More complicated conversion

src/pip/_internal/commands/show.py

@@ -2,7 +2,7 @@
 import logging
 import pathlib
 from optparse import Values
-from typing import Iterator, List, NamedTuple, Optional
+from typing import Iterator, List, NamedTuple, Optional, Tuple
 
 from pip._vendor.packaging.utils import canonicalize_name
 
@@ -66,6 +66,33 @@ class _PackageInfo(NamedTuple):
     files: Optional[List[str]]
 
 
+def _covert_legacy_entry(entry: Tuple[str, ...], info: Tuple[str, ...]) -> str:
+    """Convert a legacy installed-files.txt path into modern RECORD path.
+
+    The legacy format stores paths relative to the info directory, while the
+    modern format stores paths relative to the package root, e.g. the
+    site-packages directory.
+
+    :param entry: Path parts of the installed-files.txt entry.
+    :param info: Path parts of the egg-info directory relative to package root.
+    :returns: The converted entry.
+
+    For best compatibility with symlinks, this does not use ``abspath()`` or
+    ``Path.resolve()``, but tries to work with path parts:
+
+    1. While ``entry`` starts with ``..``, remove the equal amounts of parts
+       from ``info``; if ``info`` is empty, start appending ``..`` instead.
+    2. Join the two directly.
+    """
+    while entry and entry[0] == "..":
+        if not info or info[-1] == "..":
+            info += ("..",)
+        else:
+            info = info[:-1]
+        entry = entry[1:]
+    return str(pathlib.Path(*info, *entry))
+
+
 def search_packages_info(query: List[str]) -> Iterator[_PackageInfo]:
     """
     Gather details from installed distributions. Print distribution name,
@@ -100,7 +127,8 @@ def _files_from_record(dist: BaseDistribution) -> Optional[Iterator[str]]:
             text = dist.read_text('RECORD')
         except FileNotFoundError:
             return None
-        return (row[0] for row in csv.reader(text.splitlines()))
+        # This extra Path-str cast normalizes entries.
+        return (str(pathlib.Path(row[0])) for row in csv.reader(text.splitlines()))
 
     def _files_from_legacy(dist: BaseDistribution) -> Optional[Iterator[str]]:
         try:
@@ -112,7 +140,16 @@ def _files_from_legacy(dist: BaseDistribution) -> Optional[Iterator[str]]:
         info = dist.info_directory
         if root is None or info is None:
             return paths
-        return (str(pathlib.Path(info, p).relative_to(root)) for p in paths)
+        try:
+            info_rel = pathlib.Path(info).relative_to(root)
+        except ValueError:  # info is not relative to root.
+            return paths
+        if not info_rel.parts:  # info *is* root.
+            return paths
+        return (
+            _covert_legacy_entry(pathlib.Path(p).parts, info_rel.parts)
+            for p in paths
+        )
 
     for query_name in query_names:
         try: