How to determine a branch whether has a specified commit

How to determine a branch whether has a specified commit

[wuzhouhui]

Hi,

I know
    git branch --contains <commit>
can display all local branches that has specified commit. However, specify a
branch and commit, I don't know how to determine whether this branch contains
this commit.

I think
    git branch --contains <commit> | grep <branch name>
is not good enough. Does anyone have a better solution?

Thanks.

Re: How to determine a branch whether has a specified commit

[Bryan Turner]

On Wed, Dec 18, 2019 at 6:42 PM wuzhouhui <wuzhouhui14@mails.ucas.ac.cn> wrote:
>
> Hi,
>
> I know
>     git branch --contains <commit>
> can display all local branches that has specified commit. However, specify a
> branch and commit, I don't know how to determine whether this branch contains
> this commit.
>
> I think
>     git branch --contains <commit> | grep <branch name>

"Combine" the two commands: git branch --contains <commit> <branch
name>. That will either output the branch's name, if it contains the
commit, or nothing if it doesn't.

A different approach would be something like: git rev-list --count
<commit> ^<branch name>. If that returns a count of 0, it means the
commit is reachable from the branch. Otherwise, it'll output some
positive count indicating how many commits (including the specific
commit you asked about) are not reachable from the branch. (I suspect
you don't really need the count, so you could also use "-1" instead of
"--count".)

Hope this helps,
Bryan

Re: How to determine a branch whether has a specified commit

[Jeff King]

On Wed, Dec 18, 2019 at 07:09:36PM -0800, Bryan Turner wrote:

> > I think
> >     git branch --contains <commit> | grep <branch name>
> 
> "Combine" the two commands: git branch --contains <commit> <branch
> name>. That will either output the branch's name, if it contains the
> commit, or nothing if it doesn't.

Or "git for-each-ref --contains <commit> refs/heads/<branch>" if you're
scripting.

> A different approach would be something like: git rev-list --count
> <commit> ^<branch name>. If that returns a count of 0, it means the
> commit is reachable from the branch. Otherwise, it'll output some
> positive count indicating how many commits (including the specific
> commit you asked about) are not reachable from the branch. (I suspect
> you don't really need the count, so you could also use "-1" instead of
> "--count".)

That works, but is not quite as careful as some other techniques with
respect to looking past commits with clock skew. A more careful way is
to check that "git merge-base <commit> <branch>" is equal to <commit>.

That clock-skew thing will eventually go away once we start using
generation numbers consistently (but I don't think we do yet in
limit_list(), which handles the "^" part of the traversal).

-Peff