On Thu, Aug 30 2018, Ævar Arnfjörð Bjarmason wrote:
[Notes to self]
> diff --git a/Documentation/git-push.txt b/Documentation/git-push.txt
> index 55277a9781..0f03d36f1e 100644
> --- a/Documentation/git-push.txt
> +++ b/Documentation/git-push.txt
> @@ -74,12 +74,41 @@ without any `<refspec>` on the command line. Otherwise, missing
> `:<dst>` means to update the same ref as the `<src>`.
> +
> The object referenced by <src> is used to update the <dst> reference
> -on the remote side. By default this is only allowed if <dst> is not
> -a tag (annotated or lightweight), and then only if it can fast-forward
> -<dst>. By having the optional leading `+`, you can tell Git to update
> -the <dst> ref even if it is not allowed by default (e.g., it is not a
> -fast-forward.) This does *not* attempt to merge <src> into <dst>. See
> -EXAMPLES below for details.
> +on the remote side. Whether this is allowed depends on where in
> +`refs/*` the <dst> reference lives as described in detail below. Any
> +such update does *not* attempt to merge <src> into <dst>. See EXAMPLES
> +below for details.
> ++
> +The `refs/heads/*` namespace will only accept commit objects, and only
> +if they can be fast-forwarded.
> ++
> +The `refs/tags/*` namespace will accept any kind of object (as
> +commits, trees and blobs can be tagged), and any changes to them will
> +be rejected.
> ++
Both of these should carve out some mention for the "deletion" aspect of
"updates". I.e. you don't need --force to delete.
> +It's possible to push any type of object to any namespace outside of
> +`refs/{tags,heads}/*`. In the case of tags and commits, these will be
> +treated as if they were the commits inside `refs/heads/*` for the
> +purposes of whether the update is allowed.
> ++
> +I.e. a fast-forward of commits and tags outside `refs/{tags,heads}/*`
> +is allowed, even in cases where what's being fast-forwarded is not a
> +commit, but a tag object which happens to point to a new commit which
> +is a fast-forward of the commit the last tag (or commit) it's
> +replacing. Replacing a tag with an entirely different tag is also
> +allowed, if it points to the same commit, as well as pushing a peeled
> +tag, i.e. pushing the commit that existing tag object points to, or a
> +new tag object which an existing commit points to.
> ++
> +Tree and blob objects outside of `refs/{tags,heads}/*` will be treated
> +the same way as if they were inside `refs/tags/*`, any modification of
> +them will be rejected.
> ++
> +All of the rules described above about what's not allowed as an update
> +can be overridden by adding an the optional leading `+` to a refspec
> +(or using `--force` command line option). The only exception to this
> +is that no amount of forcing will make the `refs/heads/*` namespace
> +accept a non-commit object.
> +
> `tag <tag>` means the same as `refs/tags/<tag>:refs/tags/<tag>`.
> +
Later below this we say:
Pushing an empty <src> allows you to delete the <dst> ref from the
remote repository.
Which, perhaps given the discussion of deletions as updates, should be
mentioned earlier in some way, i.e. should we just say above all these
rules that by "update" we mean non-deletions?
