for-each-ref: let upstream/push report the remote ref name

There are times when scripts want to know not only the name of the
push branch on the remote, but also the name of the branch as known
by the remote repository.

An example of this is when a tool wants to push to the very same branch
from which it would pull automatically, i.e. the `<remote>` and the `<to>`
in `git push <remote> <from>:<to>` would be provided by
`%(upstream:remotename)` and `%(upstream:remoteref)`, respectively.

This patch offers the new suffix :remoteref for the `upstream` and `push`
atoms, allowing to show exactly that. Example:

	$ cat .git/config
	...
	[remote "origin"]
		url = https://where.do.we.come/from
		fetch = refs/heads/*:refs/remote/origin/*
	[branch "master"]
		remote = origin
		merge = refs/heads/master
	[branch "develop/with/topics"]
		remote = origin
		merge = refs/heads/develop/with/topics
	...

	$ git for-each-ref \
		--format='%(push) %(push:remoteref)' \
		refs/heads
	refs/remotes/origin/master refs/heads/master
	refs/remotes/origin/develop/with/topics refs/heads/develop/with/topics

Signed-off-by: J Wyman <jwyman@microsoft.com>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-for-each-ref.txt

@@ -142,8 +142,12 @@ upstream::
 	encountered. Append `:track,nobracket` to show tracking
 	information without brackets (i.e "ahead N, behind M").
 +
-Also respects `:remotename` to state the name of the *remote* instead of
-the ref.
+For any remote-tracking branch `%(upstream)`, `%(upstream:remotename)`
+and `%(upstream:remoteref)` refer to the name of the remote and the
+name of the tracked remote ref, respectively. In other words, the
+remote-tracking branch can be updated explicitly and individually by
+using the refspec `%(upstream:remoteref):%(upstream)` to fetch from
+`%(upstream:remotename)`.
 +
 Has no effect if the ref does not have tracking information associated
 with it.  All the options apart from `nobracket` are mutually exclusive,
@@ -152,9 +156,9 @@ but if used together the last option is selected.
 push::
 	The name of a local ref which represents the `@{push}`
 	location for the displayed ref. Respects `:short`, `:lstrip`,
-	`:rstrip`, `:track`, `:trackshort` and `:remotename` options as
-	`upstream` does. Produces an empty string if no `@{push}` ref is
-	configured.
+	`:rstrip`, `:track`, `:trackshort`, `:remotename`, and `:remoteref`
+	options as `upstream` does. Produces an empty string if no `@{push}`
+	ref is configured.
 
 HEAD::
 	'*' if HEAD matches current ref (the checked out branch), ' '

ref-filter.c

@@ -77,7 +77,7 @@ static struct used_atom {
 		struct align align;
 		struct {
 			enum {
-				RR_REF, RR_TRACK, RR_TRACKSHORT, RR_REMOTE_NAME
+				RR_REF, RR_TRACK, RR_TRACKSHORT, RR_REMOTE_NAME, RR_REMOTE_REF
 			} option;
 			struct refname_atom refname;
 			unsigned int nobracket : 1, push : 1, push_remote : 1;
@@ -164,6 +164,9 @@ static void remote_ref_atom_parser(const struct ref_format *format, struct used_
 		else if (!strcmp(s, "remotename")) {
 			atom->u.remote_ref.option = RR_REMOTE_NAME;
 			atom->u.remote_ref.push_remote = 1;
+		} else if (!strcmp(s, "remoteref")) {
+			atom->u.remote_ref.option = RR_REMOTE_REF;
+			atom->u.remote_ref.push_remote = 1;
 		} else {
 			atom->u.remote_ref.option = RR_REF;
 			refname_atom_parser_internal(&atom->u.remote_ref.refname,
@@ -1262,6 +1265,16 @@ static void fill_remote_ref_details(struct used_atom *atom, const char *refname,
 			*s = xstrdup(remote);
 		else
 			*s = "";
+	} else if (atom->u.remote_ref.option == RR_REMOTE_REF) {
+		int explicit;
+		const char *merge;
+
+		merge = remote_ref_for_branch(branch, atom->u.remote_ref.push,
+					      &explicit);
+		if (explicit)
+			*s = xstrdup(merge);
+		else
+			*s = "";
 	} else
 		die("BUG: unhandled RR_* enum");
 }

remote.c

@@ -675,6 +675,36 @@ const char *pushremote_for_branch(struct branch *branch, int *explicit)
 	return remote_for_branch(branch, explicit);
 }
 
+const char *remote_ref_for_branch(struct branch *branch, int for_push,
+				  int *explicit)
+{
+	if (branch) {
+		if (!for_push) {
+			if (branch->merge_nr) {
+				if (explicit)
+					*explicit = 1;
+				return branch->merge_name[0];
+			}
+		} else {
+			const char *dst, *remote_name =
+				pushremote_for_branch(branch, NULL);
+			struct remote *remote = remote_get(remote_name);
+
+			if (remote && remote->push_refspec_nr &&
+			    (dst = apply_refspecs(remote->push,
+						  remote->push_refspec_nr,
+						  branch->refname))) {
+				if (explicit)
+					*explicit = 1;
+				return dst;
+			}
+		}
+	}
+	if (explicit)
+		*explicit = 0;
+	return "";
+}
+
 static struct remote *remote_get_1(const char *name,
 				   const char *(*get_default)(struct branch *, int *))
 {

remote.h

@@ -223,6 +223,8 @@ struct branch {
 struct branch *branch_get(const char *name);
 const char *remote_for_branch(struct branch *branch, int *explicit);
 const char *pushremote_for_branch(struct branch *branch, int *explicit);
+const char *remote_ref_for_branch(struct branch *branch, int for_push,
+				  int *explicit);
 
 int branch_has_merge_config(struct branch *branch);
 int branch_merge_matches(struct branch *, int n, const char *);