[PATCH v4 3/3] completion: 'git diff' completes untracked paths as a last resort

We taught 'git diff' to first try to complete revisions (unless '--'
is present on the command line) and, failing that, to complete
tracked paths.  If this yields nothing, it lets the Bash default,
which offers paths in $PWD, kick in.

Teach it to complete untracked paths before giving up and letting
the Bash default kick in.  With this change,

    $ git -C another-directory diff un<TAB>

finds the 'untracked' file in another-directory and offers it as a
completion candidate.

Signed-off-by: Junio C Hamano <[email protected]>
---
 contrib/completion/git-completion.bash |  4 ++++
 t/t9902-completion.sh                  | 22 ++++++++++++++++++++--
 2 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/contrib/completion/git-completion.bash b/contrib/completion/git-completion.bash
index 845fd19f70..7741789e41 100644
--- a/contrib/completion/git-completion.bash
+++ b/contrib/completion/git-completion.bash
@@ -1985,6 +1985,10 @@ _git_diff ()
 	if [ ${#COMPREPLY[@]} -eq 0 ]; then
 		__git_complete_index_file
 	fi
+
+	if [ ${#COMPREPLY[@]} -eq 0 ]; then
+		__git_complete_index_file "--others --directory"
+	fi
 }
 
 __git_mergetools_common="diffuse diffmerge ecmerge emerge kdiff3 meld opendiff
diff --git a/t/t9902-completion.sh b/t/t9902-completion.sh
index adfaf414fd..eea4bdbb7e 100755
--- a/t/t9902-completion.sh
+++ b/t/t9902-completion.sh
@@ -2664,6 +2664,7 @@ test_expect_success 'setup for integration tests' '
 	echo more >file2 &&
 	git add file1 file2 &&
 	echo untracked >file3 &&
+	echo untracked >ufile &&
 	git commit -m one &&
 	git branch mybranch &&
 	git tag mytag
@@ -2726,21 +2727,38 @@ test_expect_success 'git diff completes tracked paths when no refs match' '
 	EOF
 '
 
+test_expect_success 'git diff [--] completes untracked paths, too' '
+	# there is no ref or tracked path that begin with u
+	test_completion "git diff u" <<-\EOF &&
+	ufile
+	EOF
+	test_completion "git diff -- u" <<-\EOF
+	ufile
+	EOF
+'
+
 test_expect_success 'git -C <path> diff completes in the specified repo' '
 	test_when_finished "rm -rf repo-for-diff" &&
 	git init repo-for-diff &&
 
-	# otherfile is tracked, oops is untracked
+	# otherfile is tracked, oops and ufile are untracked
 	echo content >repo-for-diff/otherfile &&
 	git -C repo-for-diff add otherfile &&
 	git -C repo-for-diff commit -m otherfile &&
 	echo untracked >repo-for-diff/oops &&
+	echo untracked >repo-for-diff/ufile &&
 	test_completion "git -C repo-for-diff diff o" <<-\EOF &&
 	otherfile
 	EOF
-	test_completion "git -C repo-for-diff diff -- o" <<-\EOF
+	test_completion "git -C repo-for-diff diff -- o" <<-\EOF &&
 	otherfile
 	EOF
+	test_completion "git -C repo-for-diff diff u" <<-\EOF &&
+	ufile
+	EOF
+	test_completion "git -C repo-for-diff diff -- u" <<-\EOF
+	ufile
+	EOF
 '
 
 test_expect_success 'show completes all refs' '
-- 
2.55.0-655-gb2c071042d