threads / discuss / 14185

Determining if two commits are on a separate branch

Subject: Determining if two commits are on a separate branch

## tl;dr

3 messages between Jun 27, 2008 and Jun 27, 2008.

replies: 2people: 3as markdown or json

Adr3nal D0S· Jun 27, 2008, 14:55 UTC · lore

We are making extensive use of submodules at work and we have created a number of extra scripts to simplify our usage. For example, there is git-rstatus, which recursively reports status of all submodules.

I am working on another script to check whether or not a change to any submodules jump branches. If we have commits like this:

A--B--C
   \--D

I don't care if a submodule moves from A to C or B to C, but I do care if a commit of the super-project would cause a jump from D to C or revert from C to B, effectively dropping previously committed code on the floor.

So, is there a "correct" or "best" way to determine if one commit's SHA follows directly from another's SHA in the commit history?

Michael J Gruber· Jun 27, 2008, 15:13 UTC · re: Adr3nal D0S · lore

Re: Determining if two commits are on a separate branch

Adr3nal D0S venit, vidit, dixit 27.06.2008 16:55:

Show 17 quoted lines

> We are making extensive use of submodules at work and we have created
> a number of extra scripts to simplify our usage.  For example, there
> is git-rstatus, which recursively reports status of all submodules.
> 
> I am working on another script to check whether or not a change to any
> submodules jump branches.  If we have commits like this:
> 
> A--B--C
>    \--D
> 
> I don't care if a submodule moves from A to C or B to C, but I do care
> if a commit of the super-project would cause a jump from D to C or
> revert from C to B, effectively dropping previously committed code on
> the floor.
> 
> So, is there a "correct" or "best" way to determine if one commit's
> SHA follows directly from another's SHA in the commit history?

"Directly" as in "is child of", or as in "connected by the DAG"?

"git rev-list C..B" lists all commits which are not in C but in B. If this list is empty then B is "contained" in C. This is how you can test for being connected by the DAG. For the graph above, all of the following refspecs would return an empty list, indicating connectedness:

C..B C..A B..A D..B D..A

Are those the "good ones" in your case? Then you know how to test for the bad guys ;)

Michael

Santi Béjar· Jun 27, 2008, 15:17 UTC · re: Adr3nal D0S · lore

Re: Determining if two commits are on a separate branch

On Fri, Jun 27, 2008 at 16:55, Adr3nal D0S <adr3nald0s@gmail.com> wrote: [...]

> So, is there a "correct" or "best" way to determine if one commit's
> SHA follows directly from another's SHA in the commit history?

You can compute the merge-base of these two commits and if the base is one of them then it is a fast-forward.

For example, in git.git:

$ git merge-base origin/next origin/master d54467b8c319571b5dc433b1f7e471c4b0f21caf

$ git rev-parse origin/next origin/master 3e7d305293ce93d00d5e0e6371311f7caa94f497 d54467b8c319571b5dc433b1f7e471c4b0f21caf

The merge-base is origin/master so it is an ancestor of origin/next.

HTH

Santi