datalog: dl-magic-query falls back on built-in/agg/neg goals (222/222)

Bug: dl-magic-query was always trying to seed a magic_<rel>^<adn>
fact for the query goal. For aggregate goals like (count N X (p X))
this produced a non-ground "fact" (magic_count^... N X (p X)) and
dl-add-fact! correctly rejected it, surfacing as an error.

Fix: dl-magic-query now detects built-in / aggregate / negation
goals up front and dispatches to plain dl-query for those cases —
magic-sets only applies to positive non-builtin literals against
rule-defined relations. Other shapes don't benefit from the
rewrite anyway.

1 new test confirms (count N X (p X)) returns the expected
{:N 3} via dl-magic-query.

lib/datalog/magic.sx

@@ -376,16 +376,26 @@
   dl-magic-query
   (fn
     (db query-goal)
-    (let
-      ((query-rel (dl-rel-name query-goal))
-        (query-adn (dl-adorn-goal query-goal)))
-      (let
-        ((query-args (dl-bound-args query-goal query-adn))
-          (rules (dl-rules db)))
+    ;; Magic-sets only applies to positive non-builtin / non-aggregate
+    ;; literals against rule-defined relations. For other goal shapes
+    ;; (built-ins, aggregates, EDB-only relations) the seed is either
+    ;; non-ground or unused; fall back to dl-query.
+    (cond
+      ((or (dl-builtin? query-goal)
+           (dl-aggregate? query-goal)
+           (and (dict? query-goal) (has-key? query-goal :neg)))
+        (dl-query db query-goal))
+      (else
         (let
-          ((rewritten (dl-magic-rewrite rules query-rel query-adn query-args))
-            (mdb (dl-make-db))
-            (rule-heads (dl-magic-rule-heads rules)))
+          ((query-rel (dl-rel-name query-goal))
+            (query-adn (dl-adorn-goal query-goal)))
+          (let
+            ((query-args (dl-bound-args query-goal query-adn))
+              (rules (dl-rules db)))
+            (let
+              ((rewritten (dl-magic-rewrite rules query-rel query-adn query-args))
+                (mdb (dl-make-db))
+                (rule-heads (dl-magic-rule-heads rules)))
           (do
             ;; Copy EDB facts (relations not headed by any caller rule).
             (for-each
@@ -400,4 +410,4 @@
             ;; Seed + rewritten rules.
             (dl-add-fact! mdb (get rewritten :seed))
             (for-each (fn (r) (dl-add-rule! mdb r)) (get rewritten :rules))
-            (dl-query mdb query-goal)))))))
+            (dl-query mdb query-goal)))))))))

lib/datalog/scoreboard.json

@@ -1,8 +1,8 @@
 {
   "lang": "datalog",
-  "total_passed": 221,
+  "total_passed": 222,
   "total_failed": 0,
-  "total": 221,
+  "total": 222,
   "suites": [
     {"name":"tokenize","passed":26,"failed":0,"total":26},
     {"name":"parse","passed":18,"failed":0,"total":18},
@@ -13,8 +13,8 @@
     {"name":"negation","passed":10,"failed":0,"total":10},
     {"name":"aggregates","passed":19,"failed":0,"total":19},
     {"name":"api","passed":20,"failed":0,"total":20},
-    {"name":"magic","passed":23,"failed":0,"total":23},
+    {"name":"magic","passed":24,"failed":0,"total":24},
     {"name":"demo","passed":21,"failed":0,"total":21}
   ],
-  "generated": "2026-05-08T10:29:04+00:00"
+  "generated": "2026-05-08T10:31:43+00:00"
 }

lib/datalog/scoreboard.md

@@ -1,6 +1,6 @@
 # datalog scoreboard
 
-**221 / 221 passing** (0 failure(s)).
+**222 / 222 passing** (0 failure(s)).
 
 | Suite | Passed | Total | Status |
 |-------|--------|-------|--------|
@@ -13,5 +13,5 @@
 | negation | 10 | 10 | ok |
 | aggregates | 19 | 19 | ok |
 | api | 20 | 20 | ok |
-| magic | 23 | 23 | ok |
+| magic | 24 | 24 | ok |
 | demo | 21 | 21 | ok |

lib/datalog/tests/magic.sx

@@ -197,6 +197,18 @@
         6)
 
       ;; dl-magic-query: end-to-end driver, doesn't mutate caller's db.
+      ;; dl-magic-query falls back to dl-query for built-in,
+      ;; aggregate, and negation goals (the magic seed would
+      ;; otherwise be non-ground).
+      (dl-mt-test! "magic-query falls back on aggregate"
+        (let
+          ((r (dl-magic-query
+                (dl-program "p(1). p(2). p(3).")
+                (list (quote count) (quote N) (quote X)
+                      (list (quote p) (quote X))))))
+          (and (= (len r) 1) (= (get (first r) "N") 3)))
+        true)
+
       (dl-mt-test! "magic-query equivalent to dl-query"
         (let
           ((db (dl-program