fix: BCPs can normatively cite all other standards levels (#6530)

* fix: BCPs can normatively cite all other standards levels

Fixes #6524

* Revise the logic and add tests

* Fix bug in truth table

ietf/doc/models.py

@@ -676,39 +676,59 @@ def __str__(self):
         return u"%s %s %s" % (self.source.name, self.relationship.name.lower(), self.target.name)
 
     def is_downref(self):
-
-        if self.source.type.slug!='draft' or self.relationship.slug not in ['refnorm','refold','refunk']:
+        if self.source.type.slug != "draft" or self.relationship.slug not in [
+            "refnorm",
+            "refold",
+            "refunk",
+        ]:
             return None
 
         state = self.source.get_state()
-        if state and state.slug == 'rfc':
+        if state and state.slug == "rfc":
             source_lvl = self.source.std_level.slug if self.source.std_level else None
         elif self.source.intended_std_level:
             source_lvl = self.source.intended_std_level.slug
         else:
             source_lvl = None
 
-        if source_lvl not in ['bcp','ps','ds','std']:
+        if source_lvl not in ["bcp", "ps", "ds", "std", "unkn"]:
             return None
 
-        if self.target.document.get_state().slug == 'rfc':
+        if self.target.document.get_state().slug == "rfc":
             if not self.target.document.std_level:
-                target_lvl = 'unkn'
+                target_lvl = "unkn"
             else:
                 target_lvl = self.target.document.std_level.slug
         else:
             if not self.target.document.intended_std_level:
-                target_lvl = 'unkn'
+                target_lvl = "unkn"
             else:
                 target_lvl = self.target.document.intended_std_level.slug
 
-        rank = { 'ps':1, 'ds':2, 'std':3, 'bcp':3 }
+        if self.relationship.slug not in ["refnorm", "refunk"]:
+            return None
+
+        if source_lvl in ["inf", "exp"]:
+            return None
 
-        if ( target_lvl not in rank ) or ( rank[target_lvl] < rank[source_lvl] ):
-            if self.relationship.slug == 'refnorm' and target_lvl!='unkn':
-                return "Downref"
-            else:
-                return "Possible Downref"
+        pos_downref = (
+            "Downref" if self.relationship.slug != "refunk" else "Possible Downref"
+        )
+
+        if source_lvl in ["bcp", "ps", "ds", "std"] and target_lvl in ["inf", "exp"]:
+            return pos_downref
+
+        if source_lvl == "ds" and target_lvl == "ps":
+            return pos_downref
+
+        if source_lvl == "std" and target_lvl in ["ps", "ds"]:
+            return pos_downref
+
+        if source_lvl not in ["inf", "exp"] and target_lvl == "unkn":
+            return "Possible Downref"
+
+        if source_lvl == "unkn" and target_lvl in ["ps", "ds"]:
+            return "Possible Downref"
 
         return None
 

ietf/doc/tests_models.py

@@ -0,0 +1,113 @@
+# Copyright The IETF Trust 2016-2023, All Rights Reserved
+# -*- coding: utf-8 -*-
+
+import itertools
+
+from ietf.doc.factories import WgRfcFactory
+from ietf.doc.models import RelatedDocument
+from ietf.utils.test_utils import TestCase
+
+
+class RelatedDocumentTests(TestCase):
+    def test_is_downref(self):
+        rfcs = [
+            WgRfcFactory(std_level_id=lvl)
+            for lvl in ["inf", "exp", "bcp", "ps", "ds", "std", "unkn"]
+        ]
+
+        result_matrix = {
+            # source
+            "inf": {
+                "inf": None,  # target
+                "exp": None,  # target
+                "bcp": None,  # target
+                "ps": None,  # target
+                "ds": None,  # target
+                "std": None,  # target
+                "unkn": None,  # target
+            },
+            # source
+            "exp": {
+                "inf": None,  # target
+                "exp": None,  # target
+                "bcp": None,  # target
+                "ps": None,  # target
+                "ds": None,  # target
+                "std": None,  # target
+                "unkn": None,  # target
+            },
+            # source
+            "bcp": {
+                "inf": "Downref",  # target
+                "exp": "Downref",  # target
+                "bcp": None,  # target
+                "ps": None,  # target
+                "ds": None,  # target
+                "std": None,  # target
+                "unkn": "Possible Downref",  # target
+            },
+            # source
+            "ps": {
+                "inf": "Downref",  # target
+                "exp": "Downref",  # target
+                "bcp": None,  # target
+                "ps": None,  # target
+                "ds": None,  # target
+                "std": None,  # target
+                "unkn": "Possible Downref",  # target
+            },
+            # source
+            "ds": {
+                "inf": "Downref",  # target
+                "exp": "Downref",  # target
+                "bcp": None,  # target
+                "ps": "Downref",  # target
+                "ds": None,  # target
+                "std": None,  # target
+                "unkn": "Possible Downref",  # target
+            },
+            # source
+            "std": {
+                "inf": "Downref",  # target
+                "exp": "Downref",  # target
+                "bcp": None,  # target
+                "ps": "Downref",  # target
+                "ds": "Downref",  # target
+                "std": None,  # target
+                "unkn": "Possible Downref",  # target
+            },
+            # source
+            "unkn": {
+                "inf": None,  # target
+                "exp": None,  # target
+                "bcp": None,  # target
+                "ps": "Possible Downref",  # target
+                "ds": "Possible Downref",  # target
+                "std": None,  # target
+                "unkn": "Possible Downref",  # target
+            },
+        }
+
+        for rel in ["refnorm", "refinfo", "refunk", "refold"]:
+            for source, target in itertools.product(rfcs, rfcs):
+                ref = RelatedDocument.objects.create(
+                    source=source,
+                    target=target.docalias.first(),
+                    relationship_id=rel,
+                )
+
+                result = ref.is_downref()
+
+                desired_result = (
+                    result_matrix[source.std_level_id][target.std_level_id]
+                    if ref.relationship.slug in ["refnorm", "refunk"]
+                    else None
+                )
+                if (
+                    ref.relationship.slug == "refunk"
+                    and desired_result is not None
+                    and not desired_result.startswith("Possible")
+                ):
+                    desired_result = f"Possible {desired_result}"
+
+                self.assertEqual(desired_result, result)