Adapt pip-pop to changes in pip >= 10

The pip-diff and pip-grep tools from the vendorized `pip-pop` package
import internal modules from pip. In pip >= 10, internal modules were
moved under `pip._internal`, breaking the imports. Use `try...except
ImportError` to handle both import paths.

Also, the interface of the `PackageFinder` class from one of these
modules changed. Provide a wrapper function to allow creating objects of
this type using the old interface.

vendor/pip-pop/pip-diff

@@ -12,9 +12,24 @@ Options:
 """
 import os
 from docopt import docopt
-from pip.req import parse_requirements
-from pip.index import PackageFinder
-from pip._vendor.requests import session
+
+try:  # pip >= 10
+    from pip._internal.req import parse_requirements
+    from pip._internal.download import PipSession as session
+
+    def PackageFinder(find_links, index_urls, session=None):
+        from pip._internal.index import PackageFinder
+        from pip._internal.models.search_scope import SearchScope
+        from pip._internal.models.selection_prefs import SelectionPreferences
+
+        search_scope = SearchScope.create(find_links, index_urls)
+        selection_prefs = SelectionPreferences(allow_yanked=False)
+        return PackageFinder.create(search_scope, selection_prefs, session=session)
+
+except ImportError:  # pip <= 9.0.3
+    from pip.req import parse_requirements
+    from pip.index import PackageFinder
+    from pip._vendor.requests import session
 
 requests = session()
 

vendor/pip-pop/pip-grep

@@ -10,9 +10,25 @@ Options:
 import os
 import sys
 from docopt import docopt
-from pip.req import parse_requirements
-from pip.index import PackageFinder
-from pip._vendor.requests import session
+
+try:  # pip >= 10
+    from pip._internal.req import parse_requirements
+    from pip._internal.download import PipSession as session
+
+    def PackageFinder(find_links, index_urls, session=None):
+        from pip._internal.index import PackageFinder
+        from pip._internal.models.search_scope import SearchScope
+        from pip._internal.models.selection_prefs import SelectionPreferences
+
+        search_scope = SearchScope.create(find_links, index_urls)
+        selection_prefs = SelectionPreferences(allow_yanked=False)
+        return PackageFinder.create(search_scope, selection_prefs, session=session)
+
+except ImportError:  # pip <= 9.0.3
+    from pip.req import parse_requirements
+    from pip.index import PackageFinder
+    from pip._vendor.requests import session
+
 
 requests = session()