Error while building: Argument list too long

I have a very extensive GIMP snapcraft.yaml which I’ve been working on for some time to bump the version to 2.10.0 (currently RC1). Unfortunately I’m hitting an error at the final hurdle where the gimp part is refusing to build with the following output from snapcraft:

Preparing to build gimp 
Building gimp 
/tmp/tmpd769856j: 2683: exec: /tmp/tmp3u8g0qnv: Argument list too long
Traceback (most recent call last):
  File "/snap/snapcraft/1345/bin/snapcraft", line 11, in <module>
    load_entry_point('snapcraft==2.40.1', 'console_scripts', 'snapcraft')()
  File "/snap/snapcraft/1345/usr/lib/python3.6/site-packages/pkg_resources/__init__.py", line 565, in load_entry_point
    return get_distribution(dist).load_entry_point(group, name)
  File "/snap/snapcraft/1345/usr/lib/python3.6/site-packages/pkg_resources/__init__.py", line 2631, in load_entry_point
    return ep.load()
  File "/snap/snapcraft/1345/usr/lib/python3.6/site-packages/pkg_resources/__init__.py", line 2291, in load
    return self.resolve()
  File "/snap/snapcraft/1345/usr/lib/python3.6/site-packages/pkg_resources/__init__.py", line 2297, in resolve
    module = __import__(self.module_name, fromlist=['__name__'], level=0)
  File "/snap/snapcraft/1345/lib/python3.6/site-packages/snapcraft/cli/__main__.py", line 43, in <module>
    run(prog_name='snapcraft')
  File "/snap/snapcraft/1345/lib/python3.6/site-packages/click/core.py", line 722, in __call__
    return self.main(*args, **kwargs)
  File "/snap/snapcraft/1345/lib/python3.6/site-packages/click/core.py", line 697, in main
    rv = self.invoke(ctx)
  File "/snap/snapcraft/1345/lib/python3.6/site-packages/click/core.py", line 1066, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/snap/snapcraft/1345/lib/python3.6/site-packages/click/core.py", line 895, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/snap/snapcraft/1345/lib/python3.6/site-packages/click/core.py", line 535, in invoke
    return callback(*args, **kwargs)
  File "/snap/snapcraft/1345/lib/python3.6/site-packages/snapcraft/cli/lifecycle.py", line 139, in snap
    project_options, directory=directory, output=output)
  File "/snap/snapcraft/1345/lib/python3.6/site-packages/snapcraft/internal/lifecycle/_packer.py", line 46, in snap
    execute('prime', project_options)
  File "/snap/snapcraft/1345/lib/python3.6/site-packages/snapcraft/internal/lifecycle/_runner.py", line 80, in execute
    _Executor(config, project_options).run(step, part_names)
  File "/snap/snapcraft/1345/lib/python3.6/site-packages/snapcraft/internal/lifecycle/_runner.py", line 191, in run
    self._run_step(step, part, part_names)
  File "/snap/snapcraft/1345/lib/python3.6/site-packages/snapcraft/internal/lifecycle/_runner.py", line 236, in _run_step
    getattr(part, step)()
  File "/snap/snapcraft/1345/lib/python3.6/site-packages/snapcraft/internal/pluginhandler/__init__.py", line 366, in build
    script_runner.run(scriptlet=build_scriptlet)
  File "/snap/snapcraft/1345/lib/python3.6/site-packages/snapcraft/internal/pluginhandler/_scriptlets.py", line 43, in run
    run([scriptlet_path], cwd=self._builddir)
  File "/snap/snapcraft/1345/lib/python3.6/site-packages/snapcraft/internal/common.py", line 64, in run
    subprocess.check_call(['/bin/sh', f.name] + cmd, **kwargs)
  File "/snap/snapcraft/1345/usr/lib/python3.6/subprocess.py", line 291, in check_call
    raise CalledProcessError(retcode, cmd)
subprocess.CalledProcessError: Command '['/bin/sh', '/tmp/tmpd769856j', '/tmp/tmp3u8g0qnv']' returned non-zero exit status 2.
Stopping local:snapcraft-gimp

The latest version of my source is at https://github.com/diddledan/gimp-snap/tree/2.10.0-RC1-test. Please could someone take a look to discern what is causing the error?

I’ve tried hunting for those temporary files and running with --debug. The files are deleted upon the error occuring so I can’t investigate their content, and the --debug output yields no extra information, outputting a nearly identical wall of text. I have also tried snapcraft from edge (revision 1382), which has a similar error but with different specifics where snapcraft is now executing the command that has too many arguments directly rather than writing it to a file and running that:

Preparing to build gimp 
Building gimp 
Traceback (most recent call last):
  File "/snap/snapcraft/1382/bin/snapcraft", line 11, in <module>
    load_entry_point('snapcraft==2.40.1', 'console_scripts', 'snapcraft')()
  File "/snap/snapcraft/1382/lib/python3.6/site-packages/click/core.py", line 722, in __call__
    return self.main(*args, **kwargs)
  File "/snap/snapcraft/1382/lib/python3.6/site-packages/click/core.py", line 697, in main
    rv = self.invoke(ctx)
  File "/snap/snapcraft/1382/lib/python3.6/site-packages/click/core.py", line 1066, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/snap/snapcraft/1382/lib/python3.6/site-packages/click/core.py", line 895, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/snap/snapcraft/1382/lib/python3.6/site-packages/click/core.py", line 535, in invoke
    return callback(*args, **kwargs)
  File "/snap/snapcraft/1382/lib/python3.6/site-packages/snapcraft/cli/lifecycle.py", line 139, in snap
    project_options, directory=directory, output=output)
  File "/snap/snapcraft/1382/lib/python3.6/site-packages/snapcraft/internal/lifecycle/_packer.py", line 46, in snap
    execute('prime', project_options)
  File "/snap/snapcraft/1382/lib/python3.6/site-packages/snapcraft/internal/lifecycle/_runner.py", line 80, in execute
    _Executor(config, project_options).run(step, part_names)
  File "/snap/snapcraft/1382/lib/python3.6/site-packages/snapcraft/internal/lifecycle/_runner.py", line 191, in run
    self._run_step(step, part, part_names)
  File "/snap/snapcraft/1382/lib/python3.6/site-packages/snapcraft/internal/lifecycle/_runner.py", line 236, in _run_step
    getattr(part, step)()
  File "/snap/snapcraft/1382/lib/python3.6/site-packages/snapcraft/internal/pluginhandler/__init__.py", line 386, in build
    self._runner.build()
  File "/snap/snapcraft/1382/lib/python3.6/site-packages/snapcraft/internal/pluginhandler/_runner.py", line 93, in build
    'build', self._build_scriptlet, self._builddir)
  File "/snap/snapcraft/1382/lib/python3.6/site-packages/snapcraft/internal/pluginhandler/_runner.py", line 153, in _run_scriptlet
    ['/bin/sh', '-e', '-c', script], cwd=workdir)
  File "/snap/snapcraft/1382/usr/lib/python3.6/subprocess.py", line 707, in __init__
    restore_signals, start_new_session)
  File "/snap/snapcraft/1382/usr/lib/python3.6/subprocess.py", line 1326, in _execute_child
    raise child_exception_type(errno_num, err_msg)
OSError: [Errno 7] Argument list too long
Stopping local:snapcraft-gimp