Guard against allowing ansible to ansible-base upgrades (ansible#70529)

* Guard against allowing ansible to ansible-base upgrades

* newline

* use alias

* Add an explicit line detailing this is a 1 time thing

* period

* Read __version__ and __author__ rather than import, update working, and add ability to skip conflict checks

* Remove commented code

* Re introduce removed changes from rebase

* Just use open

* Nuke unused import

setup.py

@@ -30,8 +30,81 @@
 from distutils.command.build_scripts import build_scripts as BuildScripts
 from distutils.command.sdist import sdist as SDist
 
-sys.path.insert(0, os.path.abspath('lib'))
-from ansible.release import __version__, __author__
+
+def find_package_info(*file_paths):
+    try:
+        with open(os.path.join(*file_paths), 'r') as f:
+            info_file = f.read()
+    except Exception:
+        raise RuntimeError("Unable to find package info.")
+
+    # The version line must have the form
+    # __version__ = 'ver'
+    version_match = re.search(r"^__version__ = ['\"]([^'\"]*)['\"]",
+                              info_file, re.M)
+    author_match = re.search(r"^__author__ = ['\"]([^'\"]*)['\"]",
+                             info_file, re.M)
+
+    if version_match and author_match:
+        return version_match.group(1), author_match.group(1)
+    raise RuntimeError("Unable to find package info.")
+
+
+def _validate_install_ansible_base():
+    """Validate that we can install ansible-base. Currently this only
+    cares about upgrading to ansible-base from ansible<2.10
+    """
+    if os.getenv('ANSIBLE_SKIP_CONFLICT_CHECK', '') not in ('', '0'):
+        return
+
+    # Save these for later restoring things to pre invocation
+    sys_modules = sys.modules.copy()
+    sys_modules_keys = set(sys_modules)
+
+    # Make sure `lib` isn't in `sys.path` that could confuse this
+    sys_path = sys.path[:]
+    abspath = os.path.abspath
+    sys.path[:] = [p for p in sys.path if abspath(p) != abspath('lib')]
+
+    try:
+        from ansible.release import __version__
+    except ImportError:
+        pass
+    else:
+        version_tuple = tuple(int(v) for v in __version__.split('.')[:2])
+        if version_tuple < (2, 10):
+            stars = '*' * 76
+            raise RuntimeError(
+                '''
+
+    %s
+
+    Cannot install ansible-base with a pre-existing ansible==%s
+    installation.
+
+    Installing ansible-base with ansible-2.9 or older currently installed with
+    pip is known to cause problems. Please uninstall ansible and install the new
+    version:
+
+        pip uninstall ansible
+        pip install ansible-base
+
+    If you want to skip the conflict checks and manually resolve any issues
+    afterwards, set the ANSIBLE_SKIP_CONFLICT_CHECK environment variable:
+
+        ANSIBLE_SKIP_CONFLICT_CHECK=1 pip install ansible-base
+
+    %s
+                ''' % (stars, __version__, stars)
+            )
+    finally:
+        sys.path[:] = sys_path
+        for key in sys_modules_keys.symmetric_difference(sys.modules):
+            sys.modules.pop(key, None)
+        sys.modules.update(sys_modules)
+
+
+_validate_install_ansible_base()
 
 
 SYMLINK_CACHE = 'SYMLINK_CACHE.json'
@@ -254,6 +327,8 @@ def get_dynamic_setup_params():
     }
 
 
+here = os.path.abspath(os.path.dirname(__file__))
+__version__, __author__ = find_package_info(here, 'lib', 'ansible', 'release.py')
 static_setup_params = dict(
     # Use the distutils SDist so that symlinks are not expanded
     # Use a custom Build for the same reason