lightdm: disable writing dmrc files to home

Can cause issues where lightdm prefers the last saved session in .dmrc
even if it doesn't exist anymore, preventing people from logging in to
a session.

pkgs/applications/display-managers/lightdm/default.nix

@@ -1,6 +1,6 @@
 { stdenv, fetchFromGitHub, pam, pkgconfig, autoconf, automake, libtool, libxcb
 , glib, libXdmcp, itstool, intltool, libxklavier, libgcrypt, audit, busybox
-, polkit, accountsservice, gtk-doc, gnome3, gobject-introspection, vala
+, polkit, accountsservice, gtk-doc, gnome3, gobject-introspection, vala, fetchpatch
 , withQt4 ? false, qt4
 , withQt5 ? false, qtbase
 }:
@@ -49,7 +49,14 @@ stdenv.mkDerivation rec {
   ] ++ optional withQt4 qt4
     ++ optional withQt5 qtbase;
 
-  patches = [ ./run-dir.patch ];
+  patches = [
+    ./run-dir.patch
+    # Adds option to disable writing dmrc files
+    (fetchpatch {
+      url = "https://src.fedoraproject.org/rpms/lightdm/raw/4cf0d2bed8d1c68970b0322ccd5dbbbb7a0b12bc/f/lightdm-1.25.1-disable_dmrc.patch";
+      sha256 = "06f7iabagrsiws2l75sx2jyljknr9js7ydn151p3qfi104d1541n";
+    })
+  ];
 
   preConfigure = "NOCONFIGURE=1 ./autogen.sh";
 
@@ -58,11 +65,12 @@ stdenv.mkDerivation rec {
     "--sysconfdir=/etc"
     "--disable-tests"
     "--disable-static"
+    "--disable-dmrc"
   ] ++ optional withQt4 "--enable-liblightdm-qt"
     ++ optional withQt5 "--enable-liblightdm-qt5";
 
   installFlags = [
-    "sysconfdir=\${out}/etc"
+    "sysconfdir=${placeholder ''out''}/etc"
     "localstatedir=\${TMPDIR}"
   ];
 
@@ -76,7 +84,7 @@ stdenv.mkDerivation rec {
 
   meta = {
     homepage = https://github.com/CanonicalLtd/lightdm;
-    description = "A cross-desktop display manager.";
+    description = "A cross-desktop display manager";
     platforms = platforms.linux;
     license = licenses.gpl3;
     maintainers = with maintainers; [ ocharles worldofpeace ];