checkout: don't revert file on ambiguous tracking branches

For easier understanding, here are the existing good scenarios:

  1) Have *no* file 'foo', *no* local branch 'foo' and a *single*
     remote branch 'foo'
  2) `git checkout foo` will create local branch foo, see [1]

  and

  1) Have *a* file 'foo', *no* local branch 'foo' and a *single*
     remote branch 'foo'
  2) `git checkout foo` will complain, see [3]

This patch prevents the following scenario:

  1) Have *a* file 'foo', *no* local branch 'foo' and *multiple*
     remote branches 'foo'
  2) `git checkout foo` will successfully... revert contents of
     file `foo`!

That is, adding another remote suddenly changes behavior significantly,
which is a surprise at best and could go unnoticed by user at worst.
Please see [3] which gives some real world complaints.

To my understanding, fix in [3] overlooked the case of multiple remotes,
and the whole behavior of falling back to reverting file was never
intended:

  [1] introduces the unexpected behavior. Before, there was fallback
  from not-a-ref to pathspec. This is reasonable fallback. After, there
  is another fallback from ambiguous-remote to pathspec. I understand
  that it was a copy&paste oversight.

  [2] noticed the unexpected behavior but chose to semi-document it
  instead of forbidding, because the goal of the patch series was
  focused on something else.

  [3] adds `die()` when there is ambiguity between branch and file. The
  case of multiple tracking branches is seemingly overlooked.

The new behavior: if there is no local branch and multiple remote
candidates, just die() and don't try reverting file whether it
exists (prevents surprise) or not (improves error message).

[1] Commit 70c9ac2f ("DWIM "git checkout frotz" to "git checkout -b frotz origin/frotz"" 2009-10-18)
    https://public-inbox.org/git/7vaazpxha4.fsf_-_@alter.siamese.dyndns.org/
[2] Commit ad8d5104 ("checkout: add advice for ambiguous "checkout <branch>"", 2018-06-05)
    https://public-inbox.org/git/20180502105452.17583-1-avarab@gmail.com/
[3] Commit be4908f1 ("checkout: disambiguate dwim tracking branches and local files", 2018-11-13)
    https://public-inbox.org/git/20181110120707.25846-1-pclouds@gmail.com/

Signed-off-by: Alexandr Miloslavskiy <alexandr.miloslavskiy@syntevo.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/builtin/checkout.c b/builtin/checkout.c
index 11fe4fa7e7e0e9b401a21d48e654b17c8884fb72..01c6790dab0a1dd9320825527374039aeb3bed9b 100644 (file)
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -1115,10 +1115,10 @@ static void setup_new_branch_info_and_source_tree(
 
 static const char *parse_remote_branch(const char *arg,
                                       struct object_id *rev,
-                                      int could_be_checkout_paths,
-                                      int *dwim_remotes_matched)
+                                      int could_be_checkout_paths)
 {
-       const char *remote = unique_tracking_name(arg, rev, dwim_remotes_matched);
+       int num_matches = 0;
+       const char *remote = unique_tracking_name(arg, rev, &num_matches);
 
        if (remote && could_be_checkout_paths) {
                die(_("'%s' could be both a local file and a tracking branch.\n"
@@ -1126,6 +1126,22 @@ static const char *parse_remote_branch(const char *arg,
                    arg);
        }
 
+       if (!remote && num_matches > 1) {
+           if (advice_checkout_ambiguous_remote_branch_name) {
+                   advise(_("If you meant to check out a remote tracking branch on, e.g. 'origin',\n"
+                            "you can do so by fully qualifying the name with the --track option:\n"
+                            "\n"
+                            "    git checkout --track origin/<name>\n"
+                            "\n"
+                            "If you'd like to always have checkouts of an ambiguous <name> prefer\n"
+                            "one remote, e.g. the 'origin' remote, consider setting\n"
+                            "checkout.defaultRemote=origin in your config."));
+           }
+
+           die(_("'%s' matched multiple (%d) remote tracking branches"),
+               arg, num_matches);
+       }
+
        return remote;
 }
 
@@ -1133,8 +1149,7 @@ static int parse_branchname_arg(int argc, const char **argv,
                                int dwim_new_local_branch_ok,
                                struct branch_info *new_branch_info,
                                struct checkout_opts *opts,
-                               struct object_id *rev,
-                               int *dwim_remotes_matched)
+                               struct object_id *rev)
 {
        const char **new_branch = &opts->new_branch;
        int argcount = 0;
@@ -1240,8 +1255,7 @@ static int parse_branchname_arg(int argc, const char **argv,
 
                if (recover_with_dwim) {
                        const char *remote = parse_remote_branch(arg, rev,
-                                                                could_be_checkout_paths,
-                                                                dwim_remotes_matched);
+                                                                could_be_checkout_paths);
                        if (remote) {
                                *new_branch = arg;
                                arg = remote;
@@ -1505,7 +1519,6 @@ static int checkout_main(int argc, const char **argv, const char *prefix,
                         const char * const usagestr[])
 {
        struct branch_info new_branch_info;
-       int dwim_remotes_matched = 0;
        int parseopt_flags = 0;
 
        memset(&new_branch_info, 0, sizeof(new_branch_info));
@@ -1613,8 +1626,7 @@ static int checkout_main(int argc, const char **argv, const char *prefix,
                        opts->track == BRANCH_TRACK_UNSPECIFIED &&
                        !opts->new_branch;
                int n = parse_branchname_arg(argc, argv, dwim_ok,
-                                            &new_branch_info, opts, &rev,
-                                            &dwim_remotes_matched);
+                                            &new_branch_info, opts, &rev);
                argv += n;
                argc -= n;
        } else if (!opts->accept_ref && opts->from_treeish) {
@@ -1672,28 +1684,10 @@ static int checkout_main(int argc, const char **argv, const char *prefix,
        }
 
        UNLEAK(opts);
-       if (opts->patch_mode || opts->pathspec.nr) {
-               int ret = checkout_paths(opts, new_branch_info.name);
-               if (ret && dwim_remotes_matched > 1 &&
-                   advice_checkout_ambiguous_remote_branch_name)
-                       advise(_("'%s' matched more than one remote tracking branch.\n"
-                                "We found %d remotes with a reference that matched. So we fell back\n"
-                                "on trying to resolve the argument as a path, but failed there too!\n"
-                                "\n"
-                                "If you meant to check out a remote tracking branch on, e.g. 'origin',\n"
-                                "you can do so by fully qualifying the name with the --track option:\n"
-                                "\n"
-                                "    git checkout --track origin/<name>\n"
-                                "\n"
-                                "If you'd like to always have checkouts of an ambiguous <name> prefer\n"
-                                "one remote, e.g. the 'origin' remote, consider setting\n"
-                                "checkout.defaultRemote=origin in your config."),
-                              argv[0],
-                              dwim_remotes_matched);
-               return ret;
-       } else {
+       if (opts->patch_mode || opts->pathspec.nr)
+               return checkout_paths(opts, new_branch_info.name);
+       else
                return checkout_branch(opts, &new_branch_info);
-       }
 }
 
 int cmd_checkout(int argc, const char **argv, const char *prefix)

diff --git a/t/t2024-checkout-dwim.sh b/t/t2024-checkout-dwim.sh
index fa0718c730c322bfe5f9e6642c4136a7533be5dc..accfa9aa4bd82a5f13d3ce5e3755f33f47b38e3e 100755 (executable)
--- a/t/t2024-checkout-dwim.sh
+++ b/t/t2024-checkout-dwim.sh
@@ -37,7 +37,9 @@ test_expect_success 'setup' '
                git checkout -b foo &&
                test_commit a_foo &&
                git checkout -b bar &&
-               test_commit a_bar
+               test_commit a_bar &&
+               git checkout -b ambiguous_branch_and_file &&
+               test_commit a_ambiguous_branch_and_file
        ) &&
        git init repo_b &&
        (
@@ -46,7 +48,9 @@ test_expect_success 'setup' '
                git checkout -b foo &&
                test_commit b_foo &&
                git checkout -b baz &&
-               test_commit b_baz
+               test_commit b_baz &&
+               git checkout -b ambiguous_branch_and_file &&
+               test_commit b_ambiguous_branch_and_file
        ) &&
        git remote add repo_a repo_a &&
        git remote add repo_b repo_b &&
@@ -75,6 +79,26 @@ test_expect_success 'checkout of branch from multiple remotes fails #1' '
        test_branch master
 '
 
+test_expect_success 'when arg matches multiple remotes, do not fallback to interpreting as pathspec' '
+       # create a file with name matching remote branch name
+       git checkout -b t_ambiguous_branch_and_file &&
+       >ambiguous_branch_and_file &&
+       git add ambiguous_branch_and_file &&
+       git commit -m "ambiguous_branch_and_file" &&
+
+       # modify file to verify that it will not be touched by checkout
+       test_when_finished "git checkout -- ambiguous_branch_and_file" &&
+       echo "file contents" >ambiguous_branch_and_file &&
+       cp ambiguous_branch_and_file expect &&
+
+       test_must_fail git checkout ambiguous_branch_and_file 2>err &&
+
+       test_i18ngrep "matched multiple (2) remote tracking branches" err &&
+
+       # file must not be altered
+       test_cmp expect ambiguous_branch_and_file
+'
+
 test_expect_success 'checkout of branch from multiple remotes fails with advice' '
        git checkout -B master &&
        test_might_fail git branch -D foo &&