Fix retaining anchors when using with !j2-yaml

Before this change using an anchor/alias in !j2-yaml resulted in an
exception, even if retain_anchors was set to True:

>      File "(...)/jenkins-job-builder/.tox/py38/lib/python3.8/site-packages/yaml/composer.py", line 68, in compose_node
>    raise ComposerError(None, None, "found undefined alias %r"
>    yaml.composer.ComposerError: found undefined alias '<alias-name-xxx>'

The reason was that LateYamlLoader.get_object_to_format() was calling
load() without retain_anchors=True so effectively it was resetting
anchors during deep formatting...

From now on yaml.load() is called directly to avoid unwanted
side-effects of load() which is meant to be called from other modules,
typically by parser.YamlParser().

Change-Id: I0fde43c5c27ddf78f18dc244d8dba5bd768306b7

jenkins_jobs/local_yaml.py

@@ -613,7 +613,10 @@ class LateYamlLoader(CustomLoader):
         return LateYamlLoader(self._yaml_str, copy.deepcopy(self._loader, memo))
 
     def get_object_to_format(self):
-        return load(self._yaml_str, search_path=self._loader._search_path)
+        return yaml.load(
+            self._yaml_str,
+            functools.partial(LocalLoader, search_path=self._loader._search_path),
+        )
 
 
 class Jinja2YamlLoader(Jinja2Loader):

tests/localyaml/fixtures/custom_retain_anchors_j2_yaml.yaml

@@ -0,0 +1,12 @@
+- job-template:
+    name: 'test-job-template'
+    builders:
+    - shell:
+        docker run {docker-image}
+
+- project:
+    name: test-project
+    jobs:
+    - 'test-job-template':
+        docker-image: !j2-yaml: |
+            *docker-image

tests/localyaml/fixtures/custom_retain_anchors_j2_yaml_include001.yaml

@@ -0,0 +1,3 @@
+- globals:
+    name: globals
+    docker-image: &docker-image "ubuntu:latest"

tests/localyaml/test_localyaml.py

@@ -22,6 +22,7 @@ from yaml.composer import ComposerError
 
 from jenkins_jobs.config import JJBConfig
 from jenkins_jobs.parser import YamlParser
+from jenkins_jobs.registry import ModuleRegistry
 from tests import base
 
 
@@ -118,3 +119,23 @@ class TestCaseLocalYamlRetainAnchors(base.BaseTestCase):
         jjb_config.validate()
         j = YamlParser(jjb_config)
         j.load_files([os.path.join(self.fixtures_path, f) for f in files])
+
+    def test_retain_anchors_enabled_j2_yaml(self):
+        """
+        Verify that anchors are retained across files and are properly retained when using !j2-yaml.
+        """
+
+        files = [
+            "custom_retain_anchors_j2_yaml_include001.yaml",
+            "custom_retain_anchors_j2_yaml.yaml",
+        ]
+
+        jjb_config = JJBConfig()
+        jjb_config.yamlparser["retain_anchors"] = True
+        jjb_config.validate()
+        j = YamlParser(jjb_config)
+        j.load_files([os.path.join(self.fixtures_path, f) for f in files])
+
+        registry = ModuleRegistry(jjb_config, None)
+        jobs, _ = j.expandYaml(registry)
+        self.assertEqual(jobs[0]["builders"][0]["shell"], "docker run ubuntu:latest")