Revise locally available dist reinstallation logic

A PEP-508 file:// requirement pointing to a wheel is not longer
automatically reinstalled. But an sdist from file://, or anything
specifed by a path will automatically be reinstalled.

Author: uranusjr

src/pip/_internal/resolution/resolvelib/resolver.py

@@ -111,10 +111,10 @@ def _get_ireq(
         # Determine whether to upgrade based on flags and whether the installed
         # distribution was done via a direct URL.
 
-        # Always reinstall an incoming wheel candidate on the local filesystem.
-        # This is quite fast anyway, and we can avoid drama when users want
-        # their in-development direct URL requirement automatically reinstalled.
-        if cand_link.is_file and cand_link.is_wheel:
+        # Always reinstall a direct URL on the file system if it's not specified
+        # with PEP 508. This avoids drama when users want their in-development
+        # requirement automatically reinstalled.
+        if cand_link.is_file and (ireq.req is None or ireq.req.url is None):
             return ireq
 
         # Reinstall if --upgrade is specified.