builtin-apply: do not declare patch is creation when we do not know it

When we see no context nor deleted line in the patch, we used to declare
that the patch creates a new file.  But some people create an empty file
and then apply a patch to it.  Similarly, a patch that delete everything
is not a deletion patch either.

This commit corrects these two issues.  Together with the previous commit,
it allows a diff between an empty file and a line-ful file to be treated
as both creation patch and "add stuff to an existing empty file",
depending on the context.  A new test t4126 demonstrates the fix.

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

builtin-apply.c

@@ -1143,21 +1143,6 @@ static int parse_single_patch(char *line, unsigned long size, struct patch *patc
 	if (patch->is_delete < 0 &&
 	    (newlines || (patch->fragments && patch->fragments->next)))
 		patch->is_delete = 0;
-	if (!unidiff_zero || context) {
-		/* If the user says the patch is not generated with
-		 * --unified=0, or if we have seen context lines,
-		 * then not having oldlines means the patch is creation,
-		 * and not having newlines means the patch is deletion.
-		 */
-		if (patch->is_new < 0 && !oldlines) {
-			patch->is_new = 1;
-			patch->old_name = NULL;
-		}
-		if (patch->is_delete < 0 && !newlines) {
-			patch->is_delete = 1;
-			patch->new_name = NULL;
-		}
-	}
 
 	if (0 < patch->is_new && oldlines)
 		die("new file %s depends on old contents", patch->new_name);

t/t4126-apply-empty.sh

@@ -0,0 +1,61 @@
+#!/bin/sh
+
+test_description='apply empty'
+
+. ./test-lib.sh
+
+test_expect_success setup '
+	>empty &&
+	git add empty &&
+	test_tick &&
+	git commit -m initial &&
+	for i in a b c d e
+	do
+		echo $i
+	done >empty &&
+	cat empty >expect &&
+	git diff |
+	sed -e "/^diff --git/d" \
+	    -e "/^index /d" \
+	    -e "s|a/empty|empty.orig|" \
+	    -e "s|b/empty|empty|" >patch0 &&
+	sed -e "s|empty|missing|" patch0 >patch1 &&
+	>empty &&
+	git update-index --refresh
+'
+
+test_expect_success 'apply empty' '
+	git reset --hard &&
+	>empty &&
+	rm -f missing &&
+	git apply patch0 &&
+	test_cmp expect empty
+'
+
+test_expect_success 'apply --index empty' '
+	git reset --hard &&
+	>empty &&
+	rm -f missing &&
+	git apply --index patch0 &&
+	test_cmp expect empty &&
+	git diff --exit-code
+'
+
+test_expect_success 'apply create' '
+	git reset --hard &&
+	>empty &&
+	rm -f missing &&
+	git apply patch1 &&
+	test_cmp expect missing
+'
+
+test_expect_success 'apply --index create' '
+	git reset --hard &&
+	>empty &&
+	rm -f missing &&
+	git apply --index patch1 &&
+	test_cmp expect missing &&
+	git diff --exit-code
+'
+
+test_done