Chart builder: filter/calculate transforms, data preview, and inline expression validation

src/core/expr-validate.test.ts

@@ -0,0 +1,39 @@
+import { describe, it, expect } from 'vitest';
+import { validateExpression, referencedFields } from './expr-validate';
+
+describe('validateExpression', () => {
+  it('accepts a well-formed Vega expression', () => {
+    expect(validateExpression('datum.price * datum.qty').valid).toBe(true);
+    expect(validateExpression("datum.region === 'East' && datum.value > 0").valid).toBe(true);
+  });
+
+  it('treats an empty / whitespace expression as valid (incomplete, not a mistake)', () => {
+    expect(validateExpression('').valid).toBe(true);
+    expect(validateExpression('   ').valid).toBe(true);
+  });
+
+  it('rejects a malformed expression with a message', () => {
+    const result = validateExpression('datum.price *');
+    expect(result.valid).toBe(false);
+    expect(result.error).toBeTruthy();
+  });
+});
+
+describe('referencedFields', () => {
+  it('collects datum.field and datum["field"] references, de-duplicated in order', () => {
+    expect(referencedFields("datum.price * datum['qty'] + datum.price")).toEqual(['price', 'qty']);
+  });
+
+  it('ignores function calls and non-datum identifiers', () => {
+    expect(referencedFields('toNumber(datum.amount) + PI')).toEqual(['amount']);
+  });
+
+  it('skips dynamic (computed, non-literal) access', () => {
+    expect(referencedFields('datum[someVar]')).toEqual([]);
+  });
+
+  it('returns nothing for an empty or unparseable expression', () => {
+    expect(referencedFields('')).toEqual([]);
+    expect(referencedFields('datum.price *')).toEqual([]);
+  });
+});