"git branch --contains x y" creates a branch instead of checking containment

[Per Cederqvist <cederp@opera.com>]

The "git branch --list --contains x y" command lists
all branches that contains commit x and matches the
pattern y. Reading the git-branch(1) manual page gives
the impression that "--list" is redundant, and that
you can instead write

    git branch --contains x y

That command does something completely different,
though. The "--contains x" part is silently ignored,
so it creates a branch named "y" pointing at HEAD.

Tested in git 1.8.1.1 and 1.8.1.4.

In my opinion, there are two ways to fix this:

  - change the "git branch" implementation so
    that --contains implies --list.

  - change the manual page synopsis so that
    it is clear that --contains can only be
    used if --list is also used.  Also add an
    error check to the "git branch" implementation
    so that using --contains without specifying
    --list produces a fatal error message.

Personally I would prefer the first solution.

Repeat by running these commands:

# Set up a repo with two commits.
# Branch a points to the oldest one, and
# b and master to the newest one.
mkdir contains || exit 1
cd contains
git init
touch a; git add a; git commit -m"Added a".
git branch a
touch b; git add b; git commit -m"Added b".
git branch b

git branch --list --contains a
# Prints "a", "b" and "master, as expected.

git branch --contains a
# Prints "a", "b" and "master, as expected.
# In this case, the --list option can be removed.

git branch --list --contains a b
# Prints "b", as expected.  "b" is a <pattern>.

git branch --list --contains a c
# Prints nothing, as expected, as the "c" pattern doesn't match any of
# the existing branches.

git for-each-ref
# Prints three lines: refs/heads/a, refs/heads/b and
# refs/heads/master, as expected.

git branch --contains a c
# Prints nothing, as expected, but...

git for-each-ref
# Prints four lines!  Apparently, the command above created
# refs/heads/c.

     /ceder

P.S. What I really wanted to do was "git merge-base
--is-ancestor a b", but I keep forgetting its name.