fix (Message): Harden parsing and display.

Significantly broaden error handling for initial parsing.
Add error details upon parsing error.
Add more error catchers to parser and formatter.
Remove assumptions about data fields from format and output.

bot/settings/setting_types.py

@@ -1,6 +1,7 @@
 import json
 import asyncio
 import itertools
+import traceback
 from io import StringIO
 from enum import IntEnum
 from typing import Any, Optional
@@ -753,11 +754,19 @@ class Message(SettingType):
         if as_json:
             try:
                 args = json.loads(userstr)
-            except json.JSONDecodeError:
+                if not isinstance(args, dict) or (not args.get('content', None) and not args.get('embed', None)):
+                    raise ValueError("At least one of the 'content' or 'embed' data fields are required.")
+                if 'embed' in args:
+                    discord.Embed.from_dict(
+                        args['embed']
+                    )
+            except Exception as e:
+                only_error = "".join(traceback.TracebackException.from_exception(e).format_exception_only())
                 raise UserInputError(
                     "Couldn't parse your message! "
                     "You can test and fix it on the embed builder "
-                    "[here](https://glitchii.github.io/embedbuilder/?editor=json)."
+                    "[here](https://glitchii.github.io/embedbuilder/?editor=json).\n"
+                    "```{}```".format(only_error)
                 )
             if 'embed' in args and 'timestamp' in args['embed']:
                 args['embed'].pop('timestamp')
@@ -770,6 +779,8 @@ class Message(SettingType):
         if data is None:
             return "Empty"
         value = cls._data_to_value(id, data, **kwargs)
+        if 'embed' not in value and 'content' not in value:
+            return "Invalid"
         if 'embed' not in value and len(value['content']) < 100:
             return "`{}`".format(value['content'])
         else:
@@ -788,9 +799,9 @@ class Message(SettingType):
         value = self.value
         substitutions = self.substitution_keys(ctx, **kwargs)
         args = {}
-        if 'content' in value:
+        if value.get('content', None):
             args['content'] = multiple_replace(value['content'], substitutions)
-        if 'embed' in value:
+        if value.get('embed', None):
             args['embed'] = discord.Embed.from_dict(
                 json.loads(multiple_replace(json.dumps(value['embed']), substitutions))
             )
@@ -800,7 +811,7 @@ class Message(SettingType):
         value = self.value
         args = self.args(ctx, **kwargs)
 
-        if not value:
+        if not value or not args:
             return await ctx.reply(embed=self.embed)
 
         current_str = None