libavif: build gdk-pixbuf loader and thumbnailer

https://github.com/AOMediaCodec/libavif/pull/182
https://github.com/AOMediaCodec/libavif/pull/977

Mostly mirrors webp-pixbuf-loader.

Also use prefixed names for `loaders.cache` so that users can install
multiple loaders in a profile without collisions, and move
`bin/webp-thumbnailer` to `libexec/gdk-pixbuf-thumbnailer-webp` (and
similarly for avif).

pkgs/development/libraries/gdk-pixbuf/default.nix

···
       pkg-config = testers.testMetaPkgConfig finalAttrs.finalPackage;
     };
 
-    # gdk_pixbuf_moduledir variable from gdk-pixbuf-2.0.pc
-    moduleDir = "lib/gdk-pixbuf-2.0/2.10.0/loaders";
+    # gdk_pixbuf_binarydir and gdk_pixbuf_moduledir variables from gdk-pixbuf-2.0.pc
+    binaryDir = "lib/gdk-pixbuf-2.0/2.10.0";
+    moduleDir = "${finalAttrs.passthru.binaryDir}/loaders";
   };
 
   meta = with lib; {

pkgs/development/libraries/libavif/default.nix

···
 , libjpeg
 , dav1d
 , libyuv
+, gdk-pixbuf
+, makeWrapper
 }:
+
+let
+  gdkPixbufModuleDir = "${placeholder "out"}/${gdk-pixbuf.moduleDir}";
+  gdkPixbufModuleFile = "${placeholder "out"}/${gdk-pixbuf.binaryDir}/avif-loaders.cache";
+in
 
 stdenv.mkDerivation rec {
   pname = "libavif";
···
     "-DAVIF_CODEC_DAV1D=ON" # best decoder (fast)
     "-DAVIF_CODEC_AOM_DECODE=OFF"
     "-DAVIF_BUILD_APPS=ON"
+    "-DAVIF_BUILD_GDK_PIXBUF=ON"
   ];
 
   nativeBuildInputs = [
     cmake
     pkg-config
+    gdk-pixbuf
+    makeWrapper
   ];
 
   buildInputs = [
+    gdk-pixbuf
     libaom
     zlib
     libpng
···
     dav1d
     libyuv
   ];
+
+  postPatch = ''
+    substituteInPlace contrib/gdk-pixbuf/avif.thumbnailer.in \
+      --replace '@CMAKE_INSTALL_FULL_BINDIR@/gdk-pixbuf-thumbnailer' "$out/libexec/gdk-pixbuf-thumbnailer-avif"
+  '';
+
+  env.PKG_CONFIG_GDK_PIXBUF_2_0_GDK_PIXBUF_MODULEDIR = gdkPixbufModuleDir;
+
+  postInstall = ''
+    GDK_PIXBUF_MODULEDIR=${gdkPixbufModuleDir} \
+    GDK_PIXBUF_MODULE_FILE=${gdkPixbufModuleFile} \
+    gdk-pixbuf-query-loaders --update-cache
+
+    mkdir -p "$out/bin"
+    makeWrapper ${gdk-pixbuf}/bin/gdk-pixbuf-thumbnailer "$out/libexec/gdk-pixbuf-thumbnailer-avif" \
+      --set GDK_PIXBUF_MODULE_FILE ${gdkPixbufModuleFile}
+  '';
 
   meta = with lib; {
     description  = "C implementation of the AV1 Image File Format";

pkgs/development/libraries/webp-pixbuf-loader/default.nix

···
 
 let
   inherit (gdk-pixbuf) moduleDir;
-
-  # turning lib/gdk-pixbuf-#.#/#.#.#/loaders into lib/gdk-pixbuf-#.#/#.#.#/loaders.cache
-  # removeSuffix is just in case moduleDir gets a trailing slash
-  loadersPath = (lib.strings.removeSuffix "/" gdk-pixbuf.moduleDir) + ".cache";
+  loadersPath = "${gdk-pixbuf.binaryDir}/webp-loaders.cache";
 in
 stdenv.mkDerivation rec {
   pname = "webp-pixbuf-loader";
···
   postPatch = ''
     # It looks for gdk-pixbuf-thumbnailer in this package's bin rather than the gdk-pixbuf bin. We need to patch that.
     substituteInPlace webp-pixbuf.thumbnailer.in \
-      --replace "@bindir@/gdk-pixbuf-thumbnailer" "$out/bin/webp-thumbnailer"
+      --replace "@bindir@/gdk-pixbuf-thumbnailer" "$out/libexec/gdk-pixbuf-thumbnailer-webp"
   '';
 
   postInstall = ''
···
     # It assumes gdk-pixbuf-thumbnailer can find the webp loader in the loaders.cache referenced by environment variable, breaking containment.
     # So we replace it with a wrapped executable.
     mkdir -p "$out/bin"
-    makeWrapper "${gdk-pixbuf}/bin/gdk-pixbuf-thumbnailer" "$out/bin/webp-thumbnailer" \
+    makeWrapper "${gdk-pixbuf}/bin/gdk-pixbuf-thumbnailer" "$out/libexec/gdk-pixbuf-thumbnailer-webp" \
       --set GDK_PIXBUF_MODULE_FILE "$out/${loadersPath}"
   '';