fetch: add configuration for set_head behaviour

In the current implementatio, if refs/remotes/$remote/HEAD does not exist, running fetch will create it, but if it does exist it will not do anything, which is a somewhat safe and minimal approach. Unfortunately, for users who wish to NOT have refs/remotes/$remote/HEAD set for any reason (e.g. so that `git rev-parse origin` doesn't accidentally point them somewhere they do not want to), there is no way to remove this behaviour. On the other side of the spectrum, users may want fetch to automatically update HEAD or at least give them a warning if something changed on the remote. Introduce a new setting, remote.$remote.followRemoteHEAD with four options: - "never": do not ever do anything, not even create - "create": the current behaviour, now the default behaviour - "warn": print a message if remote and local HEAD is different - "always": silently update HEAD on every change Signed-off-by: Bence Ferdinandy <[email protected]> Signed-off-by: Junio C Hamano <[email protected]>
gitgitgadget · Nov 27, 2024 · 45f327b · 45f327b
1 parent 761e62a
commit 45f327b
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Showing 5 changed files with 171 additions and 6 deletions.
diff --git a/Documentation/config/remote.txt b/Documentation/config/remote.txt
@@ -101,6 +101,17 @@ remote.<name>.serverOption::
 	The default set of server options used when fetching from this remote.
 	These server options can be overridden by the `--server-option=` command
 	line arguments.
+
+remote.<name>.followRemoteHEAD::
+	How linkgit:git-fetch[1] should handle updates to `remotes/<name>/HEAD`.
+	The default value is "create", which will create `remotes/<name>/HEAD`
+	if it exists on the remote, but not locally, but will not touch an
+	already existing local reference.  Setting to "warn" will print
+	a message if the remote has a different value, than the local one and
+	in case there is no local reference, it behaves like "create". Setting
+	to "always" will silently update it to the value on the remote.
+	Finally, setting it to "never" will never change or create the local
+	reference.
 +
 This is a multi-valued variable, and an empty value can be used in a higher
 priority configuration file (e.g. `.git/config` in a repository) to clear

diff --git a/builtin/fetch.c b/builtin/fetch.c
@@ -1579,10 +1579,35 @@ static const char *strip_refshead(const char *name){
 	return name;
 }
 
-static int set_head(const struct ref *remote_refs)
+static void report_set_head(const char *remote, const char *head_name,
+			struct strbuf *buf_prev, int updateres) {
+	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' is '%s', but we have '%s' locally.\n",
+			remote, head_name, prev_head);
+		printf("Run 'git remote set-head %s %s' to follow the change.\n",
+			remote, head_name);
+	}
+	else if (updateres && buf_prev->len) {
+		printf("'HEAD' at '%s' is '%s', "
+			"but we have a detached HEAD pointing to '%s' locally.\n",
+			remote, head_name, buf_prev->buf);
+		printf("Run 'git remote set-head %s %s' to follow the change.\n",
+			remote, head_name);
+	}
+	strbuf_release(&buf_prefix);
+}
+
+static int set_head(const struct ref *remote_refs, int follow_remote_head)
 {
-	int result = 0, is_bare;
-	struct strbuf b_head = STRBUF_INIT, b_remote_head = STRBUF_INIT;
+	int result = 0, create_only, is_bare, was_detached;
+	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;
@@ -1603,6 +1628,8 @@ static int set_head(const struct ref *remote_refs)
 		string_list_append(&heads, strip_refshead(ref->name));
 	}
 
+	if (follow_remote_head < 0)
+		goto cleanup;
 
 	if (!heads.nr)
 		result = 1;
@@ -1614,6 +1641,7 @@ static int set_head(const struct ref *remote_refs)
 	if (!head_name)
 		goto cleanup;
 	is_bare = is_bare_repository();
+	create_only = follow_remote_head == 2 ? 0 : !is_bare;
 	if (is_bare) {
 		strbuf_addstr(&b_head, "HEAD");
 		strbuf_addf(&b_remote_head, "refs/heads/%s", head_name);
@@ -1626,16 +1654,22 @@ static int set_head(const struct ref *remote_refs)
 		result = 1;
 		goto cleanup;
 	}
-	if (refs_update_symref_extended(refs, b_head.buf, b_remote_head.buf,
-					"fetch", NULL, !is_bare))
+	was_detached = refs_update_symref_extended(refs, b_head.buf, b_remote_head.buf,
+					"fetch", &b_local_head, create_only);
+	if (was_detached == -1) {
 		result = 1;
+		goto cleanup;
+	}
+	if (follow_remote_head == 1 && verbosity >= 0)
+		report_set_head(remote, head_name, &b_local_head, was_detached);
 
 cleanup:
 	free(head_name);
 	free_refs(fetch_map);
 	free_refs(matches);
 	string_list_clear(&heads, 0);
 	strbuf_release(&b_head);
+	strbuf_release(&b_local_head);
 	strbuf_release(&b_remote_head);
 	return result;
 }
@@ -1855,7 +1889,7 @@ static int do_fetch(struct transport *transport,
 				  "you need to specify exactly one branch with the --set-upstream option"));
 		}
 	}
-	if (set_head(remote_refs))
+	if (set_head(remote_refs, transport->remote->follow_remote_head))
 		;
 		/*
 		 * Way too many cases where this can go wrong

diff --git a/remote.c b/remote.c
@@ -514,6 +514,15 @@ static int handle_config(const char *key, const char *value,
 	} else if (!strcmp(subkey, "serveroption")) {
 		return parse_transport_option(key, value,
 					      &remote->server_options);
+	} else if (!strcmp(subkey, "followremotehead")) {
+		if (!strcmp(value, "never"))
+			remote->follow_remote_head = -1;
+		else if (!strcmp(value, "create"))
+			remote->follow_remote_head = 0;
+		else if (!strcmp(value, "warn"))
+			remote->follow_remote_head = 1;
+		else if (!strcmp(value, "always"))
+			remote->follow_remote_head = 2;
 	}
 	return 0;
 }

diff --git a/remote.h b/remote.h
@@ -107,6 +107,15 @@ struct remote {
 	char *http_proxy_authmethod;
 
 	struct string_list server_options;
+
+	/*
+	 * The setting for whether to update HEAD for the remote.
+	 * -1 never update
+	 * 0 create only (default)
+	 * 1 warn on change
+	 * 2 always update
+	 */
+	int follow_remote_head;
 };
 
 /**

diff --git a/t/t5510-fetch.sh b/t/t5510-fetch.sh
@@ -99,6 +99,108 @@ test_expect_success "fetch test remote HEAD change" '
 	branch=$(git rev-parse refs/remotes/origin/other) &&
 	test "z$head" = "z$branch"'
 
+test_expect_success "fetch test followRemoteHEAD never" '
+	test_when_finished "git config unset remote.origin.followRemoteHEAD" &&
+	(
+		cd "$D" &&
+		cd two &&
+		git update-ref --no-deref -d refs/remotes/origin/HEAD &&
+		git config set remote.origin.followRemoteHEAD "never" &&
+		git fetch &&
+		test_must_fail git rev-parse --verify refs/remotes/origin/HEAD
+	)
+'
+
+test_expect_success "fetch test followRemoteHEAD warn no change" '
+	test_when_finished "git config unset remote.origin.followRemoteHEAD" &&
+	(
+		cd "$D" &&
+		cd two &&
+		git rev-parse --verify refs/remotes/origin/other &&
+		git remote set-head origin other &&
+		git rev-parse --verify refs/remotes/origin/HEAD &&
+		git rev-parse --verify refs/remotes/origin/main &&
+		git config set remote.origin.followRemoteHEAD "warn" &&
+		git fetch >output &&
+		echo "${SQ}HEAD${SQ} at ${SQ}origin${SQ} is ${SQ}main${SQ}," \
+			"but we have ${SQ}other${SQ} locally." >expect &&
+		echo "Run ${SQ}git remote set-head origin main${SQ} to follow the change." >>expect &&
+		test_cmp expect output &&
+		head=$(git rev-parse refs/remotes/origin/HEAD) &&
+		branch=$(git rev-parse refs/remotes/origin/other) &&
+		test "z$head" = "z$branch"
+	)
+'
+
+test_expect_success "fetch test followRemoteHEAD warn create" '
+	test_when_finished "git config unset remote.origin.followRemoteHEAD" &&
+	(
+		cd "$D" &&
+		cd two &&
+		git update-ref --no-deref -d refs/remotes/origin/HEAD &&
+		git config set remote.origin.followRemoteHEAD "warn" &&
+		git rev-parse --verify refs/remotes/origin/main &&
+		output=$(git fetch) &&
+		test "z" = "z$output" &&
+		head=$(git rev-parse refs/remotes/origin/HEAD) &&
+		branch=$(git rev-parse refs/remotes/origin/main) &&
+		test "z$head" = "z$branch"
+	)
+'
+
+test_expect_success "fetch test followRemoteHEAD warn detached" '
+	test_when_finished "git config unset remote.origin.followRemoteHEAD" &&
+	(
+		cd "$D" &&
+		cd two &&
+		git update-ref --no-deref -d refs/remotes/origin/HEAD &&
+		git update-ref refs/remotes/origin/HEAD HEAD &&
+		HEAD=$(git log --pretty="%H") &&
+		git config set remote.origin.followRemoteHEAD "warn" &&
+		git fetch >output &&
+		echo "${SQ}HEAD${SQ} at ${SQ}origin${SQ} is ${SQ}main${SQ}," \
+			"but we have a detached HEAD pointing to" \
+			"${SQ}${HEAD}${SQ} locally." >expect &&
+		echo "Run ${SQ}git remote set-head origin main${SQ} to follow the change." >>expect &&
+		test_cmp expect output
+	)
+'
+
+test_expect_success "fetch test followRemoteHEAD warn quiet" '
+	test_when_finished "git config unset remote.origin.followRemoteHEAD" &&
+	(
+		cd "$D" &&
+		cd two &&
+		git rev-parse --verify refs/remotes/origin/other &&
+		git remote set-head origin other &&
+		git rev-parse --verify refs/remotes/origin/HEAD &&
+		git rev-parse --verify refs/remotes/origin/main &&
+		git config set remote.origin.followRemoteHEAD "warn" &&
+		output=$(git fetch --quiet) &&
+		test "z" = "z$output" &&
+		head=$(git rev-parse refs/remotes/origin/HEAD) &&
+		branch=$(git rev-parse refs/remotes/origin/other) &&
+		test "z$head" = "z$branch"
+	)
+'
+
+test_expect_success "fetch test followRemoteHEAD always" '
+	test_when_finished "git config unset remote.origin.followRemoteHEAD" &&
+	(
+		cd "$D" &&
+		cd two &&
+		git rev-parse --verify refs/remotes/origin/other &&
+		git remote set-head origin other &&
+		git rev-parse --verify refs/remotes/origin/HEAD &&
+		git rev-parse --verify refs/remotes/origin/main &&
+		git config set remote.origin.followRemoteHEAD "always" &&
+		git fetch &&
+		head=$(git rev-parse refs/remotes/origin/HEAD) &&
+		branch=$(git rev-parse refs/remotes/origin/main) &&
+		test "z$head" = "z$branch"
+	)
+'
+
 test_expect_success 'fetch --prune on its own works as expected' '
 	cd "$D" &&
 	git clone . prune &&