True Git Code Churn

A Python script to compute "true" code churn of a Git repository. Useful for software teams to openly help manage technical debt.

Code churn has several definitions, the one that to me provides the most value as a metric is:

"Code churn is when an engineer rewrites their own code in a short period of time."

Reference: https://www.pluralsight.com/blog/teams/why-code-churn-matters

Solutions that I've found online looked at changes to files irrespective whether these are new changes or edits to existing lines of code (LOC) within existing files. Hence this solution that segments line-of-code edits (churn) with new code changes (contribution).

*Tested with:

• Python versions 3.5.3 and 3.8.8.Git version 2.20.1*

How it works

This lightweight script looks at commits per author for a given date range on the current branch. For each commit it bookkeeps the files that were changed along with the LOC for each file. LOC are kept in a sparse structure and changes per LOC are taken into account as the program loops. When a change to the same LOC is detected it updates this separately to bookkeep the true code churn. Result is a print with aggregated contribution and churn per author for a given period in time.

Note: This includes the --no-merges flag as it assumes that merge commits with or without merge conflicts are not indicative of churn.

Usage

Positional (required) arguments:

• after        after a certain date, in YYYY[-MM[-DD]] format
• before     before a certain date, in YYYY[-MM[-DD]] format
• author     author string (not a committer), leave blank to scope all authors
• dir            include Git repository directory (specified as an absolute path)

Optional arguments:

• -h, --h, --help    show this help message and exit
• -exdir                   exclude Git repository subdirectory
• -start-commit    search from a certain commit, in short SHA format
• -end-commit     search to a certain commit, in short SHA format

Usage example with a specific author

python ./gitcodechurn.py after="2018-11-29" before="2019-03-01" author="an author" dir="/Users/myname/myrepo" -exdir="excluded-directory"

Output

author:       an author
contribution: 844
churn:        -28

Usage example without specifying an author

python ./gitcodechurn.py after="2018-11-29" before="2019-03-01" author="" dir="/Users/myname/myrepo" -exdir="excluded-directory"

Output

authors:      author1, author2, author3
contribution: 4423
churn:        -543

Usage example without valid before and after dates, but instead between two commit hashes

python ./gitcodechurn.py after="" before="" -start-commit="6334225" -end-commit="9af2a6e" author="" dir="/Users/myname/myrepo" -exdir="excluded-directory"

Output

authors:      author1, author2
contribution: 467
churn:        -48

Outputs can be used as part of a pipeline (not included) that generates bar charts for reports. For example: