Fix pip show of dist with legacy dependency specifiers

Author: sbidoul

src/pip/_internal/commands/show.py

@@ -2,6 +2,7 @@
 from optparse import Values
 from typing import Generator, Iterable, Iterator, List, NamedTuple, Optional
 
+from pip._vendor.packaging.requirements import InvalidRequirement
 from pip._vendor.packaging.utils import canonicalize_name
 
 from pip._internal.cli.base_command import Command
@@ -100,12 +101,19 @@ def _get_requiring_packages(current_dist: BaseDistribution) -> Iterator[str]:
         except KeyError:
             continue
 
-        requires = sorted(
-            # Avoid duplicates in requirements (e.g. due to environment markers).
-            {req.name for req in dist.iter_dependencies()},
-            key=str.lower,
-        )
-        required_by = sorted(_get_requiring_packages(dist), key=str.lower)
+        try:
+            requires = sorted(
+                # Avoid duplicates in requirements (e.g. due to environment markers).
+                {req.name for req in dist.iter_dependencies()},
+                key=str.lower,
+            )
+        except InvalidRequirement:
+            requires = sorted(dist.iter_raw_dependencies(), key=str.lower)
+
+        try:
+            required_by = sorted(_get_requiring_packages(dist), key=str.lower)
+        except InvalidRequirement:
+            required_by = ["#N/A"]
 
         try:
             entry_points_text = dist.read_text("entry_points.txt")

tests/functional/test_invalid_versions_and_specifiers.py

@@ -105,3 +105,5 @@ def test_show_require_invalid_version(
     _install_require_invalid_version(script, data)
     result = script.pip("show", "require-invalid-version")
     assert "Name: require-invalid-version\nVersion: 1.0\n" in result.stdout
+    assert "Requires: invalid-version ==2010i\n" in result.stdout
+    assert "Required-by: #N/A\n" in result.stdout