Re: [RFC 0/1] Tolerate broken headers in `packed-refs` files

[Derrick Stolee <stolee@gmail.com>]

On 3/26/2018 8:42 AM, Michael Haggerty wrote:
> [...]
>
> But there might be some tools out in the wild that have been writing
> broken headers. In that case, users who upgrade Git might suddenly
> find that they can't read repositories that they could read before. In
> fact, a tool that we wrote and use internally at GitHub was doing
> exactly that, which is how we discovered this "problem".
>
> This patch shows what it would look like to relax the parsing again,
> albeit *only* for the first line of the file, and *only* for lines
> that start with '#'.
>
> The problem with this patch is that it would make it harder for people
> who implement broken tools in the future to discover their mistakes.
> The only result of the error would be that it is slower to work with
> the `packed-refs` files that they wrote. Such an error could go
> undiscovered for a long time.

My opinion is that we shouldn't maintain back-compat with formats that 
may have been written by another tool because Git wasn't strict about 
it. As long as Git never wrote files with these formats, then they 
shouldn't be supported.

You are absolutely right that staying strict will help discover the 
tools that are writing an incorrect format.

Since most heavily-used tools that didn't spawn Git processes use 
LibGit2 to interact with Git repos, I added Ed Thomson to CC to see if 
libgit2 could ever write these bad header comments.

Thanks for writing this RFC so we can have the discussion and more 
quickly identify this issue if/when users are broken.

Thanks,
-Stolee