Raise hard error if user tries to use mention without backend installed

Signed-off-by: Tim Paine <3105306+timkpaine@users.noreply.github.com>

Author: timkpaine

csp_bot/backends/discord.py

@@ -20,4 +20,4 @@ class DiscordAdapterConfig(BaseModel):
     class DiscordMessage(Struct):
         _ignore: str = ""
 
-    mention_user_discord = lambda x: x  # noqa: E731
+    mention_user_discord = None

csp_bot/backends/slack.py

@@ -21,4 +21,4 @@ class SlackAdapterConfig(BaseModel):
     class SlackMessage(Struct):
         _ignore: str = ""
 
-    mention_user_slack = lambda x: x  # noqa: E731
+    mention_user_slack = None

csp_bot/backends/symphony.py

@@ -24,4 +24,4 @@ class SymphonyAdapterConfig(BaseModel):
     class SymphonyMessage(Struct):
         _ignore: str = ""
 
-    mention_user_symphony = lambda x: x  # noqa: E731
+    mention_user_symphony = None

csp_bot/utils.py

@@ -56,12 +56,18 @@ def recursive_format_for_message_ml(d):
 
 def mention_user(email_or_userid: str = "", backend: Backend = "symphony") -> str:
     if backend == "symphony":
+        if mention_user_symphony is None:
+            raise ImportError("Symphony adapter is not available.")
         return mention_user_symphony(email_or_userid)
     elif backend == "slack":
         if not email_or_userid.startswith("@"):
             email_or_userid = f"@{email_or_userid}"
+        if mention_user_slack is None:
+            raise ImportError("Slack adapter is not available.")
         return mention_user_slack(email_or_userid)
     elif backend == "discord":
+        if mention_user_discord is None:
+            raise ImportError("Discord adapter is not available.")
         return mention_user_discord(email_or_userid)
     else:
         raise NotImplementedError(f"Unsupported backend: {backend}")