Create a python script to list files given a directory as an input

The script will be used in generating a file that lists generated stub
files from metalava, which will be passed to soong_zip to extract
selected stub files when generating stubs from java_api_library modules
with incomplete api surface text files.

Test: build java_api_library modules in aosp/2487335
Change-Id: I36b830f14c714315f81e3fd8608d84c29f673f83

tools/Android.bp

@@ -85,3 +85,11 @@ python_binary_host {
         "libprotobuf-python",
     ],
 }
+
+python_binary_host {
+    name: "list_files",
+    main: "list_files.py",
+    srcs: [
+        "list_files.py",
+    ],
+}

tools/list_files.py

@@ -0,0 +1,102 @@
+#!/usr/bin/env python
+#
+# Copyright (C) 2023 The Android Open Source Project
+#
+# 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.
+
+from typing import List
+from glob import glob
+from pathlib import Path
+from os.path import join, relpath
+import argparse
+
+class FileLister:
+    def __init__(self, args) -> None:
+        self.out_file = args.out_file
+
+        self.folder_dir = args.dir
+        self.extensions = [e if e.startswith(".") else "." + e for e in args.extensions]
+        self.root = args.root
+        self.files_list = list()
+
+    def get_files(self) -> None:
+        """Get all files directory in the input directory including the files in the subdirectories
+
+        Recursively finds all files in the input directory.
+        Set file_list as a list of file directory strings,
+        which do not include directories but only files.
+        List is sorted in alphabetical order of the file directories.
+
+        Args:
+            dir: Directory to get the files. String.
+
+        Raises:
+            FileNotFoundError: An error occurred accessing the non-existing directory
+        """
+
+        if not dir_exists(self.folder_dir):
+            raise FileNotFoundError(f"Directory {self.folder_dir} does not exist")
+
+        if self.folder_dir[:-2] != "**":
+            self.folder_dir = join(self.folder_dir, "**")
+
+        self.files_list = list()
+        for file in sorted(glob(self.folder_dir, recursive=True)):
+            if Path(file).is_file():
+                if self.root:
+                    file = join(self.root, relpath(file, self.folder_dir[:-2]))
+                self.files_list.append(file)
+
+
+    def list(self) -> None:
+        self.get_files()
+        self.files_list = [f for f in self.files_list if not self.extensions or Path(f).suffix in self.extensions]
+        self.write()
+
+    def write(self) -> None:
+        if self.out_file == "":
+            pprint(self.files_list)
+        else:
+            write_lines(self.out_file, self.files_list)
+
+###
+# Helper functions
+###
+def pprint(l: List[str]) -> None:
+    for line in l:
+        print(line)
+
+def dir_exists(dir: str) -> bool:
+    return Path(dir).exists()
+
+def write_lines(out_file: str, lines: List[str]) -> None:
+    with open(out_file, "w+") as f:
+        f.writelines(line + '\n' for line in lines)
+
+if __name__ == '__main__':
+    parser = argparse.ArgumentParser()
+    parser.add_argument('dir', action='store', type=str,
+                        help="directory to list all subdirectory files")
+    parser.add_argument('--out', dest='out_file',
+                        action='store', default="", type=str,
+                        help="optional directory to write subdirectory files. If not set, will print to console")
+    parser.add_argument('--root', dest='root',
+                        action='store', default="", type=str,
+                        help="optional directory to replace the root directories of output.")
+    parser.add_argument('--extensions', nargs='*', default=list(), dest='extensions',
+                        help="Extensions to include in the output. If not set, all files are included")
+
+    args = parser.parse_args()
+
+    file_lister = FileLister(args)
+    file_lister.list()