completion: improve handling of --orphan option of switch/checkout

The --orphan option is used to create a local branch which is detached
from the current history. In git switch, it always resets to the empty
tree, and thus the only completion we can provide is a branch name.
Follow the same rules for -c/-C (and -b/-B) when completing the argument
to --orphan.

In the case of git switch, after we complete the argument, there is
nothing more we can complete for git switch, so do not even try. Nothing
else would be valid.

In the case of git checkout, --orphan takes a start point which it uses
to determine the checked out tree, even though it created orphaned
history.

Update the previously added test cases as they are now passing.

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

contrib/completion/git-completion.bash

@@ -1508,7 +1508,7 @@ _git_checkout ()
 		local prevword prevword="${words[cword-1]}"
 
 		case "$prevword" in
-			-b|-B)
+			-b|-B|--orphan)
 				# Complete local branches (and DWIM branch
 				# remote branch names) for an option argument
 				# specifying a new branch name. This is for
@@ -1522,14 +1522,14 @@ _git_checkout ()
 		esac
 
 		# At this point, we've already handled special completion for
-		# the arguments to -b/-B. There are 3 main things left we can
+		# the arguments to -b/-B, and --orphan. There are 3 main
-		# possibly complete:
+		# things left we can possibly complete:
-		# 1) a start-point for -b/-B or -d/--detach
+		# 1) a start-point for -b/-B, -d/--detach, or --orphan
 		# 2) a remote head, for --track
 		# 3) an arbitrary reference, possibly including DWIM names
 		#
 
-		if [ -n "$(__git_find_on_cmdline "-b -B -d --detach")" ]; then
+		if [ -n "$(__git_find_on_cmdline "-b -B -d --detach --orphan")" ]; then
 			__git_complete_refs --mode="refs"
 		elif [ -n "$(__git_find_on_cmdline "--track")" ]; then
 			__git_complete_refs --mode="remote-heads"
@@ -2387,7 +2387,7 @@ _git_switch ()
 		local prevword prevword="${words[cword-1]}"
 
 		case "$prevword" in
-			-c|-C)
+			-c|-C|--orphan)
 				# Complete local branches (and DWIM branch
 				# remote branch names) for an option argument
 				# specifying a new branch name. This is for
@@ -2400,8 +2400,15 @@ _git_switch ()
 				;;
 		esac
 
+		# Unlike in git checkout, git switch --orphan does not take
+		# a start point. Thus we really have nothing to complete after
+		# the branch name.
+		if [ -n "$(__git_find_on_cmdline "--orphan")" ]; then
+			return
+		fi
+
 		# At this point, we've already handled special completion for
-		# -c/-C. There are 3 main things left to
+		# -c/-C, and --orphan. There are 3 main things left to
 		# complete:
 		# 1) a start-point for -c/-C or -d/--detach
 		# 2) a remote head, for --track

t/t9902-completion.sh

@@ -1669,15 +1669,13 @@ test_expect_success 'git switch - with --orphan completes local branch names and
 	EOF
 '
 
-#TODO: switch --orphan does not take a start-point and thus has nothing to complete
+test_expect_success 'git switch - --orphan with branch already provided completes nothing else' '
-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_success 'git checkout - with --orphan completes local branch names and unique remote branch names' '
-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
@@ -1686,8 +1684,7 @@ test_expect_failure 'git checkout - with --orphan completes local branch names a
 	EOF
 '
 
-#TODO: checkout --orphan start-point completion should not included DWIM remote unique branch names
+test_expect_success 'git checkout - --orphan with branch already provided completes local refs for a start-point' '
-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