1108 stepper programs that end with a declaration dont show correct r…

…esult (#1597)

* Solved the problem by adding extra check for empty reduced program

* Change the test cases, the new expected behaviour should be "undefined;" instead of "" (epsilon)

---------

Co-authored-by: Martin Henz <[email protected]>

src/stepper/__tests__/__snapshots__/stepper.ts.snap

@@ -2105,6 +2105,7 @@ false ? 1 : 100 * factorial(100 - 1);
 
 exports[`Evaluation of empty code and imports Evaluate empty program 1`] = `
 "
+undefined;
 "
 `;
 

src/stepper/__tests__/stepper.ts

@@ -220,7 +220,7 @@ describe('Test single line of code is evaluated', () => {
     `
     const steps = await testEvalSteps(code)
     expect(steps.length).toBe(4)
-    expect(getLastStepAsString(steps)).toEqual('')
+    expect(getLastStepAsString(steps)).toEqual('undefined;')
   })
 
   test('Function Declaration', async () => {
@@ -231,7 +231,7 @@ describe('Test single line of code is evaluated', () => {
     `
     const steps = await testEvalSteps(code)
     expect(steps.length).toBe(4)
-    expect(getLastStepAsString(steps)).toEqual('')
+    expect(getLastStepAsString(steps)).toEqual('undefined;')
   })
 
   test('Value', async () => {
@@ -1598,7 +1598,7 @@ describe(`Evaluation of empty code and imports`, () => {
     const code = ``
     const steps = await testEvalSteps(code, mockContext())
     expect(steps.map(x => codify(x[0])).join('\n')).toMatchSnapshot()
-    expect(getLastStepAsString(steps)).toEqual('')
+    expect(getLastStepAsString(steps)).toEqual('undefined;')
   })
 })
 

src/stepper/stepper.ts

@@ -3377,6 +3377,16 @@ export async function getEvaluationSteps(
     }
     if (!limitExceeded && steps.length > 0) {
       steps[steps.length - 1][2] = 'Evaluation complete'
+      /**
+       * this is an extra check
+       * if the last step's program part is empty, we just manually add undefined to it
+       * also works when program is epsilon(empty program)
+       */
+      if ((reducedWithPath[0] as es.Program).body.length == 0) {
+        steps[steps.length - 1][0] = ast.program([
+          ast.expressionStatement(ast.identifier('undefined'))
+        ])
+      }
     }
     if (steps.length === 0) {
       steps.push([reducedWithPath[0] as es.Program, [], 'Nothing to evaluate'])