git: handle octopus merges Octopus merges in git are merge commits with more than 2 parents. To make them fit into mercurial core's assumption about commits having 0-2 parents, the git indexing code creates "sythetic" commits to represent the octopus commit as a sequence of regular 2-parent commits. The synthetic commit hashes are just an incrementing commit number (which is the same as the generated rev number). The last commit in the sequence of commits uses the actual git commit hash. As a result, `hg checkout -r <commit>` produces the same working directory as `git checkout <commit>` for all git commit hashes. The synthetic commit hashes are stored in the changelog table as any other commit - with the two parents - but they also contain the commit hash of the octopus merge commit. For example, given the git DAG (manually pruned `git log --graph`): *-. commit 23480d86e2689703b33f693907c40fbe6e1620e4 Merge branches... |\ \ | | | | | * commit 2eda9984b06c75448598ec6c0a9028e49dacf616 C | | | | * | commit 5e634a12f12fedaf7b8ef0f0fcdbb07222871953 B | |/ | | * | commit 8883a1296c5ae323a1b18d1f6410398ce43ebd3a D |/ | * commit 95f241588fded9554cae91be0fefd576f61ebfc6 A Where M is the octopus merge commit with 3 parents, the corresponding mercurial DAG is: $ hg log -G -T '{node} {desc}' @ 23480d86e2689703b33f693907c40fbe6e1620e4 Merge branches 'abc' and 'def' |\ | o 0000000000000000000000000000000000000004 Merge branches 'abc' and 'def' | |\ | | o 8883a1296c5ae323a1b18d1f6410398ce43ebd3a D | | | o---+ 2eda9984b06c75448598ec6c0a9028e49dacf616 C / / o / 5e634a12f12fedaf7b8ef0f0fcdbb07222871953 B |/ o 95f241588fded9554cae91be0fefd576f61ebfc6 A