Forward artifacts to child jobs within buildset

When providing an artifact using zuul_return this information is
currently only available in different changes. However just like
regular variables this information should be forwarded to child jobs
in the same buildset too.

Change-Id: I8fefb57ccbbd61d51f96f18e882c0ab615cb0cd0

tests/fixtures/config/provides-requires-buildset/git/common-config/zuul.yaml

@@ -0,0 +1,17 @@
+- pipeline:
+    name: check
+    manager: independent
+    post-review: true
+    trigger:
+      gerrit:
+        - event: patchset-created
+    success:
+      gerrit:
+        Verified: 1
+    failure:
+      gerrit:
+        Verified: -1
+
+- job:
+    name: base
+    parent: null

tests/fixtures/config/provides-requires-buildset/git/org_project1/README

@@ -0,0 +1 @@
+test

tests/fixtures/config/provides-requires-buildset/git/org_project1/playbooks/image-builder.yaml

@@ -0,0 +1,10 @@
+- hosts: all
+  tasks:
+    - name: Pause and let child run
+      zuul_return:
+        data:
+          zuul:
+            pause: true
+            artifacts:
+              - name: image
+                url: http://example.com/image

tests/fixtures/config/provides-requires-buildset/git/org_project1/playbooks/image-user.yaml

@@ -0,0 +1,4 @@
+- hosts: all
+  tasks:
+    - debug:
+        var: zuul.artifacts

tests/fixtures/config/provides-requires-buildset/git/org_project1/zuul.yaml

@@ -0,0 +1,15 @@
+- job:
+    name: image-builder
+    run: playbooks/image-builder.yaml
+
+- job:
+    name: image-user
+    run: playbooks/image-user.yaml
+
+- project:
+    check:
+      jobs:
+        - image-builder
+        - image-user:
+            dependencies:
+              - image-builder

tests/fixtures/config/provides-requires-buildset/main.yaml

@@ -0,0 +1,7 @@
+- tenant:
+    name: tenant-one
+    source:
+      gerrit:
+        config-projects:
+          - common-config
+          - org/project1

tests/unit/test_v3.py

@@ -5009,6 +5009,55 @@ class TestProvidesRequiresPause(AnsibleZuulTestCase):
             }])
 
 
+class TestProvidesRequiresBuildset(ZuulTestCase):
+    tenant_config_file = "config/provides-requires-buildset/main.yaml"
+
+    def test_provides_requires_buildset(self):
+        # Changes share a queue, with both running at the same time.
+        self.executor_server.hold_jobs_in_build = True
+        A = self.fake_gerrit.addFakeChange('org/project1', 'master', 'A')
+        self.executor_server.returnData(
+            'image-builder', A,
+            {'zuul':
+             {'artifacts': [
+                 {'name': 'image',
+                  'url': 'http://example.com/image',
+                  'metadata': {
+                      'type': 'container_image'
+                  }},
+             ]}}
+        )
+
+        self.fake_gerrit.addEvent(A.getPatchsetCreatedEvent(1))
+        self.waitUntilSettled()
+
+        self.assertEqual(len(self.builds), 1)
+
+        self.executor_server.hold_jobs_in_build = False
+        self.executor_server.release()
+        self.waitUntilSettled()
+
+        self.assertHistory([
+            dict(name='image-builder', result='SUCCESS', changes='1,1'),
+            dict(name='image-user', result='SUCCESS', changes='1,1'),
+        ])
+
+        build = self.getJobFromHistory('image-user', project='org/project1')
+        self.assertEqual(
+            build.parameters['zuul']['artifacts'],
+            [{
+                'project': 'org/project1',
+                'change': '1',
+                'patchset': '1',
+                'job': 'image-builder',
+                'url': 'http://example.com/image',
+                'name': 'image',
+                'metadata': {
+                    'type': 'container_image',
+                }
+            }])
+
+
 class TestProvidesRequires(ZuulDBTestCase):
     config_file = "zuul-sql-driver.conf"