fix(stepfunctions): imported State Machine sill has region and accoun…

…t from its Stack, instead of its ARN (aws#19026)

Fixes aws#17982.

----

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

packages/@aws-cdk/aws-stepfunctions/lib/state-machine.ts

@@ -142,7 +142,9 @@ abstract class StateMachineBase extends Resource implements IStateMachine {
       public readonly stateMachineArn = stateMachineArn;
       public readonly grantPrincipal = new iam.UnknownPrincipal({ resource: this });
     }
-    return new Import(scope, id);
+    return new Import(scope, id, {
+      environmentFromArn: stateMachineArn,
+    });
   }
 
   public abstract readonly stateMachineArn: string;

packages/@aws-cdk/aws-stepfunctions/test/state-machine.test.ts

@@ -277,4 +277,35 @@ describe('State Machine', () => {
       ],
     });
   });
+
+  describe('StateMachine.fromStateMachineArn()', () => {
+    let stack: cdk.Stack;
+
+    beforeEach(() => {
+      const app = new cdk.App();
+      stack = new cdk.Stack(app, 'Base', {
+        env: { account: '111111111111', region: 'stack-region' },
+      });
+    });
+
+    describe('for a state machine in a different account and region', () => {
+      let mach: stepfunctions.IStateMachine;
+
+      beforeEach(() => {
+        mach = stepfunctions.StateMachine.fromStateMachineArn(
+          stack,
+          'iMach',
+          'arn:aws:states:machine-region:222222222222:stateMachine:machine-name',
+        );
+      });
+
+      test("the state machine's region is taken from the ARN", () => {
+        expect(mach.env.region).toBe('machine-region');
+      });
+
+      test("the state machine's account is taken from the ARN", () => {
+        expect(mach.env.account).toBe('222222222222');
+      });
+    });
+  });
 });