Merge from ast-arena. This reduces the code in Python/ast.c by ~300 lines,

simplifies a lot of error handling code, and fixes many memory leaks.

Python/pyarena.c

@@ -0,0 +1,133 @@
+#include "Python.h"
+#include "pyarena.h"
+
+/* An arena list is a linked list that can store either pointers or
+   PyObjects.  The type is clear from context.
+ */
+
+typedef struct _arena_list {
+  struct _arena_list *al_next;
+  void *al_pointer;
+} PyArenaList;
+
+/* There are two linked lists in an arena, one for malloc pointers and
+   one for PyObject.  For each list, there is a pointer to the head
+   and to the tail.  The head is used to free the list.  The tail is
+   used to add a new element to the list.
+
+   The list always keeps one un-used node at the end of the list.
+*/
+
+struct _arena {
+  PyArenaList *a_malloc_head;
+  PyArenaList *a_malloc_tail;
+  PyArenaList *a_object_head;
+  PyArenaList *a_object_tail;
+};
+
+static PyArenaList*
+PyArenaList_New(void) 
+{
+  PyArenaList *alist = (PyArenaList *)malloc(sizeof(PyArenaList));
+  if (!alist)
+    return NULL;
+
+  alist->al_next = NULL;
+  alist->al_pointer = NULL;
+  return alist;
+}
+
+static void
+PyArenaList_FreeObject(PyArenaList *alist) 
+{
+  if (!alist)
+    return;
+
+  while (alist) {
+    PyArenaList *prev;
+    Py_XDECREF((PyObject *)alist->al_pointer);
+    alist->al_pointer = NULL;
+    prev = alist;
+    alist = alist->al_next;
+    free(prev);
+  }
+}
+
+static void
+PyArenaList_FreeMalloc(PyArenaList *alist)
+{
+  if (!alist)
+    return;
+
+  while (alist) {
+    PyArenaList *prev;
+    if (alist->al_pointer) {
+      free(alist->al_pointer);
+    }
+    alist->al_pointer = NULL;
+    prev = alist;
+    alist = alist->al_next;
+    free(prev);
+  }
+}
+
+
+PyArena *
+PyArena_New()
+{
+  PyArena* arena = (PyArena *)malloc(sizeof(PyArena));
+  if (!arena)
+    return NULL;
+
+  arena->a_object_head = PyArenaList_New();
+  arena->a_object_tail = arena->a_object_head;
+  arena->a_malloc_head = PyArenaList_New();
+  arena->a_malloc_tail = arena->a_malloc_head;
+  return arena;
+}
+
+void
+PyArena_Free(PyArena *arena)
+{
+  assert(arena);
+  PyArenaList_FreeObject(arena->a_object_head);
+  PyArenaList_FreeMalloc(arena->a_malloc_head);
+  free(arena);
+}
+
+void *
+PyArena_Malloc(PyArena *arena, size_t size) 
+{
+  /* A better implementation might actually use an arena.  The current
+     approach is just a trivial implementation of the API that allows
+     it to be tested.
+  */
+  void *p;
+  assert(size != 0);
+  p = malloc(size);
+  PyArena_AddMallocPointer(arena, p);
+  return p;
+}
+
+int
+PyArena_AddMallocPointer(PyArena *arena, void *pointer) 
+{
+  assert(pointer);
+  PyArenaList *tail = arena->a_malloc_tail;
+  assert(tail->al_pointer != pointer);
+  tail->al_next = PyArenaList_New();
+  tail->al_pointer = pointer;
+  arena->a_malloc_tail = tail->al_next;
+  return 1;
+}
+
+int
+PyArena_AddPyObject(PyArena *arena, PyObject *pointer) 
+{
+  assert(pointer);
+  PyArenaList *tail = arena->a_object_tail;
+  tail->al_next = PyArenaList_New();
+  tail->al_pointer = pointer;
+  arena->a_object_tail = tail->al_next;
+  return 1;
+}