Fix check for RIGHT_ATTRS in dep matcher (#8807)

* Fix check for RIGHT_ATTRs in dep matcher

If a non-anchor node does not have RIGHT_ATTRS, the dep matcher throws
an E100, which says that non-anchor nodes must have LEFT_ID, REL_OP, and
RIGHT_ID. It specifically does not say RIGHT_ATTRS is required.

A blank RIGHT_ATTRS is also valid, and patterns with one will be
excepted. While not normal, sometimes a REL_OP is enough to specify a
non-anchor node - maybe you just want the head of another node
unconditionally, for example.

This change just sets RIGHT_ATTRS to {} if not present. Alternatively
changing E100 to state RIGHT_ATTRS is required could also be reasonable.

* Fix test

This test was written on the assumption that if `RIGHT_ATTRS` isn't
present an error will be raised. Since the proposed changes make it so
an error won't be raised this is no longer necessary.

* Revert test, update error message

Error message now lists missing keys, and RIGHT_ATTRS is required.

* Use list of required keys in error message

Also removes unused key param arg.

spacy/errors.py

@@ -356,8 +356,8 @@ class Errors:
     E098 = ("Invalid pattern: expected both RIGHT_ID and RIGHT_ATTRS.")
     E099 = ("Invalid pattern: the first node of pattern should be an anchor "
             "node. The node should only contain RIGHT_ID and RIGHT_ATTRS.")
-    E100 = ("Nodes other than the anchor node should all contain LEFT_ID, "
-            "REL_OP and RIGHT_ID.")
+    E100 = ("Nodes other than the anchor node should all contain {required}, "
+            "but these are missing: {missing}")
     E101 = ("RIGHT_ID should be a new node and LEFT_ID should already have "
             "have been declared in previous edges.")
     E102 = ("Can't merge non-disjoint spans. '{token}' is already part of "

spacy/matcher/dependencymatcher.pyx

@@ -122,13 +122,17 @@ cdef class DependencyMatcher:
                     raise ValueError(Errors.E099.format(key=key))
                 visited_nodes[relation["RIGHT_ID"]] = True
             else:
-                if not(
-                    "RIGHT_ID" in relation
-                    and "RIGHT_ATTRS" in relation
-                    and "REL_OP" in relation
-                    and "LEFT_ID" in relation
-                ):
-                    raise ValueError(Errors.E100.format(key=key))
+                required_keys = set(
+                    ("RIGHT_ID", "RIGHT_ATTRS", "REL_OP", "LEFT_ID")
+                )
+                relation_keys = set(relation.keys())
+                missing = required_keys - relation_keys
+                if missing:
+                    missing_txt = ", ".join(list(missing))
+                    raise ValueError(Errors.E100.format(
+                        required=required_keys,
+                        missing=missing_txt
+                    ))
                 if (
                     relation["RIGHT_ID"] in visited_nodes
                     or relation["LEFT_ID"] not in visited_nodes