[Bug 2142762] Re: [SRU] Demote libde265 to Suggests

[Jean-Baptiste Lallement]

** Also affects: libheif (Ubuntu Noble)
   Importance: Undecided
       Status: New

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Title:
  [SRU] Demote libde265 to Suggests

Status in libheif package in Ubuntu:
  New
Status in libheif source package in Noble:
  New

Bug description:
  [ Impact ]

   * We shouldn't be including an H.265 decoder in the Ubuntu squashfs.
     In Noble, there is a dependency chain in the desktop seed that pulls
     this component in:

       cups-core-drivers -> cups-daemon -> colord -> libsane1
         -> libgphoto2-6t64 -> libgd3 -> libheif -> libheif-plugin-libde265

   * By demoting libheif1's Depends on libheif-plugin-libde265 to
     Suggests, germinate will no longer pull it into the squashfs seed.

   * The practical consequence of this change is that HEIC images
     (the default photo format on iOS/macOS devices since iOS 11) will
     not decode on a live session or freshly installed system unless the
     user explicitly installs libheif-plugin-libde265. AVIF images are
     unaffected as AV1 decoding (dav1d/aomdec) remains a hard dependency.

   * This change was already carried in ubuntu4 for the x265 encoder
     (LP: #2061089). This upload extends the same principle to the
     libde265 decoder.

  [ Test Plan ]

   Verify AVIF decoding is unaffected (dav1d/aomdec still a hard dep):

        # On a system WITHOUT libheif-plugin-libde265 installed:
        $ apt-get install --no-install-recommends libheif-examples
        $ heif-convert test.avif test.png
        # Should succeed

   Verify HEIC decoding fails gracefully without the plugin:

        # On a system WITHOUT libheif-plugin-libde265 installed:
        $ heif-convert iphone-photo.heic out.png
        # Should fail with a reasonable error not a crash or silent
          corruption.

   Verify HEIC decoding still works when the plugin is installed:

        $ apt-get install libheif-plugin-libde265
        $ heif-convert iphone-photo.heic out.png
        # Should succeed and produce a correct PNG

   Verify no regression for applications using the gdk-pixbuf loader:

        # With libheif-plugin-libde265 installed:
        $ gdk-pixbuf-query-loaders | grep heif
        $ eog iphone-photo.heic   # or any GTK image viewer
        # Should display correctly

   Once new ISOs are available, ensure the problematic packages have not
  been pulled into the squashfs,

        sudo mount -o loop,ro ubuntu-release.iso mnt
        sudo mount -o loop,ro mnt/casper/minimal.standard.squashfs squashfs
        # Ensure libheif-plugin-x265 and libheif-plugin-libde265 are not seeded
        dpkg-query --admindir=./squashfs/var/lib/dpkg -W 'libheif*'

  [ Where problems could occur ]

   * Applications that rely on libheif for HEIC thumbnailing or display
     (e.g. Nautilus via heif-thumbnailer or heif-gdk-pixbuf, GNOME
     Photos, Shotwell) will silently fail to open or thumbnail HEIC
     images on fresh installs. Users coming from iPhones are likely to
     notice this. The failure mode should be graceful (error returned to
     caller), not a crash, but this is worth confirming.

   * If any package in main or the desktop seed has an undocumented
     indirect requirement on HEIC decoding being available, that
     functionality will silently regress. The dependency chain from
     libgphoto2 makes this plausible. software that transfers photos
     from iOS cameras via gphoto2 and then previews them could be
     affected.

  [ Other Info ]
   * A similar change was already carried in ubuntu4 for the x265
     encoder (LP: #2061089). This upload extends the same principle to
     the libde265 decoder.

   * Questing also seeds the decoder by default. A similar change has
     already been released for Resolute
     (https://launchpad.net/ubuntu/+source/libheif/1.21.2-3)

   * The libde265 plugin itself is still built and still shipped in the
     archive in the libheif-plugin-libde265 binary package; only its
     installation becomes optional.

   * Users who need HEIC support can restore it with:
       sudo apt-get install libheif-plugin-libde265

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