1# Copyright 2015 Google Inc. All Rights Reserved. 2# 3# Licensed under the Apache License, Version 2.0 (the "License"); 4# you may not use this file except in compliance with the License. 5# You may obtain a copy of the License at 6# 7# http://www.apache.org/licenses/LICENSE-2.0 8# 9# Unless required by applicable law or agreed to in writing, software 10# distributed under the License is distributed on an "AS IS" BASIS, 11# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 12# See the License for the specific language governing permissions and 13# limitations under the License. 14"""Verify that the generated code is valid code. 15 16This takes a line of code and "normalizes" it. I.e., it transforms the snippet 17into something that has the potential to compile. 18 19 VerifyCode(): the main function exported by this module. 20""" 21 22import ast 23import re 24import sys 25import textwrap 26 27 28class InternalError(Exception): 29 """Internal error in verifying formatted code.""" 30 pass 31 32 33def VerifyCode(code): 34 """Verify that the reformatted code is syntactically correct. 35 36 Arguments: 37 code: (unicode) The reformatted code snippet. 38 39 Raises: 40 SyntaxError if the code was reformatted incorrectly. 41 """ 42 try: 43 compile(textwrap.dedent(code).encode('UTF-8'), '<string>', 'exec') 44 except SyntaxError: 45 try: 46 ast.parse(textwrap.dedent(code.lstrip('\n')).lstrip(), '<string>', 'exec') 47 except SyntaxError: 48 try: 49 normalized_code = _NormalizeCode(code) 50 compile(normalized_code.encode('UTF-8'), '<string>', 'exec') 51 except SyntaxError: 52 raise InternalError(sys.exc_info()[1]) 53 54 55def _NormalizeCode(code): 56 """Make sure that the code snippet is compilable.""" 57 code = textwrap.dedent(code.lstrip('\n')).lstrip() 58 59 # Split the code to lines and get rid of all leading full-comment lines as 60 # they can mess up the normalization attempt. 61 lines = code.split('\n') 62 i = 0 63 for i, line in enumerate(lines): 64 line = line.strip() 65 if line and not line.startswith('#'): 66 break 67 code = '\n'.join(lines[i:]) + '\n' 68 69 if re.match(r'(if|while|for|with|def|class|async|await)\b', code): 70 code += '\n pass' 71 elif re.match(r'(elif|else)\b', code): 72 try: 73 try_code = 'if True:\n pass\n' + code + '\n pass' 74 ast.parse( 75 textwrap.dedent(try_code.lstrip('\n')).lstrip(), '<string>', 'exec') 76 code = try_code 77 except SyntaxError: 78 # The assumption here is that the code is on a single line. 79 code = 'if True: pass\n' + code 80 elif code.startswith('@'): 81 code += '\ndef _():\n pass' 82 elif re.match(r'try\b', code): 83 code += '\n pass\nexcept:\n pass' 84 elif re.match(r'(except|finally)\b', code): 85 code = 'try:\n pass\n' + code + '\n pass' 86 elif re.match(r'(return|yield)\b', code): 87 code = 'def _():\n ' + code 88 elif re.match(r'(continue|break)\b', code): 89 code = 'while True:\n ' + code 90 elif re.match(r'print\b', code): 91 code = 'from __future__ import print_function\n' + code 92 93 return code + '\n' 94