fix(logs): respect region when importing log group (#18215)

When log group is imported it is crucial to preserve an information
about region where log group exists. Without that information it is not possible
to implement cross region logging.

fixes #18214

----

*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-logs/lib/log-group.ts

@@ -355,7 +355,9 @@ export class LogGroup extends LogGroupBase {
       public readonly logGroupName = Stack.of(scope).splitArn(baseLogGroupArn, ArnFormat.COLON_RESOURCE_NAME).resourceName!;
     }
 
-    return new Import(scope, id);
+    return new Import(scope, id, {
+      environmentFromArn: baseLogGroupArn,
+    });
   }
 
   /**

packages/@aws-cdk/aws-logs/test/loggroup.test.ts

@@ -149,7 +149,7 @@ describe('log group', () => {
 
   });
 
-  test('import from arn', () => {
+  test('import from ARN, same region', () => {
     // GIVEN
     const stack2 = new Stack();
 
@@ -166,6 +166,28 @@ describe('log group', () => {
 
   });
 
+  test('import from ARN, different region', () => {
+    // GIVEN
+    const stack = new Stack();
+    const importRegion = 'asgard-1';
+
+    // WHEN
+    const imported = LogGroup.fromLogGroupArn(stack, 'lg',
+      `arn:aws:logs:${importRegion}:123456789012:log-group:my-log-group`);
+    imported.addStream('MakeMeAStream');
+
+    // THEN
+    expect(imported.logGroupName).toEqual('my-log-group');
+    expect(imported.logGroupArn).toEqual(`arn:aws:logs:${importRegion}:123456789012:log-group:my-log-group:*`);
+    expect(imported.env.region).not.toEqual(stack.region);
+    expect(imported.env.region).toEqual(importRegion);
+
+    expect(stack).toHaveResource('AWS::Logs::LogStream', {
+      LogGroupName: 'my-log-group',
+    });
+    expect(stack).toCountResources('AWS::Logs::LogGroup', 0);
+  });
+
   test('import from name', () => {
     // GIVEN
     const stack = new Stack();