Merge branch 'bf/fetch-set-head-config'

"git fetch" honors "remote.<remote>.followRemoteHEAD" settings to
tweak the remote-tracking HEAD in "refs/remotes/<remote>/HEAD".

* bf/fetch-set-head-config:
  remote set-head: set followRemoteHEAD to "warn" if "always"
  fetch set_head: add warn-if-not-$branch option
  fetch set_head: move warn advice into advise_if_enabled
  fetch: add configuration for set_head behaviour

9 files changed, 258 insertions, 7 deletions

diff --git a/Documentation/config/remote.txt b/Documentation/config/remote.txt
index 6d8b7d6c63..4118c219c1 100644
--- a/Documentation/config/remote.txt
+++ b/Documentation/config/remote.txt
@@ -101,6 +101,19 @@ 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".
+	A variant on "warn" is "warn-if-not-$branch", which behaves like
+	"warn", but if `HEAD` on the remote is `$branch` it will be silent.
+	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/advice.c b/advice.c
index f7a5130c2c..e3dd8b468c 100644
--- a/advice.c
+++ b/advice.c
@@ -53,6 +53,7 @@ static struct {
 	[ADVICE_COMMIT_BEFORE_MERGE]			= { "commitBeforeMerge" },
 	[ADVICE_DETACHED_HEAD]				= { "detachedHead" },
 	[ADVICE_DIVERGING]				= { "diverging" },
+	[ADVICE_FETCH_SET_HEAD_WARN]			= { "fetchRemoteHEADWarn" },
 	[ADVICE_FETCH_SHOW_FORCED_UPDATES]		= { "fetchShowForcedUpdates" },
 	[ADVICE_FORCE_DELETE_BRANCH]			= { "forceDeleteBranch" },
 	[ADVICE_GRAFT_FILE_DEPRECATED]			= { "graftFileDeprecated" },
diff --git a/advice.h b/advice.h
index d7466bc0ef..cf2284ec43 100644
--- a/advice.h
+++ b/advice.h
@@ -20,6 +20,7 @@ enum advice_type {
 	ADVICE_COMMIT_BEFORE_MERGE,
 	ADVICE_DETACHED_HEAD,
 	ADVICE_DIVERGING,
+	ADVICE_FETCH_SET_HEAD_WARN,
 	ADVICE_FETCH_SHOW_FORCED_UPDATES,
 	ADVICE_FORCE_DELETE_BRANCH,
 	ADVICE_GRAFT_FILE_DEPRECATED,
diff --git a/builtin/fetch.c b/builtin/fetch.c
index f5eb2cf338..872ad49834 100644
--- a/builtin/fetch.c
+++ b/builtin/fetch.c
@@ -1579,10 +1579,47 @@ static const char *strip_refshead(const char *name){
 	return name;
 }
 
-static int set_head(const struct ref *remote_refs)
+static void set_head_advice_msg(const char *remote, const char *head_name)
 {
-	int result = 0, is_bare;
-	struct strbuf b_head = STRBUF_INIT, b_remote_head = STRBUF_INIT;
+	const char message_advice_set_head[] =
+	N_("Run 'git remote set-head %s %s' to follow the change, or set\n"
+	   "'remote.%s.followRemoteHEAD' configuration option to a different value\n"
+	   "if you do not want to see this message. Specifically running\n"
+	   "'git config set remote.%s.followRemoteHEAD %s' will disable the warning\n"
+	   "until the remote changes HEAD to something else.");
+
+	advise_if_enabled(ADVICE_FETCH_SET_HEAD_WARN, _(message_advice_set_head),
+			remote, head_name, remote, remote, head_name);
+}
+
+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);
+		set_head_advice_msg(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);
+		set_head_advice_msg(remote, head_name);
+	}
+	strbuf_release(&buf_prefix);
+}
+
+static int set_head(const struct ref *remote_refs, int follow_remote_head,
+		const char *no_warn_branch)
+{
+	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 +1640,8 @@ static int set_head(const struct ref *remote_refs)
 		string_list_append(&heads, strip_refshead(ref->name));
 	}
 
+	if (follow_remote_head == FOLLOW_REMOTE_NEVER)
+		goto cleanup;
 
 	if (!heads.nr)
 		result = 1;
@@ -1614,6 +1653,7 @@ static int set_head(const struct ref *remote_refs)
 	if (!head_name)
 		goto cleanup;
 	is_bare = is_bare_repository();
+	create_only = follow_remote_head == FOLLOW_REMOTE_ALWAYS ? 0 : !is_bare;
 	if (is_bare) {
 		strbuf_addstr(&b_head, "HEAD");
 		strbuf_addf(&b_remote_head, "refs/heads/%s", head_name);
@@ -1626,9 +1666,16 @@ 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 (verbosity >= 0 &&
+		follow_remote_head == FOLLOW_REMOTE_WARN &&
+		(!no_warn_branch || strcmp(no_warn_branch, head_name)))
+		report_set_head(remote, head_name, &b_local_head, was_detached);
 
 cleanup:
 	free(head_name);
@@ -1636,6 +1683,7 @@ cleanup:
 	free_refs(matches);
 	string_list_clear(&heads, 0);
 	strbuf_release(&b_head);
+	strbuf_release(&b_local_head);
 	strbuf_release(&b_remote_head);
 	return result;
 }
@@ -1873,7 +1921,8 @@ 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,
+		transport->remote->no_warn_branch))
 		;
 		/*
 		 * Way too many cases where this can go wrong
diff --git a/builtin/remote.c b/builtin/remote.c
index d5b81445f2..32d02ca4a0 100644
--- a/builtin/remote.c
+++ b/builtin/remote.c
@@ -1438,6 +1438,7 @@ static int set_head(int argc, const char **argv, const char *prefix,
 		b_local_head = STRBUF_INIT;
 	char *head_name = NULL;
 	struct ref_store *refs = get_main_ref_store(the_repository);
+	struct remote *remote;
 
 	struct option options[] = {
 		OPT_BOOL('a', "auto", &opt_a,
@@ -1448,8 +1449,10 @@ static int set_head(int argc, const char **argv, const char *prefix,
 	};
 	argc = parse_options(argc, argv, prefix, options,
 			     builtin_remote_sethead_usage, 0);
-	if (argc)
+	if (argc) {
 		strbuf_addf(&b_head, "refs/remotes/%s/HEAD", argv[0]);
+		remote = remote_get(argv[0]);
+	}
 
 	if (!opt_a && !opt_d && argc == 2) {
 		head_name = xstrdup(argv[1]);
@@ -1488,6 +1491,13 @@ static int set_head(int argc, const char **argv, const char *prefix,
 	}
 	if (opt_a)
 		report_set_head_auto(argv[0], head_name, &b_local_head, was_detached);
+	if (remote->follow_remote_head == FOLLOW_REMOTE_ALWAYS) {
+		struct strbuf config_name = STRBUF_INIT;
+		strbuf_addf(&config_name,
+			"remote.%s.followremotehead", remote->name);
+		git_config_set(config_name.buf, "warn");
+		strbuf_release(&config_name);
+	}
 
 cleanup:
 	free(head_name);
diff --git a/remote.c b/remote.c
index 10104d11e3..4ec5d3f47b 100644
--- a/remote.c
+++ b/remote.c
@@ -514,6 +514,24 @@ 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")) {
+		const char *no_warn_branch;
+		if (!strcmp(value, "never"))
+			remote->follow_remote_head = FOLLOW_REMOTE_NEVER;
+		else if (!strcmp(value, "create"))
+			remote->follow_remote_head = FOLLOW_REMOTE_CREATE;
+		else if (!strcmp(value, "warn")) {
+			remote->follow_remote_head = FOLLOW_REMOTE_WARN;
+			remote->no_warn_branch = NULL;
+		} else if (skip_prefix(value, "warn-if-not-", &no_warn_branch)) {
+			remote->follow_remote_head = FOLLOW_REMOTE_WARN;
+			remote->no_warn_branch = no_warn_branch;
+		} else if (!strcmp(value, "always")) {
+			remote->follow_remote_head = FOLLOW_REMOTE_ALWAYS;
+		} else {
+			warning(_("unrecognized followRemoteHEAD value '%s' ignored"),
+				value);
+		}
 	}
 	return 0;
 }
diff --git a/remote.h b/remote.h
index a7e5c4e07c..bda10dd5c8 100644
--- a/remote.h
+++ b/remote.h
@@ -59,6 +59,13 @@ struct remote_state {
 void remote_state_clear(struct remote_state *remote_state);
 struct remote_state *remote_state_new(void);
 
+	enum follow_remote_head_settings {
+		FOLLOW_REMOTE_NEVER = -1,
+		FOLLOW_REMOTE_CREATE = 0,
+		FOLLOW_REMOTE_WARN = 1,
+		FOLLOW_REMOTE_ALWAYS = 2,
+	};
+
 struct remote {
 	struct hashmap_entry ent;
 
@@ -107,6 +114,9 @@ struct remote {
 	char *http_proxy_authmethod;
 
 	struct string_list server_options;
+
+	enum follow_remote_head_settings follow_remote_head;
+	const char *no_warn_branch;
 };
 
 /**
diff --git a/t/t5505-remote.sh b/t/t5505-remote.sh
index 7411aa770d..519f7973e3 100755
--- a/t/t5505-remote.sh
+++ b/t/t5505-remote.sh
@@ -504,6 +504,17 @@ test_expect_success 'set-head --auto has no problem w/multiple HEADs' '
 	)
 '
 
+test_expect_success 'set-head changes followRemoteHEAD always to warn' '
+	(
+		cd test &&
+		git config set remote.origin.followRemoteHEAD "always" &&
+		git remote set-head --auto origin &&
+		git config get remote.origin.followRemoteHEAD >actual &&
+		echo "warn" >expect &&
+		test_cmp expect actual
+	)
+'
+
 cat >test/expect <<\EOF
 refs/remotes/origin/side2
 EOF
diff --git a/t/t5510-fetch.sh b/t/t5510-fetch.sh
index f94855ab43..2d9587059f 100755
--- a/t/t5510-fetch.sh
+++ b/t/t5510-fetch.sh
@@ -98,6 +98,144 @@ 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 &&
+		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}${SQ} locally." >expect &&
+		test_cmp expect output
+	)
+'
+
+test_expect_success "fetch test followRemoteHEAD warn quiet" '
+	test_when_finished "git config unset remote.origin.followRemoteHEAD" &&
+	(
+		cd "$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 warn-if-not-branch branch is same" '
+	test_when_finished "git config unset remote.origin.followRemoteHEAD" &&
+	(
+		cd "$D" &&
+		cd two &&
+		git rev-parse --verify refs/remotes/origin/other &&
+		git remote set-head origin other &&
+		git rev-parse --verify refs/remotes/origin/HEAD &&
+		git rev-parse --verify refs/remotes/origin/main &&
+		git config set remote.origin.followRemoteHEAD "warn-if-not-main" &&
+		actual=$(git fetch) &&
+		test "z" = "z$actual" &&
+		head=$(git rev-parse refs/remotes/origin/HEAD) &&
+		branch=$(git rev-parse refs/remotes/origin/other) &&
+		test "z$head" = "z$branch"
+	)
+'
+
+test_expect_success "fetch test followRemoteHEAD warn-if-not-branch branch is different" '
+	test_when_finished "git config unset remote.origin.followRemoteHEAD" &&
+	(
+		cd "$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-if-not-some/different-branch" &&
+		git fetch >actual &&
+		echo "${SQ}HEAD${SQ} at ${SQ}origin${SQ} is ${SQ}main${SQ}," \
+			"but we have ${SQ}other${SQ} locally." >expect &&
+		test_cmp expect actual &&
+		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 &&