Try to download the latest versions of preinstalled packages

* Will only accept Wheels (because that is all we can install
  without setuptools).
* Will still fall back to using the bundled copies of the
  preinstalled packages if it cannot access the internet.

This should prevent errors happening from too old of versions of
software being bundled with virtualenv, while still allowing people
to prevent talking to the internet with --no-download.

docs/changes.rst

@@ -29,6 +29,11 @@ Release History
 
 * Remove use of () in .bat files so ``Program Files (x86)`` works :issue:`35`
 
+* Download new releases of the preinstalled software from PyPI when there are
+  new releases available. This behavior can be disabled using
+  ``--no-download``.
+
+
 13.1.2 (2015-08-23)
 -------------------
 

docs/reference.rst

@@ -90,11 +90,13 @@ Options
    Provides an alternative prompt prefix for this
    environment.
 
-.. option:: --never-download
+.. option:: --download
 
-   DEPRECATED. Retained only for backward compatibility.
-   This option has no effect. Virtualenv never downloads
-   pip or setuptools.
+   Download preinstalled packages from PyPI.
+
+.. option:: --no-download
+
+   Do not download preinstalled packages from PyPI.
 
 .. option:: --no-site-packages
 

docs/userguide.rst

@@ -128,7 +128,7 @@ below.
 Removing an Environment
 ~~~~~~~~~~~~~~~~~~~~~~~
 
-Removing a virtual environment is simply done by deactivating it and deleting the 
+Removing a virtual environment is simply done by deactivating it and deleting the
 environment folder with all its contents::
 
     (ENV)$ deactivate
@@ -254,5 +254,3 @@ As well as the extra directories, the search order includes:
 #. The directory where virtualenv.py is located.
 #. The current directory.
 
-If no satisfactory local distributions are found, virtualenv will
-fail. Virtualenv will never download packages.

virtualenv.py

@@ -606,12 +606,19 @@ def main():
               "This option can be used multiple times.")
 
     parser.add_option(
-        '--never-download',
-        dest="never_download",
+        "--download",
+        dest="download",
         action="store_true",
-        default=True,
-        help="DEPRECATED. Retained only for backward compatibility. This option has no effect. "
-              "Virtualenv never downloads pip or setuptools.")
+        help="Download preinstalled packages from PyPI.",
+    )
+
+    parser.add_option(
+        "--no-download",
+        '--never-download',
+        dest="download",
+        action="store_false",
+        help="Do not download preinstalled packages from PyPI.",
+    )
 
     parser.add_option(
         '--prompt',
@@ -682,17 +689,13 @@ def main():
         make_environment_relocatable(home_dir)
         return
 
-    if not options.never_download:
-        logger.warn('The --never-download option is for backward compatibility only.')
-        logger.warn('Setting it to false is no longer supported, and will be ignored.')
-
     create_environment(home_dir,
                        site_packages=options.system_site_packages,
                        clear=options.clear,
                        unzip_setuptools=options.unzip_setuptools,
                        prompt=options.prompt,
                        search_dirs=options.search_dirs,
-                       never_download=True,
+                       download=options.download,
                        no_setuptools=options.no_setuptools,
                        no_pip=options.no_pip,
                        no_wheel=options.no_wheel,
@@ -811,7 +814,8 @@ def find_wheels(projects, search_dirs):
 
     return wheels
 
-def install_wheel(project_names, py_executable, search_dirs=None):
+def install_wheel(project_names, py_executable, search_dirs=None,
+                  download=False):
     if search_dirs is None:
         search_dirs = file_search_dirs()
 
@@ -825,25 +829,29 @@ def install_wheel(project_names, py_executable, search_dirs=None):
     ] + project_names
     logger.start_progress('Installing %s...' % (', '.join(project_names)))
     logger.indent += 2
+
+    env = {
+        "PYTHONPATH": pythonpath,
+        "JYTHONPATH": pythonpath,  # for Jython < 3.x
+        "PIP_FIND_LINKS": findlinks,
+        "PIP_USE_WHEEL": "1",
+        "PIP_ONLY_BINARY": ":all:",
+        "PIP_PRE": "1",
+        "PIP_USER": "0",
+    }
+
+    if not download:
+        env["PIP_NO_INDEX"] = "1"
+
     try:
-        call_subprocess(cmd, show_stdout=False,
-            extra_env = {
-                'PYTHONPATH': pythonpath,
-                'JYTHONPATH': pythonpath,  # for Jython < 3.x
-                'PIP_FIND_LINKS': findlinks,
-                'PIP_USE_WHEEL': '1',
-                'PIP_PRE': '1',
-                'PIP_NO_INDEX': '1',
-                'PIP_USER': '0'
-            }
-        )
+        call_subprocess(cmd, show_stdout=False, extra_env=env)
     finally:
         logger.indent -= 2
         logger.end_progress()
 
 def create_environment(home_dir, site_packages=False, clear=False,
                        unzip_setuptools=False,
-                       prompt=None, search_dirs=None, never_download=False,
+                       prompt=None, search_dirs=None, download=False,
                        no_setuptools=False, no_pip=False, no_wheel=False,
                        symlink=True):
     """
@@ -869,7 +877,12 @@ def create_environment(home_dir, site_packages=False, clear=False,
             to_install.append('pip')
         if not no_wheel:
             to_install.append('wheel')
-        install_wheel(to_install, py_executable, search_dirs)
+        install_wheel(
+            to_install,
+            py_executable,
+            search_dirs,
+            download=download,
+        )
 
     install_activate(home_dir, bin_dir, prompt)