Fix linter complaints and add type annotations

Author: seppeljordan

src/pip/_internal/req/req_install.py

@@ -1006,9 +1006,17 @@ def prepend_root(path):
                 f.write('\n'.join(new_lines) + '\n')
 
     def install_use_pep517(
-            self, warn_script_location, use_user_site, pycompile, prefix, root, home
+            self,
+            warn_script_location,  # type: bool
+            use_user_site,  # type: bool
+            pycompile,  # type: bool
+            prefix,  # type: Optional[str]
+            root,  # type: Optional[str]
+            home  # type: Optional[str]
     ):
-        with TempDirectory(kind='wheel') as wheel_dir, TempDirectory(kind='wheel') as build_dir:
+        # type: (...) -> None
+        with TempDirectory(kind='wheel') as wheel_dir, \
+                TempDirectory(kind='wheel') as build_dir:
             wheel_name = self.build_wheel_use_pep517(build_dir.path)
             unpack_file(
                 os.path.join(build_dir.path, wheel_name),
@@ -1023,9 +1031,9 @@ def install_use_pep517(
                 warn_script_location=warn_script_location,
                 use_user_site=use_user_site, pycompile=pycompile,
             )
-            return
 
     def build_wheel_use_pep517(self, output_directory):
+        # type: (str) -> str
         self.spin_message = 'Building wheel for %s (PEP 517)' % (self.name,)
         with self.build_env, indent_log():
             return self.pep517_backend.build_wheel(