[Bug 1803534] Re: Backport uuid based cache file naming scheme

[Łukasz Zemczak]

Hello James, or anyone else affected,

Accepted fontconfig into bionic-proposed. The package will build now and
be available at
https://launchpad.net/ubuntu/+source/fontconfig/2.12.6-0ubuntu2.3 in a
few hours, and then in the -proposed repository.

Please help us by testing this new package.  See
https://wiki.ubuntu.com/Testing/EnableProposed for documentation on how
to enable and use -proposed.  Your feedback will aid us getting this
update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug,
mentioning the version of the package you tested and change the tag from
verification-needed-bionic to verification-done-bionic. If it does not
fix the bug for you, please add a comment stating that, and change the
tag to verification-failed-bionic. In either case, without details of
your testing we will not be able to proceed.

Further information regarding the verification process can be found at
https://wiki.ubuntu.com/QATeam/PerformingSRUVerification .  Thank you in
advance for helping!

N.B. The updated package will be released to -updates after the bug(s)
fixed by this package have been verified and the package has been in
-proposed for a minimum of 7 days.

** Tags removed: verification-failed verification-failed-bionic
** Tags added: verification-needed verification-needed-bionic

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https://bugs.launchpad.net/bugs/1803534

Title:
  Backport uuid based cache file naming scheme

Status in fontconfig package in Ubuntu:
  New
Status in fontconfig source package in Bionic:
  Fix Committed

Bug description:
  Fontconfig 2.13.0 changed the cache file naming scheme to be based on
  the contents of ".uuid" file in the directory rather than a hash of
  the directory name.  On a pure debs system this doesn't really matter
  since everything is using the same libfontconfig.so.

  When snaps are involved, it can lead to some apps not seeing the cache
  files produced by a different fontconfig version.  In particular,
  while libfontconfig 2.13 can reuse 2.12's cache files for read only
  directories, the reverse is not true.  This will be a problem for apps
  built on top of the "core18" base snap when run on later Ubuntu
  releases (cosmic, disco, etc).

  By providing a backport of the UUID cache file feature to bionic for
  use by snap applications, we'd avoid this.  Having it in bionic-
  updates would be ideal so that snapcraft picks it up automatically.

  [Impact]

   * This update changes how fontconfig cache files are named, instead
  of using md5($dir), it instead uses the contents of a $dir/.uuid file.
  No changes are made to the format of the cache file contents.

   * This change is primarily intended for use by snap applications
  built with core18: as the updated libfontconfig will fall back to the
  md5 cache file names for read-only directories without a .uuid file,
  they will be able to reuse cache files from any host system running
  fontconfig >= 2.11.95

  [Test Case]

   * After installing the update, cache files should be generated in
  /var/cache/fontconfig/ with names like "07b67f7a-16ea-4440-9b6c-
  21fc9153568c-le64.cache-7" (note the extra dashes not present in the
  MD5 based cache file names).

  [Regression Potential]

   * Applications using a non-default libfontconfig could end up not
  finding the new cache files and regenerating them in
  ~/.cache/fontconfig.

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