Combine zuul.artifacts lists in zuul_return

In order to make it simple for multiple independent playbooks to return
artifacts, append the values of zuul.artifacts in zuul_return rather than
the usual method of overwriting lists.

Change-Id: I09e6076b4bb354023c5414d149d9bfa59fb3ea4b

doc/source/user/jobs.rst

@@ -807,6 +807,10 @@ the **zuul.log_url** value if set to create an absolute URL.  The
 **metadata** key is optional; if it is provided, it must be a
 dictionary; its keys and values may be anything.
 
+If *zuul_return* is invoked multiple times (e.g., via multiple
+playbooks), then the elements of **zuul.artifacts** from each
+invocation will be appended.
+
 Skipping child jobs
 ~~~~~~~~~~~~~~~~~~~
 

tests/fixtures/config/sql-driver/git/common-config/playbooks/project-test1.yaml

@@ -1,5 +1,12 @@
 - hosts: all
   tasks:
+    - name: Return artifact data
+      zuul_return:
+        data:
+          zuul:
+            artifacts:
+              - name: relative
+                url: relative/docs
     - name: Return artifact data
       zuul_return:
         data:
@@ -11,5 +18,3 @@
                 url: http://example.com/tarball
               - name: docs
                 url: http://example.com/docs
-              - name: relative
-                url: relative/docs

zuul/ansible/actiongeneral/zuul_return.py

@@ -40,6 +40,23 @@ def merge_dict(dict_a, dict_b):
     return dict_b
 
 
+def merge_data(dict_a, dict_b):
+    """
+    Merge dict_a into dict_b, handling any special cases for zuul variables
+    """
+    artifacts_a = dict_a.get('zuul', {}).get('artifacts', [])
+    if not isinstance(artifacts_a, list):
+        artifacts_a = []
+    artifacts_b = dict_b.get('zuul', {}).get('artifacts', [])
+    if not isinstance(artifacts_b, list):
+        artifacts_b = []
+    artifacts = artifacts_a + artifacts_b
+    merge_dict(dict_a, dict_b)
+    if artifacts:
+        dict_b.setdefault('zuul', {})['artifacts'] = artifacts
+    return dict_b
+
+
 def set_value(path, new_data, new_file):
     workdir = os.path.dirname(path)
     data = None
@@ -53,9 +70,9 @@ def set_value(path, new_data, new_file):
 
     if new_file:
         with open(new_file, 'r') as f:
-            merge_dict(json.load(f), data)
+            merge_data(json.load(f), data)
     if new_data:
-        merge_dict(new_data, data)
+        merge_data(new_data, data)
 
     (f, tmp_path) = tempfile.mkstemp(dir=workdir)
     try: