feat(logs): import a LogGroup from its name (#5580)

* feat(logs): import a LogGroup from its name

* reuse fromLogGroupArn

* Revert "reuse fromLogGroupArn"

This reverts commit 4916c66.

Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

packages/@aws-cdk/aws-logs/lib/log-group.ts

@@ -305,7 +305,7 @@ export interface LogGroupProps {
  */
 export class LogGroup extends LogGroupBase {
   /**
-   * Import an existing LogGroup
+   * Import an existing LogGroup given its ARN
    */
   public static fromLogGroupArn(scope: Construct, id: string, logGroupArn: string): ILogGroup {
     class Import extends LogGroupBase {
@@ -316,6 +316,23 @@ export class LogGroup extends LogGroupBase {
     return new Import(scope, id);
   }
 
+  /**
+   * Import an existing LogGroup given its name
+   */
+  public static fromLogGroupName(scope: Construct, id: string, logGroupName: string): ILogGroup {
+    class Import extends LogGroupBase {
+      public readonly logGroupName = logGroupName;
+      public readonly logGroupArn = Stack.of(scope).formatArn({
+        service: 'logs',
+        resource: 'log-group',
+        sep: ':',
+        resourceName: logGroupName,
+      });
+    }
+
+    return new Import(scope, id);
+  }
+
   /**
    * The ARN of this log group
    */

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

@@ -110,7 +110,7 @@ export = {
     test.done();
   },
 
-  'export/import'(test: Test) {
+  'import from arn'(test: Test) {
     // GIVEN
     const stack2 = new Stack();
 
@@ -119,12 +119,32 @@ export = {
     imported.addStream('MakeMeAStream');
 
     // THEN
+    test.deepEqual(imported.logGroupName, 'my-log-group');
+    test.deepEqual(imported.logGroupArn, 'arn:aws:logs:us-east-1:123456789012:log-group:my-log-group');
     expect(stack2).to(haveResource('AWS::Logs::LogStream', {
       LogGroupName: "my-log-group"
     }));
     test.done();
   },
 
+  'import from name'(test: Test) {
+    // GIVEN
+    const stack = new Stack();
+
+    // WHEN
+    const imported = LogGroup.fromLogGroupName(stack, 'lg', 'my-log-group');
+    imported.addStream('MakeMeAStream');
+
+    // THEN
+    test.deepEqual(imported.logGroupName, 'my-log-group');
+    test.ok(/^arn:.+:logs:.+:.+:log-group:my-log-group$/.test(imported.logGroupArn),
+      `LogGroup ARN ${imported.logGroupArn} does not match the expected pattern`);
+    expect(stack).to(haveResource('AWS::Logs::LogStream', {
+      LogGroupName: 'my-log-group'
+    }));
+    test.done();
+  },
+
   'extractMetric'(test: Test) {
     // GIVEN
     const stack = new Stack();