[Lorenz] Create diff_graphs.py to print differences between graphs

This is useful to see what classes and packages were added and removed
from one version to another.

For now the script just looks at nodes, but it can be easily augmented
to print out edges and cycles.

Bug: 1166855
Change-Id: Iab2a8f516d25524088c1eac27a5b5cd1f46fae51
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2630229
Commit-Queue: Henrique Nakashima <hnakashima@chromium.org>
Reviewed-by: Mohamed Heikal <mheikal@chromium.org>
Cr-Commit-Position: refs/heads/master@{#846340}

tools/android/dependency_analysis/diff_graphs.py

+#!/usr/bin/env python3
+# Copyright 2021 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+"""Command-line tool for finding differences in dependency graphs."""
+
+import argparse
+
+from typing import List, Set
+
+import graph
+import serialization
+
+
+def diff_num_graph_nodes(graph1: graph.Graph, graph2: graph.Graph, label: str):
+    before: int = graph1.num_nodes
+    after: int = graph2.num_nodes
+    diff: int = after - before
+    print(f'{label}: {diff:+} ({before} -> {after})')
+
+
+def diff_node_list(graph1: graph.Graph, graph2: graph.Graph, label: str):
+    print(f'{label} added (+) and removed (-):')
+    before_nodes: Set[str] = set(node.name for node in graph1.nodes)
+    after_nodes: Set[str] = set(node.name for node in graph2.nodes)
+    added_nodes: List[str] = sorted(after_nodes - before_nodes)
+    removed_nodes: List[str] = sorted(before_nodes - after_nodes)
+    for i, added_node in enumerate(added_nodes, start=1):
+        print(f'+ [{i:4}] {added_node}')
+    for i, removed_node in enumerate(removed_nodes, start=1):
+        print(f'- [{i:4}] {removed_node}')
+
+
+def main():
+    arg_parser = argparse.ArgumentParser(
+        description='Given two JSON dependency graphs, output the differences '
+        'between them.')
+    required_arg_group = arg_parser.add_argument_group('required arguments')
+    required_arg_group.add_argument(
+        '-b',
+        '--before',
+        required=True,
+        help='Path to the JSON file containing the "before" dependency graph. '
+        'See the README on how to generate this file.')
+    required_arg_group.add_argument(
+        '-a',
+        '--after',
+        required=True,
+        help='Path to the JSON file containing the "after" dependency graph.')
+    arguments = arg_parser.parse_args()
+
+    class_graph_before, package_graph_before, _ = \
+        serialization.load_class_and_package_graphs_from_file(arguments.before)
+    class_graph_after, package_graph_after, _ = \
+        serialization.load_class_and_package_graphs_from_file(arguments.after)
+    diff_num_graph_nodes(class_graph_before, class_graph_after,
+                         'Total Java class count')
+    diff_num_graph_nodes(package_graph_before, package_graph_after,
+                         'Total Java package count')
+
+    print()
+    diff_node_list(class_graph_before, class_graph_after, 'Java classes')
+    print()
+    diff_node_list(package_graph_before, package_graph_after, 'Java packages')
+
+
+if __name__ == '__main__':
+    main()