Improve generated `GHC.Prim` docs

Summary:
* Extended `genprimcode` to generate Haddock-compatible deprecations,
  as well as displaying information about which functions are LLVM-only
  and which functions can fail with an unchecked exception.

* Ported existing deprecations to the new format, and also added a
  deprecation on `par#` (see Trac #15227).

* Emit an error on fixity/deprecation of builtins, unless we are
  processing the module in which that name is defined (see Trac #15233).
  That means the following is no longer accepted (outside of `GHC.Types`):

```
infixr 7 :
{-# DEPRECATED (:) "cons is deprecated" #-}
```

* Generate `data (->) a b` with docs and fixity in `GHC.Prim`. This
  means: GHC can now parse `data (->) a b` and `infixr 0 ->` (only in
  `GHC.Prim`) and `genprimcode` can digest `primtype (->) a b` (See Trac
  #4861)

as well as some misc fixes along the way.

Reviewers: bgamari, RyanGlScott

Reviewed By: RyanGlScott

Subscribers: RyanGlScott, rwbarton, mpickering, carter

GHC Trac Issues: #15227, #15233, #4861

Differential Revision: https://phabricator.haskell.org/D5167

1 files changed, 12 insertions, 2 deletions

diff --git a/compiler/rename/RnEnv.hs b/compiler/rename/RnEnv.hs
index 516c43c14a..c28f47e43d 100644
--- a/compiler/rename/RnEnv.hs
+++ b/compiler/rename/RnEnv.hs
@@ -1508,8 +1508,18 @@ lookupLocalTcNames ctxt what rdr_name
        ; when (null names) $ addErr (head errs) -- Bleat about one only
        ; return names }
   where
-    lookup rdr = do { name <- lookupBindGroupOcc ctxt what rdr
-                    ; return (fmap ((,) rdr) name) }
+    lookup rdr = do { this_mod <- getModule
+                    ; nameEither <- lookupBindGroupOcc ctxt what rdr
+                    ; return (guard_builtin_syntax this_mod rdr nameEither) }
+
+    -- Guard against the built-in syntax (ex: `infixl 6 :`), see #15233
+    guard_builtin_syntax this_mod rdr (Right name)
+      | Just _ <- isBuiltInOcc_maybe (occName rdr)
+      , this_mod /= nameModule name
+      = Left (hsep [text "Illegal", what, text "of built-in syntax:", ppr rdr])
+      | otherwise
+      = Right (rdr, name)
+    guard_builtin_syntax _ _ (Left err) = Left err
 
 dataTcOccs :: RdrName -> [RdrName]
 -- Return both the given name and the same name promoted to the TcClsName