Merge branch 'jc/branch-desc-typoavoidance' into maint

* jc/branch-desc-typoavoidance:
  branch --edit-description: protect against mistyped branch name
  tests: add write_script helper function

builtin/branch.c

@@ -768,6 +768,8 @@ int cmd_branch(int argc, const char **argv, const char *prefix)
 				      with_commit, argv);
 	else if (edit_description) {
 		const char *branch_name;
+		struct strbuf branch_ref = STRBUF_INIT;
+
 		if (detached)
 			die("Cannot give description to detached HEAD");
 		if (!argc)
@@ -776,6 +778,19 @@ int cmd_branch(int argc, const char **argv, const char *prefix)
 			branch_name = argv[0];
 		else
 			usage_with_options(builtin_branch_usage, options);
+
+		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 such branch '%s'.", branch_name);
+		}
+		strbuf_release(&branch_ref);
+
 		if (edit_branch_description(branch_name))
 			return 1;
 	} else if (rename) {

t/t3200-branch.sh

@@ -3,11 +3,8 @@
 # Copyright (c) 2005 Amos Waterland
 #
 
-test_description='git branch --foo should not create bogus branch
+test_description='git branch assorted tests'
 
-This test runs git branch --help and checks that the argument is properly
-handled.  Specifically, that a bogus branch is not created.
-'
 . ./test-lib.sh
 
 test_expect_success \
@@ -620,4 +617,40 @@ test_expect_success 'use set-upstream on the current branch' '
 
 '
 
+test_expect_success 'use --edit-description' '
+	write_script editor <<-\EOF &&
+		echo "New contents" >"$1"
+	EOF
+	EDITOR=./editor git branch --edit-description &&
+		write_script editor <<-\EOF &&
+		git stripspace -s <"$1" >"EDITOR_OUTPUT"
+	EOF
+	EDITOR=./editor git branch --edit-description &&
+	echo "New contents" >expect &&
+	test_cmp EDITOR_OUTPUT expect
+'
+
+test_expect_success 'detect typo in branch name when using --edit-description' '
+	write_script editor <<-\EOF &&
+		echo "New contents" >"$1"
+	EOF
+	(
+		EDITOR=./editor &&
+		export EDITOR &&
+		test_must_fail git branch --edit-description no-such-branch
+	)
+'
+
+test_expect_success 'refuse --edit-description on unborn branch for now' '
+	write_script editor <<-\EOF &&
+		echo "New contents" >"$1"
+	EOF
+	git checkout --orphan unborn &&
+	(
+		EDITOR=./editor &&
+		export EDITOR &&
+		test_must_fail git branch --edit-description
+	)
+'
+
 test_done

t/test-lib.sh

@@ -381,11 +381,20 @@ test_config () {
 	git config "$@"
 }
 
+
 test_config_global () {
 	test_when_finished "test_unconfig --global '$1'" &&
 	git config --global "$@"
 }
 
+write_script () {
+	{
+		echo "#!${2-"$SHELL_PATH"}" &&
+		cat
+	} >"$1" &&
+	chmod +x "$1"
+}
+
 # Use test_set_prereq to tell that a particular prerequisite is available.
 # The prerequisite can later be checked for in two ways:
 #