completion: add tests showing subpar switch/checkout --orphan logic

Similar to -c/-C, --orphan takes an argument which is the branch name to
use. We ought to complete this branch name using similar rules as to how
we complete new branch names for -c/-C and -b/-B. Namely, limit the
total number of options provided by completing to the local branches.

Additionally, git switch --orphan does not take any start point and will
always create using the empty-tree. Thus, after the branch name is
completed, git switch --orphan should not complete any references.

Add test cases showing the expected behavior of --orphan, for both the
argument and starting point.

Signed-off-by: Jacob Keller <jacob.keller@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t9902-completion.sh

@@ -1688,6 +1688,45 @@ test_expect_failure 'git checkout - for -B with --no-track, complete local branc
 	EOF
 '
 
+#TODO: --orphan argument completion should not include all references
+test_expect_failure 'git switch - with --orphan completes local branch names and unique remote branch names' '
+	test_completion "git switch --orphan " <<-\EOF
+	branch-in-other Z
+	master Z
+	master-in-other Z
+	matching-branch Z
+	EOF
+'
+
+#TODO: switch --orphan does not take a start-point and thus has nothing to complete
+test_expect_failure 'git switch - --orphan with branch already provided completes nothing else' '
+	test_completion "git switch --orphan master " <<-\EOF
+
+	EOF
+'
+
+#TODO: --orphan argument completion should not include all references
+test_expect_failure 'git checkout - with --orphan completes local branch names and unique remote branch names' '
+	test_completion "git checkout --orphan " <<-\EOF
+	branch-in-other Z
+	master Z
+	master-in-other Z
+	matching-branch Z
+	EOF
+'
+
+#TODO: checkout --orphan start-point completion should not included DWIM remote unique branch names
+test_expect_failure 'git checkout - --orphan with branch already provided completes local refs for a start-point' '
+	test_completion "git checkout --orphan master " <<-\EOF
+	HEAD Z
+	master Z
+	matching-branch Z
+	matching-tag Z
+	other/branch-in-other Z
+	other/master-in-other Z
+	EOF
+'
+
 test_expect_success 'teardown after ref completion' '
 	git branch -d matching-branch &&
 	git tag -d matching-tag &&