[3.x] Add !Transform and !GetStackOutput short forms

lib/utils/serverless-utils/README.md

@@ -28,8 +28,10 @@ Notes:
 
 - `cloudformation-schema.js` intentionally diverges from upstream: it removes
   implicit YAML timestamp resolution and re-registers `!!timestamp` as an
-  explicit type (https://github.com/oss-serverless/osls/issues/438). Preserve
-  this when re-syncing.
+  explicit type (https://github.com/oss-serverless/osls/issues/438), and it
+  adds the `!Transform` and `!GetStackOutput` short forms that upstream lacks
+  (https://github.com/oss-serverless/osls/issues/450). Preserve this when
+  re-syncing.
 - `config.js` is a locally owned fork. It intentionally keeps the synchronous
   `get('frameworkId')` and `get('meta.created_at')` lookups that Bref v2/v3 use
   for best-effort telemetry if a future compatibility shim routes

lib/utils/serverless-utils/cloudformation-schema.js

@@ -11,6 +11,7 @@ const functionNames = [
   'FindInMap',
   'GetAtt',
   'GetAZs',
+  'GetStackOutput',
   'If',
   'ImportValue',
   'Join',
@@ -20,6 +21,7 @@ const functionNames = [
   'Select',
   'Split',
   'Sub',
+  'Transform',
 ];
 
 const yamlType = (name, kind) => {

test/unit/lib/utils/serverless-utils/cloudformation-schema.test.js

@@ -17,4 +17,17 @@ describe('serverless-utils/cloudformation-schema', () => {
   it('should construct a Date for an explicit timestamp tag', () => {
     expect(load('date: !!timestamp 2020-12-12').date).to.be.instanceOf(Date);
   });
+
+  it('should construct the Transform and GetStackOutput short forms', () => {
+    expect(
+      load(
+        'value: !Transform\n  Name: AWS::Include\n  Parameters:\n    Location: s3://bucket/x.yml'
+      ).value
+    ).to.deep.equal({
+      'Fn::Transform': { Name: 'AWS::Include', Parameters: { Location: 's3://bucket/x.yml' } },
+    });
+    expect(
+      load('value: !GetStackOutput\n  StackName: producer\n  OutputName: VpcId').value
+    ).to.deep.equal({ 'Fn::GetStackOutput': { StackName: 'producer', OutputName: 'VpcId' } });
+  });
 });