fix(snap): put gnome-platform first so SVG icons load (#822)

core24 desktop-launch rebuilds gdk-pixbuf-loaders.cache from the first
LD_LIBRARY_PATH directory that ends in the arch triplet. Stage-packages
drop a gdk-pixbuf tree without libpixbufloader_svg.so at
$SNAP/usr/lib/<triplet>, ahead of gnome-platform, so About-page SVGs
fail with "Image type svg is not supported".

Fixes the same core24 GTK3 gap documented at:
https://forum.snapcraft.io/t/missing-svg-support-for-gtk3-in-core24/48851

snap/snapcraft.yaml

@@ -68,6 +68,15 @@ apps:
       PATH: $SNAP/usr/bin:$SNAP/bin:$PATH
       # PortAudio opens ALSA first. Point at snap-local config that routes to Pulse.
       ALSA_CONFIG_PATH: $SNAP/etc/asound.conf
+      # core24 gnome-46-2404: desktop-launch rebuilds gdk-pixbuf-loaders.cache
+      # by running query-loaders, which picks the SVG loader from the first
+      # LD_LIBRARY_PATH entry ending in /$CRAFT_ARCH_TRIPLET. Stage-packages
+      # (via libavcodec and friends) put a gdk-pixbuf tree without
+      # libpixbufloader_svg.so at $SNAP/usr/lib/$CRAFT_ARCH_TRIPLET, ahead of
+      # gnome-platform. About page and other GdkPixbuf SVG loads then fail
+      # with "Image type svg is not supported".
+      # https://forum.snapcraft.io/t/missing-svg-support-for-gtk3-in-core24/48851
+      LD_LIBRARY_PATH: $SNAP/gnome-platform/usr/lib/$CRAFT_ARCH_TRIPLET:$LD_LIBRARY_PATH
 
 # Make ALSA data/plugins visible at the paths libasound expects.
 layout:

tests/test_snap_packaging.py

@@ -31,6 +31,22 @@ def test_snapcraft_recipe_and_gui_assets() -> None:
     assert SNAP_PNG.stat().st_size > 0
 
 
+def test_snap_puts_gnome_platform_first_on_ld_library_path() -> None:
+    """core24 gdk-pixbuf finds libpixbufloader_svg.so only if gnome-platform wins.
+
+    Stage-packages pull a second gdk-pixbuf (no SVG loader) into
+    $SNAP/usr/lib/<triplet>. desktop-launch's query-loaders walks the first
+    LD_LIBRARY_PATH entry that ends in that triplet, so gnome-platform must
+    come first or About-page SVGs fail with "Image type svg is not supported".
+    """
+    doc = yaml.safe_load(SNAPCRAFT_YAML.read_text(encoding="utf-8"))
+    env = (doc.get("apps") or {}).get("vocalinux", {}).get("environment") or {}
+    ld_path = env.get("LD_LIBRARY_PATH")
+    assert isinstance(ld_path, str)
+    assert ld_path.startswith("$SNAP/gnome-platform/usr/lib/$CRAFT_ARCH_TRIPLET:")
+    assert ld_path.endswith(":$LD_LIBRARY_PATH")
+
+
 def test_snap_strips_pygobject_and_uses_gnome_gi() -> None:
     """Pip must not build PyGObject; GI comes from the gnome extension."""
     text = SNAPCRAFT_YAML.read_text(encoding="utf-8")