From f0a0b50fea9a0189dc0095390757d428471b64c9 Mon Sep 17 00:00:00 2001
From: Zubin Duggal <zubin.duggal@gmail.com>
Date: Fri, 14 Jan 2022 17:18:21 +0530
Subject: TH: fix pretty printing of GADTs with multiple constuctors (#20842)

---
 libraries/template-haskell/Language/Haskell/TH/Ppr.hs | 2 +-
 testsuite/tests/th/T19363.stdout                      | 3 ++-
 testsuite/tests/th/T20842.hs                          | 9 +++++++++
 testsuite/tests/th/T20842.stdout                      | 3 +++
 testsuite/tests/th/all.T                              | 1 +
 5 files changed, 16 insertions(+), 2 deletions(-)
 create mode 100644 testsuite/tests/th/T20842.hs
 create mode 100644 testsuite/tests/th/T20842.stdout

diff --git a/libraries/template-haskell/Language/Haskell/TH/Ppr.hs b/libraries/template-haskell/Language/Haskell/TH/Ppr.hs
index d9ae558c15..9627f5c256 100644
--- a/libraries/template-haskell/Language/Haskell/TH/Ppr.hs
+++ b/libraries/template-haskell/Language/Haskell/TH/Ppr.hs
@@ -452,7 +452,7 @@ ppr_data maybeInst ctxt t argsDoc ksig cs decs
                  Just n -> pprName' Applied n <+> argsDoc
                  Nothing -> argsDoc
             <+> ksigDoc <+> maybeWhere,
-         nest nestDepth (sep (pref $ map ppr cs)),
+         nest nestDepth (vcat (pref $ map ppr cs)),
          if null decs
            then empty
            else nest nestDepth
diff --git a/testsuite/tests/th/T19363.stdout b/testsuite/tests/th/T19363.stdout
index b6d2c30790..fe404302a8 100644
--- a/testsuite/tests/th/T19363.stdout
+++ b/testsuite/tests/th/T19363.stdout
@@ -1,5 +1,6 @@
 data Operator_0
-    = (:*_1) GHC.Types.Int | (:**_2) {(^**_3) :: GHC.Types.Int}
+    = (:*_1) GHC.Types.Int
+    | (:**_2) {(^**_3) :: GHC.Types.Int}
 data (%*%_4) = (:%*%_5)
 {-# COMPLETE (:%*%_5) :: (%*%_4) #-}
 {-# ANN type (%*%_4) "yargh" #-}
diff --git a/testsuite/tests/th/T20842.hs b/testsuite/tests/th/T20842.hs
new file mode 100644
index 0000000000..6758ea732a
--- /dev/null
+++ b/testsuite/tests/th/T20842.hs
@@ -0,0 +1,9 @@
+{-# LANGUAGE TemplateHaskell, GADTs #-}
+module Main where
+
+import Language.Haskell.TH
+
+main :: IO ()
+main = do
+  x <- [d| data MyData where { D1 :: MyData; D2 :: Bool -> MyData } |]
+  putStrLn $ pprint x
diff --git a/testsuite/tests/th/T20842.stdout b/testsuite/tests/th/T20842.stdout
new file mode 100644
index 0000000000..8113be91e4
--- /dev/null
+++ b/testsuite/tests/th/T20842.stdout
@@ -0,0 +1,3 @@
+data MyData_0 where
+    D1_1 :: MyData_0
+    D2_2 :: GHC.Types.Bool -> MyData_0
diff --git a/testsuite/tests/th/all.T b/testsuite/tests/th/all.T
index aa953098ce..79cd9ca7d1 100644
--- a/testsuite/tests/th/all.T
+++ b/testsuite/tests/th/all.T
@@ -544,3 +544,4 @@ test('T20590', normal, compile, ['-v0 -ddump-splices -dsuppress-uniques'])
 test('T20773', only_ways(['ghci']), ghci_script, ['T20773.script'])
 test('T20884', normal, compile_fail, [''])
 test('T21038', normal, compile, [''])
+test('T20842', normal, compile_and_run, [''])
-- 
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