Re: [BUG] fetching all remote branches results in failed multiple updates

["SZEDER Gábor" <szeder.dev@gmail.com>]

On Thu, Mar 07, 2019 at 09:44:47PM +0000, Alexander Huynh wrote:
> Hello all,
> 
> When running the latest release of git, I receive an error when attempting to
> fetch all remote branches from a repo:
> 
>     fatal: multiple updates for ref 'refs/remotes/origin/maint' not allowed
> 
> The specific ref that it fails on changes depending on the repository, but the
> end result is the repo isn't cloned.
> 
> The specific configuration that causes this bug is the `remote.origin.fetch`
> option, specifically:
> 
>     [remote "origin"]
>     	fetch = +refs/heads/*:refs/remotes/origin/*
> 
> These settings are listed as an example in "CONFIGURED REMOTE-TRACKING
> BRANCHES" of git-fetch(1), as well as expanded upon in
> https://stackoverflow.com/a/40739835.
> 
> I'm running git version 2.21.0.
> 
> Full reproduction steps are below:
> 
>     [root@chabuduo ~]# useradd -m git-test -s /bin/bash
>     [root@chabuduo ~]# sudo --preserve-env=SSH_AUTH_SOCK -u git-test -i
>     [git-test@chabuduo ~]$ git --version
>     git version 2.21.0
>     [git-test@chabuduo ~]$ cat > ~/.gitconfig
>     [remote "origin"]
>     	fetch = +refs/heads/*:refs/remotes/origin/*

Why do you do this?

First, this is the default refspec configuration that clone will fetch
and set up in the clone's config file anyway.  You don't have to set
it.

Second, setting repository-specific stuff like the default fetch
refspec in the global configuration is not such a good idea.

So the simplest workaround is:

  rm ~/.gitconfig; git clone git@github.com:git/git.git

>     [git-test@chabuduo ~]$ cat ~/.gitconfig
>     [remote "origin"]
>     	fetch = +refs/heads/*:refs/remotes/origin/*
>     [git-test@chabuduo ~]$ git clone git@github.com:git/git.git
>     Cloning into 'git'...
>     Warning: Permanently added the RSA host key for IP address '192.30.255.112' to the list of known hosts.
>     remote: Enumerating objects: 265113, done.
>     remote: Total 265113 (delta 0), reused 0 (delta 0), pack-reused 265113
>     Receiving objects: 100% (265113/265113), 113.20 MiB | 5.49 MiB/s, done.
>     Resolving deltas: 100% (196542/196542), done.
>     fatal: multiple updates for ref 'refs/remotes/origin/maint' not allowed

Anyway, this is a side-effect of 515be83382 (clone: respect additional
configured fetch refspecs during initial fetch, 2018-11-14).  Since
then the same refspec comes up twice in remote->fetch, once from the
configuration and once the explicitly added default refspec.  And
since 'git clone' doesn't run a fully-fledged 'git fetch' and has its
own simple refs-to-refspec matching logic, it ends up trying to write
each ref twice, once for each of the two refspecs, in a single ref
transaction.