Only pretty-print binders in closed type families with -fprint-explicit-foralls

Previously, we were unconditionally pretty-printing all type variable
binders when pretty-printing closed type families (e.g., in the output
of `:info` in GHCi). This threw me for a loop, so let's guard this behind
the `-fprint-explicit-foralls` flag.

Test Plan: make test TEST=T13420

Reviewers: goldfire, austin, bgamari

Reviewed By: bgamari

Subscribers: rwbarton, thomie

GHC Trac Issues: #13420

Differential Revision: https://phabricator.haskell.org/D3497

5 files changed, 20 insertions, 4 deletions

diff --git a/testsuite/tests/ghci/scripts/T13420.hs b/testsuite/tests/ghci/scripts/T13420.hs
new file mode 100644
index 0000000000..6b84e65cb2
--- /dev/null
+++ b/testsuite/tests/ghci/scripts/T13420.hs
@@ -0,0 +1,7 @@
+{-# LANGUAGE TypeFamilies #-}
+module T13420 where
+
+type family F a where
+  F [Int] = Bool
+  F [a]   = Double
+  F (a b) = Char
diff --git a/testsuite/tests/ghci/scripts/T13420.script b/testsuite/tests/ghci/scripts/T13420.script
new file mode 100644
index 0000000000..aba31bf7c2
--- /dev/null
+++ b/testsuite/tests/ghci/scripts/T13420.script
@@ -0,0 +1,2 @@
+:load T13420
+:i F
diff --git a/testsuite/tests/ghci/scripts/T13420.stdout b/testsuite/tests/ghci/scripts/T13420.stdout
new file mode 100644
index 0000000000..e6b81adc41
--- /dev/null
+++ b/testsuite/tests/ghci/scripts/T13420.stdout
@@ -0,0 +1,6 @@
+type family F a :: *
+  where
+      F [Int] = Bool
+      F [a] = Double
+      F (a b) = Char
+  	-- Defined at T13420.hs:4:1
diff --git a/testsuite/tests/ghci/scripts/T7939.stdout b/testsuite/tests/ghci/scripts/T7939.stdout
index 2b2c8b73ad..db2590c930 100644
--- a/testsuite/tests/ghci/scripts/T7939.stdout
+++ b/testsuite/tests/ghci/scripts/T7939.stdout
@@ -15,13 +15,13 @@ type family H (a :: Bool) :: Bool
 H :: Bool -> Bool
 type family J (a :: [k]) :: Bool
   where
-    [k] J k '[] = 'False
-    [k, (h :: k), (t :: [k])] J k (h : t) = 'True
+      J k '[] = 'False
+      J k (h : t) = 'True
   	-- Defined at T7939.hs:17:1
 J :: [k] -> Bool
 type family K (a1 :: [a]) :: Maybe a
   where
-    [a] K a '[] = 'Nothing
-    [a, (h :: a), (t :: [a])] K a (h : t) = 'Just h
+      K a '[] = 'Nothing
+      K a (h : t) = 'Just h
   	-- Defined at T7939.hs:21:1
 K :: [a] -> Maybe a
diff --git a/testsuite/tests/ghci/scripts/all.T b/testsuite/tests/ghci/scripts/all.T
index 917537b9e7..ae0a5283f9 100755
--- a/testsuite/tests/ghci/scripts/all.T
+++ b/testsuite/tests/ghci/scripts/all.T
@@ -251,6 +251,7 @@ test('T12550', normal, ghci_script, ['T12550.script'])
 test('StaticPtr', normal, ghci_script, ['StaticPtr.script'])
 test('T13202', normal, ghci_script, ['T13202.script'])
 test('T13202a', normal, ghci_script, ['T13202a.script'])
+test('T13420', normal, ghci_script, ['T13420.script'])
 test('T13466', normal, ghci_script, ['T13466.script'])
 test('GhciCurDir', normal, ghci_script, ['GhciCurDir.script'])
 test('T13591', expect_broken(13591), ghci_script, ['T13591.script'])