Refactor named wildcards (again)

Michal's work on #10982, #11098, refactored the handling of named
wildcards by making them more like ordinary type variables.

This patch takes the same idea to its logical conclusion, resulting
in a much tidier, tighter implementation.

Read Note [The wildcard story for types] in HsTypes.

Changes:

 * Named wildcards are ordinary type variables, throughout

 * HsType no longer has a data constructor for named wildcards
   (was NamedWildCard in HsWildCardInfo).  Named wildcards are
   simply HsTyVars

 * Similarly named wildcards disappear from Template Haskell

 * I refactored RnTypes to avoid polluting LocalRdrEnv with something
   as narrow as named wildcards.  Instead the named wildcard set is
   carried in RnTyKiEnv.

There is a submodule update for Haddock.

5 files changed, 19 insertions, 13 deletions

diff --git a/testsuite/tests/ghci/scripts/T11098.stdout b/testsuite/tests/ghci/scripts/T11098.stdout
index 27ddd486ca..2b86289e18 100644
--- a/testsuite/tests/ghci/scripts/T11098.stdout
+++ b/testsuite/tests/ghci/scripts/T11098.stdout
@@ -1,3 +1,3 @@
-[SigD foo_1 (ForallT [PlainTV a_0] [] (AppT (AppT ArrowT (VarT a_0)) (VarT a_0))),FunD foo_1 [Clause [VarP x_2] (NormalB (VarE x_2)) []]]

-"[SigD foo_ (AppT (AppT ArrowT (WildCardT (Just _a_))) (WildCardT (Just _a_))),FunD foo_ [Clause [VarP x_] (NormalB (VarE x_)) []]]"

-[SigD foo_6 (ForallT [PlainTV _a_5] [] (AppT (AppT ArrowT (VarT _a_5)) (VarT _a_5))),FunD foo_6 [Clause [VarP x_7] (NormalB (VarE x_7)) []]]

+[SigD foo_1 (ForallT [PlainTV a_0] [] (AppT (AppT ArrowT (VarT a_0)) (VarT a_0))),FunD foo_1 [Clause [VarP x_2] (NormalB (VarE x_2)) []]]
+"[SigD foo_ (AppT (AppT ArrowT (VarT _a_)) (VarT _a_)),FunD foo_ [Clause [VarP x_] (NormalB (VarE x_)) []]]"
+[SigD foo_6 (ForallT [PlainTV _a_5] [] (AppT (AppT ArrowT (VarT _a_5)) (VarT _a_5))),FunD foo_6 [Clause [VarP x_7] (NormalB (VarE x_7)) []]]
diff --git a/testsuite/tests/partial-sigs/should_compile/Splices.hs b/testsuite/tests/partial-sigs/should_compile/Splices.hs
index 9202c18995..c877248e88 100644
--- a/testsuite/tests/partial-sigs/should_compile/Splices.hs
+++ b/testsuite/tests/partial-sigs/should_compile/Splices.hs
@@ -1,5 +1,5 @@
-{-# LANGUAGE TemplateHaskell #-}
-{-# LANGUAGE NamedWildCards #-}
+{-# LANGUAGE TemplateHaskell, NamedWildCards #-}
+
 module Splices where
 
 import Language.Haskell.TH
diff --git a/testsuite/tests/partial-sigs/should_compile/SplicesUsed.hs b/testsuite/tests/partial-sigs/should_compile/SplicesUsed.hs
index 21e599dcf6..8a5abb3085 100644
--- a/testsuite/tests/partial-sigs/should_compile/SplicesUsed.hs
+++ b/testsuite/tests/partial-sigs/should_compile/SplicesUsed.hs
@@ -1,5 +1,5 @@
-{-# LANGUAGE TemplateHaskell #-}
-{-# LANGUAGE PartialTypeSignatures #-}
+{-# LANGUAGE TemplateHaskell, PartialTypeSignatures, NamedWildCards #-}
+
 module SplicesUsed where
 
 import Splices
diff --git a/testsuite/tests/partial-sigs/should_fail/NamedExtraConstraintsWildcard.hs b/testsuite/tests/partial-sigs/should_fail/NamedExtraConstraintsWildcard.hs
index 28bb8362ce..c9a00f33cc 100644
--- a/testsuite/tests/partial-sigs/should_fail/NamedExtraConstraintsWildcard.hs
+++ b/testsuite/tests/partial-sigs/should_fail/NamedExtraConstraintsWildcard.hs
@@ -1,4 +1,4 @@
-{-# LANGUAGE PartialTypeSignatures, NamedWildCards #-}
+{-# LANGUAGE ConstraintKinds, PartialTypeSignatures, NamedWildCards #-}
 module NamedExtraConstraintsWildcard where
 
 foo :: (Eq a, _a) => a -> a
diff --git a/testsuite/tests/partial-sigs/should_fail/NamedExtraConstraintsWildcard.stderr b/testsuite/tests/partial-sigs/should_fail/NamedExtraConstraintsWildcard.stderr
index 47e9b99135..bb1a481a1e 100644
--- a/testsuite/tests/partial-sigs/should_fail/NamedExtraConstraintsWildcard.stderr
+++ b/testsuite/tests/partial-sigs/should_fail/NamedExtraConstraintsWildcard.stderr
@@ -1,5 +1,11 @@
-

-NamedExtraConstraintsWildcard.hs:4:15: error:

-    Named wildcard ‘_a’ not allowed as an extra-contraint

-      Use an anonymous wildcard instead

-      in the type signature for ‘foo’

+
+NamedExtraConstraintsWildcard.hs:5:1: error:
+    • Could not deduce: t0
+      from the context: (Eq a, t)
+        bound by the inferred type for ‘foo’:
+                   (Eq a, t) => a -> a
+        at NamedExtraConstraintsWildcard.hs:5:1-15
+    • In the ambiguity check for the inferred type for ‘foo’
+      To defer the ambiguity check to use sites, enable AllowAmbiguousTypes
+      When checking the inferred type
+        foo :: forall a (t :: Constraint). (Eq a, t) => a -> a