Actions
Jeena and I were working to branch MediaWiki for 1.36. We ran ./branch.py REL1_36 --core --branchpoint e497482ee4e0da58d2f3f6ec996f8b20f64b2d80 --core-version 1.36.0-beta --task T279456 to branch MediaWiki core and create a patch.
Expected outcome
The patch is created and pushed to gerrit.
Actual outcome
Gerrit rejects the patch as having implicit merges (the difference between REL1_36 and master at the time we ran it).
Analysis
The do_core_work method runs git('checkout', '-B', branch) against (implicitly) master from with clone('mediawiki/core'), rather than from the branch point (which the branch method doesn't pass through).