diff: fix removal of unmodified deltas

When finding similar deltas, count the targets that are tagged to be deleted.
Apply deletions even in the absense of rewrites or updates.

src/libgit2/diff_tform.c

@@ -810,7 +810,7 @@ int git_diff_find_similar(
 	git_diff_find_options opts = GIT_DIFF_FIND_OPTIONS_INIT;
 	size_t num_deltas, num_srcs = 0, num_tgts = 0;
 	size_t tried_srcs = 0, tried_tgts = 0;
-	size_t num_rewrites = 0, num_updates = 0, num_bumped = 0;
+	size_t num_rewrites = 0, num_updates = 0, num_bumped = 0, num_to_delete = 0;
 	size_t sigcache_size;
 	void **sigcache = NULL; /* cache of similarity metric file signatures */
 	diff_find_match *tgt2src = NULL;
@@ -852,11 +852,14 @@ int git_diff_find_similar(
 
 		if ((tgt->flags & GIT_DIFF_FLAG__TO_SPLIT) != 0)
 			num_rewrites++;
+
+		if ((tgt->flags & GIT_DIFF_FLAG__TO_DELETE) != 0)
+		  num_to_delete++;
 	}
 
-	/* if there are no candidate srcs or tgts, we're done */
+	/* If there are no candidate srcs or tgts, no need to find matches */
 	if (!num_srcs || !num_tgts)
-		goto cleanup;
+		goto split_and_delete;
 
 	src2tgt = git__calloc(num_deltas, sizeof(diff_find_match));
 	GIT_ERROR_CHECK_ALLOC(src2tgt);
@@ -1093,13 +1096,14 @@ find_best_matches:
 		}
 	}
 
+split_and_delete:
 	/*
 	 * Actually split and delete entries as needed
 	 */
 
-	if (num_rewrites > 0 || num_updates > 0)
+	if (num_rewrites > 0 || num_updates > 0 || num_to_delete > 0)
 		error = apply_splits_and_deletes(
-			diff, diff->deltas.length - num_rewrites,
+			diff, diff->deltas.length - num_rewrites - num_to_delete,
 			FLAG_SET(&opts, GIT_DIFF_BREAK_REWRITES) &&
 			!FLAG_SET(&opts, GIT_DIFF_BREAK_REWRITES_FOR_RENAMES_ONLY));
 

tests/libgit2/diff/rename.c

@@ -1441,6 +1441,47 @@ void test_diff_rename__can_delete_unmodified_deltas(void)
 	git_str_dispose(&c1);
 }
 
+void test_diff_rename__can_delete_unmodified_deltas_without_changes(void)
+{
+	git_str c1 = GIT_STR_INIT;
+	git_index *index;
+	git_tree *tree;
+	git_diff *diff;
+	git_diff_options diffopts = GIT_DIFF_OPTIONS_INIT;
+	git_diff_find_options opts = GIT_DIFF_FIND_OPTIONS_INIT;
+	diff_expects exp;
+
+	cl_git_pass(
+		git_revparse_single((git_object **)&tree, g_repo, "HEAD^{tree}"));
+
+	cl_git_pass(git_repository_index(&index, g_repo));
+	cl_git_pass(git_index_read_tree(index, tree));
+
+	diffopts.flags = GIT_DIFF_INCLUDE_UNMODIFIED;
+
+	cl_git_pass(git_diff_tree_to_index(&diff, g_repo, tree, index, &diffopts));
+
+	memset(&exp, 0, sizeof(exp));
+	cl_git_pass(git_diff_foreach(
+		diff, diff_file_cb, diff_binary_cb, diff_hunk_cb, diff_line_cb, &exp));
+	cl_assert_equal_i(4, exp.files);
+	cl_assert_equal_i(4, exp.file_status[GIT_DELTA_UNMODIFIED]);
+
+	opts.flags = GIT_DIFF_FIND_ALL | GIT_DIFF_FIND_REMOVE_UNMODIFIED;
+	cl_git_pass(git_diff_find_similar(diff, &opts));
+
+	memset(&exp, 0, sizeof(exp));
+	cl_git_pass(git_diff_foreach(
+		diff, diff_file_cb, diff_binary_cb, diff_hunk_cb, diff_line_cb, &exp));
+	cl_assert_equal_i(0, exp.files);
+
+	git_diff_free(diff);
+	git_tree_free(tree);
+	git_index_free(index);
+
+	git_str_dispose(&c1);
+}
+
 void test_diff_rename__matches_config_behavior(void)
 {
 	const char *sha0 = INITIAL_COMMIT;