return branch heads in repo log method

[rlizzo]

Motivation and Context

Why is this change required? What problem does it solve?:

Add more useful branch info to log output

If it fixes an open issue, please link to the issue here:

• closes [BUG REPORT] repo log doesn't return branch information when return_contents is True #123

Description

Describe your changes in detail:

branch_heads key now returned along side the rest of the info.

Types of changes

What types of changes does your code introduce? Put an x in all the boxes that apply:

• Documentation update
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Is this PR ready for review, or a work in progress?

• Ready for review
• Work in progress

How Has This Been Tested?

Put an x in the boxes that apply:

• Current tests cover modifications made
• New tests have been added to the test suite
• Modifications were made to existing tests to support these changes
• Tests may be needed, but they are not included when the PR was proposed
• I don't know. Help!

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have signed (or will sign when prompted) the tensorwork CLA.
• I have added tests to cover my changes.
• All new and existing tests passed.

[codecov]

Codecov Report

Merging #125 into master will increase coverage by 0.06%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##           master    #125      +/-   ##
=========================================
+ Coverage   92.03%   92.1%   +0.06%     
=========================================
  Files          60      60              
  Lines       10005   10087      +82     
  Branches      997     999       +2     
=========================================
+ Hits         9208    9290      +82     
  Misses        582     582              
  Partials      215     215

Impacted Files	Coverage Δ
tests/test_visualizations.py	100% <100%> (ø)	⬆️
src/hangar/repository.py	96.64% <100%> (+0.12%)	⬆️
src/hangar/utils.py	82.99% <100%> (ø)	⬆️

[rlizzo]

@hhsecond, does this work for your purposes?

I chose to go with a mapping between

'commit_digest' -> List['BranchName1', 'BranchName2']

rather than a reverse mapping of branch names to (possibly duplicate) commits in order to keep in line with the other layout of results (ancestors -> List[ commid_digest(s) ] / commit_digest -> Dict[ commit_message, time, etc. ])

ie.

'ancestors': {
    '0ff3f2ec156ab8e1026b5271630ccae4556cc260': [''],
    '3c9530ac0da1106c0acbe1201900c51548bbcdd9'': ['fed88489ab6e59913aee935169b15fe68755d82c'],
    'fed88489ab6e59913aee935169b15fe68755d82c': ['0ff3f2ec156ab8e1026b5271630ccae4556cc260']
}

'specs': {'0ff3f2ec156ab8e1026b5271630ccae4556cc260': {
                'commit_message': 'first commit adding training images and labels',
                'commit_time': 1562203787.257128, 'commit_user': 'Foo User', 'commit_email': 'foo@bar.com'},
          '3c9530ac0da1106c0acbe1201900c51548bbcdd9': {
                'commit_message': 'added testing labels only',
                'commit_time': 1562203787.388417, 'commit_user': 'Foo User', 'commit_email': 'foo@bar.com'},
          'fed88489ab6e59913aee935169b15fe68755d82c': {
                'commit_message': 'added testing images only',
                'commit_time': 1562203787.372292, 'commit_user': 'Foo User', 'commit_email': 'foo@bar.com'}}
}

so that the result now includes something which looks like:

'branch_heads': {
        '3c9530ac0da1106c0acbe1201900c51548bbcdd9': ['add-test'],
        'e5ea58dd9c7ffacd45fb128ddc00aced08d13889': ['add-validation'],
        '074f81d6b9fa5fa856175d47c7cc95cc4a839965': ['master', 'dev-branch'],
}

I could make a case for both mapping directions, so let me know if you have an opinion to add. I'm OK either way.

[hhsecond]

Looks good for my use case

[rlizzo]

Great! Merging now!