[Port] Fix stack overflow when diffing wide objects

circe/shared/src/test/scala/diffson/circe/CirceTestObjectDiff.scala

@@ -0,0 +1,22 @@
+/*
+ * Copyright 2024 Diffson Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package diffson.circe
+
+import diffson.jsonpatch.TestObjectDiff
+import io.circe.Json
+
+class CirceTestObjectDiff extends TestObjectDiff[Json]

core/src/main/scala/diffson/jsonpatch/JsonDiff.scala

@@ -48,11 +48,14 @@ class JsonDiff[Json](diffArray: Boolean, rememberOld: Boolean)(implicit J: Jsony
       case (fld, value1) :: fields1 =>
         fields2.get(fld) match {
           case Some(value2) =>
-            fieldsDiff(fields1, fields2 - fld, path).flatMap(d => diff(value1, value2, path / fld).map(_ ++ d))
+            Eval
+              .defer(fieldsDiff(fields1, fields2 - fld, path))
+              .flatMap(d => diff(value1, value2, path / fld).map(_ ++ d))
           case None =>
             // field is not in the second object, delete it
-            fieldsDiff(fields1, fields2, path).map(
-              _.prepend(Remove(path / fld, if (rememberOld) Some(value1) else None)))
+            Eval
+              .defer(fieldsDiff(fields1, fields2, path))
+              .map(_.prepend(Remove(path / fld, if (rememberOld) Some(value1) else None)))
         }
       case Nil =>
         Eval.now(Chain.fromSeq(fields2.toList).map { case (fld, value) => Add(path / fld, value) })

testkit/shared/src/main/scala/diffson/TestObjectDiff.scala

@@ -0,0 +1,44 @@
+/*
+ * Copyright 2024 Diffson Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package diffson
+package jsonpatch
+
+import org.scalatest.flatspec.AnyFlatSpec
+import org.scalatest.matchers.should.Matchers
+import diffson.jsonpatch.JsonDiff
+import diffson.lcs.Patience
+
+abstract class TestObjectDiff[J](implicit J: Jsony[J]) extends AnyFlatSpec with Matchers {
+
+  implicit val lcsalg: Patience[J] = new Patience[J]
+
+  val diff = new JsonDiff[J](false, false)
+
+  "a wide object diffed with an empty one" should "not cause stack overflows" in {
+    val json1 = J.makeObject((1 to 10000).map(i => s"key$i" -> J.Null).toMap)
+    val json2 = J.makeObject(Map.empty)
+
+    diff.diff(json1, json2)
+  }
+
+  "a wide object diffed with itself" should "not cause stack overflows" in {
+    val json1 = J.makeObject((1 to 10000).map(i => s"key$i" -> J.Null).toMap)
+
+    diff.diff(json1, json1)
+  }
+
+}