fetch: set remote/HEAD if it does not exist

If the user has remote/HEAD set already and it looks like it has changed
on the server, then print a message, otherwise set it if we can.
Silently pass if the user already has the same remote/HEAD set as
reported by the server or if we encounter any errors along the way.

Signed-off-by: Bence Ferdinandy <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: ferdinandyb

builtin/fetch.c

@@ -1577,6 +1577,80 @@ static int backfill_tags(struct display_state *display_state,
 	return retcode;
 }
 
+static void report_set_head(const char *remote, const char *head_name,
+			struct strbuf *buf_prev) {
+	struct strbuf buf_prefix = STRBUF_INIT;
+	const char *prev_head = NULL;
+
+	strbuf_addf(&buf_prefix, "refs/remotes/%s/", remote);
+	skip_prefix(buf_prev->buf, buf_prefix.buf, &prev_head);
+
+	if (prev_head && strcmp(prev_head, head_name)) {
+		printf("'HEAD' at '%s' has changed from '%s' to '%s'\n",
+			remote, prev_head, head_name);
+		printf("Run 'git remote set-head %s %s' to follow the change.\n",
+			remote, head_name);
+	}
+}
+
+static const char *strip_refshead(const char *name){
+	skip_prefix(name, "refs/heads/", &name);
+	return name;
+}
+
+static int set_head(const struct ref *remote_refs)
+{
+	int result = 0;
+	struct strbuf b_head = STRBUF_INIT, b_remote_head = STRBUF_INIT,
+		b_local_head = STRBUF_INIT;
+	const char *remote = gtransport->remote->name;
+	char *head_name = NULL;
+	struct ref *ref, *matches;
+	struct ref *fetch_map = NULL, **fetch_map_tail = &fetch_map;
+	struct refspec_item refspec = {
+		.force = 0,
+		.pattern = 1,
+		.src = (char *) "refs/heads/*",
+		.dst = (char *) "refs/heads/*",
+	};
+	struct string_list heads = STRING_LIST_INIT_DUP;
+	struct ref_store *refs = get_main_ref_store(the_repository);
+
+	get_fetch_map(remote_refs, &refspec, &fetch_map_tail, 0);
+	matches = guess_remote_head(find_ref_by_name(remote_refs, "HEAD"),
+				    fetch_map, 1);
+	for (ref = matches; ref; ref = ref->next) {
+		string_list_append(&heads, strip_refshead(ref->name));
+	}
+
+
+	if (!heads.nr)
+		result = 1;
+	else if (heads.nr > 1)
+		result = 1;
+	else
+		head_name = xstrdup(heads.items[0].string);
+	if (head_name) {
+		strbuf_addf(&b_head, "refs/remotes/%s/HEAD", remote);
+		strbuf_addf(&b_remote_head, "refs/remotes/%s/%s", remote, head_name);
+		/* make sure it's valid */
+		if (!refs_ref_exists(refs, b_remote_head.buf))
+			result = 1;
+		else if (refs_update_symref(refs, b_head.buf, b_remote_head.buf,
+					"remote set-head", &b_local_head, 1))
+			result = 1;
+		else
+			report_set_head(remote, head_name, &b_local_head);
+
+		free(head_name);
+	}
+
+	strbuf_release(&b_head);
+	strbuf_release(&b_local_head);
+	strbuf_release(&b_remote_head);
+	return result;
+}
+
 static int do_fetch(struct transport *transport,
 		    struct refspec *rs,
 		    const struct fetch_config *config)
@@ -1646,6 +1720,8 @@ static int do_fetch(struct transport *transport,
 				    "refs/tags/");
 	}
 
+	strvec_push(&transport_ls_refs_options.ref_prefixes, "HEAD");
+
 	if (must_list_refs) {
 		trace2_region_enter("fetch", "remote_refs", the_repository);
 		remote_refs = transport_get_remote_refs(transport,
@@ -1790,6 +1866,12 @@ static int do_fetch(struct transport *transport,
 				  "you need to specify exactly one branch with the --set-upstream option"));
 		}
 	}
+	if (set_head(remote_refs))
+		;
+		/*
+		 * Way too many cases where this can go wrong
+		 * so let's just fail silently for now.
+		 */
 
 cleanup:
 	if (retcode) {

t/t4207-log-decoration-colors.sh

@@ -59,7 +59,8 @@ ${c_reset}${c_tag}tag: ${c_reset}${c_tag}v1.0${c_reset}${c_commit}, \
 ${c_reset}${c_tag}tag: ${c_reset}${c_tag}B${c_reset}${c_commit})${c_reset} B
 ${c_commit}COMMIT_ID${c_reset}${c_commit} (${c_reset}\
 ${c_tag}tag: ${c_reset}${c_tag}A1${c_reset}${c_commit}, \
-${c_reset}${c_remoteBranch}other/main${c_reset}${c_commit})${c_reset} A1
+${c_reset}${c_remoteBranch}other/main${c_reset}${c_commit}, \
+${c_reset}${c_remoteBranch}other/HEAD${c_reset}${c_commit})${c_reset} A1
 	${c_commit}COMMIT_ID${c_reset}${c_commit} (${c_reset}\
 ${c_stash}refs/stash${c_reset}${c_commit})${c_reset} On main: Changes to A.t
 	${c_commit}COMMIT_ID${c_reset}${c_commit} (${c_reset}\

t/t5505-remote.sh

@@ -71,7 +71,7 @@ test_expect_success 'add another remote' '
 		cd test &&
 		git remote add -f second ../two &&
 		tokens_match "origin second" "$(git remote)" &&
-		check_tracking_branch second main side another &&
+		check_tracking_branch second main side another HEAD &&
 		git for-each-ref "--format=%(refname)" refs/remotes |
 		sed -e "/^refs\/remotes\/origin\//d" \
 		    -e "/^refs\/remotes\/second\//d" >actual &&
@@ -473,7 +473,7 @@ test_expect_success 'set-head --auto has no problem w/multiple HEADs' '
 		cd test &&
 		git fetch two "refs/heads/*:refs/remotes/two/*" &&
 		git remote set-head --auto two >output 2>&1 &&
-		echo "'\''two/HEAD'\'' is now created and points to '\''main'\''" >expect &&
+		echo "'\''two/HEAD'\'' is unchanged and points to '\''main'\''" >expect &&
 		test_cmp expect output
 	)
 '
@@ -764,6 +764,7 @@ test_expect_success 'reject --no-no-tags' '
 cat >one/expect <<\EOF
   apis/main
   apis/side
+  drosophila/HEAD -> drosophila/main
   drosophila/another
   drosophila/main
   drosophila/side
@@ -781,6 +782,7 @@ test_expect_success 'update' '
 '
 
 cat >one/expect <<\EOF
+  drosophila/HEAD -> drosophila/main
   drosophila/another
   drosophila/main
   drosophila/side
@@ -793,7 +795,7 @@ EOF
 test_expect_success 'update with arguments' '
 	(
 		cd one &&
-		for b in $(git branch -r)
+		for b in $(git branch -r | grep -v HEAD)
 		do
 		git branch -r -d $b || exit 1
 		done &&
@@ -836,7 +838,7 @@ EOF
 test_expect_success 'update default' '
 	(
 		cd one &&
-		for b in $(git branch -r)
+		for b in $(git branch -r | grep -v HEAD)
 		do
 		git branch -r -d $b || exit 1
 		done &&
@@ -848,6 +850,7 @@ test_expect_success 'update default' '
 '
 
 cat >one/expect <<\EOF
+  drosophila/HEAD -> drosophila/main
   drosophila/another
   drosophila/main
   drosophila/side
@@ -870,7 +873,7 @@ test_expect_success 'update default (overridden, with funny whitespace)' '
 test_expect_success 'update (with remotes.default defined)' '
 	(
 		cd one &&
-		for b in $(git branch -r)
+		for b in $(git branch -r | grep -v HEAD)
 		do
 		git branch -r -d $b || exit 1
 		done &&