Added remote.<name>.annex-push and remote.<name>.annex-pull

The former can be useful to make remotes that don't get fully synced with
local changes, which comes up in a lot of situations.

The latter was mostly added for symmetry, but could be useful (though less
likely to be).

Implementing `remote.<name>.annex-pull` was a bit tricky, as there's no one
place where git-annex pulls/fetches from remotes. I audited all
instances of "fetch" and "pull". A few cases were left not checking this
config:

* Git.Repair can try to pull missing refs from a remote, and if the local
  repo is corrupted, that seems a reasonable thing to do even though
  the config would normally prevent it.
* Assistant.WebApp.Gpg and Remote.Gcrypt and Remote.Git do fetches
  as part of the setup process of a remote. The config would probably not
  be set then, and having the setup fail seems worse than honoring it if it
  is already set.

I have not prevented all the code that does a "merge" from merging branches
from remotes with remote.<name>.annex-pull=false. That could perhaps
be done, but it would need a way to map from branch name to remote name,
and the way refspecs work makes that hard to get really correct. So if the
user fetches manually, the git-annex branch will get merged, for example.
Anther way of looking at/justifying this is that the setting is called
"annex-pull", not "annex-merge".

This commit was supported by the NSF-funded DataLad project.

1 files changed, 19 insertions, 0 deletions

diff --git a/doc/tips/semi-synchronized_remotes/comment_1_d0459d72b7e0441fe833a5c8e1588a4f._comment b/doc/tips/semi-synchronized_remotes/comment_1_d0459d72b7e0441fe833a5c8e1588a4f._comment
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+[[!comment format=mdwn
+ username="joey"
+ subject="""comment 1"""
+ date="2017-04-05T16:11:57Z"
+ content="""
+Setting `remote.<name>.annex-readonly=true` prevents git-annex sync
+from pushing changes to the remote. It also prevents any git-annex command
+from copying annexed file contents to the remote, or deleting annexed file
+contents. So I think it's ideal for this kind of situation.
+
+There does seem to be room for configs to prevent sync from pulling/pushing
+without making the remote fully readonly. For example, the remote might be
+a source of content, that only knows about the files it added and not other
+files in the local repository, so dropping files from it should be allowed
+but not pushing to it.
+
+So, I've added `remote.<name>.annex-push` and
+`remote.<name>.annex-pull`.
+"""]]