[bug-65939] add partial fix for clearing formula with circular ref

git-svn-id: https://svn.apache.org/repos/asf/poi/trunk@1898677 13f79535-47bb-0310-9956-ffa450edef68

poi-ooxml/src/test/java/org/apache/poi/xssf/usermodel/TestFormulaEval.java

@@ -0,0 +1,28 @@
+package org.apache.poi.xssf.usermodel;
+
+import org.apache.poi.ss.usermodel.CellType;
+import org.junit.jupiter.api.Test;
+
+import java.io.IOException;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+class TestFormulaEval {
+    @Test
+    void testCircularRef() throws IOException {
+        try (XSSFWorkbook wb = new XSSFWorkbook()) {
+            XSSFSheet sheet = wb.createSheet();
+            XSSFRow row = sheet.createRow(0);
+            XSSFCell cell = row.createCell(0);
+            cell.setCellFormula("A1");
+            XSSFFormulaEvaluator formulaEvaluator = wb.getCreationHelper().createFormulaEvaluator();
+            // the following assert should probably be NUMERIC not ERROR (from testing in Excel itself)
+            assertEquals(CellType.ERROR, formulaEvaluator.evaluateFormulaCell(cell));
+
+            cell.setCellFormula(null);
+            formulaEvaluator.notifyUpdateCell(cell);
+            //the following assert should probably be BLANK not ERROR
+            assertEquals(CellType.ERROR, cell.getCellType());
+        }
+    }
+}

poi/src/main/java/org/apache/poi/ss/formula/CellCacheEntry.java

@@ -114,7 +114,9 @@ abstract class CellCacheEntry implements ICacheEntry {
         for (int i = 0; i < formulaCells.length; i++) {
             FormulaCellCacheEntry fc = formulaCells[i];
             fc.clearFormulaEntry();
-            fc.recurseClearCachedFormulaResults();
+            if (fc != this) {
+                fc.recurseClearCachedFormulaResults();
+            }
         }
     }
 

poi/src/test/java/org/apache/poi/ss/formula/TestFormulaEval.java

@@ -0,0 +1,53 @@
+/*
+ *  ====================================================================
+ *    Licensed to the Apache Software Foundation (ASF) under one or more
+ *    contributor license agreements.  See the NOTICE file distributed with
+ *    this work for additional information regarding copyright ownership.
+ *    The ASF licenses this file to You 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 org.apache.poi.ss.formula;
+
+import org.apache.poi.hssf.usermodel.HSSFCell;
+import org.apache.poi.hssf.usermodel.HSSFFormulaEvaluator;
+import org.apache.poi.hssf.usermodel.HSSFRow;
+import org.apache.poi.hssf.usermodel.HSSFSheet;
+import org.apache.poi.hssf.usermodel.HSSFWorkbook;
+import org.apache.poi.ss.usermodel.CellType;
+import org.junit.jupiter.api.Disabled;
+import org.junit.jupiter.api.Test;
+
+import java.io.IOException;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+class TestFormulaEval {
+
+    @Disabled("https://bz.apache.org/bugzilla/show_bug.cgi?id=65939")
+    @Test
+    void testCircularRef() throws IOException {
+        try (HSSFWorkbook wb = new HSSFWorkbook()) {
+            HSSFSheet sheet = wb.createSheet();
+            HSSFRow row = sheet.createRow(0);
+            HSSFCell cell = row.createCell(0);
+            cell.setCellFormula("A1");
+            HSSFFormulaEvaluator formulaEvaluator = wb.getCreationHelper().createFormulaEvaluator();
+            // the following assert should probably be NUMERIC not ERROR (from testing in Excel itself)
+            assertEquals(CellType.ERROR, formulaEvaluator.evaluateFormulaCell(cell));
+
+            cell.setCellFormula(null); //this line fails
+            formulaEvaluator.notifyUpdateCell(cell);
+        }
+    }
+}