Fix comparisons for abstract specs (#20341)

bug only relevant for python3

lib/spack/spack/spec.py

@@ -3517,8 +3517,11 @@ def ne_dag(self, other, deptypes=True):
 
     def _cmp_node(self):
         """Comparison key for just *this node* and not its deps."""
-        return (self.name,
+        # Name or namespace None will lead to invalid comparisons for abstract
-                self.namespace,
+        # specs. Replace them with the empty string, which is not a valid spec
+        # name nor namespace so it will not create spurious equalities.
+        return (self.name or '',
+                self.namespace or '',
                 tuple(self.versions),
                 self.variants,
                 self.architecture,

lib/spack/spack/test/spec_syntax.py

@@ -2,7 +2,7 @@
 # Spack Project Developers. See the top-level COPYRIGHT file for details.
 #
 # SPDX-License-Identifier: (Apache-2.0 OR MIT)
-
+import itertools
 import os
 import pytest
 import shlex
@@ -806,3 +806,26 @@ def test_kv_with_spaces(self):
     ])
     def test_target_tokenization(self, expected_tokens, spec_string):
         self.check_lex(expected_tokens, spec_string)
+
+    @pytest.mark.regression('20310')
+    def test_compare_abstract_specs(self):
+        """Spec comparisons must be valid for abstract specs.
+
+        Check that the spec cmp_key appropriately handles comparing specs for
+        which some attributes are None in exactly one of two specs"""
+        # Add fields in order they appear in `Spec._cmp_node`
+        constraints = [
+            None,
+            'foo',
+            'foo.foo',
+            'foo.foo@foo',
+            'foo.foo@foo+foo',
+            'foo.foo@foo+foo arch=foo-foo-foo',
+            'foo.foo@foo+foo arch=foo-foo-foo %foo',
+            'foo.foo@foo+foo arch=foo-foo-foo %foo cflags=foo',
+        ]
+        specs = [Spec(s) for s in constraints]
+
+        for a, b in itertools.product(specs, repeat=2):
+            # Check that we can compare without raising an error
+            assert a <= b or b < a