Precompile python sources

This signifigantly improves the startup time of soong-built
python binaries. For example, running
`m apexer && time out/host/linux-x86/bin/apexer` gives
0.734s before this cl, and 0.094s after.

Fixes: 259718110
Test: Presubmits
Change-Id: Ib19e83e2c60c39a849525be117279c318de3afa7

python/scripts/precompile_python.py

@@ -0,0 +1,61 @@
+#!/usr/bin/env python3
+# Copyright 2023 Google Inc. All rights reserved.
+#
+# 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.
+
+import argparse
+import py_compile
+import os
+import shutil
+import tempfile
+import zipfile
+
+# This file needs to support both python 2 and 3.
+
+
+def process_one_file(name, inf, outzip):
+    if not name.endswith('.py'):
+        outzip.writestr(name, inf.read())
+        return
+
+    # Unfortunately py_compile requires the input/output files to be written
+    # out to disk.
+    with tempfile.NamedTemporaryFile(prefix="Soong_precompile_", delete=False) as tmp:
+        shutil.copyfileobj(inf, tmp)
+        in_name = tmp.name
+    with tempfile.NamedTemporaryFile(prefix="Soong_precompile_", delete=False) as tmp:
+        out_name = tmp.name
+    try:
+        py_compile.compile(in_name, out_name, name, doraise=True)
+        with open(out_name, 'rb') as f:
+            outzip.writestr(name + 'c', f.read())
+    finally:
+        os.remove(in_name)
+        os.remove(out_name)
+
+
+def main():
+    parser = argparse.ArgumentParser()
+    parser.add_argument('src_zip')
+    parser.add_argument('dst_zip')
+    args = parser.parse_args()
+
+    with open(args.dst_zip, 'wb') as outf, open(args.src_zip, 'rb') as inf:
+        with zipfile.ZipFile(outf, mode='w') as outzip, zipfile.ZipFile(inf, mode='r') as inzip:
+            for name in inzip.namelist():
+                with inzip.open(name, mode='r') as inzipf:
+                    process_one_file(name, inzipf, outzip)
+
+
+if __name__ == "__main__":
+    main()