[Resolves Sceptre#723] Fix update command with change sets for multip…

…le stacks

Previously the update command would exit if any change sets status
was not equal to READY. However, when a stack does not contain
any updates, it will not be READY since there is nothing to execute.
This should not prevent other change sets to be executed.

To get around this, we introduce another change set status, NO_CHANGES,
and handle that gracefully.

To clean up the output a bit, we also pass on describing the changes
for empty change sets.

sceptre/cli/update.py

@@ -57,23 +57,38 @@ def update_command(ctx, path, change_set, verbose, yes):
         try:
             # Wait for change set to be created
             statuses = plan.wait_for_cs_completion(change_set_name)
-            # Exit if change set fails to create
+
+            at_least_one_ready = False
+
             for status in list(statuses.values()):
-                if status != StackChangeSetStatus.READY:
+                # Exit if change set fails to create
+                if status not in (StackChangeSetStatus.READY, StackChangeSetStatus.NO_CHANGES):
+                    write("Failed to create change set", context.output_format)
                     exit(1)
 
+                if status == StackChangeSetStatus.READY:
+                    at_least_one_ready = True
+
+            # If none are ready, and we haven't exited, there are no changes
+            if not at_least_one_ready:
+                write("No changes detected", context.output_format)
+                exit(0)
+
             # Describe changes
             descriptions = plan.describe_change_set(change_set_name)
-            for description in list(descriptions.values()):
+            for stack, description in descriptions.items():
+                # No need to print if there are no changes
+                if statuses[stack] == StackChangeSetStatus.NO_CHANGES:
+                    continue
+
                 if not verbose:
                     description = simplify_change_set_description(description)
                 write(description, context.output_format)
 
             # Execute change set if happy with changes
             if yes or click.confirm("Proceed with stack update?"):
                 plan.execute_change_set(change_set_name)
-        except Exception as e:
-            raise e
+
         finally:
             # Clean up by deleting change set
             plan.delete_change_set(change_set_name)

sceptre/plan/actions.py

@@ -884,6 +884,7 @@ def _get_cs_status(self, change_set_name):
         cs_description = self.describe_change_set(change_set_name)
 
         cs_status = cs_description["Status"]
+        cs_reason = cs_description.get("StatusReason")
         cs_exec_status = cs_description["ExecutionStatus"]
         possible_statuses = [
             "CREATE_PENDING", "CREATE_IN_PROGRESS",
@@ -915,6 +916,12 @@ def _get_cs_status(self, change_set_name):
                 cs_exec_status in ["UNAVAILABLE", "AVAILABLE"]
         ):
             return StackChangeSetStatus.PENDING
+        elif (
+                cs_status == "FAILED" and
+                cs_reason is not None and
+                self.change_set_creation_failed_due_to_no_changes(cs_reason)
+        ):
+            return StackChangeSetStatus.NO_CHANGES
         elif (
                 cs_status in ["DELETE_COMPLETE", "FAILED"] or
                 cs_exec_status in [

sceptre/stack_status.py

@@ -25,3 +25,4 @@ class StackChangeSetStatus(object):
     PENDING = "pending"
     READY = "ready"
     DEFUNCT = "defunct"
+    NO_CHANGES = "no changes"

tests/test_actions.py

@@ -1088,6 +1088,17 @@ def test_get_cs_status_handles_all_statuses(
                 )
                 assert response == returns[i]
 
+        mock_describe_change_set.return_value = {
+            "Status": "FAILED",
+            "StatusReason": "The submitted information didn't contain changes. "
+                            "Submit different information to create a change set.",
+            "ExecutionStatus": "UNAVAILABLE"
+        }
+        response = self.actions._get_cs_status(
+            sentinel.change_set_name
+        )
+        assert response == scss.NO_CHANGES
+
         for status in return_values['Status']:
             mock_describe_change_set.return_value = {
                 "Status": status,

tests/test_cli.py

@@ -21,7 +21,7 @@
 from sceptre.exceptions import SceptreException
 from sceptre.plan.actions import StackActions
 from sceptre.stack import Stack
-from sceptre.stack_status import StackStatus
+from sceptre.stack_status import StackChangeSetStatus, StackStatus
 
 
 class TestCli(object):
@@ -484,6 +484,92 @@ def test_stack_commands(self, command, success, yes_flag, exit_code):
         run_command.assert_called_with()
         assert result.exit_code == exit_code
 
+    @pytest.mark.parametrize(
+        "change_set_status,yes_flag,exit_code,verbose_flag", [
+            (StackChangeSetStatus.READY, True, 0, True),
+            (StackChangeSetStatus.READY, True, 0, False),
+            (StackChangeSetStatus.READY, False, 0, True),
+            (StackChangeSetStatus.READY, False, 0, False),
+            (StackChangeSetStatus.NO_CHANGES, True, 0, True),
+            (StackChangeSetStatus.NO_CHANGES, False, 0, False),
+            (StackChangeSetStatus.NO_CHANGES, True, 0, False),
+            (StackChangeSetStatus.NO_CHANGES, False, 0, True),
+            (StackChangeSetStatus.DEFUNCT, True, 1, True),
+            (StackChangeSetStatus.DEFUNCT, False, 1, False),
+            (StackChangeSetStatus.DEFUNCT, True, 1, False),
+            (StackChangeSetStatus.DEFUNCT, False, 1, True),
+        ]
+    )
+    def test_update_with_change_set(self, change_set_status, yes_flag, exit_code, verbose_flag):
+        create_command = self.mock_stack_actions.create_change_set
+        wait_command = self.mock_stack_actions.wait_for_cs_completion
+        execute_command = self.mock_stack_actions.execute_change_set
+        delete_command = self.mock_stack_actions.delete_change_set
+        describe_command = self.mock_stack_actions.describe_change_set
+
+        wait_command.return_value = change_set_status
+
+        response = {
+            "VerboseProperty": "VerboseProperty",
+            "ChangeSetName": "ChangeSetName",
+            "CreationTime": "CreationTime",
+            "ExecutionStatus": "ExecutionStatus",
+            "StackName": "StackName",
+            "Status": "Status",
+            "StatusReason": "StatusReason",
+            "Changes": [
+                {
+                    "ResourceChange": {
+                        "Action": "Action",
+                        "LogicalResourceId": "LogicalResourceId",
+                        "PhysicalResourceId": "PhysicalResourceId",
+                        "Replacement": "Replacement",
+                        "ResourceType": "ResourceType",
+                        "Scope": "Scope",
+                        "VerboseProperty": "VerboseProperty"
+                    }
+                }
+            ]
+        }
+
+        if not verbose_flag:
+            del response["VerboseProperty"]
+            del response["Changes"][0]["ResourceChange"]["VerboseProperty"]
+
+        describe_command.return_value = response
+
+        kwargs = {"args": ["update", "--change-set", "dev/vpc.yaml"]}
+
+        if yes_flag:
+            kwargs["args"].append("-y")
+        else:
+            kwargs["input"] = "y\n"
+
+        if verbose_flag:
+            kwargs["args"].append("-v")
+
+        result = self.runner.invoke(cli, **kwargs)
+
+        change_set_name = create_command.call_args[0][0]
+        assert 'change-set' in change_set_name
+
+        assert wait_command.called_with(change_set_name)
+        assert delete_command.called_with(change_set_name)
+
+        if change_set_status == StackChangeSetStatus.READY:
+            assert execute_command.called_with(change_set_name)
+            assert describe_command.called_with(change_set_name)
+            output = result.output.splitlines()[0]
+            assert yaml.safe_load(output) == response
+
+        if change_set_status == StackChangeSetStatus.DEFUNCT:
+            assert "Failed to create change set" in result.output
+
+        if change_set_status == StackChangeSetStatus.NO_CHANGES:
+            assert "No changes detected" in result.output
+
+        assert result.exit_code == exit_code
+
     @pytest.mark.parametrize(
         "command, ignore_dependencies", [
             ("create", True),