diff -c -p: do not die on submodules

The combine diff logic knew only about blobs (and their checked-out form
in the work tree, either regular files or symlinks), and barfed when fed
submodules.  This "externalizes" gitlinks in the same way as the normal
patch generation codepath does (i.e. "Subproject commit Xxx\n") to fix the
issue.

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

combine-diff.c

@@ -6,6 +6,7 @@
 #include "quote.h"
 #include "xdiff-interface.h"
 #include "log-tree.h"
+#include "refs.h"
 
 static struct combine_diff_path *intersect_paths(struct combine_diff_path *curr, int n, int num_parent)
 {
@@ -90,18 +91,24 @@ struct sline {
 	unsigned long *p_lno;
 };
 
-static char *grab_blob(const unsigned char *sha1, unsigned long *size)
+static char *grab_blob(const unsigned char *sha1, unsigned int mode, unsigned long *size)
 {
 	char *blob;
 	enum object_type type;
-	if (is_null_sha1(sha1)) {
+
+	if (S_ISGITLINK(mode)) {
+		blob = xmalloc(100);
+		*size = snprintf(blob, 100,
+				 "Subproject commit %s\n", sha1_to_hex(sha1));
+	} else if (is_null_sha1(sha1)) {
 		/* deleted blob */
 		*size = 0;
 		return xcalloc(1, 1);
+	} else {
+		blob = read_sha1_file(sha1, &type, size);
+		if (type != OBJ_BLOB)
+			die("object '%s' is not a blob!", sha1_to_hex(sha1));
 	}
-	blob = read_sha1_file(sha1, &type, size);
-	if (type != OBJ_BLOB)
-		die("object '%s' is not a blob!", sha1_to_hex(sha1));
 	return blob;
 }
 
@@ -197,7 +204,8 @@ static void consume_line(void *state_, char *line, unsigned long len)
 	}
 }
 
-static void combine_diff(const unsigned char *parent, mmfile_t *result_file,
+static void combine_diff(const unsigned char *parent, unsigned int mode,
+			 mmfile_t *result_file,
 			 struct sline *sline, unsigned int cnt, int n,
 			 int num_parent)
 {
@@ -213,7 +221,7 @@ static void combine_diff(const unsigned char *parent, mmfile_t *result_file,
 	if (!cnt)
 		return; /* result deleted */
 
-	parent_file.ptr = grab_blob(parent, &sz);
+	parent_file.ptr = grab_blob(parent, mode, &sz);
 	parent_file.size = sz;
 	xpp.flags = XDF_NEED_MINIMAL;
 	memset(&xecfg, 0, sizeof(xecfg));
@@ -692,7 +700,7 @@ static void show_patch_diff(struct combine_diff_path *elem, int num_parent,
 	context = opt->context;
 	/* Read the result of merge first */
 	if (!working_tree_file)
-		result = grab_blob(elem->sha1, &result_size);
+		result = grab_blob(elem->sha1, elem->mode, &result_size);
 	else {
 		/* Used by diff-tree to read from the working tree */
 		struct stat st;
@@ -712,9 +720,13 @@ static void show_patch_diff(struct combine_diff_path *elem, int num_parent,
 			}
 			result[len] = 0;
 			elem->mode = canon_mode(st.st_mode);
-		}
-		else if (0 <= (fd = open(elem->path, O_RDONLY)) &&
-			 !fstat(fd, &st)) {
+		} else if (S_ISDIR(st.st_mode)) {
+			unsigned char sha1[20];
+			if (resolve_gitlink_ref(elem->path, "HEAD", sha1) < 0)
+				result = grab_blob(elem->sha1, elem->mode, &result_size);
+			else
+				result = grab_blob(sha1, elem->mode, &result_size);
+		} else if (0 <= (fd = open(elem->path, O_RDONLY))) {
 			size_t len = xsize_t(st.st_size);
 			ssize_t done;
 			int is_file, i;
@@ -807,7 +819,9 @@ static void show_patch_diff(struct combine_diff_path *elem, int num_parent,
 			}
 		}
 		if (i <= j)
-			combine_diff(elem->parent[i].sha1, &result_file, sline,
+			combine_diff(elem->parent[i].sha1,
+				     elem->parent[i].mode,
+				     &result_file, sline,
 				     cnt, i, num_parent);
 		if (elem->parent[i].mode != elem->mode)
 			mode_differs = 1;

t/t4027-diff-submodule.sh

@@ -57,4 +57,43 @@ test_expect_success 'git diff (empty submodule dir)' '
 	test_cmp empty actual.empty
 '
 
+test_expect_success 'conflicted submodule setup' '
+
+	# 39 efs
+	c=fffffffffffffffffffffffffffffffffffffff
+	(
+		echo "000000 $_z40 0	sub"
+		echo "160000 1$c 1	sub"
+		echo "160000 2$c 2	sub"
+		echo "160000 3$c 3	sub"
+	) | git update-index --index-info &&
+	echo >expect.nosub '\''diff --cc sub
+index 2ffffff,3ffffff..0000000
+--- a/sub
++++ b/sub
+@@@ -1,1 -1,1 +1,1 @@@
+- Subproject commit 2fffffffffffffffffffffffffffffffffffffff
+ -Subproject commit 3fffffffffffffffffffffffffffffffffffffff
+++Subproject commit 0000000000000000000000000000000000000000'\'' &&
+
+	hh=$(git rev-parse HEAD) &&
+	sed -e "s/$_z40/$hh/" expect.nosub >expect.withsub
+
+'
+
+test_expect_success 'combined (empty submodule)' '
+	rm -fr sub && mkdir sub &&
+	git diff >actual &&
+	test_cmp expect.nosub actual
+'
+
+test_expect_success 'combined (with submodule)' '
+	rm -fr sub &&
+	git clone --no-checkout . sub &&
+	git diff >actual &&
+	test_cmp expect.withsub actual
+'
+
+
+
 test_done