[PATCH 2/3] diff-files --raw: handle intent-to-add files correctly

["Johannes Schindelin via GitGitGadget" <gitgitgadget@gmail.com>]

From: Johannes Schindelin <johannes.schindelin@gmx.de>

In `run_diff_files()`, files that have been staged with the intention to
add are queued without a valid OID in the `diff_filepair`.

When the output mode is, say, `DIFF_FORMAT_PATCH`, the
`diff_fill_oid_info()` function, called from `run_diff()`, will remedy
that situation by reading the file contents from disk.

However, when the output mode is `DIFF_FORMAT_RAW`, that does not hold
true, and the output will contain a bogus OID (and the flag `M` for
"modified" instead of the correct `A` for "added").

As a consequence, `git difftool -d` (which relies on `git diff-files
--raw`'s output) does not work correctly.

Let's fix this specifically by imitating `diff_fill_oid_info()`.

Note: we can only do that for diff formats that do not actually need the
file contents, such as `DIFF_FORMAT_PATCH`: `run_diff()` would try to
read the blob contents, but that blob might not have been written to
Git's object database.

This fixes https://github.com/git-for-windows/git/issues/2677

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
---
 diff-lib.c             | 14 ++++++++++++++
 t/t4000-diff-format.sh | 10 ++++++++++
 2 files changed, 24 insertions(+)

diff --git a/diff-lib.c b/diff-lib.c
index 15bb45776e4..4af8f811ae8 100644
--- a/diff-lib.c
+++ b/diff-lib.c
@@ -223,6 +223,20 @@ int run_diff_files(struct rev_info *revs, unsigned int option)
 					       the_hash_algo->empty_blob, 0,
 					       ce->name, 0);
 				continue;
+			} else if (ce_intent_to_add(ce) &&
+				   !(revs->diffopt.output_format &
+				     ~(DIFF_FORMAT_RAW | DIFF_FORMAT_NAME_STATUS))) {
+				struct object_id oid;
+				int ret = lstat(ce->name, &st);
+
+				if (ret < 0)
+					oidclr(&oid);
+				else
+					ret = index_path(istate, &oid,
+						 ce->name, &st, 0);
+				diff_addremove(&revs->diffopt, '+', ce->ce_mode,
+					       &oid, ret >= 0, ce->name, 0);
+				continue;
 			}
 
 			changed = match_stat_with_submodule(&revs->diffopt, ce, &st,
diff --git a/t/t4000-diff-format.sh b/t/t4000-diff-format.sh
index e5116a76a1c..48ff4e250b5 100755
--- a/t/t4000-diff-format.sh
+++ b/t/t4000-diff-format.sh
@@ -89,4 +89,14 @@ test_expect_success 'git diff-files --patch --no-patch does not show the patch'
 	test_must_be_empty err
 '
 
+test_expect_success 'git diff-files --raw handles intent-to-add files correctly' '
+	echo 123 >ita &&
+	git add -N ita &&
+	printf ":000000 100644 %s %s A\\tita\n" \
+		$ZERO_OID $(git hash-object --stdin <ita) >expect &&
+	git diff-files --raw ita >actual &&
+	test_cmp expect actual
+'
+
+
 test_done
-- 
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