Regression in 1.6.4: Can’t sum relations with different attrs

I'm upgrading from 1.6.3 to 1.6.4 and started getting a new exception with one of my queries Can’t sum relations with different attrs.

I've created a reproduction. It's as small as I can make it, though it's still somewhat complicated.

(let [db (-> (d/empty-db {:parent {:db/valueType :db.type/ref}})
             (d/with [{:db/id "alice"
                       :name "alice"}
                      {:db/id "bob"
                       :name "bob"}
                      {:db/id "clara"
                       :name "clara"}
                      [:db/add "alice" :parent "bob"]
                      [:db/add "bob" :parent "clara"]])
             :db-after)]
  (for [name ["alice" "bob" "clara"]]
    [name
     (try
       (d/q '[:find ?x ?y
              :in $ ?name
              :where
              [?x :name ?name]
              (or-join
               [?x ?y]
               (and [?x :parent ?z]
                    [?z :parent ?y])
               [?y :parent ?x])]
            db
            name)
       (catch Exception e
         e))]))

In 1.6.3 this produces

(["alice" #{[1 3]}] 
 ["bob" #{[2 1]}]
 ["clara" #{[3 2]}])

In 1.6.4 it produces

(["alice" #{[1 3]}] 
 ["bob" #{[2 1]}] 
 ["clara" #error {
 :cause "Can’t sum relations with different attrs: {?x \"e\"} and {?x 0, ?y 1}"
 :data {:error :query/where}
 :via
 [{:type clojure.lang.ExceptionInfo
   :message "Can’t sum relations with different attrs: {?x \"e\"} and {?x 0, ?y 1}"
   :data {:error :query/where}
   :at [datascript.query$sum_rel invokeStatic "query.cljc" 160]}]
 :trace
 [[datascript.query$sum_rel invokeStatic "query.cljc" 160]
  [datascript.query$sum_rel invoke "query.cljc" 147]
  [clojure.core.protocols$fn__8285 invokeStatic "protocols.clj" 167]
  [clojure.core.protocols$fn__8285 invoke "protocols.clj" 123]
  [clojure.core.protocols$fn__8239$G__8234__8248 invoke "protocols.clj" 693]
  [clojure.core.protocols$seq_reduce invokeStatic "protocols.clj" 27]
  [clojure.core.protocols$fn__8272 invokeStatic "protocols.clj" 74]
  [clojure.core.protocols$fn__8272 invoke "protocols.clj" 74]
  [clojure.core.protocols$fn__8213$G__8208__8226 invoke "protocols.clj" 693]
  [clojure.core$reduce invokeStatic "core.clj" 6951]
  [clojure.core$reduce invoke "core.clj" 6937]
  [datascript.query$_resolve_clause invokeStatic "query.cljc" 774]
  [datascript.query$_resolve_clause invoke "query.cljc" 733]
  [datascript.query$_resolve_clause invokeStatic "query.cljc" 735]
  [datascript.query$_resolve_clause invoke "query.cljc" 733]
  [datascript.query$resolve_clause invokeStatic "query.cljc" 828]
  [datascript.query$resolve_clause invoke "query.cljc" 820]
  [clojure.lang.PersistentVector reduce "PersistentVector.java" 418]
  [clojure.core$reduce invokeStatic "core.clj" 6954]
  [clojure.core$reduce invoke "core.clj" 6937]
  [datascript.query$_q invokeStatic "query.cljc" 832]
  [datascript.query$_q invoke "query.cljc" 830]
  [datascript.query$q invokeStatic "query.cljc" 997]
  [datascript.query$q doInvoke "query.cljc" 982]
  [clojure.lang.RestFn invoke "RestFn.java" 442]
  SNIP]}])

From playing with variations of the query, the error seems to come from the second clause of the and inside the or-join. I don't know the internals of datascript, but my guess is that something like this has started happening:

✅ When ?x is bound to "alice", then because "alice"'s :parent is "bob", the first clause of the and binds ?z to "bob". Then the second clause of the and is run, and ?y is added to the relation. Since both ?x and ?y are bound by both parts of the or-join, they can be "summed".
❌ However, when ?x is bound to "clara", then because "clara" has no :parent, the first clause in the and has no tuples, and so the second clause is never "run", and ?y is never added to the relation. So, the first part of the or-join ends up with only ?x bound, which leads to the error when it's summed with the second part which has both ?x and ?y.

tonsky / datascript

Regression in 1.6.4: Can’t sum relations with different attrs #468