[PATCH v8 2/5] fetch: extract collect_upstream_from_remote() helper

["Harald Nordgren via GitGitGadget" <gitgitgadget@gmail.com>]

From: Harald Nordgren <haraldnordgren@gmail.com>

When a fetch has no refspec to work from, we fall back to guessing
what to fetch: the remote's configured fetch refspec if there is one,
and separately, whether the current branch's upstream lives on this
remote. The latter is independent of the former on purpose: a narrow
refspec (for example from "git remote add -t") can leave the current
branch's own upstream uncovered, and we still need to be able to fetch
it.

That "does this branch build on this remote" check was inlined for
just the current branch. Move it into its own function,
collect_upstream_from_remote(), so the same logic can be reused for
branches other than just the current one.

Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 builtin/fetch.c | 43 ++++++++++++++++++++++++++++---------------
 remote.c        | 15 +++++++++++++++
 remote.h        |  9 +++++++++
 3 files changed, 52 insertions(+), 15 deletions(-)

diff --git a/builtin/fetch.c b/builtin/fetch.c
index c1c65c7528..4753656288 100644
--- a/builtin/fetch.c
+++ b/builtin/fetch.c
@@ -1962,23 +1962,36 @@ static int do_fetch(struct transport *transport,
 
 	if (rs->nr) {
 		refspec_ref_prefixes(rs, &transport_ls_refs_options.ref_prefixes);
+	} else if (transport->remote->fetch.nr) {
+		struct string_list tracked = STRING_LIST_INIT_DUP;
+		struct string_list_item *item;
+
+		refspec_ref_prefixes(&transport->remote->fetch,
+				     &transport_ls_refs_options.ref_prefixes);
+		if (follow_remote_head != FOLLOW_REMOTE_NEVER)
+			do_set_head = 1;
+
+		/*
+		 * The configured refspec may not cover the current
+		 * branch's upstream (e.g. a narrowed -t refspec), so
+		 * make sure we can still fetch it regardless.
+		 */
+		collect_upstream_from_remote(the_repository, &tracked,
+					      transport->remote, NULL);
+		for_each_string_list_item(item, &tracked)
+			strvec_push(&transport_ls_refs_options.ref_prefixes,
+				    item->string);
+		string_list_clear(&tracked, 0);
 	} else {
-		struct branch *branch = branch_get(NULL);
+		struct string_list tracked = STRING_LIST_INIT_DUP;
+		struct string_list_item *item;
 
-		if (transport->remote->fetch.nr) {
-			refspec_ref_prefixes(&transport->remote->fetch,
-					     &transport_ls_refs_options.ref_prefixes);
-			if (follow_remote_head != FOLLOW_REMOTE_NEVER)
-				do_set_head = 1;
-		}
-		if (branch && branch_has_merge_config(branch) &&
-		    !strcmp(branch->remote_name, transport->remote->name)) {
-			int i;
-			for (i = 0; i < branch->merge_nr; i++) {
-				strvec_push(&transport_ls_refs_options.ref_prefixes,
-					    branch->merge[i]->src);
-			}
-		}
+		collect_upstream_from_remote(the_repository, &tracked,
+					      transport->remote, NULL);
+		for_each_string_list_item(item, &tracked)
+			strvec_push(&transport_ls_refs_options.ref_prefixes,
+				    item->string);
+		string_list_clear(&tracked, 0);
 
 		/*
 		 * If there are no refs specified to fetch, then we just
diff --git a/remote.c b/remote.c
index 99a086ea5a..5e980625b8 100644
--- a/remote.c
+++ b/remote.c
@@ -1884,6 +1884,21 @@ int branch_merge_matches(struct branch *branch,
 	return refname_match(branch->merge[i]->src, refname);
 }
 
+void collect_upstream_from_remote(struct repository *repo,
+				   struct string_list *tracked,
+				   struct remote *remote,
+				   const char *refname)
+{
+	struct branch *branch = repo_branch_get(repo, refname);
+
+	if (!branch_has_merge_config(branch) ||
+	    strcmp(branch->remote_name, remote->name))
+		return;
+
+	for (int i = 0; i < branch->merge_nr; i++)
+		string_list_insert(tracked, branch->merge[i]->src);
+}
+
 __attribute__((format (printf,2,3)))
 static char *error_buf(struct strbuf *err, const char *fmt, ...)
 {
diff --git a/remote.h b/remote.h
index ac485a584d..7c86c529b6 100644
--- a/remote.h
+++ b/remote.h
@@ -359,6 +359,15 @@ int branch_has_merge_config(struct branch *branch);
 
 int branch_merge_matches(struct branch *, int n, const char *);
 
+/*
+ * If refname's branch builds on remote, add its upstream on remote to
+ * tracked. A NULL refname means the current branch.
+ */
+void collect_upstream_from_remote(struct repository *repo,
+				   struct string_list *tracked,
+				   struct remote *remote,
+				   const char *refname);
+
 /* list of the remote in a group as configured */
 struct remote_group_data {
 	const char *name;
-- 
gitgitgadget