old_contents: #!/usr/bin/env python3
  
  # Copyright 2013-2016 The Meson development team
  
  # 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.
  
  import os
  import sys
  import argparse
  import pickle
  import platform
  import subprocess
  
  import mesonbuild
  
  options = None
  
  parser = argparse.ArgumentParser()
  parser.add_argument('args', nargs='+')
  
  def is_windows():
      platname = platform.system().lower()
      return platname == 'windows' or 'mingw' in platname
  
  def run_with_mono(fname):
      if fname.endswith('.exe') and not is_windows():
          return True
      return False
  
  def run_exe(exe):
      if exe.fname[0].endswith('.jar'):
          cmd = ['java', '-jar'] + exe.fname
      elif not exe.is_cross and run_with_mono(exe.fname[0]):
          cmd = ['mono'] + exe.fname
      else:
          if exe.is_cross:
              if exe.exe_runner is None:
                  raise Exception('BUG: Trying to run cross-compiled exes with no wrapper')
              else:
                  cmd = [exe.exe_runner] + exe.fname
          else:
              cmd = exe.fname
      child_env = os.environ.copy()
      child_env.update(exe.env)
      if len(exe.extra_paths) > 0:
          child_env['PATH'] = child_env['PATH'] + ';'.join([''] + exe.extra_paths)
      p = subprocess.Popen(cmd + exe.cmd_args,
                           stdout=subprocess.PIPE,
                           stderr=subprocess.PIPE,
                           env=child_env,
                           cwd=exe.workdir)
  
  def run(args):
      global options
      options = parser.parse_args(args)
      if len(options.args) != 1:
          print('Test runner for Meson. Do not run on your own, mmm\'kay?')
          print(sys.argv[0] + ' [data file]')
      exe_data_file = options.args[0]
      exe = pickle.load(open(exe_data_file, 'rb'))
      run_exe(exe)
  
  if __name__ == '__main__':
      sys.exit(run(sys.argv[1:]))
  
new_contents: #!/usr/bin/env python3
  
  # Copyright 2013-2016 The Meson development team
  
  # 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.
  
  import os
  import sys
  import argparse
  import pickle
  import platform
  import subprocess
  
  import mesonbuild
  
  options = None
  
  parser = argparse.ArgumentParser()
  parser.add_argument('args', nargs='+')
  
  def is_windows():
      platname = platform.system().lower()
      return platname == 'windows' or 'mingw' in platname
  
  def run_with_mono(fname):
      if fname.endswith('.exe') and not is_windows():
          return True
      return False
  
  def run_exe(exe):
      if exe.fname[0].endswith('.jar'):
          cmd = ['java', '-jar'] + exe.fname
      elif not exe.is_cross and run_with_mono(exe.fname[0]):
          cmd = ['mono'] + exe.fname
      else:
          if exe.is_cross:
              if exe.exe_runner is None:
                  raise Exception('BUG: Trying to run cross-compiled exes with no wrapper')
              else:
                  cmd = [exe.exe_runner] + exe.fname
          else:
              cmd = exe.fname
      child_env = os.environ.copy()
      child_env.update(exe.env)
      if len(exe.extra_paths) > 0:
          child_env['PATH'] = ';'.join(exe.extra_paths + ['']) + child_env['PATH']
      p = subprocess.Popen(cmd + exe.cmd_args,
                           stdout=subprocess.PIPE,
                           stderr=subprocess.PIPE,
                           env=child_env,
                           cwd=exe.workdir)
  
  def run(args):
      global options
      options = parser.parse_args(args)
      if len(options.args) != 1:
          print('Test runner for Meson. Do not run on your own, mmm\'kay?')
          print(sys.argv[0] + ' [data file]')
      exe_data_file = options.args[0]
      exe = pickle.load(open(exe_data_file, 'rb'))
      run_exe(exe)
  
  if __name__ == '__main__':
      sys.exit(run(sys.argv[1:]))
  
subject: prepend extra_paths to PATH instead of appending