Add --classes optional flag in list_files

The flag enables list_files to output a list of .class files pattern
that will be generated when compiling the java files in the input
directory. The flag can be used to extract the appropriate class files
from stub jar file provided via dep_api_srcs in per api scope
sdk_library generated java_api_library modules.

Test: m --build-from-text-stub in same topic
Bug: 275570206
Change-Id: I134fcd9781024dcb6781297d02645f5fb9befb18

tools/list_files.py

@@ -18,6 +18,7 @@ from typing import List
 from glob import glob
 from pathlib import Path
 from os.path import join, relpath
+from itertools import chain
 import argparse
 
 class FileLister:
@@ -27,7 +28,8 @@ class FileLister:
         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()
+        self.files_list : List[str] = list()
+        self.classes = args.classes
 
     def get_files(self) -> None:
         """Get all files directory in the input directory including the files in the subdirectories
@@ -61,6 +63,26 @@ class FileLister:
     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]
+
+        # If files_list is as below:
+        # A/B/C.java
+        # A/B/D.java
+        # A/B/E.txt
+        # --classes flag converts files_list in the following format:
+        # A/B/C.class
+        # A/B/C$*.class
+        # A/B/D.class
+        # A/B/D$*.class
+        # Additional `$*`-suffixed line is appended after each line
+        # to take multiple top level classes in a single java file into account.
+        # Note that non-java files in files_list are filtered out.
+        if self.classes:
+            self.files_list = list(chain.from_iterable([
+                (class_files := str(Path(ff).with_suffix(".class")),
+                 class_files.replace(".class", "$*.class"))
+                 for ff in self.files_list if ff.endswith(".java")
+            ]))
+
         self.write()
 
     def write(self) -> None:
@@ -95,6 +117,10 @@ if __name__ == '__main__':
                         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")
+    parser.add_argument('--classes', dest='classes', action=argparse.BooleanOptionalAction,
+                        help="Optional flag. If passed, outputs a list of pattern of class files \
+                                that will be produced by compiling java files in the input dir. \
+                                Non-java files in the input directory will be ignored.")
 
     args = parser.parse_args()