From 6d6bea759fc799e5536dc5ecd24a55f8e2f95246 Mon Sep 17 00:00:00 2001
From: Brent Yorgey <byorgey@gmail.com>
Date: Fri, 10 May 2024 14:13:45 -0500
Subject: [PATCH] avoid GHC `head` warning with explicit pattern matching +
 custom error

---
 .../Swarm/Web/Tournament/Database/Query.hs                 | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/src/swarm-tournament/Swarm/Web/Tournament/Database/Query.hs b/src/swarm-tournament/Swarm/Web/Tournament/Database/Query.hs
index 70f5eb8a9..cbbb7a871 100644
--- a/src/swarm-tournament/Swarm/Web/Tournament/Database/Query.hs
+++ b/src/swarm-tournament/Swarm/Web/Tournament/Database/Query.hs
@@ -1,7 +1,6 @@
 {-# LANGUAGE OverloadedStrings #-}
 {-# OPTIONS_GHC -fno-warn-orphans #-}
 {-# OPTIONS_GHC -fno-warn-unrecognised-pragmas #-}
-{-# OPTIONS_GHC -fno-warn-x-partial #-}
 
 {-# HLINT ignore "Functor law" #-}
 
@@ -211,8 +210,12 @@ getUserId conn userAlias = do
       <$> query conn "SELECT id FROM users WHERE alias = ?;" (Only userAlias)
   maybe insertNew return maybeId
  where
+  -- Avoid GHC warning re: partiality of head
+  queryHead = \case
+    [] -> error "Query result in getUserId should never be empty!"
+    hd : _ -> hd
   insertNew =
-    fmap (UserId . fromOnly . head)
+    fmap (UserId . fromOnly . queryHead)
       $ query
         conn
         "INSERT INTO users (alias) VALUES (?) RETURNING id;"