scripts: Add wrapper script for all codegen

Simplify running the 3 different code generators with a wrapper script.
Provides options:
    --verify         diff generator output and repo files
    --incremental    only touh files that actually changed

Add wrapper script to CMake as VulkanVL_generated_source target

Change-Id: I9d8440092748adf546602bd1f1b204470cf161aa
diff --git a/scripts/generate_source.py b/scripts/generate_source.py
new file mode 100755
index 0000000..4b3b606
--- /dev/null
+++ b/scripts/generate_source.py
@@ -0,0 +1,136 @@
+#!/usr/bin/env python3
+# Copyright (c) 2019 The Khronos Group Inc.
+# Copyright (c) 2019 Valve Corporation
+# Copyright (c) 2019 LunarG, Inc.
+# Copyright (c) 2019 Google Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+# Author: Mike Schuchardt <mikes@lunarg.com>
+
+import argparse
+import filecmp
+import os
+import shutil
+import subprocess
+import sys
+import tempfile
+
+# files to exclude from --verify check
+verify_exclude = ['.clang-format']
+
+# helper to define paths relative to this file
+def script_relative(path):
+    return os.path.abspath(os.path.join(os.path.dirname(__file__), path))
+
+def main(argv):
+    parser = argparse.ArgumentParser(description='Generate source code for this repository')
+    parser.add_argument('registry', metavar='REGISTRY_PATH', help='path to the Vulkan-Headers registry directory')
+    group = parser.add_mutually_exclusive_group()
+    group.add_argument('-i', '--incremental', action='store_true', help='only update repo files that change')
+    group.add_argument('-v', '--verify', action='store_true', help='verify repo files match generator output')
+    args = parser.parse_args(argv)
+
+    gen_cmds = [*[[script_relative('lvl_genvk.py'),
+                   '-registry', os.path.abspath(os.path.join(args.registry,  'vk.xml')),
+                   '-quiet',
+                   filename] for filename in ["chassis.cpp",
+                                              "chassis.h",
+                                              "layer_chassis_dispatch.cpp",
+                                              "layer_chassis_dispatch.h",
+                                              "object_tracker.cpp",
+                                              "object_tracker.h",
+                                              "parameter_validation.cpp",
+                                              "parameter_validation.h",
+                                              "thread_safety.cpp",
+                                              "thread_safety.h",
+                                              "vk_dispatch_table_helper.h",
+                                              "vk_enum_string_helper.h",
+                                              "vk_extension_helper.h",
+                                              "vk_layer_dispatch_table.h",
+                                              "vk_object_types.h",
+                                              "vk_safe_struct.cpp",
+                                              "vk_safe_struct.h",
+                                              "vk_typemap_helper.h"]],
+                [script_relative('vk_validation_stats.py'),
+                 os.path.abspath(os.path.join(args.registry, 'validusage.json')),
+                 '-export_header'],
+                [script_relative('external_revision_generator.py'),
+                 '--rev_file', script_relative('known_good.json'),
+                 '-s', 'SPIRV_TOOLS_COMMIT_ID',
+                 '-o', 'spirv_tools_commit_id.h']]
+
+    repo_dir = script_relative('../layers/generated')
+
+    # get directory where generators will run
+    if args.verify or args.incremental:
+        # generate in temp directory so we can compare or copy later
+        temp_obj = tempfile.TemporaryDirectory(prefix='VulkanVL_generated_source_')
+        temp_dir = temp_obj.name
+        gen_dir = temp_dir
+    else:
+        # generate directly in the repo
+        gen_dir = repo_dir
+
+    # run each code generator
+    for cmd in gen_cmds:
+        print(' '.join(cmd))
+        try:
+            subprocess.check_call([sys.executable] + cmd,
+                                  # ignore generator output, vk_validation_stats.py is especially noisy
+                                  stdout=subprocess.DEVNULL,
+                                  cwd=gen_dir)
+        except Exception as e:
+            print('ERROR:', str(e))
+            return 1
+
+    # optional post-generation steps
+    if args.verify:
+        # compare contents of temp dir and repo
+        temp_files = set(os.listdir(temp_dir))
+        repo_files = set(os.listdir(repo_dir))
+        files_match = True
+        for filename in sorted((temp_files | repo_files) - set(verify_exclude)):
+            if filename not in repo_files:
+                print('ERROR: Missing repo file', filename)
+                files_match = False
+            elif filename not in temp_files:
+                print('ERROR: Missing generator for', filename)
+                files_match = False
+            elif not filecmp.cmp(os.path.join(temp_dir, filename),
+                               os.path.join(repo_dir, filename),
+                               shallow=False):
+                print('ERROR: Repo files do not match generator output for', filename)
+                files_match = False
+
+        # return code for test scripts
+        if files_match:
+            print('SUCCESS: Repo files match generator output')
+            return 0
+        return 1
+
+    elif args.incremental:
+        # copy missing or differing files from temp directory to repo
+        for filename in os.listdir(temp_dir):
+            temp_filename = os.path.join(temp_dir, filename)
+            repo_filename = os.path.join(repo_dir, filename)
+            if not os.path.exists(repo_filename) or \
+               not filecmp.cmp(temp_filename, repo_filename, shallow=False):
+                print('update', repo_filename)
+                shutil.copyfile(temp_filename, repo_filename)
+
+    return 0
+
+if __name__ == '__main__':
+    sys.exit(main(sys.argv[1:]))
+