test: detect circular formulas

cli/src/osf.ts

@@ -120,7 +120,7 @@ class FormulaEvaluator {
   private data: SpreadsheetData;
   private formulas: Map<string, string>;
   private computed: Map<string, CellValue>;
-  private evaluating: Set<string>; // For circular reference detection
+  private evaluating: Set<string>; // For circular reference detection; see cli/tests/cli.test.ts
 
   constructor(data: SpreadsheetData, formulas: FormulaDefinition[]) {
     this.data = { ...data };
@@ -175,7 +175,7 @@ class FormulaEvaluator {
   getCellValue(row: number, col: number): CellValue {
     const key = `${row},${col}`;
 
-    // Check for circular reference
+    // Check for circular reference (validated by cli/tests/cli.test.ts)
     if (this.evaluating.has(key)) {
       throw new Error(`Circular reference detected at cell ${this.coordsToCellRef(row, col)}`);
     }
@@ -725,6 +725,14 @@ function exportJson(doc: OSFDocument): string {
           // Get all computed values including formulas
           const allValues = evaluator.getAllComputedValues(maxRow, maxCol);
 
+          // Fail if any formula evaluation resulted in an error (e.g., circular references)
+          const errorCell = Object.values(allValues).find(
+            v => typeof v === 'string' && v.startsWith('#ERROR:')
+          );
+          if (typeof errorCell === 'string') {
+            throw new Error(errorCell.replace('#ERROR: ', ''));
+          }
+
           // Convert to array format with computed values
           const computedData = Object.entries(allValues).map(([cell, value]) => {
             const [r, c] = cell.split(',').map(Number);

cli/tests/cli.test.ts

@@ -60,6 +60,20 @@ const FORMULA_TEST_OSF = `@meta {
   formula (2,4): "=C1+C2";
 }`;
 
+const CIRCULAR_FORMULA_OSF = `@meta {
+  title: "Circular Formula Test";
+}
+
+@sheet {
+  name: "CycleSheet";
+  cols: [A, B];
+  data {
+    (2,1) = 1;
+  }
+  formula (1,1): "=B1";
+  formula (1,2): "=A1";
+}`;
+
 const INVALID_OSF = `@meta {
   title: "Unclosed Block"
   // Missing closing brace`;
@@ -377,6 +391,25 @@ describe('OSF CLI', () => {
       }
     });
 
+    it('should fail exporting OSF with circular formulas to JSON', () => {
+      const cycleFile = join(TEST_FIXTURES_DIR, 'cycle_test.osf');
+      writeFileSync(cycleFile, CIRCULAR_FORMULA_OSF, 'utf8');
+
+      try {
+        const result = execSync(`node "${CLI_PATH}" export "${cycleFile}" --target json`, {
+          encoding: 'utf8',
+        });
+        expect.fail(`Expected export to fail but succeeded with output: ${result}`);
+      } catch (err: any) {
+        const output = (err.stderr || err.stdout) as string;
+        expect(output).toContain('Circular reference detected');
+      } finally {
+        if (existsSync(cycleFile)) {
+          unlinkSync(cycleFile);
+        }
+      }
+    });
+
     it('should export OSF to file', () => {
       execSync(`node "${CLI_PATH}" export "${testFile}" --output "${outputFile}"`, {
         encoding: 'utf8',