fix: handle CloudFormation intrinsic functions in Arguments.StateMachineArn

[lracicot]

Fixes #704

Summary

• When using JSONata QueryLanguage with a CloudFormation intrinsic function (e.g. !Sub or Fn::Sub) as StateMachineArn in Arguments, getStateMachineArn() crashes with TypeError: state.Arguments.StateMachineArn.trim is not a function because it assumes the value is a string, but intrinsic functions resolve to objects like {"Fn::Sub": "..."}.
• Added a type check before calling .trim() — when StateMachineArn is not a string (i.e. a CloudFormation intrinsic), return it as-is for use in the IAM policy resource. This matches the existing behavior for Parameters.StateMachineArn which already handles intrinsics correctly.

Reproduction

# serverless.yml — this crashes on deploy
stepFunctions:
  stateMachines:
    Workflow:
      definition:
        States:
          InvokeChild:
            Type: Task
            Resource: 'arn:aws:states:::states:startExecution.sync:2'
            QueryLanguage: JSONata
            Arguments:
              StateMachineArn: !Sub "arn:aws:states:${AWS::Region}:${AWS::AccountId}:stateMachine:ChildMachine"
              Input:
                key: "{% $states.input.value %}"
            End: true

TypeError: state.Arguments.StateMachineArn.trim is not a function
    at getStateMachineArn (compileIamRole.js:452:55)

Changes

• lib/deploy/stepFunctions/compileIamRole.js: Check typeof arn !== 'string' before calling .trim() in getStateMachineArn()
• lib/deploy/stepFunctions/compileIamRole.test.js: Added test case for JSONata with CloudFormation intrinsic StateMachineArn

Test plan

• All 104 existing tests pass
• New test case verifies Fn::Sub object is passed through correctly as the IAM policy resource

[pkg-pr-new]

Open in StackBlitz

npm i https://pkg.pr.new/serverless-operations/serverless-step-functions@709

commit: 9114fb8