fix "list modification count"

GitOrigin-RevId: a28e00e2be6e1ddad11c48c644c61cb355a4a6e3

platform/configuration-store-impl/testSrc/StoredPropertyStateTest.kt

@@ -1,6 +1,5 @@
-// Copyright 2000-2020 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license that can be found in the LICENSE file.
+// Copyright 2000-2021 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license that can be found in the LICENSE file.
 @file:Suppress("UsePropertyAccessSyntax")
-
 package com.intellij.configurationStore
 
 import com.intellij.openapi.components.BaseState
@@ -188,6 +187,54 @@ class StoredPropertyStateTest {
     assertThat(state.modificationCount).isNotEqualTo(oldModificationCount)
     assertThat(state.isEqualToDefault()).isFalse()
   }
+
+  @Test
+  fun `list modification count`() {
+    class TestOptions : BaseState() {
+      @get:XMap
+      val foo by list<NestedState>()
+    }
+
+    val state = TestOptions()
+    var oldModificationCount = state.modificationCount
+
+    val list = state.foo
+    list.clear()
+    list.add(NestedState())
+    list.add(NestedState())
+    assertThat(state.modificationCount).isNotEqualTo(oldModificationCount)
+    assertThat(state.isEqualToDefault()).isFalse()
+
+    val element = serialize(state)
+    assertThat(element).isEqualTo("""
+    <TestOptions>
+      <foo>
+        <list>
+          <NestedState />
+          <NestedState />
+        </list>
+      </foo>
+    </TestOptions>""")
+
+    oldModificationCount = state.modificationCount
+    list.clear()
+    assertThat(state.modificationCount).isNotEqualTo(oldModificationCount)
+    assertThat(state.isEqualToDefault()).isTrue()
+
+    val firstElement = NestedState()
+    list.add(firstElement)
+    list.add(NestedState())
+
+    oldModificationCount = state.modificationCount
+    firstElement.childProperty = "33"
+    assertThat(state.modificationCount).isNotEqualTo(oldModificationCount)
+    assertThat(state.isEqualToDefault()).isFalse()
+
+    oldModificationCount = state.modificationCount
+    assertThat(list.remove(firstElement)).isTrue()
+    assertThat(state.modificationCount).isNotEqualTo(oldModificationCount)
+    assertThat(state.isEqualToDefault()).isFalse()
+  }
 }
 
 internal class AState(languageLevel: String? = null, nestedComplex: NestedState? = null) : BaseState() {

platform/object-serializer/src/stateProperties/CollectionStoredProperty.kt

@@ -1,4 +1,4 @@
-// Copyright 2000-2020 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license that can be found in the LICENSE file.
+// Copyright 2000-2021 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license that can be found in the LICENSE file.
 package com.intellij.serialization.stateProperties
 
 import com.intellij.openapi.components.BaseState
@@ -53,5 +53,26 @@ open class CollectionStoredProperty<E : Any, C : MutableCollection<E>>(protected
 }
 
 internal class ListStoredProperty<T : Any> : CollectionStoredProperty<T, SmartList<T>>(SmartList(), null) {
-  override fun getModificationCount() = value.modificationCount.toLong()
+  private var modCount = 0L
+  private var lastItemModCount = 0L
+
+  override fun getModificationCount(): Long {
+    modCount = value.modificationCount.toLong()
+    var itemModCount = 0L
+    for (item in value) {
+      if (item is BaseState) {
+        itemModCount += item.modificationCount
+      }
+      else {
+        // or all values are BaseState or not
+        return modCount
+      }
+    }
+
+    if (itemModCount != lastItemModCount) {
+      lastItemModCount = itemModCount
+      modCount++
+    }
+    return modCount
+  }
 }