Date: Wed, 21 May 2014 16:25:02 -0400
From: "David A. Harding" <dave@dtrt.org>
To: Chris Beams <chris@beams.io>
Message-ID: <20140521202502.GA439@localhost.localdomain>
References: <CA+s+GJBNWh0Py9KB4Y+B19ACeHOygtkLrPw5SbZ0SrVs50pqvg@mail.gmail.com>
	<7B48B9D4-5FB0-42CA-A462-C20D3F345A9A@beams.io>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <7B48B9D4-5FB0-42CA-A462-C20D3F345A9A@beams.io>
User-Agent: Mutt/1.5.21 (2010-09-15)
Cc: Bitcoin Dev <bitcoin-development@lists.sourceforge.net>
Subject: Re: [Bitcoin-development] PSA: Please sign your git commits
Precedence: list

On Wed, May 21, 2014 at 06:39:44PM +0200, Chris Beams wrote:
> I [was] searching for a way to enable signing by default [...]
> Unfortunately, there isn't one, meaning it's likely that most folks
> will forget to do this most of the time.

For all of my projects, I now I put this script in
.git/hooks/post-commit and post-merge:

    #!/bin/bash -eu

    if ! git log -n1 --show-signature | grep -q 'gpg: Good signature'
    then
        yes "FORGOT TO SIGN COMMIT MESSAGE"
        exit 1
    fi

So anytime I forget to sign, I get an obvious error and can immediately
run git commit --amend -S.

To automatically add a script like the one above to all new projects (plus
quickly add it old current projects), you can follow these instructions:

    http://stackoverflow.com/questions/2293498/git-commit-hooks-global-settings

> If you're really serious about it, you should probably reject pull
> requests without signed commits; otherwise, signing becomes
> meaningless because only honest authors do it

I find signing my commits quite useful even on projects without a
default signing policy because it lets me diff from the last time I
provably reviewed the code.  Here's my script for that:

    #!/bin/bash -eu

    KEY=F29EC4B7

    last_signed_commit=$( git log --topo-order --show-signature --pretty=oneline \
        | grep -m1 " gpg: Signature made.*RSA key ID $KEY" \
        | sed 's/ .*//' \
        | grep .
    ) || { echo "No signed commit found.  Dying..." ; exit 1 ; }

    set -x
    git diff $last_signed_commit

By diffing against the last signed commit I made, I also review any
commits that were made using my name but which I didn't actually make,
such as squashes and rebases of my commits (and, of course, forgeries).

For anyone who's bored and wants to read a lot of text, I think the
definitive work on git signing is this:

    http://mikegerwitz.com/papers/git-horror-story.html

-Dave
-- 
David A. Harding