Merge branch 'jc/trivial-threeway-binary-merge' into maint

The "git apply -3" code path learned not to bother the lower level
merge machinery when the three-way merge can be trivially resolved
without the content level merge.

* jc/trivial-threeway-binary-merge:
  apply: resolve trivial merge without hitting ll-merge with "--3way"

apply.c

@@ -3468,6 +3468,21 @@ static int load_preimage(struct apply_state *state,
 	return 0;
 }
 
+static int resolve_to(struct image *image, const struct object_id *result_id)
+{
+	unsigned long size;
+	enum object_type type;
+
+	clear_image(image);
+
+	image->buf = read_object_file(result_id, &type, &size);
+	if (!image->buf || type != OBJ_BLOB)
+		die("unable to read blob object %s", oid_to_hex(result_id));
+	image->len = size;
+
+	return 0;
+}
+
 static int three_way_merge(struct apply_state *state,
 			   struct image *image,
 			   char *path,
@@ -3479,6 +3494,12 @@ static int three_way_merge(struct apply_state *state,
 	mmbuffer_t result = { NULL };
 	int status;
 
+	/* resolve trivial cases first */
+	if (oideq(base, ours))
+		return resolve_to(image, theirs);
+	else if (oideq(base, theirs) || oideq(ours, theirs))
+		return resolve_to(image, ours);
+
 	read_mmblob(&base_file, base);
 	read_mmblob(&our_file, ours);
 	read_mmblob(&their_file, theirs);

t/t4108-apply-threeway.sh

@@ -230,4 +230,49 @@ test_expect_success 'apply with --3way --cached and conflicts' '
 	test_cmp expect.diff actual.diff
 '
 
+test_expect_success 'apply binary file patch' '
+	git reset --hard main &&
+	cp "$TEST_DIRECTORY/test-binary-1.png" bin.png &&
+	git add bin.png &&
+	git commit -m "add binary file" &&
+
+	cp "$TEST_DIRECTORY/test-binary-2.png" bin.png &&
+
+	git diff --binary >bin.diff &&
+	git reset --hard &&
+
+	# Apply must succeed.
+	git apply bin.diff
+'
+
+test_expect_success 'apply binary file patch with 3way' '
+	git reset --hard main &&
+	cp "$TEST_DIRECTORY/test-binary-1.png" bin.png &&
+	git add bin.png &&
+	git commit -m "add binary file" &&
+
+	cp "$TEST_DIRECTORY/test-binary-2.png" bin.png &&
+
+	git diff --binary >bin.diff &&
+	git reset --hard &&
+
+	# Apply must succeed.
+	git apply --3way --index bin.diff
+'
+
+test_expect_success 'apply full-index patch with 3way' '
+	git reset --hard main &&
+	cp "$TEST_DIRECTORY/test-binary-1.png" bin.png &&
+	git add bin.png &&
+	git commit -m "add binary file" &&
+
+	cp "$TEST_DIRECTORY/test-binary-2.png" bin.png &&
+
+	git diff --full-index >bin.diff &&
+	git reset --hard &&
+
+	# Apply must succeed.
+	git apply --3way --index bin.diff
+'
+
 test_done