get_config_settings errors on blank lines returned by git config --list

[GavinMasterson]

Issue Description

When running git filter-repo, I get an error from the get_config_settings function.

Cause

The output of line 1556's subproc.check_output(git config --list.split(), cwd=repo_working_dir) is equivalent to:

output = b'''[email protected]
user.name=My Name

includeif.gitdir/i:~/work/.path=~/work/.gitconfig-work
[email protected]
user.name=My Name

credential.helper=cache
init.defaultbranch=main
includeif.hasconfig:remote.*.url:[email protected]:work/**.path=~/work/.gitconfig-work
credential.helper=cache
init.defaultbranch=main
core.repositoryformatversion=0
core.filemode=true
core.bare=false
core.logallrefupdates=true'''

The conversion of the output object to the returned dict fails with the message:

Traceback (most recent call last):
File "/usr/bin/git-filter-repo", line 4151, in
main()
File "/usr/bin/git-filter-repo", line 4148, in main
filter.run()
File "/usr/bin/git-filter-repo", line 4068, in run
self._run_sanity_checks()
File "/usr/bin/git-filter-repo", line 2931, in _run_sanity_checks
self._config_settings = GitUtils.get_config_settings(target_working_dir)
File "/usr/bin/git-filter-repo", line 1563, in get_config_settings
return dict(line.split(b'=', maxsplit=1)
ValueError: dictionary update sequence element #2 has length 1; 2 is required

Potential Solution

I fixed the issue by modifying the function as follows:

@staticmethod
  def get_config_settings(repo_working_dir):
    output = ''
    try:
      output = subproc.check_output('git config --list'.split(),
                                    cwd=repo_working_dir)
    except subprocess.CalledProcessError as e: # pragma: no cover
      raise SystemExit('fatal: {}'.format(e))
    
    # Changes start here -->
    decoded_output = output.decode('utf-8')
    lines = [line for line in decoded_output.split('\n') if line.strip()]
    # FIXME: Ignores multi-valued keys, just let them overwrite for now
    return dict(line.split('=', maxsplit=1) for line in lines if '=' in line)

There are probably better ways to solve the issue that do not involve an opinionated decoding step, as I cannot tell what side-effects the decoding step may have in repos that are not UTF-8 encoded.

Summary

When running my desired git filter-repo ... command with this function, the command works as intended, and raises no error.