Fix alacritty for ubuntu

alacritty/default.nix

@@ -19,6 +19,8 @@
 
   alacrittyUnwrap = pkgs.writeShellScript "alacritty-unwrap" ''
     unset LD_LIBRARY_PATH
+    unset LIBGL_DRIVERS_PATH
+    unset LIBVA_DRIVERS_PATH
     unset __EGL_VENDOR_LIBRARY_DIRS
     exec "$@"
   '';
@@ -49,10 +51,36 @@
   '';
 
   alacritty = pkgs.writeShellScriptBin "alacritty" ''
-    # TODO this might break things, especially if the machine is not using
-    # nvidia, but more investigation is needed. But it at least lets us get rid
-    # of nixGL.
-    export LD_LIBRARY_PATH=/usr/lib
+    set -e -x
+
+    host_ld_lib_path="$(
+      ldconfig -v 2>/dev/null \
+      | grep -v ^$'\t' \
+      | tr -s ':\n' ':' \
+      | head -c-1 \
+    )"
+
+    bin_ld_lib_path="$(
+      objdump -x ${pkgs.alacritty}/bin/alacritty \
+      | grep "RUNPATH" \
+      | awk '{print $2}' \
+    )"
+
+    host_dri_path="$(
+      echo "$host_ld_lib_path" \
+      | tr -s ':' '\n' \
+      | while read d; do if [ -d "$d/dri" ]; then echo "$d"/dri; fi; done \
+      | tr '\n' ':' \
+      | head -c-1
+    )"
+
+    # overwrite LD_LIBRARY_PATH such that the binary's ld search path is still
+    # searched first, but afterwards the host's ld search path is looked
+    # through. Similarly, the dri paths are set to be the hosts. This allows us
+    # to use the host's graphics drivers for alacritty.
+    export LD_LIBRARY_PATH="$bin_ld_lib_path":"$host_ld_lib_path"
+    export LIBGL_DRIVERS_PATH="$host_dri_path"
+    export LIBVA_DRIVERS_PATH="$host_dri_path"
     export __EGL_VENDOR_LIBRARY_DIRS=/usr/share/glvnd/egl_vendor.d
 
     exec ${pkgs.alacritty}/bin/alacritty \