Diff now invoked immediately and its result stored inside object to

avoid calls on repeated accesses and allow implementation of other
variants
Fixed indentation in diff implementation

include/pygit2/types.h

@@ -29,6 +29,7 @@ OBJECT_STRUCT(Blob, git_blob, blob)
 OBJECT_STRUCT(Tag, git_tag, tag)
 OBJECT_STRUCT(Index, git_index, index)
 OBJECT_STRUCT(Walker, git_revwalk, walk)
+OBJECT_STRUCT(Diff, git_diff_list, diff)
 
 typedef struct {
     PyObject_HEAD
@@ -36,12 +37,6 @@ typedef struct {
     const git_tree_entry *entry;
 } TreeEntry;
 
-typedef struct {
-    PyObject_HEAD
-    Tree *t0;
-    Tree *t1;
-} Diff;
-
 typedef struct {
     PyObject_HEAD
     int old_start;

src/pygit2/diff.c

@@ -114,33 +114,16 @@ static int diff_file_cb(void *cb_data, git_diff_delta *delta, float progress)
 PyObject *
 Diff_changes(Diff *self)
 {
-    git_diff_options opts = {0};
-    git_diff_list *changes;
-    int err;
-
-    err = git_diff_tree_to_tree(
-              self->t0->repo->repo,
-              &opts,
-              self->t0->tree,
-              self->t1->tree,
-              &changes);
-
-    if(err < 0) {
-        Error_set(err);
-        return NULL;
-    }
-    
     PyObject *payload;
     payload = PyDict_New();
 
     git_diff_foreach(
-      changes,
+        self->diff,
         payload,
         &diff_file_cb,
         &diff_hunk_cb,
         &diff_data_cb
     );
-    git_diff_list_free(changes);
 
     return payload;
 }
@@ -159,29 +142,12 @@ static int diff_print_cb(
     return 0;
 }
 
-
 PyObject *
 Diff_patch(Diff *self)
 {
-    git_diff_options opts = {0};
-    git_diff_list *changes;
-    int err;
-
-    err = git_diff_tree_to_tree(
-              self->t0->repo->repo,
-              &opts,
-              self->t0->tree,
-              self->t1->tree,
-              &changes);
-
-    if(err < 0) {
-        Error_set(err);
-        return NULL;
-    }
-
     PyObject *patch = PyBytes_FromString("");
 
-    git_diff_print_patch(changes, &patch, &diff_print_cb);
+    git_diff_print_patch(self->diff, &patch, &diff_print_cb);
 
     return patch;
 }
@@ -271,23 +237,20 @@ PyTypeObject HunkType = {
     0,                                         /* tp_new            */
 };
 
-
 static void
 Diff_dealloc(Diff *self)
 {
-    Py_XDECREF(self->t0);
-    Py_XDECREF(self->t1);
+    git_diff_list_free(self->diff);
+    Py_XDECREF(self->repo);
     PyObject_Del(self);
 }
 
-
 PyGetSetDef Diff_getseters[] = {
     {"changes", (getter)Diff_changes, NULL, "raw changes", NULL},
     {"patch", (getter)Diff_patch, NULL, "patch", NULL},
     {NULL}
 };
 
-
 PyTypeObject DiffType = {
     PyVarObject_HEAD_INIT(NULL, 0)
     "pygit2.Diff",                             /* tp_name           */

src/pygit2/tree.c

@@ -231,21 +231,33 @@ Tree_getitem(Tree *self, PyObject *value)
 PyObject *
 Tree_diff_tree(Tree *self, PyObject *args)
 {
+    git_diff_options opts = {0};
+    git_diff_list *diff;
+    int err;
+
     Diff *py_diff;
     Tree *py_tree;
 
-    if (!PyArg_ParseTuple(args, "O!", &TreeType, &py_tree)) {
+    if (!PyArg_ParseTuple(args, "O!", &TreeType, &py_tree))
         return NULL;
-    }
+    if (py_tree->repo->repo != self->repo->repo)
+        return Error_set(GIT_ERROR);
+
+    err = git_diff_tree_to_tree(
+              self->repo->repo,
+              &opts,
+              self->tree,
+              py_tree->tree,
+              &diff);
+    if (err < 0)
+        return Error_set(err);
 
     py_diff = PyObject_New(Diff, &DiffType);
     if (py_diff) {
         Py_INCREF(py_diff);
-        Py_INCREF(py_tree);
-        Py_INCREF(self);
-
-        py_diff->t0 = self;
-        py_diff->t1 = py_tree;
+        Py_INCREF(self->repo);
+        py_diff->repo = self->repo;
+        py_diff->diff = diff;
     }
 
     return (PyObject*)py_diff;