gnu: lightdm: Apply patch to fix color depth issue with VNC.

* gnu/packages/patches/lightdm-vnc-color-depth.patch: New patch.
* gnu/local.mk (dist_patch_DATA): Register it.
* gnu/packages/display-managers.scm (lightdm): Apply it.

gnu/local.mk

@@ -1362,6 +1362,7 @@ dist_patch_DATA =						\
   %D%/packages/patches/libziparchive-add-includes.patch		\
   %D%/packages/patches/lightdm-arguments-ordering.patch		\
   %D%/packages/patches/lightdm-vncserver-check.patch		\
+  %D%/packages/patches/lightdm-vnc-color-depth.patch		\
   %D%/packages/patches/localed-xorg-keyboard.patch		\
   %D%/packages/patches/kdiagram-Fix-missing-link-libraries.patch \
   %D%/packages/patches/kiki-level-selection-crash.patch		\

gnu/packages/display-managers.scm

@@ -270,7 +270,8 @@ experience for your users, your family and yourself")
                (base32
                 "1wr60c946p8jz9kb8zi4cd8d4mkcy7infbvlfzwajiglc22nblxn"))
               (patches (search-patches "lightdm-arguments-ordering.patch"
-                                       "lightdm-vncserver-check.patch"))))
+                                       "lightdm-vncserver-check.patch"
+                                       "lightdm-vnc-color-depth.patch"))))
     (build-system gnu-build-system)
     (arguments
      '(#:parallel-tests? #f             ; fails when run in parallel

gnu/packages/patches/lightdm-vnc-color-depth.patch

@@ -0,0 +1,81 @@
+There is no longer support for 8 bit color depth in TigerVNC (see:
+https://github.com/TigerVNC/tigervnc/commit/e86d8720ba1e79b486ca29a5c2b27fa25811e6a2);
+using it causes a fatal error.
+
+Submitted upstream at: https://github.com/canonical/lightdm/pull/265.
+
+diff --git a/data/lightdm.conf b/data/lightdm.conf
+index 0df38429..60e3e8b4 100644
+--- a/data/lightdm.conf
++++ b/data/lightdm.conf
+@@ -160,4 +160,4 @@
+ #listen-address=
+ #width=1024
+ #height=768
+-#depth=8
++#depth=24
+diff --git a/src/x-server-xvnc.c b/src/x-server-xvnc.c
+index 68340d53..27ca4454 100644
+--- a/src/x-server-xvnc.c
++++ b/src/x-server-xvnc.c
+@@ -127,7 +127,7 @@ x_server_xvnc_init (XServerXVNC *server)
+     XServerXVNCPrivate *priv = x_server_xvnc_get_instance_private (server);
+     priv->width = 1024;
+     priv->height = 768;
+-    priv->depth = 8;
++    priv->depth = 24;
+ }
+ 
+ static void
+diff --git a/tests/scripts/vnc-command.conf b/tests/scripts/vnc-command.conf
+index 0f1e25fd..335956d9 100644
+--- a/tests/scripts/vnc-command.conf
++++ b/tests/scripts/vnc-command.conf
+@@ -19,7 +19,7 @@ command=Xvnc -option
+ #?VNC-CLIENT CONNECT
+ 
+ # Xvnc server starts
+-#?XVNC-0 START GEOMETRY=1024x768 DEPTH=8 OPTION=TRUE
++#?XVNC-0 START GEOMETRY=1024x768 DEPTH=24 OPTION=TRUE
+ 
+ # Daemon connects when X server is ready
+ #?*XVNC-0 INDICATE-READY
+diff --git a/tests/scripts/vnc-guest.conf b/tests/scripts/vnc-guest.conf
+index 431bb244..ce2b97db 100644
+--- a/tests/scripts/vnc-guest.conf
++++ b/tests/scripts/vnc-guest.conf
+@@ -21,7 +21,7 @@ user-session=default
+ #?VNC-CLIENT CONNECT
+ 
+ # Xvnc server starts
+-#?XVNC-0 START GEOMETRY=1024x768 DEPTH=8 OPTION=FALSE
++#?XVNC-0 START GEOMETRY=1024x768 DEPTH=24 OPTION=FALSE
+ 
+ # Daemon connects when X server is ready
+ #?*XVNC-0 INDICATE-READY
+diff --git a/tests/scripts/vnc-login.conf b/tests/scripts/vnc-login.conf
+index cdfe17b8..f0d65b7f 100644
+--- a/tests/scripts/vnc-login.conf
++++ b/tests/scripts/vnc-login.conf
+@@ -21,7 +21,7 @@ user-session=default
+ #?VNC-CLIENT CONNECT
+ 
+ # Xvnc server starts
+-#?XVNC-0 START GEOMETRY=1024x768 DEPTH=8 OPTION=FALSE
++#?XVNC-0 START GEOMETRY=1024x768 DEPTH=24 OPTION=FALSE
+ 
+ # Daemon connects when X server is ready
+ #?*XVNC-0 INDICATE-READY
+diff --git a/tests/scripts/vnc-open-file-descriptors.conf b/tests/scripts/vnc-open-file-descriptors.conf
+index 753c84dd..e5d35730 100644
+--- a/tests/scripts/vnc-open-file-descriptors.conf
++++ b/tests/scripts/vnc-open-file-descriptors.conf
+@@ -21,7 +21,7 @@ user-session=default
+ #?VNC-CLIENT CONNECT
+ 
+ # Xvnc server starts
+-#?XVNC-0 START GEOMETRY=1024x768 DEPTH=8 OPTION=FALSE
++#?XVNC-0 START GEOMETRY=1024x768 DEPTH=24 OPTION=FALSE
+ 
+ # Daemon connects when X server is ready
+ #?*XVNC-0 INDICATE-READY