[kotlin-dfa] Fix anchor for array store (KTIJ-24314)

GitOrigin-RevId: 795f7978bd12cc4cf02abff89c913b9cc5583b14

java/java-analysis-impl/src/com/intellij/codeInspection/dataFlow/java/inst/FoldArrayInstruction.java

@@ -41,4 +41,9 @@ public class FoldArrayInstruction extends EvalInstruction {
     DfType type = SpecialField.ARRAY_LENGTH.asDfType(myTargetType.meet(DfTypes.NOT_NULL_OBJECT), DfTypes.intValue(arguments.length));
     return factory.fromDfType(type);
   }
+
+  @Override
+  public String toString() {
+    return "FOLD_ARRAY " + myTargetType;
+  }
 }

plugins/kotlin/idea/src/org/jetbrains/kotlin/idea/inspections/dfa/KtControlFlowBuilder.kt

@@ -348,7 +348,13 @@ class KtControlFlowBuilder(val factory: DfaValueFactory, val context: KtExpressi
         for (idx in indexes) {
             processExpression(idx)
             val lastIndex = idx == indexes.last()
-            val anchor = if (lastIndex) KotlinExpressionAnchor(expr) else null
+            val anchor = if (lastIndex) {
+                if (storedValue != null)
+                    KotlinExpressionAnchor(PsiTreeUtil.findCommonParent(expr, storedValue) as? KtExpression ?: expr)
+                else
+                    KotlinExpressionAnchor(expr)
+            }
+            else null
             val expectedType = if (lastIndex) expr.getKotlinType()?.toDfType() ?: DfType.TOP else DfType.TOP
             var indexType = idx.getKotlinType()
             val constructor = indexType?.constructor as? IntegerLiteralTypeConstructor

plugins/kotlin/idea/tests/testData/inspections/dfa/Arrays.kt

@@ -56,4 +56,10 @@ fun nullableArraySize(x : Array<Int>?) {
 
     }
 }
-data class X(val x: Int)
+data class X(val x: Int)
+fun storeNull() {
+    // KTIJ-24314
+    val array: Array<Int?> = arrayOf(0)
+    array[0] = 1
+    array[0] = null
+}