Keep existing stack tags for patch update

When updating a stack, we overwrite the existing tags.
So if no tags are specified during update, all existing
tags are removed. It would atleast be good to keep the
existing tags when doing a patch update (with `--existing`).

Change-Id: I910fe5237605405791eb6daa81c422bf7fd9eaa1
Closes-Bug: #1701098
(cherry picked from commit ed0beb6871b9a64c7a51ea85fd824e7c406343b3)

3 files changed, 42 insertions, 2 deletions

diff --git a/heat/engine/service.py b/heat/engine/service.py
index ab47c3777..13896cf32 100644
--- a/heat/engine/service.py
+++ b/heat/engine/service.py
@@ -927,6 +927,9 @@ class EngineService(service.ServiceBase):
         common_params.setdefault(rpc_api.PARAM_DISABLE_ROLLBACK,
                                  current_stack.disable_rollback)
 
+        if args.get(rpc_api.PARAM_EXISTING):
+            common_params.setdefault(rpc_api.STACK_TAGS,
+                                     current_stack.tags)
         current_kwargs.update(common_params)
         updated_stack = parser.Stack(cnxt, stack_name, tmpl,
                                      **current_kwargs)
diff --git a/heat/tests/engine/service/test_stack_update.py b/heat/tests/engine/service/test_stack_update.py
index c54f149ff..7dac6ba08 100644
--- a/heat/tests/engine/service/test_stack_update.py
+++ b/heat/tests/engine/service/test_stack_update.py
@@ -322,6 +322,41 @@ resources:
                              tmpl.env.params)
             self.assertEqual(stk.identifier(), result)
 
+    def test_stack_update_with_tags(self):
+        """Test case for updating stack with tags.
+
+        Create a stack with tags, then update with/without
+        rpc_api.PARAM_EXISTING.
+        """
+        stack_name = 'service_update_test_stack_existing_tags'
+        api_args = {rpc_api.PARAM_TIMEOUT: 60,
+                    rpc_api.PARAM_EXISTING: True}
+        t = template_format.parse(tools.wp_template)
+
+        stk = utils.parse_stack(t, stack_name=stack_name, tags=['tag1'])
+        stk.set_stack_user_project_id('1234')
+        self.assertEqual(['tag1'], stk.tags)
+
+        self.patchobject(stack.Stack, 'validate')
+
+        # update keep old tags
+        _, _, updated_stack = self.man._prepare_stack_updates(
+            self.ctx, stk, t, {}, None, None, api_args, None)
+        self.assertEqual(['tag1'], updated_stack.tags)
+
+        # with new tags
+        api_args[rpc_api.STACK_TAGS] = ['tag2']
+        _, _, updated_stack = self.man._prepare_stack_updates(
+            self.ctx, stk, t, {}, None, None, api_args, None)
+        self.assertEqual(['tag2'], updated_stack.tags)
+
+        # with no PARAM_EXISTING flag and no tags
+        del api_args[rpc_api.PARAM_EXISTING]
+        del api_args[rpc_api.STACK_TAGS]
+        _, _, updated_stack = self.man._prepare_stack_updates(
+            self.ctx, stk, t, {}, None, None, api_args, None)
+        self.assertIsNone(updated_stack.tags)
+
     def test_stack_update_existing_registry(self):
         # Use a template with existing flag and ensure the
         # environment registry is preserved.
diff --git a/heat/tests/utils.py b/heat/tests/utils.py
index acccc73d7..9c9743ea4 100644
--- a/heat/tests/utils.py
+++ b/heat/tests/utils.py
@@ -90,7 +90,8 @@ def dummy_context(user='test_username', tenant_id='test_tenant_id',
 
 
 def parse_stack(t, params=None, files=None, stack_name=None,
-                stack_id=None, timeout_mins=None, cache_data=None):
+                stack_id=None, timeout_mins=None,
+                cache_data=None, tags=None):
     params = params or {}
     files = files or {}
     ctx = dummy_context()
@@ -100,7 +101,8 @@ def parse_stack(t, params=None, files=None, stack_name=None,
     if stack_name is None:
         stack_name = random_name()
     stk = stack.Stack(ctx, stack_name, templ, stack_id=stack_id,
-                      timeout_mins=timeout_mins, cache_data=cache_data)
+                      timeout_mins=timeout_mins,
+                      cache_data=cache_data, tags=tags)
     stk.store()
     return stk