fix(region-info): EMR service principal incorrect in China (#20014)

Fixes #19867.

----

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

Author: rix0rrr

packages/@aws-cdk/region-info/lib/default.ts

@@ -106,6 +106,11 @@ export class Default {
         case 'ec2':
           return partitional;
 
+        case 'elasticmapreduce':
+          return region.startsWith('cn-')
+            ? partitional
+            : universal;
+
         // Services with a universal principal across all regions/partitions (the default case)
         default:
           return universal;

packages/@aws-cdk/region-info/test/default.test.ts

@@ -53,15 +53,28 @@ describe('servicePrincipal', () => {
       expect(Default.servicePrincipal('codedeploy', cnRegion, 'amazonaws.com.cn')).toBe(`codedeploy.${cnRegion}.amazonaws.com.cn`);
     });
   }
-
 });
 
 
 describe('spot-check some service principals', () => {
   test('ssm', () => {
-    expect(Default.servicePrincipal('ssm.amazonaws.com', 'us-east-1', 'x')).toBe('ssm.amazonaws.com');
-    expect(Default.servicePrincipal('ssm.amazonaws.com', 'eu-north-1', 'x')).toBe('ssm.amazonaws.com');
-    expect(Default.servicePrincipal('ssm.amazonaws.com', 'ap-east-1', 'x')).toBe('ssm.ap-east-1.amazonaws.com');
-    expect(Default.servicePrincipal('ssm.amazonaws.com', 'eu-south-1', 'x')).toBe('ssm.eu-south-1.amazonaws.com');
+    expectServicePrincipals('ssm.amazonaws.com', {
+      'us-east-1': 'ssm.amazonaws.com',
+      'eu-north-1': 'ssm.amazonaws.com',
+      'ap-east-1': 'ssm.ap-east-1.amazonaws.com',
+      'eu-south-1': 'ssm.eu-south-1.amazonaws.com',
+    });
   });
+
+  test('EMR', () => {
+    expectServicePrincipals('elasticmapreduce.amazonaws.com', {
+      'us-east-1': 'elasticmapreduce.amazonaws.com',
+      'cn-north-1': 'elasticmapreduce.EXTENSION', // amazonaws.com.cn in China
+      'us-iso-east-1': 'elasticmapreduce.amazonaws.com',
+    });
+  });
+
+  function expectServicePrincipals(principal: string, regionMap: Record<string, string>) {
+    expect(Object.fromEntries(Object.keys(regionMap).map(reg => [reg, Default.servicePrincipal(principal, reg, 'EXTENSION')]))).toEqual(regionMap);
+  }
 });