Add url.<base>.pushInsteadOf: URL rewriting for push only

This configuration option allows systematically rewriting fetch-only URLs
to push-capable URLs when used with push.  For instance:

[url "ssh://example.org/"]
    pushInsteadOf = "git://example.org/"

This will allow clones of "git://example.org/path/to/repo" to subsequently
push to "ssh://example.org/path/to/repo", without manually configuring
pushurl for that remote.

Includes documentation for the new option, bash completion updates, and
test cases (both that pushInsteadOf applies to push, that it does not
apply to fetch, and that it is ignored when pushURL is already defined).

Signed-off-by: Josh Triplett <josh@joshtriplett.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/config.txt

@@ -1500,6 +1500,19 @@ url.<base>.insteadOf::
 	never-before-seen repository on the site.  When more than one
 	insteadOf strings match a given URL, the longest match is used.
 
+url.<base>.pushInsteadOf::
+	Any URL that starts with this value will not be pushed to;
+	instead, it will be rewritten to start with <base>, and the
+	resulting URL will be pushed to. In cases where some site serves
+	a large number of repositories, and serves them with multiple
+	access methods, some of which do not allow push, this feature
+	allows people to specify a pull-only URL and have git
+	automatically use an appropriate URL to push, even for a
+	never-before-seen repository on the site.  When more than one
+	pushInsteadOf strings match a given URL, the longest match is
+	used.  If a remote has an explicit pushurl, git will ignore this
+	setting for that remote.
+
 user.email::
 	Your email address to be recorded in any newly created commits.
 	Can be overridden by the 'GIT_AUTHOR_EMAIL', 'GIT_COMMITTER_EMAIL', and

Documentation/urls.txt

@@ -67,3 +67,21 @@ For example, with this:
 a URL like "work:repo.git" or like "host.xz:/path/to/repo.git" will be
 rewritten in any context that takes a URL to be "git://git.host.xz/repo.git".
 
+If you want to rewrite URLs for push only, you can create a
+configuration section of the form:
+
+------------
+	[url "<actual url base>"]
+		pushInsteadOf = <other url base>
+------------
+
+For example, with this:
+
+------------
+	[url "ssh://example.org/"]
+		pushInsteadOf = git://example.org/
+------------
+
+a URL like "git://example.org/path/to/repo.git" will be rewritten to
+"ssh://example.org/path/to/repo.git" for pushes, but pulls will still
+use the original URL.