Re: [RFC v2 1/1] refspec: add support for negative refspecs

> From: Jacob Keller <jacob.keller@gmail.com>
>
> Both fetch and push support pattern refspecs which allow fetching or
> pushing references that match a specific pattern. Because these patterns
> are globs, they have somewhat limited ability to express more complex
> situations.
>
> For example, suppose you wish to fetch all branches from a remote except
> for a specific one. To allow this, you must setup a set of refspecs
> which match only the branches you want. Because refspecs are either
> explicit name matches, or simple globs, many patterns cannot be
> expressed.
>
> Add support for a new type of refspec, referred to as "negative"
> refspecs. These are prefixed with a '^' and mean "exclude any ref
> matching this refspec". They can only have one "side" which always
> refers to the source. During a fetch, this refers to the name of the ref
> on the remote. During a push, this refers to the name of the ref on the
> local side.
>
> With negative refspecs, users can express more complex patterns. For
> example:
>
>  git fetch origin refs/heads/*:refs/remotes/origin/* ^refs/heads/dontwant
>
> will fetch all branches on origin into remotes/origin, but will exclude
> fetching the branch named dontwant.
>
> Refspecs today are commutative, meaning that order doesn't expressly
> matter. Rather than forcing an implied order, negative refspecs will
> always be applied last. That is, in order to match, a ref must match at
> least one positive refspec, and match none of the negative refspecs.
> This is similar to how negative pathspecs work.
>
> Signed-off-by: Jacob Keller <jacob.keller@gmail.com>
> ---
>
> I realize this probably needs to be broken down into multiple patches, but I
> haven't quite figured out the best way to do that. I'd like to avoid the
> case where a commit has support for parsing negative refspecs but code paths
> which use refspecs aren't handling them correctly. Thoughts?
>
> Splitting would also allow additional space for explanations of some of the
> trickier logic.
>
> I am also definitely looking for more test ideas, to help make sure we
> cover a good variety of the flows.