diff-files --raw: show correct post-image of intent-to-add files

The documented behavior of `git diff-files --raw` is to display

	[...] 0{40} if creation, unmerged or "look at work tree".

on the right hand (i.e. postimage) side. This happens for files that
have unstaged modifications, and for files that are unmodified but
stat-dirty.

For intent-to-add files, we used to show the empty blob's hash instead.
In c26022ea8f (diff: convert diff_addremove to struct object_id,
2017-05-30), we made that worse by inadvertently changing that to the
hash of the empty tree.

Let's make the behavior consistent with files that have unstaged
modifications (which applies to intent-to-add files, too) by showing
all-zero values also for intent-to-add files.

Accordingly, this patch adjusts the expectations set by the regression
test introduced in feea6946a5 (diff-files: treat "i-t-a" files as
"not-in-index", 2020-06-20).

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff-lib.c

@@ -220,8 +220,7 @@ int run_diff_files(struct rev_info *revs, unsigned int option)
 			} else if (revs->diffopt.ita_invisible_in_index &&
 				   ce_intent_to_add(ce)) {
 				diff_addremove(&revs->diffopt, '+', ce->ce_mode,
-					       the_hash_algo->empty_tree, 0,
-					       ce->name, 0);
+					       &null_oid, 0, ce->name, 0);
 				continue;
 			}
 

t/t2203-add-intent.sh

@@ -240,7 +240,6 @@ test_expect_success 'i-t-a files shown as new for "diff", "diff-files"; not-new
 
 	hash_e=$(git hash-object empty) &&
 	hash_n=$(git hash-object not-empty) &&
-	hash_t=$(git hash-object -t tree /dev/null) &&
 
 	cat >expect.diff_p <<-EOF &&
 	diff --git a/empty b/empty
@@ -259,8 +258,8 @@ test_expect_success 'i-t-a files shown as new for "diff", "diff-files"; not-new
 	 create mode 100644 not-empty
 	EOF
 	cat >expect.diff_a <<-EOF &&
-	:000000 100644 0000000 $(git rev-parse --short $hash_t) A$(printf "\t")empty
-	:000000 100644 0000000 $(git rev-parse --short $hash_t) A$(printf "\t")not-empty
+	:000000 100644 0000000 0000000 A$(printf "\t")empty
+	:000000 100644 0000000 0000000 A$(printf "\t")not-empty
 	EOF
 
 	git add -N empty not-empty &&