Add a script to generate the Java-class-to-objc-header mapping for J2ObjC. Previously the mapping is generated directly by J2ObjC through j2objc_wrapper.py.

RELNOTES:None.

--
PiperOrigin-RevId: 151138711
MOS_MIGRATED_REVID=151138711

tools/j2objc/j2objc_header_map.py

diff --git a/tools/j2objc/j2objc_header_map.py b/tools/j2objc/j2objc_header_map.py
new file mode 100644
index 0000000..090d54f
--- /dev/null
+++ b/tools/j2objc/j2objc_header_map.py
@@ -0,0 +1,129 @@
+#!/usr/bin/python2.7
+
+# Copyright 2017 The Bazel Authors. 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.
+
+"""A script to generate Java class to ObjC header mapping for J2ObjC.
+
+This script generates a text file containing mapping between top-level Java
+classes to associated ObjC headers, generated by J2ObjC.
+
+The mapping file is used by dependent J2ObjC transpilation actions to locate
+the correct header import paths for dependent Java classes.
+
+Inside the script, we read the Java source files and source jars of a single
+Java rule, and parse out the package names from the package statements, using
+regular expression matching.
+
+Note that we cannot guarantee 100% correctness by using just regular expression,
+but it should be good enough. This allows us to avoid doing any further complex
+parsing of the source files and keep the script light-weight without other
+dependencies. In the future, we can consider implementing a simple Java lexer
+here that correctly parses the package statements out of Java files.
+"""
+
+import argparse
+import os
+import re
+import zipfile
+
+_PACKAGE_RE = re.compile(r'(package)\s+([\w\.]+);')
+
+
+def _get_file_map_entry(java_file_path, java_file):
+  """Returns the top-level Java class and header file path tuple.
+
+  Args:
+    java_file_path: The file path of the source Java file.
+    java_file: The actual file of the source java file.
+  Returns:
+    A tuple containing top-level Java class and associated header file path. Or
+    None if no package statement exists in the source file.
+  """
+  for line in java_file:
+    stripped_line = line.strip()
+    package_statement = _PACKAGE_RE.search(stripped_line)
+
+    # We identified a potential package statement.
+    if package_statement:
+      preceding_characters = stripped_line[0:package_statement.start(1)]
+      # We have preceding characters before the package statement. We need to
+      # look further into them.
+      if preceding_characters:
+        # Skip comment line.
+        if preceding_characters.startswith('//'):
+          continue
+
+        # Preceding characters also must end with a space, represent an end
+        # of comment, or end of a statement.
+        # Otherwise, we skip the current line.
+        if not (preceding_characters[len(preceding_characters) - 1].isspace() or
+                preceding_characters.endswith(';') or
+                preceding_characters.endswith('*/')):
+          continue
+      package_name = package_statement.group(2)
+      class_name = os.path.splitext(os.path.basename(java_file_path))[0]
+      header_file = os.path.splitext(java_file_path)[0] + '.h'
+      return (package_name + '.' + class_name, header_file)
+  return None
+
+
+def main():
+  parser = argparse.ArgumentParser(fromfile_prefix_chars='@')
+  parser.add_argument(
+      '--source_files',
+      required=False,
+      help='The source files')
+  parser.add_argument(
+      '--source_jars',
+      required=False,
+      help='The source jars.')
+  parser.add_argument(
+      '--output_mapping_file',
+      required=False,
+      help='The output mapping file')
+
+  args, _ = parser.parse_known_args()
+  class_to_header_map = dict()
+
+  # Process the source files.
+  if args.source_files:
+    source_files = args.source_files.split(',')
+    for source_file in source_files:
+      with open(source_file, 'r') as f:
+        entry = _get_file_map_entry(source_file, f)
+        if entry:
+          class_to_header_map[entry[0]] = entry[1]
+
+  # Process the source jars.
+  if args.source_jars:
+    source_jars = args.source_jars.split(',')
+    for source_jar in source_jars:
+      with zipfile.ZipFile(source_jar, 'r') as jar:
+        for jar_entry in jar.namelist():
+          if jar_entry.endswith('.java'):
+            with jar.open(jar_entry) as jar_entry_file:
+              entry = _get_file_map_entry(jar_entry, jar_entry_file)
+              if entry:
+                class_to_header_map[entry[0]] = entry[1]
+
+  # Generate the output header mapping file.
+  if args.output_mapping_file:
+    with open(args.output_mapping_file, 'w') as output_mapping_file:
+      for class_name in sorted(class_to_header_map):
+        header_path = class_to_header_map[class_name]
+        output_mapping_file.write(class_name + '=' + header_path + '\n')
+
+if __name__ == '__main__':
+  main()