nixos/sway: Improve the module and adapt it to NixOS

This commit contains the following changes:
- nixos/sway: Remove the beta references
- sway: Drop buildDocs
- nixos/sway: Improve the documentation
- sway,nixos/sway: Adapt Sway to NixOS
  - Copy the default configuration file to /etc/sway/config (Sway will
    still load the identical file from the Nix store but this makes it
    easier to copy the default configuration file).
  - This will also remove all references to the Nix store from the
    default configuration file as they will eventually be garbage
    collected which is a problem if the user copies it.
  - I've also decided to drop the default wallpaper (alternatively we
    could copy it to a fixed location).
- nixos/sway: Drop the package option

pkgs/applications/window-managers/sway/default.nix

@@ -4,7 +4,6 @@
 , wayland, libxkbcommon, pcre, json_c, dbus, libevdev
 , pango, cairo, libinput, libcap, pam, gdk_pixbuf
 , wlroots, wayland-protocols
-, buildDocs ? true
 }:
 
 stdenv.mkDerivation rec {
@@ -26,11 +25,10 @@ stdenv.mkDerivation rec {
       url = "https://github.com/swaywm/sway/commit/bcde298a719f60b9913133dbd2a169dedbc8dd7d.patch";
       sha256 = "0r583nmqvq43ib93yv6flw8pj833v32lbs0q0xld56s3rnzvvdcp";
     })
+    ./sway-config-no-nix-store-references.patch
   ];
 
-  nativeBuildInputs = [
-    pkgconfig meson ninja
-  ] ++ stdenv.lib.optional buildDocs scdoc;
+  nativeBuildInputs = [ pkgconfig meson ninja scdoc ];
 
   buildInputs = [
     wayland libxkbcommon pcre json_c dbus libevdev
@@ -41,11 +39,12 @@ stdenv.mkDerivation rec {
   enableParallelBuilding = true;
 
   mesonFlags = [
-    "-Dxwayland=enabled" "-Dgdk-pixbuf=enabled" "-Dtray=enabled"
-  ] ++ stdenv.lib.optional buildDocs "-Dman-pages=enabled";
+    "-Ddefault-wallpaper=false" "-Dxwayland=enabled" "-Dgdk-pixbuf=enabled"
+    "-Dtray=enabled" "-Dman-pages=enabled"
+  ];
 
   meta = with stdenv.lib; {
-    description = "i3-compatible window manager for Wayland";
+    description = "i3-compatible tiling Wayland compositor";
     homepage    = https://swaywm.org;
     license     = licenses.mit;
     platforms   = platforms.linux;

pkgs/applications/window-managers/sway/sway-config-no-nix-store-references.patch

@@ -0,0 +1,21 @@
+diff --git a/config.in b/config.in
+--- a/config.in
++++ b/config.in
+@@ -21,8 +21,8 @@ set $menu dmenu_path | dmenu | xargs swaymsg exec
+ 
+ ### Output configuration
+ #
+-# Default wallpaper (more resolutions are available in @datadir@/backgrounds/sway/)
+-output * bg @datadir@/backgrounds/sway/Sway_Wallpaper_Blue_1920x1080.png fill
++# Default wallpaper
++#output * bg ~/.config/sway/backgrounds/Sway_Wallpaper_Blue_1920x1080.png fill
+ #
+ # Example configuration:
+ #
+@@ -213,5 +213,3 @@ bar {
+         inactive_workspace #32323200 #32323200 #5c5c5c
+     }
+ }
+-
+-include @sysconfdir@/sway/config.d/*
+