Malformed YAML throws Grow into an inconsistent state, and the development server must be restarted

[jeremydw]

Steps to reproduce:

1. Make an edit to a YAML file that introduces invalid YAML syntax.
2. Load a page.
3. Fix the YAML.
4. Refresh the page.
5. Grow still crashes on load / displays old YAML data.

Expected behavior: Grow should recover and operate normally once YAML syntax is fixed.

[jeremydw]

The issue has to do with the routes cache. Traceback from an issue.

Traceback (most recent call last):
  File "growsdk/threading", line 810, in __bootstrap_inner
  File "growsdk/watchdog.observers.api", line 241, in run
  File "growsdk/watchdog.observers.api", line 408, in dispatch_events
  File "growsdk/watchdog.observers.api", line 403, in _dispatch_event
  File "growsdk/watchdog.events", line 486, in dispatch
  File "growsdk/grow.pods.preprocessors.file_watchers", line 45, in on_created
  File "growsdk/grow.pods.preprocessors.file_watchers", line 41, in handle
  File "growsdk/grow.pods.preprocessors.routes_cache", line 11, in run
  File "growsdk/grow.pods.routes", line 47, in reset_cache
  File "growsdk/grow.pods.routes", line 59, in _build_routing_map
  File "growsdk/grow.pods.collectionz.collectionz", line 190, in list_servable_documents
  File "growsdk/grow.pods.collectionz.collectionz", line 184, in list_documents
  File "growsdk/grow.pods.collectionz.collectionz", line 171, in process
  File "growsdk/grow.common.structures", line 144, in insert
  File "growsdk/grow.pods.collectionz.documents", line 94, in order
  File "growsdk/webapp2", line 726, in __get__
  File "growsdk/grow.pods.collectionz.documents", line 67, in fields
  File "growsdk/webapp2", line 726, in __get__
  File "growsdk/grow.pods.collectionz.documents", line 79, in tagged_fields
  File "growsdk/webapp2", line 726, in __get__
  File "growsdk/grow.pods.collectionz.documents", line 75, in format
  File "growsdk/grow.pods.collectionz.formats", line 34, in get
  File "growsdk/grow.pods.collectionz.formats", line 27, in __init__
  File "growsdk/grow.pods.collectionz.formats", line 61, in load
  File "growsdk/yaml", line 71, in load
  File "growsdk/yaml.constructor", line 37, in get_single_data
  File "growsdk/yaml.composer", line 36, in get_single_node
  File "growsdk/yaml.composer", line 55, in compose_document
  File "growsdk/yaml.composer", line 84, in compose_node
  File "growsdk/yaml.composer", line 133, in compose_mapping_node
  File "growsdk/yaml.composer", line 82, in compose_node
  File "growsdk/yaml.composer", line 111, in compose_sequence_node
  File "growsdk/yaml.composer", line 84, in compose_node
  File "growsdk/yaml.composer", line 127, in compose_mapping_node
  File "growsdk/yaml.parser", line 98, in check_event
  File "growsdk/yaml.parser", line 439, in parse_block_mapping_key
ParserError: while parsing a block mapping
  in "<string>", line 150, column 5:
      - name: Foo
        ^
expected <block end>, but found '-'
  in "<string>", line 152, column 5:
        - title: "Foo  ... 
        ^