From mboxrd@z Thu Jan  1 00:00:00 1970
From: Christian Couder <christian.couder@gmail.com>
Subject: Re: [BUG] git bisect start fails when stale bisect data is left behind
Date: Tue, 6 Sep 2011 09:48:34 +0200
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To: Joel Kaasinen <joel@zenrobotics.com>
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Hi,

On Mon, Sep 5, 2011 at 1:15 PM, Joel Kaasinen <joel@zenrobotics.com> wrote:
> Hi,
>
> Just bumped into a weird bug: bisect refused to start. It seems some
> previous bisect had left around state that referred to a
> now-nonexistent branch.
>
> How to reproduce:
> $ echo foo > .git/BISECT_START
> $ git bisect start HEAD HEAD^
>
> Fails with "fatal: invalid reference:" on git 1.7.6.

Yeah, it looks like a very old behavior.
I'd suggest a simple improvement in the error message like this:

diff --git a/git-bisect.sh b/git-bisect.sh
index c21e33c..bd7155b 100755
--- a/git-bisect.sh
+++ b/git-bisect.sh
@@ -67,7 +67,8 @@ bisect_start() {
        then
                # Reset to the rev from where we started.
                start_head=$(cat "$GIT_DIR/BISECT_START")
-               git checkout "$start_head" -- || exit
+               git checkout "$start_head" -- ||
+               die "Could not checkout previous start point
'$start_head'. Try 'git bisect reset <branch>' first."
        else
                # Get rev from where we start.
                case "$head" in

If there is no objection I will provide a proper patch.

Thanks,
Christian.