Spack doesn't run site customization when started

fixes spack#9206
fixes spack#9034

A possible solution to spack#9206 is to avoid running `import site` and all
the initialization procedures that this entails. This requires us to use
`python -S` as an interpreter, instead of plain `python`.

Of course things can't be that simple. In Linux (but not in BSD or
MacOS) the shebang pass a single string argument to the interpreter.
More details on the subject are here:

http://sambal.org/2014/02/passing-options-node-shebang-line/
https://github.com/smikes/node/blob/minus-x-switch/doc/Minus-X-Switch-Proposal.md#shebang-interpretation

but the bottom line is that this requires us to have a wrapper bash
script that invokes the interpreter with the correct option.

Finally, as now we are not picking up anything from the 'site', we need
to vendor `setuptools` (which was still missing).

bin/spack

@@ -1,36 +1,8 @@
-#!/usr/bin/env python
+#!/usr/bin/env bash
 #
 # Copyright 2013-2018 Lawrence Livermore National Security, LLC and other
 # Spack Project Developers. See the top-level COPYRIGHT file for details.
 #
 # SPDX-License-Identifier: (Apache-2.0 OR MIT)
 
-from __future__ import print_function
-
-import os
-import sys
-
-if sys.version_info[:2] < (2, 6):
-    v_info = sys.version_info[:3]
-    sys.exit("Spack requires Python 2.6 or higher."
-             "This is Python %d.%d.%d." % v_info)
-
-# Find spack's location and its prefix.
-spack_file = os.path.realpath(os.path.expanduser(__file__))
-spack_prefix = os.path.dirname(os.path.dirname(spack_file))
-
-# Allow spack libs to be imported in our scripts
-spack_lib_path = os.path.join(spack_prefix, "lib", "spack")
-sys.path.insert(0, spack_lib_path)
-
-# Add external libs
-spack_external_libs = os.path.join(spack_lib_path, "external")
-
-if sys.version_info[:2] == (2, 6):
-    sys.path.insert(0, os.path.join(spack_external_libs, 'py26'))
-
-sys.path.insert(0, spack_external_libs)
-
-# Once we've set up the system path, run the spack main method
-import spack.main  # noqa
-sys.exit(spack.main.main())
+exec /usr/bin/env python -S $0.py "$@"

bin/spack.py

@@ -0,0 +1,65 @@
+#!/usr/bin/env python
+#
+# Copyright 2013-2018 Lawrence Livermore National Security, LLC and other
+# Spack Project Developers. See the top-level COPYRIGHT file for details.
+#
+# SPDX-License-Identifier: (Apache-2.0 OR MIT)
+
+# Spack uses `python -S` as an interpreter to avoid the issue reported in:
+#
+# https://github.com/spack/spack/issues/9206
+#
+# Unfortunately not running `import site` by default causes all sort of
+# inconsistencies as:
+#
+# - the system built-in modules that get linked into a virtual-env differ
+#   among python versions and might not include `__future__` or `inpect`
+#   (this means that `python -S` might prevent importing those modules)
+#
+# - the `site.py` used in Python 2.7 virtual environments is that of Python 2.6
+#   (https://github.com/pypa/virtualenv/issues/355)
+#
+# The hack below is needed to restore built-in modules from the system if
+# they are missing. It assumes that the module `re` is always present as a
+# built-in, and adds its real path to the end of `sys.path` to recover all
+# the other system modules.
+try:
+    import __future__  # noqa
+    import inspect  # noqa
+except ImportError:
+    # If `__future__` is not there, it's very likely we are within
+    # a Python 2.7 virtual environment. If `inspect` is not there
+    # it could be a Python 3.6 virtual environment.
+    import os.path
+    import re
+    import sys
+    re_realpath = os.path.realpath(re.__file__.replace('.pyc', '.py'))
+    sys.path.append(os.path.dirname(re_realpath))
+
+import os
+import sys
+
+if sys.version_info[:2] < (2, 6):
+    v_info = sys.version_info[:3]
+    sys.exit("Spack requires Python 2.6 or higher."
+             "This is Python %d.%d.%d." % v_info)
+
+# Find spack's location and its prefix.
+spack_file = os.path.realpath(os.path.expanduser(__file__))
+spack_prefix = os.path.dirname(os.path.dirname(spack_file))
+
+# Allow spack libs to be imported in our scripts
+spack_lib_path = os.path.join(spack_prefix, "lib", "spack")
+sys.path.insert(0, spack_lib_path)
+
+# Add external libs
+spack_external_libs = os.path.join(spack_lib_path, "external")
+
+if sys.version_info[:2] == (2, 6):
+    sys.path.insert(0, os.path.join(spack_external_libs, 'py26'))
+
+sys.path.insert(0, spack_external_libs)
+
+# Once we've set up the system path, run the spack main method
+import spack.main  # noqa
+sys.exit(spack.main.main())

lib/spack/spack/main.py

@@ -290,6 +290,7 @@ def format_help(self, level='short'):
 def make_argument_parser(**kwargs):
     """Create an basic argument parser without any subcommands added."""
     parser = SpackArgumentParser(
+        prog='spack',
         formatter_class=SpackHelpFormatter, add_help=False,
         description=(
             "A flexible package manager that supports multiple versions,\n"

lib/spack/spack/paths.py

@@ -23,7 +23,7 @@
 bin_path = os.path.join(prefix, "bin")
 
 #: The spack script itself
-spack_script = os.path.join(bin_path, "spack")
+spack_script = os.path.join(bin_path, "spack.py")
 
 # spack directory hierarchy
 lib_path              = os.path.join(prefix, "lib", "spack")