Re: [PATCH] checkout: add --fetch to fetch remote before resolving start-point

> From: Harald Nordgren <haraldnordgren@gmail.com>
> 
> 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>
> ---
>      checkout: add --fetch to fetch remote before resolving start-point
>      
>      A workflow I run several times a day looks like:
>      
>      git fetch origin
>      git checkout -b new_branch origin/some-branch
>      
>      
>      The first command exists purely to make the second one see an up-to-date
>      view of the remote. If I forget it, origin/some-branch points at a stale
>      commit, and I end up creating a local branch from the wrong starting
>      point.
>      
>      This series teaches git checkout (and git switch) a new --fetch flag
>      that folds the two steps into one:
>      
>      git checkout --fetch -b new_branch origin/some-branch
>      
>      
>      When the start-point argument names a configured remote — either bare
>      (origin, which resolves to the remote's default branch) or in / form —
>      git fetch is run before the start-point is resolved. If the fetch fails,
>      the checkout aborts and no local branch is created.
>      
>      A new checkout.autoFetch config option enables the same behavior by
>      default, for users who always want it.
> 
> Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-2281%2FHaraldNordgren%2Fcheckout-fetch-start-point-v1
> Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-2281/HaraldNordgren/checkout-fetch-start-point-v1
> Pull-Request: https://github.com/git/git/pull/2281
> 
>   builtin/checkout.c    | 48 ++++++++++++++++++++++++++++++++++++++--
>   t/t7201-co.sh         | 51 +++++++++++++++++++++++++++++++++++++++++++
>   t/t9902-completion.sh |  1 +
>   3 files changed, 98 insertions(+), 2 deletions(-)
> 
> diff --git a/builtin/checkout.c b/builtin/checkout.c
> index e031e61886..c8fbc4923b 100644
> --- a/builtin/checkout.c
> +++ b/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()
>   	};
>   
> diff --git a/t/t7201-co.sh b/t/t7201-co.sh
> index 9bcf7c0b40..60ddebd9c3 100755
> --- a/t/t7201-co.sh
> +++ b/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
> diff --git a/t/t9902-completion.sh b/t/t9902-completion.sh
> index 2f9a597ec7..dc1d63669f 100755
> --- a/t/t9902-completion.sh
> +++ b/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
> 
> base-commit: 94f057755b7941b321fd11fec1b2e3ca5313a4e0