Fix an issue with deconcretization/reconcretization of environments (#41294)

lib/spack/spack/solver/asp.py

@@ -2675,15 +2675,13 @@ def literal_specs(self, specs):
             self.gen.fact(fn.pkg_fact(spec.name, fn.condition_trigger(condition_id, trigger_id)))
             self.gen.fact(fn.condition_reason(condition_id, f"{spec} requested explicitly"))
 
-            # Effect imposes the spec
             imposed_spec_key = str(spec), None
             cache = self._effect_cache[spec.name]
-            msg = (
-                "literal specs have different requirements. clear cache before computing literals"
-            )
-            assert imposed_spec_key not in cache, msg
-            effect_id = next(self._id_counter)
-            requirements = self.spec_clauses(spec)
+            if imposed_spec_key in cache:
+                effect_id, requirements = cache[imposed_spec_key]
+            else:
+                effect_id = next(self._id_counter)
+                requirements = self.spec_clauses(spec)
             root_name = spec.name
             for clause in requirements:
                 clause_name = clause.args[0]

lib/spack/spack/test/env.py

@@ -778,3 +778,32 @@ def test_env_with_include_def_missing(mutable_mock_env_path, mock_packages):
     with e:
         with pytest.raises(UndefinedReferenceError, match=r"which does not appear"):
             e.concretize()
+
+
+@pytest.mark.regression("41292")
+def test_deconcretize_then_concretize_does_not_error(mutable_mock_env_path, mock_packages):
+    """Tests that, after having deconcretized a spec, we can reconcretize an environment which
+    has 2 or more user specs mapping to the same concrete spec.
+    """
+    mutable_mock_env_path.mkdir()
+    spack_yaml = mutable_mock_env_path / ev.manifest_name
+    spack_yaml.write_text(
+        """spack:
+      specs:
+      # These two specs concretize to the same hash
+      - c
+      - c@1.0
+      # Spec used to trigger the bug
+      - a
+      concretizer:
+        unify: true
+    """
+    )
+    e = ev.Environment(mutable_mock_env_path)
+    with e:
+        e.concretize()
+        e.deconcretize(spack.spec.Spec("a"), concrete=False)
+        e.concretize()
+    assert len(e.concrete_roots()) == 3
+    all_root_hashes = set(x.dag_hash() for x in e.concrete_roots())
+    assert len(all_root_hashes) == 2