This directory contains the HarfBuzz source from the upstream repo:
https://github.com/harfbuzz/harfbuzz

Current version: 2.7.4 [commit 7236c7e29cef1c2d76c7a284c5081ff4d3aa1127]

UPDATING:

Our in-tree copy of HarfBuzz does not depend on any generated files from the
upstream build system. Therefore, it should be sufficient to simply overwrite
the in-tree files one the updated ones from upstream to perform updates.

To simplify this, the in-tree copy can be updated by running
  sh update.sh
from within the gfx/harfbuzz directory.

If the collection of source files changes, manual updates to moz.build may be
needed as we don't use the upstream makefiles.