checkout: disambiguate dwim tracking branches and local files

When checkout dwim is added in [1], it is restricted to only dwim when
certain conditions are met and fall back to default checkout behavior
otherwise. It turns out falling back could be confusing. One of the
conditions to turn

git checkout frotz

to

git checkout -b frotz origin/frotz

is that frotz must not exist as a file. But when the user comes to
expect "git checkout frotz" to create the branch "frotz" and there
happens to be a file named "frotz", git's silently reverting "frotz"
file content is not helping. This is reported in Git mailing list [2]
and even used as an example of "Git is bad" elsewhere [3].

We normally try to do the right thing, but when there are multiple
"right things" to do, it's best to leave it to the user to decide.
Check this case, ask the user to to disambiguate:

- "git checkout -- foo" will check out path "foo"
- "git checkout foo --" will dwim and create branch "foo" [4]

For users who do not want dwim, use --no-guess. It's useless in this
particular case because "git checkout --no-guess foo --" will just
fail. But it could be used by scripts.

[1] 70c9ac2f19 (DWIM "git checkout frotz" to "git checkout -b frotz
origin/frotz" - 2009-10-18)
[2] https://public-inbox.org/git/CACsJy8B2TVr1g+k+eSQ=pBEO3WN4_LtgLo9gpur8X7Z9GOFL_A@mail.gmail.com/
[3] https://news.ycombinator.com/item?id=18230655
[4] a047fafc78 (checkout: allow dwim for branch creation for "git
checkout $branch --" - 2013-10-18)

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/Documentation/git-checkout.txt b/Documentation/git-checkout.txt
index 801de2f7645bf0b1fc506da58d469519abca8863..6acc3d98e7422be7f313b0a203a61565fae212c5 100644 (file)
--- a/Documentation/git-checkout.txt
+++ b/Documentation/git-checkout.txt
@@ -276,6 +276,10 @@ section of linkgit:git-add[1] to learn how to operate the `--patch` mode.
        Just like linkgit:git-submodule[1], this will detach the
        submodules HEAD.
 
+--no-guess::
+       Do not attempt to create a branch if a remote tracking branch
+       of the same name exists.
+
 <branch>::
        Branch to checkout; if it refers to a branch (i.e., a name that,
        when prepended with "refs/heads/", is a valid ref), then that

diff --git a/builtin/checkout.c b/builtin/checkout.c
index acdafc6e4c4d104aadcbe7492a8045e16e83ba50..4744e8c0a72eae901308e5484a1c6f312e7278b9 100644 (file)
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -1079,9 +1079,12 @@ static int parse_branchname_arg(int argc, const char **argv,
                 */
                int recover_with_dwim = dwim_new_local_branch_ok;
 
-               if (!has_dash_dash &&
-                   (check_filename(opts->prefix, arg) || !no_wildcard(arg)))
+               int could_be_checkout_paths = !has_dash_dash &&
+                       check_filename(opts->prefix, arg);
+
+               if (!has_dash_dash && !no_wildcard(arg))
                        recover_with_dwim = 0;
+
                /*
                 * Accept "git checkout foo" and "git checkout foo --"
                 * as candidates for dwim.
@@ -1094,6 +1097,10 @@ static int parse_branchname_arg(int argc, const char **argv,
                        const char *remote = unique_tracking_name(arg, rev,
                                                                  dwim_remotes_matched);
                        if (remote) {
+                               if (could_be_checkout_paths)
+                                       die(_("'%s' could be both a local file and a tracking branch.\n"
+                                             "Please use -- (and optionally --no-guess) to disambiguate"),
+                                           arg);
                                *new_branch = arg;
                                arg = remote;
                                /* DWIMmed to create local branch, case (3).(b) */
@@ -1228,7 +1235,7 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
        struct checkout_opts opts;
        struct branch_info new_branch_info;
        char *conflict_style = NULL;
-       int dwim_new_local_branch = 1;
+       int dwim_new_local_branch, no_dwim_new_local_branch = 0;
        int dwim_remotes_matched = 0;
        struct option options[] = {
                OPT__QUIET(&opts.quiet, N_("suppress progress reporting")),
@@ -1258,8 +1265,8 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
                OPT_BOOL('p', "patch", &opts.patch_mode, N_("select hunks interactively")),
                OPT_BOOL(0, "ignore-skip-worktree-bits", &opts.ignore_skipworktree,
                         N_("do not limit pathspecs to sparse entries only")),
-               OPT_HIDDEN_BOOL(0, "guess", &dwim_new_local_branch,
-                               N_("second guess 'git checkout <no-such-branch>'")),
+               OPT_BOOL(0, "no-guess", &no_dwim_new_local_branch,
+                        N_("do not second guess 'git checkout <no-such-branch>'")),
                OPT_BOOL(0, "ignore-other-worktrees", &opts.ignore_other_worktrees,
                         N_("do not check if another worktree is holding the given ref")),
                { OPTION_CALLBACK, 0, "recurse-submodules", NULL,
@@ -1282,6 +1289,7 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
        argc = parse_options(argc, argv, prefix, options, checkout_usage,
                             PARSE_OPT_KEEP_DASHDASH);
 
+       dwim_new_local_branch = !no_dwim_new_local_branch;
        if (opts.show_progress < 0) {
                if (opts.quiet)
                        opts.show_progress = 0;

diff --git a/t/t2024-checkout-dwim.sh b/t/t2024-checkout-dwim.sh
index 69b6774d10a9d90790316e9feb0f718593465c76..fa0718c730c322bfe5f9e6642c4136a7533be5dc 100755 (executable)
--- a/t/t2024-checkout-dwim.sh
+++ b/t/t2024-checkout-dwim.sh
@@ -278,4 +278,35 @@ test_expect_success 'loosely defined local base branch is reported correctly' '
        test_cmp expect actual
 '
 
+test_expect_success 'reject when arg could be part of dwim branch' '
+       git remote add foo file://non-existent-place &&
+       git update-ref refs/remotes/foo/dwim-arg HEAD &&
+       echo foo >dwim-arg &&
+       git add dwim-arg &&
+       echo bar >dwim-arg &&
+       test_must_fail git checkout dwim-arg &&
+       test_must_fail git rev-parse refs/heads/dwim-arg -- &&
+       grep bar dwim-arg
+'
+
+test_expect_success 'disambiguate dwim branch and checkout path (1)' '
+       git update-ref refs/remotes/foo/dwim-arg1 HEAD &&
+       echo foo >dwim-arg1 &&
+       git add dwim-arg1 &&
+       echo bar >dwim-arg1 &&
+       git checkout -- dwim-arg1 &&
+       test_must_fail git rev-parse refs/heads/dwim-arg1 -- &&
+       grep foo dwim-arg1
+'
+
+test_expect_success 'disambiguate dwim branch and checkout path (2)' '
+       git update-ref refs/remotes/foo/dwim-arg2 HEAD &&
+       echo foo >dwim-arg2 &&
+       git add dwim-arg2 &&
+       echo bar >dwim-arg2 &&
+       git checkout dwim-arg2 -- &&
+       git rev-parse refs/heads/dwim-arg2 -- &&
+       grep bar dwim-arg2
+'
+
 test_done

diff --git a/t/t9902-completion.sh b/t/t9902-completion.sh
index 175f83d7042a0fb9f093bc6f25e1d0b25ce548af..aa92f8523000ffe177aecb6477752de639d2e6d3 100755 (executable)
--- a/t/t9902-completion.sh
+++ b/t/t9902-completion.sh
@@ -1434,7 +1434,8 @@ test_expect_success 'double dash "git checkout"' '
        --ignore-other-worktrees Z
        --recurse-submodules Z
        --progress Z
-       --no-quiet Z
+       --guess Z
+       --no-guess Z
        --no-... Z
        EOF
 '