Any way to tell if a set of SHAs are reachable from HEAD or a specific branch?

[eamodio]

In GitLens, we are using git log --all --date-order to build the Graph visualization, but since we haven't been able to find a way to get git log to include all stashes we first call git stash list to get all the stash SHAs, and then use stdin to pipe them into the git log --all --date-order --stdin call. This works well for that usage, though it would be great to not have to pipe them in.

But when we want to filter the Graph to a single branch (or HEAD), we can't just pipe the same stash SHAs into the git log call, as it will then pull in any commits required to make those stash SHAs "reachable".

Is there a way (without looping over each SHA) to validate if those SHAs are reachable from a specific branch or HEAD? Or is there a way to get git log to not include them if they are not reachable?

Thanks!

[dscho]

My immediate reaction is to pipe the SHAs to git rev-list ^HEAD --stdin to find out which ones are not reachable. Would that help?

[dscho]

This command will show many SHAs, of course. At first I thought that --no-walk could suppress the unneeded ones, but that would probably not work because it would not suppress the reachable ones.

[dscho]

Another option I considered was using git merge-base --all HEAD <SHA>..., but that is subject to command-line length limits, as it does not have any --stdin option (yet). On the other hand, it might be a good solution if you call the command as often as needed: you just have to build the intersection of SHAs in the input and output to find the reachable ones.

[dscho]

I am a bit confused, though, as no stash revision will be reachable from HEAD, by virtue of its construction.

[dscho]

Also note that the merge-base method will accidentally exclude input SHAs from the output if another input SHA is reachable from them.