boot.loader.grub: add theme option

Co-authored-by: Eelco Dolstra <edolstra@gmail.com>

Co-authored-by: Samuel Dionne-Riel <samuel@dionne-riel.com>

nixos/modules/system/boot/loader/grub/install-grub.pl

@@ -6,9 +6,11 @@ use File::Basename;
 use File::Path;
 use File::stat;
 use File::Copy;
+use File::Copy::Recursive qw(rcopy pathrm);
 use File::Slurp;
 use File::Temp;
 use JSON;
+use File::Find;
 require List::Compare;
 use POSIX;
 use Cwd;
@@ -82,6 +84,7 @@ my $gfxpayloadBios = get("gfxpayloadBios");
 my $bootloaderId = get("bootloaderId");
 my $forceInstall = get("forceInstall");
 my $font = get("font");
+my $theme = get("theme");
 $ENV{'PATH'} = get("path");
 
 die "unsupported GRUB version\n" if $grubVersion != 1 && $grubVersion != 2;
@@ -370,6 +373,28 @@ else {
             fi
         ";
     }
+
+    rmtree("$bootPath/theme") or die "cannot clean up theme folder in $bootPath\n" if -e "$bootPath/theme";
+
+    if ($theme) {
+        # Copy theme
+        rcopy($theme, "$bootPath/theme") or die "cannot copy $theme to $bootPath\n";
+        $conf .= "
+            # Sets theme.
+            set theme=" . ($grubBoot->path eq "/" ? "" : $grubBoot->path) . "/theme/theme.txt
+            export theme
+            # Load theme fonts, if any
+         ";
+
+         find( { wanted => sub {
+             if ($_ =~ /\.pf2$/i) {
+                 $font = File::Spec->abs2rel($File::Find::name, $theme);
+                 $conf .= "
+                     loadfont " . ($grubBoot->path eq "/" ? "" : $grubBoot->path) . "/theme/$font
+                 ";
+             }
+         }, no_chdir => 1 }, $theme );
+     }
 }
 
 $conf .= "$extraConfig\n";