Issue 2539 - Move VCS abstraction part of ensure_dependencies into a separate module

script_compiler.py

Index: script_compiler.py
===================================================================
new file mode 100644
--- /dev/null
+++ b/script_compiler.py
@@ -0,0 +1,40 @@
+# coding: utf-8
+
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+import importlib
+import inspect
+
+def multiline_repr(str):

[Sebastian Noack, 2015/05/19 11:52:41]

Nit: Please avoid variable names conflicting with built-ins like "str".

+  return "'''%s'''" % str.replace('\\', '\\\\').replace("'", "\\'")

[Sebastian Noack, 2015/05/19 11:52:41]

Note that you only need to escape quotes if followed by at least two more
quotes. This is another feature of Python's triple-quote syntax beside allowing
newlines, and makes the resulting code a little more readable:

  re.sub(r"(\\|'(?=''))", r'\\\1', s)

+
+def compile_script(main, modules=[]):
+  '''
+    Combines the source code of a main module and a number of additional modules
+    in a single Python script.
+  '''
+
+  yield '#!/usr/bin/env python\n'

[Sebastian Noack, 2015/05/19 11:52:41]

I'd rather pass in the file object and use the print statement instead returning
generator here. That way you don't need a loop in the calling code, and don't
need to hard-code the newline character here.

+  yield 'modules = []\n'
+  for module in modules + [main]:
+    path = inspect.getsourcefile(reload(importlib.import_module(module)))
+    with open(path, 'rb') as file:
+      data = file.read()
+      yield 'modules.append((%s, %s))\n' % (repr(module), multiline_repr(data))
+
+  yield '''
+import imp
+import importlib

[Sebastian Noack, 2015/05/19 11:52:41]

importlib isn't used in the generated file.

+import sys
+
+if __name__ == '__main__':
+  for module, source in modules:

[Sebastian Noack, 2015/05/19 11:52:41]

IMO, both, the generated and the generating code would be simpler if you unroll
the loop and inline the main script:

  def get_module_source(module):
    filename = inspect.getsourcefile(importlib.import_module(module))
    with open(filename, 'rb') as file:
      return file.read()

  def compile_script(file, main, modules):
    print >>file, 'import imp'
    print >>file, 'import sys'
    print >>file
  
    for module in modules:
      print >>file, 'module = imp.new_module(%r)' % module
      print >>file, 'sys.modules[%r] = module' % module
      source = get_module_source(module)
      if source:
        print >>file, 'exec %s in module.__dict__' %
multiline_repr(get_module_source(module))
      print >>file
    
    print >>file, 'del imp, sys, module'
    print >>file
    print >>file, get_module_source(main)

+    m = imp.new_module(module)
+    if (module, source) == modules[-1]:
+      m.__name__ = __name__
+      m.__file__ = __file__
+    exec source in m.__dict__
+    sys.modules[module] = m
+'''