diff-index.c: "git diff" has no need to read blob from the standard input

Only "diff --no-index -" does.  Bolting the logic into the low-level
function diff_populate_filespec() was a layering violation from day
one.  Move populate_from_stdin() function out of the generic diff.c
to its only user, diff-index.c.

Also make sure "-" from the command line stays a special token "read
from the standard input", even if we later decide to sanitize the
result from prefix_filename() function in a few obvious ways,
e.g. removing unnecessary "./" prefix, duplicated slashes "//" in
the middle, etc.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 12 insertions, 0 deletions

diff --git a/t/t7501-commit.sh b/t/t7501-commit.sh
index 3ad04363b..e6cf6ee9e 100755
--- a/t/t7501-commit.sh
+++ b/t/t7501-commit.sh
@@ -458,4 +458,16 @@ test_expect_success 'amend can copy notes' '
 
 '
 
+test_expect_success 'commit a file whose name is a dash' '
+	git reset --hard &&
+	for i in 1 2 3 4 5
+	do
+		echo $i
+	done >./- &&
+	git add ./- &&
+	test_tick &&
+	git commit -m "add dash" >output </dev/null &&
+	test_i18ngrep " changed, 5 insertions" output
+'
+
 test_done