Copy over the app/ and python/ subdirectories.

As announced in mid April, RE2 will take a dependency on Abseil in the
`main` branch. This change is one of (quite probably) many that should
ultimately see the `abseil` branch removed.

Change-Id: I0ae5a6643f77d2ebf675443cea7cba558b8c7fef
Reviewed-on: https://code-review.googlesource.com/c/re2/+/61230
Reviewed-by: Alex Chernyakhovsky <achernya@google.com>
Reviewed-by: Paul Wankadia <junyer@google.com>

python/setup.py

@@ -0,0 +1,106 @@
+# Copyright 2019 The RE2 Authors.  All Rights Reserved.
+# Use of this source code is governed by a BSD-style
+# license that can be found in the LICENSE file.
+
+import os
+import setuptools
+import setuptools.command.build_ext
+import shutil
+import sys
+
+long_description = r"""A drop-in replacement for the re module.
+
+It uses RE2 under the hood, of course, so various PCRE features
+(e.g. backreferences, look-around assertions) are not supported.
+See https://github.com/google/re2/wiki/Syntax for the canonical
+reference, but known syntactic "gotchas" relative to Python are:
+
+  * PCRE supports \Z and \z; RE2 supports \z; Python supports \z,
+    but calls it \Z. You must rewrite \Z to \z in pattern strings.
+
+Known differences between this module's API and the re module's API:
+
+  * The error class does not provide any error information as attributes.
+  * The Options class replaces the re module's flags with RE2's options as
+    gettable/settable properties. Please see re2.h for their documentation.
+  * The pattern string and the input string do not have to be the same type.
+    Any str will be encoded to UTF-8.
+  * The pattern string cannot be str if the options specify Latin-1 encoding.
+
+Known issues with regard to building the C++ extension:
+
+  * Building requires RE2 to be installed on your system.
+    On Debian, for example, install the libre2-dev package.
+  * Building requires pybind11 to be installed on your system OR venv.
+    On Debian, for example, install the pybind11-dev package.
+    For a venv, install the pybind11 package from PyPI.
+  * Building on macOS is known to work, but has been known to fail.
+    For example, the system Python may not know which compiler flags
+    to set when building bindings for software installed by Homebrew;
+    see https://docs.brew.sh/Homebrew-and-Python#brewed-python-modules.
+  * Building on Windows has not been tested yet and will probably fail.
+"""
+
+
+class BuildExt(setuptools.command.build_ext.build_ext):
+
+  def build_extension(self, ext):
+    if 'RUNNER_OS' not in os.environ:
+      return super().build_extension(ext)
+
+    # For @pybind11_bazel's `python_configure()`.
+    os.environ['PYTHON_BIN_PATH'] = sys.executable
+
+    cmd = ['bazel', 'clean', '--expunge']
+    self.spawn(cmd)
+
+    cmd = ['bazel', 'build', '--compilation_mode=opt']
+    cmd.append(f'--config={os.environ["RUNNER_OS"].lower()}')
+    if 'BAZEL_CPU' in os.environ:
+      cmd.append(f'--cpu={os.environ["BAZEL_CPU"].lower()}')
+    cmd += ['--', ':all']
+    self.spawn(cmd)
+
+    # This ensures that f'_re2.{importlib.machinery.EXTENSION_SUFFIXES[0]}'
+    # is the filename in the destination directory, which is what's needed.
+    shutil.copyfile('../bazel-bin/python/_re2.so',
+                    self.get_ext_fullpath(ext.name))
+
+
+def include_dirs():
+  try:
+    import pybind11
+    yield pybind11.get_include()
+  except ModuleNotFoundError:
+    pass
+
+
+ext_module = setuptools.Extension(
+    name='_re2',
+    sources=['_re2.cc'],
+    include_dirs=list(include_dirs()),
+    libraries=['re2'],
+    extra_compile_args=['-fvisibility=hidden'],
+)
+
+setuptools.setup(
+    name='google-re2',
+    version='1.0',
+    description='RE2 Python bindings',
+    long_description=long_description,
+    long_description_content_type='text/plain',
+    author='The RE2 Authors',
+    author_email='re2-dev@googlegroups.com',
+    url='https://github.com/google/re2',
+    py_modules=['re2'],
+    ext_modules=[ext_module],
+    classifiers=[
+        'Development Status :: 5 - Production/Stable',
+        'Intended Audience :: Developers',
+        'License :: OSI Approved :: BSD License',
+        'Programming Language :: C++',
+        'Programming Language :: Python :: 3.7',
+    ],
+    cmdclass={'build_ext': BuildExt},
+    python_requires='~=3.7',
+)