status: Add a baseline field to git_status_options for comparing to trees other than HEAD

include/git2/status.h

@@ -173,12 +173,16 @@ typedef enum {
  * The `pathspec` is an array of path patterns to match (using
  * fnmatch-style matching), or just an array of paths to match exactly if
  * `GIT_STATUS_OPT_DISABLE_PATHSPEC_MATCH` is specified in the flags.
+ *
+ * The `baseline` is the tree to be used for comparison to the working directory
+ * and index; defaults to HEAD.
  */
 typedef struct {
 	unsigned int      version;
 	git_status_show_t show;
 	unsigned int      flags;
 	git_strarray      pathspec;
+	git_tree          *baseline;
 } git_status_options;
 
 #define GIT_STATUS_OPTIONS_VERSION 1

src/status.c

@@ -281,12 +281,16 @@ int git_status_list_new(
 		(error = git_repository_index(&index, repo)) < 0)
 		return error;
 	
+	if (opts != NULL && opts->baseline != NULL) {
+		head = opts->baseline;
+	} else {
 		/* if there is no HEAD, that's okay - we'll make an empty iterator */
 		if ((error = git_repository_head_tree(&head, repo)) < 0) {
 			if (error != GIT_ENOTFOUND && error != GIT_EUNBORNBRANCH)
 				goto done;
 			giterr_clear();
 		}
+	}
 
 	/* refresh index from disk unless prevented */
 	if ((flags & GIT_STATUS_OPT_NO_REFRESH) == 0 &&
@@ -377,6 +381,7 @@ done:
 
 	*out = status;
 
+	if (opts == NULL || opts->baseline != head)
 		git_tree_free(head);
 	git_index_free(index);
 

tests/status/worktree.c

@@ -1280,3 +1280,34 @@ void test_status_worktree__with_directory_in_pathlist(void)
 	git_status_list_free(statuslist);
 }
 
+void test_status_worktree__at_head_parent(void)
+{
+	git_repository *repo = cl_git_sandbox_init("empty_standard_repo");
+	git_status_options opts = GIT_STATUS_OPTIONS_INIT;
+	git_status_list *statuslist;
+	git_tree *parent_tree;
+	const git_status_entry *status;
+
+	cl_git_mkfile("empty_standard_repo/file1", "ping");
+	stage_and_commit(repo, "file1");
+
+	cl_git_pass(git_repository_head_tree(&parent_tree, repo));
+
+	cl_git_mkfile("empty_standard_repo/file2", "pong");
+	stage_and_commit(repo, "file2");
+
+	cl_git_rewritefile("empty_standard_repo/file2", "pyng");
+
+	opts.show = GIT_STATUS_SHOW_INDEX_AND_WORKDIR;
+	opts.baseline = parent_tree;
+	cl_git_pass(git_status_list_new(&statuslist, repo, &opts));
+
+	cl_assert_equal_sz(1, git_status_list_entrycount(statuslist));
+	status = git_status_byindex(statuslist, 0);
+	cl_assert(status != NULL);
+	cl_assert_equal_s("file2", status->index_to_workdir->old_file.path);
+	cl_assert_equal_i(GIT_STATUS_WT_MODIFIED | GIT_STATUS_INDEX_NEW, status->status);
+
+	git_tree_free(parent_tree);
+	git_status_list_free(statuslist);
+}