1 files changed, 18 insertions, 1 deletions
diff --git a/compiler/prelude/PrelInfo.hs b/compiler/prelude/PrelInfo.hs
index 8e26d80a6a..47f41fbf73 100644
--- a/compiler/prelude/PrelInfo.hs
+++ b/compiler/prelude/PrelInfo.hs
@@ -21,6 +21,7 @@ module PrelInfo (
         -- * Known-key names
         isKnownKeyName,
         lookupKnownKeyName,
+        lookupKnownNameInfo,
 
         -- ** Internal use
         -- | 'knownKeyNames' is exported to seed the original name cache only;
@@ -59,6 +60,7 @@ import Id
 import Name
 import NameEnv
 import MkId
+import Outputable
 import TysPrim
 import TysWiredIn
 import HscTypes
@@ -66,7 +68,6 @@ import Class
 import TyCon
 import UniqFM
 import Util
-import Panic
 import {-# SOURCE #-} TcTypeNats ( typeNatTyCons )
 
 import Control.Applicative ((<|>))
@@ -197,6 +198,22 @@ isKnownKeyName n =
 knownKeysMap :: UniqFM Name
 knownKeysMap = listToUFM [ (nameUnique n, n) | n <- knownKeyNames ]
 
+-- | Given a 'Unique' lookup any associated arbitrary SDoc's to be displayed by
+-- GHCi's ':info' command.
+lookupKnownNameInfo :: Name -> SDoc
+lookupKnownNameInfo name = case lookupNameEnv knownNamesInfo name of
+    -- If we do find a doc, we add comment delimeters to make the output
+    -- of ':info' valid Haskell.
+    Nothing  -> empty
+    Just doc -> vcat [text "{-", doc, text "-}"]
+
+-- A map from Uniques to SDocs, used in GHCi's ':info' command. (#12390)
+knownNamesInfo :: NameEnv SDoc
+knownNamesInfo = unitNameEnv coercibleTyConName $
+    vcat [ text "Coercible is a special constraint with custom solving rules."
+         , text "It is not a class."
+         , text "Please see section 9.14.4 of the user's guide for details." ]
+
 {-
 We let a lot of "non-standard" values be visible, so that we can make
 sense of them in interface pragmas. It's cool, though they all have