branch: support for shortcuts like @{-1}, completed

branch command with options "edit-description", "set-upstream-to" and
"unset-upstream" expects a branch name.  Since ae5a6c3684 (checkout:
implement "@{-N}" shortcut name for N-th last branch, 2009-01-17) a
branch can be specified using shortcuts like @{-1}.  Those shortcuts
need to be resolved when considering the arguments.

We can modify the description of the previously checked out branch with:

$ git branch --edit--description @{-1}

We can modify the upstream of the previously checked out branch with:

$ git branch --set-upstream-to upstream @{-1}
$ git branch --unset-upstream @{-1}

Signed-off-by: Rubén Justo <rjusto@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/branch.c

@@ -791,31 +791,33 @@ int cmd_branch(int argc, const char **argv, const char *prefix)
 	} else if (edit_description) {
 		const char *branch_name;
 		struct strbuf branch_ref = STRBUF_INIT;
+		struct strbuf buf = STRBUF_INIT;
+		int ret = 1; /* assume failure */
 
 		if (!argc) {
 			if (filter.detached)
 				die(_("Cannot give description to detached HEAD"));
 			branch_name = head;
-		} else if (argc == 1)
-			branch_name = argv[0];
-		else
+		} else if (argc == 1) {
+			strbuf_branchname(&buf, argv[0], INTERPRET_BRANCH_LOCAL);
+			branch_name = buf.buf;
+		} else {
 			die(_("cannot edit description of more than one branch"));
+		}
 
 		strbuf_addf(&branch_ref, "refs/heads/%s", branch_name);
-		if (!ref_exists(branch_ref.buf)) {
-			strbuf_release(&branch_ref);
-
-			if (!argc)
-				return error(_("No commit on branch '%s' yet."),
-					     branch_name);
-			else
-				return error(_("No branch named '%s'."),
-					     branch_name);
-		}
+		if (!ref_exists(branch_ref.buf))
+			ret = error(!argc
+			      ? _("No commit on branch '%s' yet.")
+			      : _("No branch named '%s'."),
+			      branch_name);
+		else if (!edit_branch_description(branch_name))
+			ret = 0; /* happy */
+
 		strbuf_release(&branch_ref);
+		strbuf_release(&buf);
 
-		if (edit_branch_description(branch_name))
-			return 1;
+		return ret;
 	} else if (copy) {
 		if (!argc)
 			die(_("branch name required"));
@@ -835,9 +837,15 @@ int cmd_branch(int argc, const char **argv, const char *prefix)
 		else
 			die(_("too many arguments for a rename operation"));
 	} else if (new_upstream) {
-		struct branch *branch = branch_get(argv[0]);
+		struct branch *branch;
+		struct strbuf buf = STRBUF_INIT;
 
-		if (argc > 1)
+		if (!argc)
+			branch = branch_get(NULL);
+		else if (argc == 1) {
+			strbuf_branchname(&buf, argv[0], INTERPRET_BRANCH_LOCAL);
+			branch = branch_get(buf.buf);
+		} else
 			die(_("too many arguments to set new upstream"));
 
 		if (!branch) {
@@ -854,11 +862,17 @@ int cmd_branch(int argc, const char **argv, const char *prefix)
 		dwim_and_setup_tracking(the_repository, branch->name,
 					new_upstream, BRANCH_TRACK_OVERRIDE,
 					quiet);
+		strbuf_release(&buf);
 	} else if (unset_upstream) {
-		struct branch *branch = branch_get(argv[0]);
+		struct branch *branch;
 		struct strbuf buf = STRBUF_INIT;
 
-		if (argc > 1)
+		if (!argc)
+			branch = branch_get(NULL);
+		else if (argc == 1) {
+			strbuf_branchname(&buf, argv[0], INTERPRET_BRANCH_LOCAL);
+			branch = branch_get(buf.buf);
+		} else
 			die(_("too many arguments to unset upstream"));
 
 		if (!branch) {
@@ -871,6 +885,7 @@ int cmd_branch(int argc, const char **argv, const char *prefix)
 		if (!branch_has_merge_config(branch))
 			die(_("Branch '%s' has no upstream information"), branch->name);
 
+		strbuf_reset(&buf);
 		strbuf_addf(&buf, "branch.%s.remote", branch->name);
 		git_config_set_multivar(buf.buf, NULL, NULL, CONFIG_FLAGS_MULTI_REPLACE);
 		strbuf_reset(&buf);

t/t3204-branch-name-interpretation.sh

@@ -133,4 +133,28 @@ test_expect_success 'checkout does not treat remote @{upstream} as a branch' '
 	expect_branch HEAD one
 '
 
+test_expect_success 'edit-description via @{-1}' '
+	git checkout -b desc-branch &&
+	git checkout -b non-desc-branch &&
+	write_script editor <<-\EOF &&
+		echo "Branch description" >"$1"
+	EOF
+	EDITOR=./editor git branch --edit-description @{-1} &&
+	test_must_fail git config branch.non-desc-branch.description &&
+	git config branch.desc-branch.description >actual &&
+	printf "Branch description\n\n" >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success 'modify branch upstream via "@{-1}" and "@{-1}@{upstream}"' '
+	git checkout -b upstream-branch &&
+	git checkout -b upstream-other -t upstream-branch &&
+	git branch --set-upstream-to upstream-other @{-1} &&
+	git config branch.upstream-branch.merge >actual &&
+	echo "refs/heads/upstream-other" >expect &&
+	test_cmp expect actual &&
+	git branch --unset-upstream @{-1}@{upstream} &&
+	test_must_fail git config branch.upstream-other.merge
+'
+
 test_done