fix(stepfunctions-tasks): EvaluateExpression does not support JSON paths with dash

packages/@aws-cdk/aws-stepfunctions-tasks/lib/evaluate-expression.ts

@@ -72,7 +72,7 @@ export class EvaluateExpression extends sfn.TaskStateBase {
    * @internal
    */
   protected _renderTask(): any {
-    const matches = this.props.expression.match(/\$[.\[][.a-zA-Z[\]0-9]+/g);
+    const matches = this.props.expression.match(/\$[.\[][.a-zA-Z[\]0-9-_]+/g);
 
     let expressionAttributeValues = {};
     if (matches) {

packages/@aws-cdk/aws-stepfunctions-tasks/test/eval-nodejs10.x-handler.test.ts

@@ -58,3 +58,19 @@ test('with duplicated entries', async () => {
   const evaluated = await handler(event);
   expect(evaluated).toBe(2);
 });
+
+test('with dash and underscore in path', async () => {
+  // GIVEN
+  const event: Event = {
+    expression: '$.a_b + $.c-d + $[_e]',
+    expressionAttributeValues: {
+      '$.a_b': 1,
+      '$.c-d': 2,
+      '$[_e]': 3,
+    },
+  };
+
+  // THEN
+  const evaluated = await handler(event);
+  expect(evaluated).toBe(6);
+});

packages/@aws-cdk/aws-stepfunctions-tasks/test/evaluate-expression.test.ts

@@ -62,3 +62,28 @@ test('expression does not contain paths', () => {
     },
   });
 });
+
+test('with dash and underscore in path', () => {
+  // WHEN
+  const task = new tasks.EvaluateExpression(stack, 'Task', {
+    expression: '$.a_b + $.c-d + $[_e]',
+  });
+  new sfn.StateMachine(stack, 'SM', {
+    definition: task,
+  });
+
+  expect(stack).toHaveResource('AWS::StepFunctions::StateMachine', {
+    DefinitionString: {
+      'Fn::Join': [
+        '',
+        [
+          '{"StartAt":"Task","States":{"Task":{"End":true,"Type":"Task","Resource":"',
+          {
+            'Fn::GetAtt': ['Evala0d2ce44871b4e7487a1f5e63d7c3bdc4DAC06E1', 'Arn'],
+          },
+          '","Parameters":{"expression":"$.a_b + $.c-d + $[_e]","expressionAttributeValues":{"$.a_b.$":"$.a_b","$.c-d.$":"$.c-d","$[_e].$":"$[_e]"}}}}}',
+        ],
+      ],
+    },
+  });
+});