[Resolves #1388] Handle failures gracefully in stack outputs

sceptre/resolvers/stack_output.py

@@ -6,7 +6,12 @@
 
 from botocore.exceptions import ClientError
 
-from sceptre.exceptions import DependencyStackMissingOutputError, StackDoesNotExistError
+from sceptre.exceptions import (
+ DependencyStackMissingOutputError,
+ StackDoesNotExistError,
+ SceptreException,
+)
+
 from sceptre.helpers import normalise_path, sceptreise_path
 from sceptre.resolvers import Resolver
 
@@ -108,7 +113,13 @@ def setup(self):
  """
  Adds dependency to a Stack.
  """
- dep_stack_name, self.output_key = self.argument.split("::")
+ try:
+ dep_stack_name, self.output_key = self.argument.split("::")
+ except ValueError as err:
+ raise SceptreException(
+ "!stack_output arg should match STACK_NAME::OUTPUT_KEY"
+ ) from err
+
  self.dependency_stack_name = sceptreise_path(normalise_path(dep_stack_name))
  self.stack.dependencies.append(self.dependency_stack_name)
 
@@ -120,7 +131,6 @@ def resolve(self):
  :rtype: str
  """
  self.logger.debug("Resolving Stack output: {0}".format(self.argument))
-
  friendly_stack_name = self.dependency_stack_name.replace(TEMPLATE_EXTENSION, "")
 
  stack = next(
@@ -163,21 +173,43 @@ def resolve(self):
  """
  self.logger.debug("Resolving external Stack output: {0}".format(self.argument))
 
- profile = None
- region = None
- sceptre_role = None
  arguments = shlex.split(self.argument)
 
+ if not arguments:
+ message = "!stack_output_external requires at least one argument"
+ raise SceptreException(message)
+
  stack_argument = arguments[0]
+ stack_args = iter(stack_argument.split("::"))
+
+ try:
+ dependency_stack_name = next(stack_args)
+ output_key = next(stack_args)
+
+ except StopIteration as err:
+ message = "!stack_output_external arg should match STACK_NAME::OUTPUT_KEY"
+ raise SceptreException(message) from err
+
+ profile = region = sceptre_role = None
+
  if len(arguments) > 1:
- extra_args = arguments[1].split("::", 2)
- profile, region, sceptre_role = extra_args + (3 - len(extra_args)) * [None]
+ extra_args = iter(arguments[1].split("::"))
+
+ profile = next(extra_args, None)
+ region = next(extra_args, None)
+ sceptre_role = next(extra_args, None)
+
+ try:
+ next(extra_args)
+ message = (
+ "!stack_output_external second arg should be "
+ "in the format 'PROFILE[::REGION[::SCEPTRE_ROLE]]'"
+ )
+ raise SceptreException(message)
+
+ except StopIteration:
+ pass
 
- dependency_stack_name, output_key = stack_argument.split("::")
  return self._get_output_value(
- dependency_stack_name,
- output_key,
- profile or None,
- region or None,
- sceptre_role or None,
+ dependency_stack_name, output_key, profile, region, sceptre_role
  )

tests/test_resolvers/test_stack_output.py

@@ -5,6 +5,7 @@
 
 from sceptre.exceptions import DependencyStackMissingOutputError
 from sceptre.exceptions import StackDoesNotExistError
+from sceptre.exceptions import SceptreException
 
 from botocore.exceptions import ClientError
 
@@ -58,7 +59,10 @@ def test_resolver__badly_formatted(self, mock_get_output_value):
 
  stack_output_resolver = StackOutput("not_a_valid_stack_output", stack)
 
- with pytest.raises(ValueError, match="not enough values to unpack"):
+ with pytest.raises(
+ SceptreException,
+ match="!stack_output arg should match STACK_NAME::OUTPUT_KEY",
+ ):
  stack_output_resolver.setup()
 
  @patch("sceptre.resolvers.stack_output.StackOutput._get_output_value")
@@ -191,7 +195,10 @@ def test_resolve__badly_formatted(self, mock_get_output_value):
  "not_a_valid_stack_output", stack
  )
 
- with pytest.raises(ValueError, match="not enough values to unpack"):
+ with pytest.raises(
+ SceptreException,
+ match="!stack_output_external arg should match STACK_NAME::OUTPUT_KEY",
+ ):
  stack_output_external_resolver.resolve()
 
  @patch("sceptre.resolvers.stack_output.StackOutputExternal._get_output_value")