checkout: add --fetch to fetch remote before resolving start-point

Add a --fetch option to git checkout and git switch, plus a
checkout.autoFetch config to enable it by default. When set and the
start-point argument names a configured remote (either bare, like
"origin", or prefixed, like "origin/foo"), fetch that remote before
resolving the ref. Aborts the checkout if the fetch fails.

Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>

Author: HaraldNordgren

builtin/checkout.c

@@ -30,7 +30,9 @@
 #include "repo-settings.h"
 #include "resolve-undo.h"
 #include "revision.h"
+#include "run-command.h"
 #include "setup.h"
+#include "strvec.h"
 #include "submodule.h"
 #include "symlinks.h"
 #include "trace2.h"
@@ -61,6 +63,7 @@ struct checkout_opts {
 	int count_checkout_paths;
 	int overlay_mode;
 	int dwim_new_local_branch;
+	int auto_fetch;
 	int discard_changes;
 	int accept_ref;
 	int accept_pathspec;
@@ -112,6 +115,34 @@ struct branch_info {
 	char *checkout;
 };
 
+static void fetch_remote_for_start_point(const char *arg)
+{
+	const char *slash;
+	char *remote_name;
+	struct remote *remote;
+	struct child_process cmd = CHILD_PROCESS_INIT;
+
+	if (!arg || !*arg)
+		return;
+
+	slash = strchr(arg, '/');
+	if (slash == arg)
+		return;
+	remote_name = slash ? xstrndup(arg, slash - arg) : xstrdup(arg);
+
+	remote = remote_get(remote_name);
+	if (!remote || !remote_is_configured(remote, 1)) {
+		free(remote_name);
+		return;
+	}
+
+	strvec_pushl(&cmd.args, "fetch", remote_name, NULL);
+	cmd.git_cmd = 1;
+	free(remote_name);
+	if (run_command(&cmd))
+		die(_("failed to fetch start-point '%s'"), arg);
+}
+
 static void branch_info_release(struct branch_info *info)
 {
 	free(info->name);
@@ -1237,6 +1268,10 @@ static int git_checkout_config(const char *var, const char *value,
 		opts->dwim_new_local_branch = git_config_bool(var, value);
 		return 0;
 	}
+	if (!strcmp(var, "checkout.autofetch")) {
+		opts->auto_fetch = git_config_bool(var, value);
+		return 0;
+	}
 
 	if (starts_with(var, "submodule."))
 		return git_default_submodule_config(var, value, NULL);
@@ -1942,8 +1977,13 @@ static int checkout_main(int argc, const char **argv, const char *prefix,
 			opts->dwim_new_local_branch &&
 			opts->track == BRANCH_TRACK_UNSPECIFIED &&
 			!opts->new_branch;
-		int n = parse_branchname_arg(argc, argv, dwim_ok, which_command,
-					     &new_branch_info, opts, &rev);
+		int n;
+
+		if (opts->auto_fetch)
+			fetch_remote_for_start_point(argv[0]);
+
+		n = parse_branchname_arg(argc, argv, dwim_ok, which_command,
+					 &new_branch_info, opts, &rev);
 		argv += n;
 		argc -= n;
 	} else if (!opts->accept_ref && opts->from_treeish) {
@@ -2052,6 +2092,8 @@ int cmd_checkout(int argc,
 		OPT_BOOL(0, "overlay", &opts.overlay_mode, N_("use overlay mode (default)")),
 		OPT_BOOL(0, "auto-advance", &opts.auto_advance,
 			 N_("auto advance to the next file when selecting hunks interactively")),
+		OPT_BOOL(0, "fetch", &opts.auto_fetch,
+			 N_("fetch from the remote first if <start-point> is a remote-tracking ref")),
 		OPT_END()
 	};
 
@@ -2102,6 +2144,8 @@ int cmd_switch(int argc,
 			 N_("second guess 'git switch <no-such-branch>'")),
 		OPT_BOOL(0, "discard-changes", &opts.discard_changes,
 			 N_("throw away local modifications")),
+		OPT_BOOL(0, "fetch", &opts.auto_fetch,
+			 N_("fetch from the remote first if <start-point> is a remote-tracking ref")),
 		OPT_END()
 	};
 

t/t7201-co.sh

@@ -801,4 +801,55 @@ test_expect_success 'tracking info copied with autoSetupMerge=inherit' '
 	test_cmp_config "" --default "" branch.main2.merge
 '
 
+test_expect_success 'setup upstream for --fetch tests' '
+	git checkout main &&
+	git init fetch_upstream &&
+	test_commit -C fetch_upstream u_main &&
+	git remote add fetch_upstream fetch_upstream &&
+	git fetch fetch_upstream &&
+	git -C fetch_upstream checkout -b fetch_new &&
+	test_commit -C fetch_upstream u_new
+'
+
+test_expect_success 'checkout --fetch -b picks up branch created upstream after clone' '
+	git checkout main &&
+	test_must_fail git rev-parse --verify refs/remotes/fetch_upstream/fetch_new &&
+	git checkout --fetch -b local_new fetch_upstream/fetch_new &&
+	test_cmp_rev refs/remotes/fetch_upstream/fetch_new HEAD
+'
+
+test_expect_success 'checkout --fetch with bare remote name fetches the remote' '
+	git checkout main &&
+	git -C fetch_upstream checkout -b fetch_new2 &&
+	test_commit -C fetch_upstream u_new2 &&
+	test_must_fail git rev-parse --verify refs/remotes/fetch_upstream/fetch_new2 &&
+	git checkout --fetch -b local_from_remote fetch_upstream &&
+	git rev-parse --verify refs/remotes/fetch_upstream/fetch_new2
+'
+
+test_expect_success 'checkout --fetch aborts and does not create branch on fetch failure' '
+	git checkout main &&
+	test_might_fail git branch -D bogus &&
+	test_must_fail git checkout --fetch -b bogus fetch_upstream/does_not_exist &&
+	test_must_fail git rev-parse --verify refs/heads/bogus
+'
+
+test_expect_success 'checkout.autoFetch=true enables fetching without --fetch' '
+	git checkout main &&
+	git -C fetch_upstream checkout -b fetch_cfg &&
+	test_commit -C fetch_upstream u_cfg &&
+	test_must_fail git rev-parse --verify refs/remotes/fetch_upstream/fetch_cfg &&
+	git -c checkout.autoFetch=true checkout -b local_cfg fetch_upstream/fetch_cfg &&
+	test_cmp_rev refs/remotes/fetch_upstream/fetch_cfg HEAD
+'
+
+test_expect_success 'switch --fetch -c picks up branch created upstream after clone' '
+	git checkout main &&
+	git -C fetch_upstream checkout -b fetch_switch &&
+	test_commit -C fetch_upstream u_switch &&
+	test_must_fail git rev-parse --verify refs/remotes/fetch_upstream/fetch_switch &&
+	git switch --fetch -c local_switch fetch_upstream/fetch_switch &&
+	test_cmp_rev refs/remotes/fetch_upstream/fetch_switch HEAD
+'
+
 test_done

t/t9902-completion.sh

@@ -2602,6 +2602,7 @@ test_expect_success 'double dash "git checkout"' '
 	--ignore-other-worktrees Z
 	--recurse-submodules Z
 	--auto-advance Z
+	--fetch Z
 	--progress Z
 	--guess Z
 	--no-guess Z