Fix installers to be insensitive to extras iteration order.

pex/installer.py

@@ -33,7 +33,8 @@ def function_wrapper(self, *args, **kw):
 
 class InstallerBase(object):
   SETUP_BOOTSTRAP_HEADER = "import sys"
-  SETUP_BOOTSTRAP_MODULE = "sys.path.insert(0, %(path)r); import %(module)s"
+  SETUP_BOOTSTRAP_PYPATH = "sys.path.insert(0, %(path)r)"
+  SETUP_BOOTSTRAP_MODULE = "import %(module)s"
   SETUP_BOOTSTRAP_FOOTER = """
 __file__ = 'setup.py'
 sys.argv[0] = 'setup.py'
@@ -85,15 +86,21 @@ def capability(self):
 
   @property
   def bootstrap_script(self):
+    bootstrap_sys_paths = []
     bootstrap_modules = []
     for module, requirement in self.mixins().items():
       path = self._interpreter.get_location(requirement)
       if not path:
         assert not self._strict  # This should be caught by validation
         continue
-      bootstrap_modules.append(self.SETUP_BOOTSTRAP_MODULE % {'path': path, 'module': module})
+      bootstrap_sys_paths.append(self.SETUP_BOOTSTRAP_PYPATH % {'path': path})
+      bootstrap_modules.append(self.SETUP_BOOTSTRAP_MODULE % {'module': module})
     return '\n'.join(
-        [self.SETUP_BOOTSTRAP_HEADER] + bootstrap_modules + [self.SETUP_BOOTSTRAP_FOOTER])
+      [self.SETUP_BOOTSTRAP_HEADER] +
+      bootstrap_sys_paths +
+      bootstrap_modules +
+      [self.SETUP_BOOTSTRAP_FOOTER]
+    )
 
   def run(self):
     if self._installed is not None:

pex/testing.py

@@ -126,13 +126,13 @@ def write_zipfile(directory, dest, reverse=False):
 
 @contextlib.contextmanager
 def make_installer(name='my_project', version='0.0.0', installer_impl=EggInstaller, zip_safe=True,
-                   install_reqs=None):
+                   install_reqs=None, **kwargs):
   interp = {'project_name': name,
             'version': version,
             'zip_safe': zip_safe,
             'install_requires': install_reqs or []}
   with temporary_content(PROJECT_CONTENT, interp=interp) as td:
-    yield installer_impl(td)
+    yield installer_impl(td, **kwargs)
 
 
 @contextlib.contextmanager

tests/test_installer.py

@@ -0,0 +1,60 @@
+# Copyright 2018 Pants project contributors (see CONTRIBUTORS.md).
+# Licensed under the Apache License, Version 2.0 (see LICENSE).
+import contextlib
+from collections import OrderedDict
+
+import pytest
+
+from pex.bin.pex import get_interpreter
+from pex.installer import WheelInstaller
+from pex.testing import ensure_python_interpreter, make_installer, temporary_dir
+from pex.version import SETUPTOOLS_REQUIREMENT, WHEEL_REQUIREMENT
+
+
+class OrderableInstaller(WheelInstaller):
+  def __init__(self, source_dir, strict=True, interpreter=None, install_dir=None, mixins=None):
+    self._mixins = mixins
+    super(OrderableInstaller, self).__init__(source_dir, strict, interpreter, install_dir)
+
+  def mixins(self):
+    return self._mixins
+
+
+@contextlib.contextmanager
+def bare_interpreter():
+  with temporary_dir() as interpreter_cache:
+    yield get_interpreter(
+      python_interpreter=ensure_python_interpreter('3.6.3'),
+      interpreter_cache_dir=interpreter_cache,
+      repos=None,
+      use_wheel=True
+    )
+
+
+@contextlib.contextmanager
+def wheel_installer(*mixins):
+  with bare_interpreter() as interpreter:
+    with make_installer(installer_impl=OrderableInstaller,
+                        interpreter=interpreter,
+                        mixins=OrderedDict(mixins)) as installer:
+      yield installer
+
+
+WHEEL_EXTRA = ('wheel', WHEEL_REQUIREMENT)
+SETUPTOOLS_EXTRA = ('setuptools', SETUPTOOLS_REQUIREMENT)
+
+
+def test_wheel_before_setuptools():
+  with wheel_installer(WHEEL_EXTRA, SETUPTOOLS_EXTRA) as installer:
+    installer.bdist()
+
+
+def test_setuptools_before_wheel():
+  with wheel_installer(SETUPTOOLS_EXTRA, WHEEL_EXTRA) as installer:
+    installer.bdist()
+
+
+def test_no_wheel():
+  with wheel_installer(SETUPTOOLS_EXTRA) as installer:
+    with pytest.raises(installer.InstallFailure):
+      installer.bdist()