Fix #2943: preserve falsy formula results (0, false, empty string) in copy

lib/doc/cell.js

@@ -749,9 +749,10 @@ class FormulaValue {
   _copyModel(model) {
     const copy = {};
     const cp = name => {
-      const value = model[name];
-      if (value) {
-        copy[name] = value;
+      // Use 'in' check so falsy results (0, false, '') survive the copy.
+      // See exceljs/exceljs#2943.
+      if (name in model && model[name] !== undefined) {
+        copy[name] = model[name];
       }
     };
     cp('formula');
@@ -869,13 +870,19 @@ class FormulaValue {
   }
 
   toCsvString() {
-    return `${this.model.result || ''}`;
+    // Preserve falsy results (0, false, '') instead of collapsing to ''.
+    // See exceljs/exceljs#2943.
+    const {result} = this.model;
+    return result === null || result === undefined ? '' : `${result}`;
   }
 
   release() {}
 
   toString() {
-    return this.model.result ? this.model.result.toString() : '';
+    // Preserve falsy results (0, false, '') instead of collapsing to ''.
+    // See exceljs/exceljs#2943.
+    const {result} = this.model;
+    return result === null || result === undefined ? '' : result.toString();
   }
 }
 

lib/xlsx/xform/sheet/cell-xform.js

@@ -348,7 +348,9 @@ class CellXform extends BaseXform {
         // first guess on cell type
         if (model.formula || model.shareType) {
           model.type = Enums.ValueType.Formula;
-          if (model.value) {
+          if (model.value !== undefined) {
+            // Use !== undefined so an empty <v></v> (e.g. result === '')
+            // is preserved instead of dropped. See exceljs/exceljs#2943.
             if (this.t === 'str') {
               model.result = utils.xmlDecode(model.value);
             } else if (this.t === 'b') {
@@ -359,6 +361,9 @@ class CellXform extends BaseXform {
               model.result = parseFloat(model.value);
             }
             model.value = undefined;
+          } else if (this.t === 'str') {
+            // Empty string formula result: <c t="str"><f>...</f><v/></c>
+            model.result = '';
           }
         } else if (model.value !== undefined) {
           switch (this.t) {

spec/integration/issues/issue-2943-formula-falsy-result.spec.js

@@ -0,0 +1,107 @@
+const ExcelJS = verquire('exceljs');
+
+// Regression test for exceljs/exceljs#2943.
+// Copying a formula cell whose cached result is a falsy value (0, false, '')
+// previously dropped the `result` field because `_copyModel` used a truthy
+// check (`if (value)`).
+
+describe('github issue 2943 - copy formula cell with falsy result', () => {
+  it('preserves result === 0 when copying formula cell value', () => {
+    const wb = new ExcelJS.Workbook();
+    const ws = wb.addWorksheet('s');
+    ws.getCell('B1').value = {formula: 'A1-A1', result: 0};
+
+    ws.getCell('C1').value = ws.getCell('B1').value;
+
+    expect(ws.getCell('C1').value).to.deep.equal({formula: 'A1-A1', result: 0});
+    expect(ws.getCell('C1').value.result).to.equal(0);
+  });
+
+  it('preserves result === false when copying formula cell value', () => {
+    const wb = new ExcelJS.Workbook();
+    const ws = wb.addWorksheet('s');
+    ws.getCell('B1').value = {formula: 'FALSE()', result: false};
+
+    ws.getCell('C1').value = ws.getCell('B1').value;
+
+    expect(ws.getCell('C1').value).to.deep.equal({formula: 'FALSE()', result: false});
+    expect(ws.getCell('C1').value.result).to.equal(false);
+  });
+
+  it('preserves result === "" when copying formula cell value', () => {
+    const wb = new ExcelJS.Workbook();
+    const ws = wb.addWorksheet('s');
+    ws.getCell('B1').value = {formula: '""', result: ''};
+
+    ws.getCell('C1').value = ws.getCell('B1').value;
+
+    expect(ws.getCell('C1').value).to.deep.equal({formula: '""', result: ''});
+    expect(ws.getCell('C1').value.result).to.equal('');
+  });
+
+  it('preserves result === 0 across xlsx round-trip', async () => {
+    const wb = new ExcelJS.Workbook();
+    const ws = wb.addWorksheet('s');
+    ws.getCell('B1').value = {formula: 'A1-A1', result: 0};
+
+    const buffer = await wb.xlsx.writeBuffer();
+    const wb2 = new ExcelJS.Workbook();
+    await wb2.xlsx.load(buffer);
+
+    expect(wb2.getWorksheet('s').getCell('B1').value).to.deep.equal({formula: 'A1-A1', result: 0});
+  });
+
+  it('preserves result === false across xlsx round-trip', async () => {
+    const wb = new ExcelJS.Workbook();
+    const ws = wb.addWorksheet('s');
+    ws.getCell('B1').value = {formula: 'FALSE()', result: false};
+
+    const buffer = await wb.xlsx.writeBuffer();
+    const wb2 = new ExcelJS.Workbook();
+    await wb2.xlsx.load(buffer);
+
+    expect(wb2.getWorksheet('s').getCell('B1').value).to.deep.equal({
+      formula: 'FALSE()',
+      result: false,
+    });
+  });
+
+  it('preserves result === "" across xlsx round-trip', async () => {
+    const wb = new ExcelJS.Workbook();
+    const ws = wb.addWorksheet('s');
+    ws.getCell('B1').value = {formula: '""', result: ''};
+
+    const buffer = await wb.xlsx.writeBuffer();
+    const wb2 = new ExcelJS.Workbook();
+    await wb2.xlsx.load(buffer);
+
+    expect(wb2.getWorksheet('s').getCell('B1').value).to.deep.equal({formula: '""', result: ''});
+  });
+
+  it('toCsvString returns "0" for falsy numeric result', () => {
+    const wb = new ExcelJS.Workbook();
+    const ws = wb.addWorksheet('s');
+    const cell = ws.getCell('B1');
+    cell.value = {formula: 'A1-A1', result: 0};
+
+    expect(cell.toCsvString()).to.equal('0');
+  });
+
+  it('toString returns "0" for falsy numeric result', () => {
+    const wb = new ExcelJS.Workbook();
+    const ws = wb.addWorksheet('s');
+    const cell = ws.getCell('B1');
+    cell.value = {formula: 'A1-A1', result: 0};
+
+    expect(cell.toString()).to.equal('0');
+  });
+
+  it('toCsvString returns "false" for boolean false result', () => {
+    const wb = new ExcelJS.Workbook();
+    const ws = wb.addWorksheet('s');
+    const cell = ws.getCell('B1');
+    cell.value = {formula: 'FALSE()', result: false};
+
+    expect(cell.toCsvString()).to.equal('false');
+  });
+});