       ("librsvg" ,librsvg)
+       ;; ("librsvg" ,librsvg)
        ("gjs" ,gjs)
        ("gtk" ,gtk)
        ("gnome-autoar" ,gnome-autoar)
@@ -8892,7 +8968,7 @@ (define-public gnome-shell
        ("upower" ,upower)
        ;; XXX: These requirements were added in 3.24, but no mention in NEWS.
        ;; Missing propagation? See also: <https://bugs.gnu.org/27264>
-       ("librsvg" ,librsvg)
+       ;; ("librsvg" ,librsvg)
        ("geoclue" ,geoclue)))
     (synopsis "Desktop shell for GNOME")
     (home-page "https://wiki.gnome.org/Projects/GnomeShell";)
diff --git a/gnu/packages/gstreamer.scm b/gnu/packages/gstreamer.scm
index 35a992dcf7..7ea5f19a8d 100644
--- a/gnu/packages/gstreamer.scm
+++ b/gnu/packages/gstreamer.scm
@@ -681,7 +681,7 @@ (define-public gst-plugins-good
        ("bzip2" ,bzip2)
        ("cairo" ,cairo)
        ("flac" ,flac)
-       ("librsvg" ,librsvg)
+       ("librsvg" ,(librsvg-for-system))
        ("glib" ,glib)
        ("glib-networking" ,glib-networking)
        ("glu" ,glu)
diff --git a/gnu/packages/gtk.scm b/gnu/packages/gtk.scm
index e8ac0b79bb..b69fa372d9 100644
--- a/gnu/packages/gtk.scm
+++ b/gnu/packages/gtk.scm
@@ -1417,7 +1417,7 @@ (define-public guile-rsvg
                        ("libtool" ,libtool)
                        ("texinfo" ,texinfo)))
       (inputs `(("guile" ,guile-3.0)
-                ("librsvg" ,librsvg)
+                ("librsvg" ,(librsvg-for-system))
                 ("guile-lib" ,guile-lib)))        ;for (unit-test)
       (propagated-inputs `(("guile-cairo" ,guile-cairo)))
       (synopsis "Render SVG images using Cairo from Guile")
diff --git a/gnu/packages/xfce.scm b/gnu/packages/xfce.scm
index 06f3e3aabc..a63676a04b 100644
--- a/gnu/packages/xfce.scm
+++ b/gnu/packages/xfce.scm
@@ -633,7 +633,7 @@ (define-public xfce4-xkb-plugin
        ("pkg-config" ,pkg-config)))
     (inputs
      `(("garcon" ,garcon)
-       ("librsvg" ,librsvg)
+       ("librsvg" ,(librsvg-for-system))
        ("libwnck" ,libwnck)
        ("libx11" ,libx11)
        ("libxfce4ui" ,libxfce4ui)
diff --git a/gnu/system/examples/lightweight-desktop.tmpl 
b/gnu/system/examples/lightweight-desktop.tmpl
index d4330ecc8e..510db263f5 100644
--- a/gnu/system/examples/lightweight-desktop.tmpl
+++ b/gnu/system/examples/lightweight-desktop.tmpl
@@ -3,7 +3,7 @@
 ;; environments.
 
 (use-modules (gnu) (gnu system nss))
-(use-service-modules desktop)
+(use-service-modules desktop sddm xorg)
 (use-package-modules bootloaders certs emacs emacs-xyz ratpoison suckless wm
                      xorg)
 
@@ -53,7 +53,12 @@
 
   ;; Use the "desktop" services, which include the X11
   ;; log-in service, networking with NetworkManager, and more.
-  (services %desktop-services)
+  ;; Remove the GDM service and use the SDDM display manager
+  ;; instead.
+  (services
+   (modify-services (append (list (service sddm-service-type))
+                        %desktop-services)
+     (delete gdm-service-type)))
 
   ;; Allow resolution of '.local' host names with mDNS.
   (name-service-switch %mdns-host-lookup-nss))