I am trying to update the yosys package to a new upstream version,
following the instructions in debian/README.source in the source code,
ie by running:

  gbp import-orig --component=abc --uscan

When I then try to run gbp buildpackage, I get an error similar to this
(this is for the current 0.64 version, I get a similar error after
importing 0.65):

  gbp:info: Creating /home/pere/src/fpga/yosys_0.64.orig.tar.gz
  gbp:error: Error creating yosys_0.64.orig.tar.gz: Pristine-tar
    couldn't checkout "yosys_0.64.orig.tar.gz": fatal: ambiguous argument
    'e7c1bc2e358704e5670443fb49ee9cd62ae12bfe^{tree}': unknown revision or
    path not in the working tree.

  Use '--' to separate paths from revisions, like this:
  'git <command> [<revision>...] -- [<file>...]'
  fatal: not a valid object name:
    e7c1bc2e358704e5670443fb49ee9cd62ae12bfe^{tree}

  tar: This does not look like a tar archive
  tar: Exiting with failure status due to previous errors
  pristine-tar: command failed: git archive --format=tar
    e7c1bc2e358704e5670443fb49ee9cd62ae12bfe\^\{tree\} | (cd
    '/tmp/pristine-tar.iJeBWZzuII' && tar x)

This break the CI build of yosys on salsa, which fail the same way.

The error look similar to the archived issues reported in
<URL: https://bugs-devel.debian.org/977083 > and
<URL: https://bugs-devel.debian.org/917789 >, but I am unable to figure
out from reading these BTS reports how to work around the problem and
get 'gbp buildpackage' working.

I've also tried 'gbp export-orig --component=abc', which fail like this:

  gbp:error: Couldn't find upstream tree 'upstream/0.64^{tree}' to
    create orig tarball via pristine-tar

Any clues to spare?