From e021ee13f909e6eb7c019b5cd1acf9eac0cd0f67 Mon Sep 17 00:00:00 2001
From: Colin <colin@uninsane.org>
Date: Wed, 19 Mar 2025 06:59:49 +0000
Subject: [PATCH 1/2] makeFontsCache: fix cross compilation

lifting the `callPackage` to scope level ensures splicing works as expected.
we still need to emulate fc-cache to produce usable cache entries though.
---
 .../libraries/fontconfig/make-fonts-cache.nix  | 18 ++++++++++++++----
 pkgs/top-level/all-packages.nix                |  5 +----
 2 files changed, 15 insertions(+), 8 deletions(-)

diff --git a/pkgs/development/libraries/fontconfig/make-fonts-cache.nix b/pkgs/development/libraries/fontconfig/make-fonts-cache.nix
index a1ac7d1b9859..9054cf6756ba 100644
--- a/pkgs/development/libraries/fontconfig/make-fonts-cache.nix
+++ b/pkgs/development/libraries/fontconfig/make-fonts-cache.nix
@@ -1,13 +1,20 @@
 {
-  runCommand,
-  lib,
+  buildPackages,
   fontconfig,
+  lib,
+  runCommand,
+  stdenv,
+}:
+let
+  fontconfig' = fontconfig;
+in
+{
+  fontconfig ? fontconfig',
   fontDirectories,
 }:
 
 runCommand "fc-cache"
   {
-    nativeBuildInputs = [ fontconfig.bin ];
     preferLocalBuild = true;
     allowSubstitutes = false;
     passAsFile = [ "fontDirs" ];
@@ -29,8 +36,11 @@ runCommand "fc-cache"
     cat "$fontDirsPath" >> fonts.conf
     echo "</fontconfig>" >> fonts.conf
 
+    # N.B.: fc-cache keys its cache entries by architecture.
+    # We must invoke the host `fc-cache` (not the build fontconfig) if we want
+    # the cache to be usable by the host.
     mkdir -p $out
-    fc-cache -sv
+    ${stdenv.hostPlatform.emulator buildPackages} ${lib.getExe' fontconfig "fc-cache"} -sv
 
     # This is not a cache dir in the normal sense -- it won't be automatically
     # recreated.
diff --git a/pkgs/top-level/all-packages.nix b/pkgs/top-level/all-packages.nix
index db392a2b84ea..9d8ccbae637d 100644
--- a/pkgs/top-level/all-packages.nix
+++ b/pkgs/top-level/all-packages.nix
@@ -8764,10 +8764,7 @@ with pkgs;
 
   makeFontsConf = callPackage ../development/libraries/fontconfig/make-fonts-conf.nix { };
 
-  makeFontsCache = let fontconfig_ = fontconfig; in {fontconfig ? fontconfig_, fontDirectories}:
-    callPackage ../development/libraries/fontconfig/make-fonts-cache.nix {
-      inherit fontconfig fontDirectories;
-    };
+  makeFontsCache = callPackage ../development/libraries/fontconfig/make-fonts-cache.nix { };
 
   freenect = callPackage ../development/libraries/freenect {
     inherit (darwin.apple_sdk.frameworks) Cocoa GLUT;

From 9435a2b422f090b25f4aa5aee53be1341626672d Mon Sep 17 00:00:00 2001
From: Colin <colin@uninsane.org>
Date: Wed, 19 Mar 2025 07:53:24 +0000
Subject: [PATCH 2/2] nixos/fonts: ship fontconfig caches even for
 cross-compiled hosts

---
 nixos/modules/config/fonts/fontconfig.nix | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/nixos/modules/config/fonts/fontconfig.nix b/nixos/modules/config/fonts/fontconfig.nix
index 984daec20431..89c537ff3868 100644
--- a/nixos/modules/config/fonts/fontconfig.nix
+++ b/nixos/modules/config/fonts/fontconfig.nix
@@ -58,7 +58,7 @@ let
       <fontconfig>
         <!-- Font directories -->
         ${lib.concatStringsSep "\n" (map (font: "<dir>${font}</dir>") config.fonts.packages)}
-        ${lib.optionalString (pkgs.stdenv.hostPlatform == pkgs.stdenv.buildPlatform) ''
+        ${lib.optionalString (pkgs.stdenv.hostPlatform.emulatorAvailable pkgs.buildPackages) ''
           <!-- Pre-generated font caches -->
           <cachedir>${cache}</cachedir>
           ${lib.optionalString (pkgs.stdenv.hostPlatform.isx86_64 && cfg.cache32Bit) ''