Work around mypy quirks

Author: pradyunsg

src/pip/_internal/pep425tags.py

@@ -105,6 +105,8 @@ def get_abi_tag():
     (CPython 2, PyPy)."""
     soabi = get_config_var('SOABI')
     impl = get_abbr_impl()
+    abi = None  # type: Optional[str]
+
     if not soabi and impl in {'cp', 'pp'} and hasattr(sys, 'maxunicode'):
         d = ''
         m = ''
@@ -129,8 +131,7 @@ def get_abi_tag():
         abi = 'cp' + soabi.split('-')[1]
     elif soabi:
         abi = soabi.replace('.', '_').replace('-', '_')
-    else:
-        abi = None
+
     return abi
 
 
@@ -353,6 +354,7 @@ def get_supported(
 
         # Current version, current API (built specifically for our Python):
         for abi in abis:
+            assert abi
             for arch in arches:
                 supported.append(('%s%s' % (impl, versions[0]), abi, arch))
 
@@ -362,6 +364,7 @@ def get_supported(
             if version in {'31', '30'}:
                 break
             for abi in abi3s:   # empty set if not Python 3
+                assert abi
                 for arch in arches:
                     supported.append(("%s%s" % (impl, version), abi, arch))
 

src/pip/_internal/utils/appdirs.py

@@ -239,7 +239,9 @@ def _get_win_folder_with_ctypes(csidl_name):
         if ctypes.windll.kernel32.GetShortPathNameW(buf.value, buf2, 1024):
             buf = buf2
 
-    return buf.value
+    # On Python 2, ctypes.create_unicode_buffer().value returns "unicode",
+    # which isn't the same as str in the annotation above.
+    return buf.value  # type: ignore
 
 
 if WINDOWS:

src/pip/_internal/utils/misc.py

@@ -65,9 +65,9 @@
 except ImportError:
     # typing's cast() isn't supported in code comments, so we need to
     # define a dummy, no-op version.
-    def cast(typ, val):
+    def cast(typ, val):  # type: ignore
         return val
-    VersionInfo = None
+    VersionInfo = None  # type: ignore
 
 
 __all__ = ['rmtree', 'display_path', 'backup_dir',