Fix generation of the header of the patch

src/diff.c

@@ -256,9 +256,6 @@ static int diff_delta__from_two(
 	return 0;
 }
 
-#define DIFF_SRC_PREFIX_DEFAULT "a/"
-#define DIFF_DST_PREFIX_DEFAULT "b/"
-
 static char *diff_strdup_prefix(const char *prefix)
 {
 	size_t len = strlen(prefix);

src/diff.h

@@ -13,6 +13,9 @@
 #include "iterator.h"
 #include "repository.h"
 
+#define DIFF_SRC_PREFIX_DEFAULT "a/"
+#define DIFF_DST_PREFIX_DEFAULT "b/"
+
 enum {
 	GIT_DIFFCAPS_HAS_SYMLINKS     = (1 << 0), /* symlinks on platform? */
 	GIT_DIFFCAPS_ASSUME_UNCHANGED = (1 << 1), /* use stat? */

src/diff_output.c

@@ -553,9 +553,16 @@ static int print_patch_file(void *data, git_diff_delta *delta, float progress)
 	const char *oldpath = delta->old.path;
 	const char *newpfx = pi->diff->opts.dst_prefix;
 	const char *newpath = delta->new.path;
+	int result;
 
 	GIT_UNUSED(progress);
 
+	if (!oldpfx)
+		oldpfx = DIFF_SRC_PREFIX_DEFAULT;
+
+	if (!newpfx)
+		newpfx = DIFF_DST_PREFIX_DEFAULT;
+
 	git_buf_clear(pi->buf);
 	git_buf_printf(pi->buf, "diff --git %s%s %s%s\n", oldpfx, delta->old.path, newpfx, delta->new.path);
 
@@ -567,8 +574,8 @@ static int print_patch_file(void *data, git_diff_delta *delta, float progress)
 		oldpath = "/dev/null";
 	}
 	if (git_oid_iszero(&delta->new.oid)) {
-		oldpfx = "";
-		oldpath = "/dev/null";
+		newpfx = "";
+		newpath = "/dev/null";
 	}
 
 	if (delta->binary != 1) {
@@ -579,9 +586,12 @@ static int print_patch_file(void *data, git_diff_delta *delta, float progress)
 	if (git_buf_oom(pi->buf))
 		return -1;
 
-	if (pi->print_cb(pi->cb_data, GIT_DIFF_LINE_FILE_HDR, pi->buf->ptr) < 0 ||
-		delta->binary != 1)
-		return -1;
+    result = pi->print_cb(pi->cb_data, GIT_DIFF_LINE_FILE_HDR, pi->buf->ptr);
+    if (result < 0)
+        return result;
+
+    if (delta->binary != 1)
+        return 0;
 
 	git_buf_clear(pi->buf);
 	git_buf_printf(

tests-clar/diff/patch.c

@@ -0,0 +1,68 @@
+#include "clar_libgit2.h"
+#include "diff_helpers.h"
+
+static git_repository *g_repo = NULL;
+
+void test_diff_patch__initialize(void)
+{
+	g_repo = cl_git_sandbox_init("status");
+}
+
+void test_diff_patch__cleanup(void)
+{
+	cl_git_sandbox_cleanup();
+}
+
+#define EXPECTED_OUTPUT "diff --git a/subdir.txt b/subdir.txt\n" \
+	"deleted file mode 100644\n" \
+	"index e8ee89e..0000000\n" \
+	"--- a/subdir.txt\n" \
+	"+++ /dev/null\n"
+
+static int check_removal_cb(
+	void *cb_data,
+	char line_origin,
+	const char *formatted_output)
+{
+	GIT_UNUSED(cb_data);
+
+	if (line_origin != 'F')
+		return 0;
+
+	if (strcmp(EXPECTED_OUTPUT, formatted_output) == 0)
+		return 0;
+
+	return -1;
+}
+
+void test_diff_patch__can_properly_display_the_removal_of_a_file(void)
+{
+	/*
+	* $ git diff 26a125e..735b6a2
+	* diff --git a/subdir.txt b/subdir.txt
+	* deleted file mode 100644
+	* index e8ee89e..0000000
+	* --- a/subdir.txt
+	* +++ /dev/null
+	* @@ -1,2 +0,0 @@
+	* -Is it a bird?
+	* -Is it a plane?
+	*/
+
+	const char *one_sha = "26a125e";
+	const char *another_sha = "735b6a2";
+	git_tree *one, *another;
+	git_diff_list *diff;
+
+	one = resolve_commit_oid_to_tree(g_repo, one_sha);
+	another = resolve_commit_oid_to_tree(g_repo, another_sha);
+
+	cl_git_pass(git_diff_tree_to_tree(g_repo, NULL, one, another, &diff));
+
+	cl_git_pass(git_diff_print_patch(diff, NULL, check_removal_cb));
+
+	git_diff_list_free(diff);
+
+	git_tree_free(another);
+	git_tree_free(one);
+}