# Copyright 2015 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.

"""Verify that the generated code is valid code.

This takes a line of code and "normalizes" it. I.e., it transforms the snippet

into something that has the potential to compile.

VerifyCode(): the main function exported by this module.

"""

import ast

import re

import sys

import textwrap

class InternalError(Exception):

"""Internal error in verifying formatted code."""

pass

def VerifyCode(code):

"""Verify that the reformatted code is syntactically correct.

Arguments:

code: (unicode) The reformatted code snippet.

Raises:

SyntaxError if the code was reformatted incorrectly.

"""

try:

compile(textwrap.dedent(code).encode('UTF-8'), '<string>', 'exec')

except SyntaxError:

try:

ast.parse(textwrap.dedent(code.lstrip('\n')).lstrip(), '<string>', 'exec')

except SyntaxError:

try:

normalized_code = _NormalizeCode(code)

compile(normalized_code.encode('UTF-8'), '<string>', 'exec')

except SyntaxError:

raise InternalError(sys.exc_info()[1])

def _NormalizeCode(code):

"""Make sure that the code snippet is compilable."""

code = textwrap.dedent(code.lstrip('\n')).lstrip()

# Split the code to lines and get rid of all leading full-comment lines as

# they can mess up the normalization attempt.

lines = code.split('\n')

i = 0

for i, line in enumerate(lines):

line = line.strip()

if line and not line.startswith('#'):

break

code = '\n'.join(lines[i:]) + '\n'

if re.match(r'(if|while|for|with|def|class)\b', code):

code += '\n pass'

elif re.match(r'(elif|else)\b', code):

try:

try_code = 'if True:\n pass\n' + code + '\n pass'

ast.parse(

textwrap.dedent(try_code.lstrip('\n')).lstrip(), '<string>', 'exec')

code = try_code

except SyntaxError:

# The assumption here is that the code is on a single line.

code = 'if True: pass\n' + code

elif code.startswith('@'):

code += '\ndef _():\n pass'

elif re.match(r'try\b', code):

code += '\n pass\nexcept:\n pass'

elif re.match(r'(except|finally)\b', code):

code = 'try:\n pass\n' + code + '\n pass'

elif re.match(r'(return|yield)\b', code):

code = 'def _():\n ' + code

elif re.match(r'(continue|break)\b', code):

code = 'while True:\n ' + code

elif re.match(r'print\b', code):

code = 'from __future__ import print_function\n' + code

return code + '\n'