From 62f071c0e7ebfff4c9b15872e67c8d9a8ded671b Mon Sep 17 00:00:00 2001
From: Morrow <themorrowm@gmail.com>
Date: Thu, 27 Jan 2022 15:58:46 +0200
Subject: [PATCH] Fix #1879

---
 .../src/Wingman/KnownStrategies/QuickCheck.hs              | 5 +++--
 plugins/hls-tactics-plugin/test/CodeAction/AutoSpec.hs     | 1 +
 .../golden/GoldenArbitrarySingleConstructor.expected.hs    | 7 +++++++
 .../test/golden/GoldenArbitrarySingleConstructor.hs        | 6 ++++++
 4 files changed, 17 insertions(+), 2 deletions(-)
 create mode 100644 plugins/hls-tactics-plugin/test/golden/GoldenArbitrarySingleConstructor.expected.hs
 create mode 100644 plugins/hls-tactics-plugin/test/golden/GoldenArbitrarySingleConstructor.hs

diff --git a/plugins/hls-tactics-plugin/src/Wingman/KnownStrategies/QuickCheck.hs b/plugins/hls-tactics-plugin/src/Wingman/KnownStrategies/QuickCheck.hs
index 4cc1d4afb8..b14e4b8348 100644
--- a/plugins/hls-tactics-plugin/src/Wingman/KnownStrategies/QuickCheck.hs
+++ b/plugins/hls-tactics-plugin/src/Wingman/KnownStrategies/QuickCheck.hs
@@ -43,8 +43,9 @@ deriveArbitrary = do
               mempty
               mempty
               mempty
-          $ noLoc $
-              let' [valBind (fromString "terminal") $ list $ fmap genExpr terminal] $
+          $ noLoc $ case terminal of
+            [onlyCon] -> genExpr onlyCon -- See #1879
+            _ -> let' [valBind (fromString "terminal") $ list $ fmap genExpr terminal] $
                 appDollar (mkFunc "sized") $ lambda [bvar' (mkVarOcc "n")] $
                   case' (infixCall "<=" (mkVal "n") (int 1))
                     [ match [conP (fromString "True") []] $
diff --git a/plugins/hls-tactics-plugin/test/CodeAction/AutoSpec.hs b/plugins/hls-tactics-plugin/test/CodeAction/AutoSpec.hs
index 9322b0912b..4075183ee6 100644
--- a/plugins/hls-tactics-plugin/test/CodeAction/AutoSpec.hs
+++ b/plugins/hls-tactics-plugin/test/CodeAction/AutoSpec.hs
@@ -72,6 +72,7 @@ spec = do
 
   describe "known" $ do
     autoTest 25 13 "GoldenArbitrary"
+    autoTest  6 13 "GoldenArbitrarySingleConstructor"
     autoTestNoWhitespace
               6 10 "KnownBigSemigroup"
     autoTest  4 10 "KnownThetaSemigroup"
diff --git a/plugins/hls-tactics-plugin/test/golden/GoldenArbitrarySingleConstructor.expected.hs b/plugins/hls-tactics-plugin/test/golden/GoldenArbitrarySingleConstructor.expected.hs
new file mode 100644
index 0000000000..786e381ca8
--- /dev/null
+++ b/plugins/hls-tactics-plugin/test/golden/GoldenArbitrarySingleConstructor.expected.hs
@@ -0,0 +1,7 @@
+data Gen a
+
+data Obj = Obj Int Bool Char String
+
+arbitrary :: Gen Obj
+arbitrary
+  = (((Obj <$> arbitrary) <*> arbitrary) <*> arbitrary) <*> arbitrary
\ No newline at end of file
diff --git a/plugins/hls-tactics-plugin/test/golden/GoldenArbitrarySingleConstructor.hs b/plugins/hls-tactics-plugin/test/golden/GoldenArbitrarySingleConstructor.hs
new file mode 100644
index 0000000000..a6a7d171a3
--- /dev/null
+++ b/plugins/hls-tactics-plugin/test/golden/GoldenArbitrarySingleConstructor.hs
@@ -0,0 +1,6 @@
+data Gen a
+
+data Obj = Obj Int Bool Char String
+
+arbitrary :: Gen Obj
+arbitrary = _
\ No newline at end of file