.

wcfs/internal/xbtree.py

+# -*- coding: utf-8 -*-
+# Copyright (C) 2020  Nexedi SA and Contributors.
+#                     Kirill Smelkov <kirr@nexedi.com>
+#
+# This program is free software: you can Use, Study, Modify and Redistribute
+# it under the terms of the GNU General Public License version 3, or (at your
+# option) any later version, as published by the Free Software Foundation.
+#
+# You can also Link and Combine this program with other software covered by
+# the terms of any of the Free Software licenses or any of the Open Source
+# Initiative approved licenses and Convey the resulting work. Corresponding
+# source of such a combination shall include the source code for all other
+# software used.
+#
+# This program is distributed WITHOUT ANY WARRANTY; without even the implied
+# warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+#
+# See COPYING file for full licensing terms.
+# See https://www.nexedi.com/licensing for rationale and options.
+
+"""Package xbtree provides utilities for inspecting/manipulating internal structure of BTrees.
+
+It is primarily used to verify ΔBTail in wcfs.
+
+
+XXX Typology:
+"""
+
+# Tree represents internal tree node.
+class Tree:
+    #   .keyv       () of keys
+    #   .children   () of children  len(.children) == len(.keyv) + 1
+    def __init__(tree, keyv, *children):
+        assert len(children) == len(keyv) + 1
+        tree.keyv     = tuple(keyv)
+        tree.children = tuple(children)
+
+    def __eq__(a, b):
+        if not isinstance(b, Tree):
+            return False
+        return (a.keyv == b.keyv) and (a.children == b.children)    # XXX don't compare .children here?
+    def __hash__(tree):
+        return hash(tree.keyv) ^ hash(tree.children)                # XXX children ^^^
+
+
+# StructureOf returns internal structure of the tree.
+def StructureOf(tree):
+    1/0
+
+# TypologyOf returns topology encoding for internal structure of the tree.
+#
+# See top-level docstring for what topology is.
+def TypologyOf(tree):
+    1/0
+    treeStruct = StructureOf(tree)
+    # XXX convert struct -> topology

wcfs/internal/xbtree_test.py

+# -*- coding: utf-8 -*-
+# Copyright (C) 2020  Nexedi SA and Contributors.
+#                     Kirill Smelkov <kirr@nexedi.com>
+#
+# This program is free software: you can Use, Study, Modify and Redistribute
+# it under the terms of the GNU General Public License version 3, or (at your
+# option) any later version, as published by the Free Software Foundation.
+#
+# You can also Link and Combine this program with other software covered by
+# the terms of any of the Free Software licenses or any of the Open Source
+# Initiative approved licenses and Convey the resulting work. Corresponding
+# source of such a combination shall include the source code for all other
+# software used.
+#
+# This program is distributed WITHOUT ANY WARRANTY; without even the implied
+# warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+#
+# See COPYING file for full licensing terms.
+# See https://www.nexedi.com/licensing for rationale and options.
+
+from wendelin.wcfs.internal import xbtree
+from BTrees.tests import testBTrees
+
+def test_topologyOf():
+    T = xbtree.Tree
+
+    # XXX empty
+
+    # XXX 1 k->v
+
+    # XXX known degenerate topology
+    # https://github.com/zopefoundation/ZODB/commit/6cd24e99f89b
+    # https://github.com/zopefoundation/BTrees/blob/4.7.2-1-g078ba60/BTrees/tests/testBTrees.py#L20
+    t, keys = testBTrees.DegenerateBTree("testBasicOps")._build_degenerate_tree()
+    assert keys == [1, 3, 5, 7, 11]
+
+    assert xbtree.StructureOf(t) == T([4],
+                                       T([2],
+                                            T([]), T([])),
+                                       T([],
+                                            T([6, 10],
+                                                T([], T([])),
+                                                T([]),
+                                                T([])) ))
+
+    """
+    assert xbtree.TopologyOf(t) == ( (4,),
+                                     ((2,),      ()),
+                                     (((), ()),  (6, 10)),
+    """
+