Restore GIT_DIFF_LINE_BINARY usage

This restores the usage of GIT_DIFF_LINE_BINARY for the diff
output line that reads "Binary files x and y differ" so that it
can be optionally colorized independently of the file header.

include/git2/diff.h

@@ -391,7 +391,7 @@ typedef enum {
 	 */
 	GIT_DIFF_LINE_FILE_HDR  = 'F',
 	GIT_DIFF_LINE_HUNK_HDR  = 'H',
-	GIT_DIFF_LINE_BINARY    = 'B'  /**< Deprecated, will not be returned */
+	GIT_DIFF_LINE_BINARY    = 'B' /**< For "Binary files x and y differ" */
 } git_diff_line_t;
 
 /**

src/diff_print.c

@@ -228,16 +228,35 @@ static int diff_print_oid_range(
 	return 0;
 }
 
-int git_diff_delta__format_file_header(
+static int diff_delta_format_with_paths(
 	git_buf *out,
 	const git_diff_delta *delta,
 	const char *oldpfx,
 	const char *newpfx,
-	int oid_strlen)
+	const char *template)
 {
 	const char *oldpath = delta->old_file.path;
 	const char *newpath = delta->new_file.path;
 
+	if (git_oid_iszero(&delta->old_file.oid)) {
+		oldpfx = "";
+		oldpath = "/dev/null";
+	}
+	if (git_oid_iszero(&delta->new_file.oid)) {
+		newpfx = "";
+		newpath = "/dev/null";
+	}
+
+	return git_buf_printf(out, template, oldpfx, oldpath, newpfx, newpath);
+}
+
+int git_diff_delta__format_file_header(
+	git_buf *out,
+	const git_diff_delta *delta,
+	const char *oldpfx,
+	const char *newpfx,
+	int oid_strlen)
+{
 	if (!oldpfx)
 		oldpfx = DIFF_OLD_PREFIX_DEFAULT;
 	if (!newpfx)
@@ -248,28 +267,14 @@ int git_diff_delta__format_file_header(
 	git_buf_clear(out);
 
 	git_buf_printf(out, "diff --git %s%s %s%s\n",
-		oldpfx, oldpath, newpfx, newpath);
+		oldpfx, delta->old_file.path, newpfx, delta->new_file.path);
 
 	if (diff_print_oid_range(out, delta, oid_strlen) < 0)
 		return -1;
 
-	if (git_oid_iszero(&delta->old_file.oid)) {
-		oldpfx = "";
-		oldpath = "/dev/null";
-	}
-	if (git_oid_iszero(&delta->new_file.oid)) {
-		newpfx = "";
-		newpath = "/dev/null";
-	}
-
-	if ((delta->flags & GIT_DIFF_FLAG_BINARY) == 0) {
-		git_buf_printf(out, "--- %s%s\n", oldpfx, oldpath);
-		git_buf_printf(out, "+++ %s%s\n", newpfx, newpath);
-	} else {
-		git_buf_printf(
-			out, "Binary files %s%s and %s%s differ\n",
-			oldpfx, oldpath, newpfx, newpath);
-	}
+	if ((delta->flags & GIT_DIFF_FLAG_BINARY) == 0)
+		diff_delta_format_with_paths(
+			out, delta, oldpfx, newpfx, "--- %s%s\n+++ %s%s\n");
 
 	return git_buf_oom(out) ? -1 : 0;
 }
@@ -278,8 +283,10 @@ static int diff_print_patch_file(
 	const git_diff_delta *delta, float progress, void *data)
 {
 	diff_print_info *pi = data;
-	const char *oldpfx = pi->diff ? pi->diff->opts.old_prefix : NULL;
-	const char *newpfx = pi->diff ? pi->diff->opts.new_prefix : NULL;
+	const char *oldpfx =
+		pi->diff ? pi->diff->opts.old_prefix : DIFF_OLD_PREFIX_DEFAULT;
+	const char *newpfx =
+		pi->diff ? pi->diff->opts.new_prefix : DIFF_NEW_PREFIX_DEFAULT;
 	uint32_t opts_flags = pi->diff ? pi->diff->opts.flags : GIT_DIFF_NORMAL;
 
 	GIT_UNUSED(progress);
@@ -299,6 +306,20 @@ static int diff_print_patch_file(
 			git_buf_cstr(pi->buf), git_buf_len(pi->buf), pi->payload))
 		return callback_error();
 
+	if ((delta->flags & GIT_DIFF_FLAG_BINARY) == 0)
+		return 0;
+
+	git_buf_clear(pi->buf);
+
+	if (diff_delta_format_with_paths(
+			pi->buf, delta, oldpfx, newpfx,
+			"Binary files %s%s and %s%s differ\n") < 0)
+		return -1;
+
+	if (pi->print_cb(delta, NULL, GIT_DIFF_LINE_BINARY,
+			git_buf_cstr(pi->buf), git_buf_len(pi->buf), pi->payload))
+		return callback_error();
+
 	return 0;
 }