push doc: correct lies about how push refspecs work

There's complex rules governing whether a push is allowed to take
place depending on whether we're pushing to refs/heads/*, refs/tags/*
or refs/not-that/*. See is_branch() in refs.c, and the various
assertions in refs/files-backend.c. (e.g. "trying to write non-commit
object %s to branch '%s'").

This documentation has never been quite correct, but went downhill
after dbfeddb12e ("push: require force for refs under refs/tags/",
2012-11-29) when we started claiming that <dst> couldn't be a tag
object, which is incorrect. After some of the logic in that patch was
changed in 256b9d70a4 ("push: fix "refs/tags/ hierarchy cannot be
updated without --force"", 2013-01-16) the docs weren't updated, and
we've had some version of documentation that confused whether <src>
was a tag or not with whether <dst> would accept either an annotated
tag object or the commit it points to.

This makes the intro somewhat more verbose & complex, perhaps we
should have a shorter description here and split the full complexity
into a dedicated section. Very few users will find themselves needing
to e.g. push blobs or trees to refs/custom-namespace/* (or blobs or
trees at all), and that could be covered separately as an advanced
topic.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
pull/535/head
Ævar Arnfjörð Bjarmason 4 years ago committed by Junio C Hamano
parent 8da6128c26
commit fe802bd21e
  1. 52
      Documentation/git-push.txt
  2. 7
      Documentation/gitrevisions.txt

@ -74,14 +74,50 @@ 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.).
+
Pushing an empty <src> allows you to delete the <dst> ref from
the remote repository.
on the remote side. Whether this is allowed depends on where in
`refs/*` the <dst> reference lives as described in detail below, in
those sections "update" means any modifications except deletes, which
as noted after the next few sections are treated differently.
+
The `refs/heads/*` namespace will only accept commit objects, and
updates 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 updates to them will
be rejected.
+
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 update 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. Hooks and configuration can also override
or amend these rules, see e.g. `receive.denyNonFastForwards` in
linkgit:git-config[1] and`pre-receive` and `update` in
linkgit:githooks[5].
+
Pushing an empty <src> allows you to delete the <dst> ref from the
remote repository. Deletions are always accepted without a leading `+`
in the refspec (or `--force`), except when forbidden by configuration
or hooks. See `receive.denyDeletes` in linkgit:git-config[1] and
`pre-receive` and `update` in linkgit:githooks[5].
+
The special refspec `:` (or `+:` to allow non-fast-forward updates)
directs Git to push "matching" branches: for every branch that exists on

@ -19,9 +19,10 @@ walk the revision graph (such as linkgit:git-log[1]), all commits which are
reachable from that commit. For commands that walk the revision graph one can
also specify a range of revisions explicitly.
In addition, some Git commands (such as linkgit:git-show[1]) also take
revision parameters which denote other objects than commits, e.g. blobs
("files") or trees ("directories of files").
In addition, some Git commands (such as linkgit:git-show[1] and
linkgit:git-push[1]) can also take revision parameters which denote
other objects than commits, e.g. blobs ("files") or trees
("directories of files").
include::revisions.txt[]

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