librsvg: fix cross

gobject-introspection doesn't cross build at the moment, and doesn't
work well with cross even when it does, so this is far more likely to
keep working if we just disable it when cross compiling.

pkgs/development/libraries/librsvg/default.nix

@@ -12,10 +12,12 @@
 , ApplicationServices
 , Foundation
 , libobjc
+, rustPlatform
 , rustc
 , cargo
 , gnome
 , vala
+, withIntrospection ? stdenv.hostPlatform == stdenv.buildPlatform
 , gobject-introspection
 , nixosTests
 }:
@@ -31,6 +33,8 @@ stdenv.mkDerivation rec {
     sha256 = "//thsIzVKCqq4UegKzBRZqdCb60iqLlCdwjw8vxCbrw=";
   };
 
+  cargoVendorDir = "vendor";
+
   strictDeps = true;
 
   depsBuildBuild = [ pkg-config ];
@@ -41,6 +45,8 @@ stdenv.mkDerivation rec {
     rustc
     cargo
     vala
+    rustPlatform.cargoSetupHook
+  ] ++ lib.optionals withIntrospection [
     gobject-introspection
   ] ++ lib.optionals stdenv.isDarwin [
     ApplicationServices
@@ -52,6 +58,7 @@ stdenv.mkDerivation rec {
     bzip2
     pango
     libintl
+  ] ++ lib.optionals withIntrospection [
     gobject-introspection
   ] ++ lib.optionals stdenv.isDarwin [
     libobjc
@@ -64,12 +71,12 @@ stdenv.mkDerivation rec {
   ];
 
   configureFlags = [
-    "--enable-introspection"
-  ] ++ lib.optionals (!stdenv.isDarwin) [
+    (lib.enableFeature withIntrospection "introspection")
+
     # Vapi does not build on MacOS.
     # https://github.com/NixOS/nixpkgs/pull/117081#issuecomment-827782004
-    "--enable-vala"
-  ] ++ [
+    (lib.enableFeature (withIntrospection && !stdenv.isDarwin) "vala")
+
     "--enable-installed-tests"
     "--enable-always-build-tests"
   ] ++ lib.optional stdenv.isDarwin "--disable-Bsymbolic";
@@ -101,11 +108,11 @@ stdenv.mkDerivation rec {
         -i gdk-pixbuf-loader/librsvg.thumbnailer.in
   '';
 
-  # Merge gdkpixbuf and librsvg loaders
-  postInstall = ''
-    mv $GDK_PIXBUF/loaders.cache $GDK_PIXBUF/loaders.cache.tmp
-    cat ${gdk-pixbuf.out}/lib/gdk-pixbuf-2.0/2.10.0/loaders.cache $GDK_PIXBUF/loaders.cache.tmp > $GDK_PIXBUF/loaders.cache
-    rm $GDK_PIXBUF/loaders.cache.tmp
+  # Not generated when cross compiling.
+  postInstall = lib.optionalString (stdenv.hostPlatform == stdenv.buildPlatform) ''
+    # Merge gdkpixbuf and librsvg loaders
+    cat ${gdk-pixbuf.out}/lib/gdk-pixbuf-2.0/2.10.0/loaders.cache $GDK_PIXBUF/loaders.cache > $GDK_PIXBUF/loaders.cache.tmp
+    mv $GDK_PIXBUF/loaders.cache.tmp $GDK_PIXBUF/loaders.cache
   '';
 
   passthru = {