Correct handling of branch.$name.merge in builtin-fetch

My prior bug fix for git-push titled "Don't configure remote "." to
fetch everything to itself" actually broke t5520 as we were unable
to evaluate a branch configuration of:

  [branch "copy"]
    remote = .
    merge = refs/heads/master

as remote "." did not have a "remote...fetch" configuration entry to
offer up refs/heads/master as a possible candidate available to be
fetched and merged.  In shell script git-fetch and prior to the above
mentioned commit this was hardcoded for a url of "." to be the set of
local branches.

Chasing down this bug led me to the conclusion that our prior behavior
with regards to branch.$name.merge was incorrect.  In the shell script
based git-fetch implementation we only fetched and merged a branch if
it appeared both in branch.$name.merge *and* in remote.$r.fetch, where
$r = branch.$name.remote.  In other words in the following config file:

  [remote "origin"]
    url = git://git.kernel.org/pub/scm/git/git.git
    fetch = refs/heads/master:refs/remotes/origin/master
  [branch "master"]
    remote = origin
    merge = refs/heads/master
  [branch "pu"]
    remote = origin
    merge = refs/heads/pu

Attempting to run `git pull` while on branch "pu" would always give
the user "Already up-to-date" as git-fetch did not fetch pu and thus
did not mark it for merge in .git/FETCH_HEAD.  The configured merge
would always be ignored and the user would be left scratching her
confused head wondering why merge did not work on "pu" but worked
fine on "master".

If we are using the "default fetch" specification for the current
branch and the current branch has a branch.$name.merge configured
we now union it with the list of refs in remote.$r.fetch.  This
way the above configuration does what the user expects it to do,
which is to fetch only "master" by default but when on "pu" to
fetch both "master" and "pu".

This uncovered some breakage in the test suite where old-style Cogito
branches (.git/branches/$r) did not fetch the branches listed in
.git/config for merging and thus did not actually merge them if the
user tried to use `git pull` on that branch.  Junio and I discussed
it on list and felt that the union approach here makes more sense to
DWIM for the end-user than silently ignoring their configured request
so the test vectors for t5515 have been updated to include for-merge
lines in .git/FETCH_HEAD where they have been configured for-merge
in .git/config.

Since we are now performing a union of the fetch specification and
the merge specification and we cannot allow a branch to be listed
twice (otherwise it comes out twice in .git/FETCH_HEAD) we need to
perform a double loop here over all of the branch.$name.merge lines
and try to set their merge flag if we have already schedule that
branch for fetching by remote.$r.fetch.  If no match is found then
we must add new specifications to fetch the branch but not store it
as no local tracking branch has been designated.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

builtin-fetch.c

@@ -28,20 +28,37 @@ static void unlock_pack_on_signal(int signo)
 	raise(signo);
 }
 
-static void find_merge_config(struct ref *ref_map, struct remote *remote)
+static void add_merge_config(struct ref **head,
+		           struct ref *remote_refs,
+		           struct branch *branch,
+		           struct ref ***tail)
 {
-	struct ref *rm = ref_map;
-	struct branch *branch = branch_get(NULL);
+	int i;
 
-	for (rm = ref_map; rm; rm = rm->next) {
-		if (!branch_has_merge_config(branch)) {
-			if (remote && remote->fetch &&
-			    !strcmp(remote->fetch[0].src, rm->name))
-				rm->merge = 1;
-		} else {
-			if (branch_merges(branch, rm->name))
+	for (i = 0; i < branch->merge_nr; i++) {
+		struct ref *rm, **old_tail = *tail;
+		struct refspec refspec;
+
+		for (rm = *head; rm; rm = rm->next) {
+			if (branch_merge_matches(branch, i, rm->name)) {
 				rm->merge = 1;
+				break;
+			}
 		}
+		if (rm)
+			continue;
+
+		/* Not fetched to a tracking branch?  We need to fetch
+		 * it anyway to allow this branch's "branch.$name.merge"
+		 * to be honored by git-pull.
+		 */
+		refspec.src = branch->merge[i]->src;
+		refspec.dst = NULL;
+		refspec.pattern = 0;
+		refspec.force = 0;
+		get_fetch_map(remote_refs, &refspec, tail);
+		for (rm = *old_tail; rm; rm = rm->next)
+			rm->merge = 1;
 	}
 }
 
@@ -76,17 +93,22 @@ static struct ref *get_ref_map(struct transport *transport,
 	} else {
 		/* Use the defaults */
 		struct remote *remote = transport->remote;
-		if (remote->fetch_refspec_nr) {
+		struct branch *branch = branch_get(NULL);
+		int has_merge = branch_has_merge_config(branch);
+		if (remote && (remote->fetch_refspec_nr || has_merge)) {
 			for (i = 0; i < remote->fetch_refspec_nr; i++) {
 				get_fetch_map(remote_refs, &remote->fetch[i], &tail);
 				if (remote->fetch[i].dst &&
 				    remote->fetch[i].dst[0])
 					*autotags = 1;
+				if (!i && !has_merge && ref_map &&
+				    !strcmp(remote->fetch[0].src, ref_map->name))
+					ref_map->merge = 1;
 			}
-			find_merge_config(ref_map, remote);
+			if (has_merge)
+				add_merge_config(&ref_map, remote_refs, branch, &tail);
 		} else {
 			ref_map = get_remote_ref(remote_refs, "HEAD");
-
 			ref_map->merge = 1;
 		}
 	}

remote.c

@@ -772,16 +772,13 @@ int branch_has_merge_config(struct branch *branch)
 	return branch && !!branch->merge;
 }
 
-int branch_merges(struct branch *branch, const char *refname)
+int branch_merge_matches(struct branch *branch,
+		                 int i,
+		                 const char *refname)
 {
-	int i;
-	if (!branch)
+	if (!branch || i < 0 || i >= branch->merge_nr)
 		return 0;
-	for (i = 0; i < branch->merge_nr; i++) {
-		if (ref_matches_abbrev(branch->merge[i]->src, refname))
-			return 1;
-	}
-	return 0;
+	return ref_matches_abbrev(branch->merge[i]->src, refname);
 }
 
 static struct ref *get_expanded_map(struct ref *remote_refs,

remote.h

@@ -88,7 +88,6 @@ struct branch {
 struct branch *branch_get(const char *name);
 
 int branch_has_merge_config(struct branch *branch);
-
-int branch_merges(struct branch *branch, const char *refname);
+int branch_merge_matches(struct branch *, int n, const char *);
 
 #endif

t/t5515/fetch.br-branches-default-merge

@@ -1,5 +1,6 @@
 # br-branches-default-merge
 754b754407bf032e9a2f9d5a9ad05ca79a6b228f	not-for-merge	branch 'master' of ../
+0567da4d5edd2ff4bb292a465ba9e64dcad9536b		branch 'three' of ../
 754b754407bf032e9a2f9d5a9ad05ca79a6b228f	not-for-merge	tag 'tag-master' of ../
 8e32a6d901327a23ef831511badce7bf3bf46689	not-for-merge	tag 'tag-one' of ../
 22feea448b023a2d864ef94b013735af34d238ba	not-for-merge	tag 'tag-one-tree' of ../

t/t5515/fetch.br-branches-default-merge_branches-default

@@ -1,5 +1,6 @@
 # br-branches-default-merge branches-default
 754b754407bf032e9a2f9d5a9ad05ca79a6b228f	not-for-merge	branch 'master' of ../
+0567da4d5edd2ff4bb292a465ba9e64dcad9536b		branch 'three' of ../
 754b754407bf032e9a2f9d5a9ad05ca79a6b228f	not-for-merge	tag 'tag-master' of ../
 8e32a6d901327a23ef831511badce7bf3bf46689	not-for-merge	tag 'tag-one' of ../
 22feea448b023a2d864ef94b013735af34d238ba	not-for-merge	tag 'tag-one-tree' of ../

t/t5515/fetch.br-branches-default-octopus

@@ -1,5 +1,7 @@
 # br-branches-default-octopus
 754b754407bf032e9a2f9d5a9ad05ca79a6b228f	not-for-merge	branch 'master' of ../
+8e32a6d901327a23ef831511badce7bf3bf46689		branch 'one' of ../
+6134ee8f857693b96ff1cc98d3e2fd62b199e5a8		branch 'two' of ../
 754b754407bf032e9a2f9d5a9ad05ca79a6b228f	not-for-merge	tag 'tag-master' of ../
 8e32a6d901327a23ef831511badce7bf3bf46689	not-for-merge	tag 'tag-one' of ../
 22feea448b023a2d864ef94b013735af34d238ba	not-for-merge	tag 'tag-one-tree' of ../

t/t5515/fetch.br-branches-default-octopus_branches-default

@@ -1,5 +1,7 @@
 # br-branches-default-octopus branches-default
 754b754407bf032e9a2f9d5a9ad05ca79a6b228f	not-for-merge	branch 'master' of ../
+8e32a6d901327a23ef831511badce7bf3bf46689		branch 'one' of ../
+6134ee8f857693b96ff1cc98d3e2fd62b199e5a8		branch 'two' of ../
 754b754407bf032e9a2f9d5a9ad05ca79a6b228f	not-for-merge	tag 'tag-master' of ../
 8e32a6d901327a23ef831511badce7bf3bf46689	not-for-merge	tag 'tag-one' of ../
 22feea448b023a2d864ef94b013735af34d238ba	not-for-merge	tag 'tag-one-tree' of ../

t/t5515/fetch.br-branches-one-merge

@@ -1,5 +1,6 @@
 # br-branches-one-merge
 8e32a6d901327a23ef831511badce7bf3bf46689	not-for-merge	branch 'one' of ../
+0567da4d5edd2ff4bb292a465ba9e64dcad9536b		branch 'three' of ../
 754b754407bf032e9a2f9d5a9ad05ca79a6b228f	not-for-merge	tag 'tag-master' of ../
 8e32a6d901327a23ef831511badce7bf3bf46689	not-for-merge	tag 'tag-one' of ../
 22feea448b023a2d864ef94b013735af34d238ba	not-for-merge	tag 'tag-one-tree' of ../

t/t5515/fetch.br-branches-one-merge_branches-one

@@ -1,5 +1,6 @@
 # br-branches-one-merge branches-one
 8e32a6d901327a23ef831511badce7bf3bf46689	not-for-merge	branch 'one' of ../
+0567da4d5edd2ff4bb292a465ba9e64dcad9536b		branch 'three' of ../
 754b754407bf032e9a2f9d5a9ad05ca79a6b228f	not-for-merge	tag 'tag-master' of ../
 8e32a6d901327a23ef831511badce7bf3bf46689	not-for-merge	tag 'tag-one' of ../
 22feea448b023a2d864ef94b013735af34d238ba	not-for-merge	tag 'tag-one-tree' of ../

t/t5515/fetch.br-branches-one-octopus

@@ -1,5 +1,6 @@
 # br-branches-one-octopus
 8e32a6d901327a23ef831511badce7bf3bf46689		branch 'one' of ../
+6134ee8f857693b96ff1cc98d3e2fd62b199e5a8		branch 'two' of ../
 754b754407bf032e9a2f9d5a9ad05ca79a6b228f	not-for-merge	tag 'tag-master' of ../
 8e32a6d901327a23ef831511badce7bf3bf46689	not-for-merge	tag 'tag-one' of ../
 22feea448b023a2d864ef94b013735af34d238ba	not-for-merge	tag 'tag-one-tree' of ../

t/t5515/fetch.br-branches-one-octopus_branches-one

@@ -1,5 +1,6 @@
 # br-branches-one-octopus branches-one
 8e32a6d901327a23ef831511badce7bf3bf46689		branch 'one' of ../
+6134ee8f857693b96ff1cc98d3e2fd62b199e5a8		branch 'two' of ../
 754b754407bf032e9a2f9d5a9ad05ca79a6b228f	not-for-merge	tag 'tag-master' of ../
 8e32a6d901327a23ef831511badce7bf3bf46689	not-for-merge	tag 'tag-one' of ../
 22feea448b023a2d864ef94b013735af34d238ba	not-for-merge	tag 'tag-one-tree' of ../