Refactor tuple constraints

Make tuple constraints be handled by a perfectly ordinary
type class, with the component constraints being the
superclasses:
    class (c1, c2) => (c2, c2)

This change was provoked by

  #10359  inability to re-use a given tuple
          constraint as a whole

  #9858   confusion between term tuples
          and constraint tuples

but it's generally a very nice simplification. We get rid of
 -  In Type, the TuplePred constructor of PredTree,
    and all the code that dealt with TuplePreds
 -  In TcEvidence, the constructors EvTupleMk, EvTupleSel

See Note [How tuples work] in TysWiredIn.

Of course, nothing is ever entirely simple. This one
proved quite fiddly.

- I did quite a bit of renaming, which makes this patch
  touch a lot of modules. In partiuclar tupleCon -> tupleDataCon.

- I made constraint tuples known-key rather than wired-in.
  This is different to boxed/unboxed tuples, but it proved
  awkward to have all the superclass selectors wired-in.
  Easier just to use the standard mechanims.

- While I was fiddling with known-key names, I split the TH Name
  definitions out of DsMeta into a new module THNames.  That meant
  that the known-key names can all be gathered in PrelInfo, without
  causing module loops.

- I found that the parser was parsing an import item like
      T( .. )
  as a *data constructor* T, and then using setRdrNameSpace to
  fix it.  Stupid!  So I changed the parser to parse a *type
  constructor* T, which means less use of setRdrNameSpace.

  I also improved setRdrNameSpace to behave better on Exact Names.
  Largely on priciple; I don't think it matters a lot.

- When compiling a data type declaration for a wired-in thing like
  tuples (,), or lists, we don't really need to look at the
  declaration.  We have the wired-in thing!  And not doing so avoids
  having to line up the uniques for data constructor workers etc.
  See Note [Declarations for wired-in things]

- I found that FunDeps.oclose wasn't taking superclasses into
  account; easily fixed.

- Some error message refactoring for invalid constraints in TcValidity

- Haddock needs to absorb the change too; so there is a submodule update

9 files changed, 67 insertions, 78 deletions

diff --git a/testsuite/tests/typecheck/should_fail/T9858a.stderr b/testsuite/tests/typecheck/should_fail/T9858a.stderr
index 2f815b1824..61c62eaeec 100644
--- a/testsuite/tests/typecheck/should_fail/T9858a.stderr
+++ b/testsuite/tests/typecheck/should_fail/T9858a.stderr
@@ -1,14 +1,14 @@
-
-T9858a.hs:28:18: error:
-    No instance for (Typeable
-                       (((() :: Constraint), (() :: Constraint)) => ()))
-      (maybe you haven't applied a function to enough arguments?)
-      arising from a use of ‘cast’
-    In the expression: cast e
-    In the expression: case cast e of { Just e' -> ecast e' }
-    In an equation for ‘supercast’:
-        supercast
-          = case cast e of { Just e' -> ecast e' }
-          where
-              e = Refl
-              e :: E PX PX
+

+T9858a.hs:28:18: error:

+    No instance for (Typeable

+                       ((() :: Constraint, () :: Constraint) => ()))

+      (maybe you haven't applied a function to enough arguments?)

+      arising from a use of ‘cast’

+    In the expression: cast e

+    In the expression: case cast e of { Just e' -> ecast e' }

+    In an equation for ‘supercast’:

+        supercast

+          = case cast e of { Just e' -> ecast e' }

+          where

+              e = Refl

+              e :: E PX PX

diff --git a/testsuite/tests/typecheck/should_fail/fd-loop.stderr b/testsuite/tests/typecheck/should_fail/fd-loop.stderr
index 96fbc3ef18..44a0618181 100644
--- a/testsuite/tests/typecheck/should_fail/fd-loop.stderr
+++ b/testsuite/tests/typecheck/should_fail/fd-loop.stderr
@@ -1,12 +1,12 @@
-
-fd-loop.hs:12:10:
-    Variable ‘b’ occurs more often than in the instance head
-      in the constraint: C a b
-    (Use UndecidableInstances to permit this)
-    In the instance declaration for ‘Eq (T a)’
-
-fd-loop.hs:12:10:
-    Variable ‘b’ occurs more often than in the instance head
-      in the constraint: Eq b
-    (Use UndecidableInstances to permit this)
-    In the instance declaration for ‘Eq (T a)’
+

+fd-loop.hs:12:10: error:

+    Variable ‘b’ occurs more often

+      in the constraint ‘C a b’ than in the instance head

+    (Use UndecidableInstances to permit this)

+    In the instance declaration for ‘Eq (T a)’

+

+fd-loop.hs:12:10: error:

+    Variable ‘b’ occurs more often

+      in the constraint ‘Eq b’ than in the instance head

+    (Use UndecidableInstances to permit this)

+    In the instance declaration for ‘Eq (T a)’

diff --git a/testsuite/tests/typecheck/should_fail/tcfail108.stderr b/testsuite/tests/typecheck/should_fail/tcfail108.stderr
index 3a2e5a5657..da766582b3 100644
--- a/testsuite/tests/typecheck/should_fail/tcfail108.stderr
+++ b/testsuite/tests/typecheck/should_fail/tcfail108.stderr
@@ -1,6 +1,6 @@
 

 tcfail108.hs:7:10: error:

-    Variable ‘f’ occurs more often than in the instance head

-      in the constraint: Eq (f (Rec f))

+    Variable ‘f’ occurs more often

+      in the constraint ‘Eq (f (Rec f))’ than in the instance head

     (Use UndecidableInstances to permit this)

     In the instance declaration for ‘Eq (Rec f)’

diff --git a/testsuite/tests/typecheck/should_fail/tcfail154.stderr b/testsuite/tests/typecheck/should_fail/tcfail154.stderr
index 9014b643df..903f61b7de 100644
--- a/testsuite/tests/typecheck/should_fail/tcfail154.stderr
+++ b/testsuite/tests/typecheck/should_fail/tcfail154.stderr
@@ -1,6 +1,6 @@
-
-tcfail154.hs:12:10:
-    Variable ‘a’ occurs more often than in the instance head
-      in the constraint: C a a
-    (Use UndecidableInstances to permit this)
-    In the instance declaration for ‘Eq (T a)’
+

+tcfail154.hs:12:10: error:

+    Variable ‘a’ occurs more often

+      in the constraint ‘C a a’ than in the instance head

+    (Use UndecidableInstances to permit this)

+    In the instance declaration for ‘Eq (T a)’

diff --git a/testsuite/tests/typecheck/should_fail/tcfail157.stderr b/testsuite/tests/typecheck/should_fail/tcfail157.stderr
index acdc7df8cf..113e0cc67e 100644
--- a/testsuite/tests/typecheck/should_fail/tcfail157.stderr
+++ b/testsuite/tests/typecheck/should_fail/tcfail157.stderr
@@ -1,12 +1,12 @@
-
-tcfail157.hs:27:10:
-    Variable ‘b’ occurs more often than in the instance head
-      in the constraint: E m a b
-    (Use UndecidableInstances to permit this)
-    In the instance declaration for ‘Foo m (a -> ())’
-
-tcfail157.hs:27:10:
-    Variable ‘b’ occurs more often than in the instance head
-      in the constraint: Foo m b
-    (Use UndecidableInstances to permit this)
-    In the instance declaration for ‘Foo m (a -> ())’
+

+tcfail157.hs:27:10: error:

+    Variable ‘b’ occurs more often

+      in the constraint ‘E m a b’ than in the instance head

+    (Use UndecidableInstances to permit this)

+    In the instance declaration for ‘Foo m (a -> ())’

+

+tcfail157.hs:27:10: error:

+    Variable ‘b’ occurs more often

+      in the constraint ‘Foo m b’ than in the instance head

+    (Use UndecidableInstances to permit this)

+    In the instance declaration for ‘Foo m (a -> ())’

diff --git a/testsuite/tests/typecheck/should_fail/tcfail213.stderr b/testsuite/tests/typecheck/should_fail/tcfail213.stderr
index a6b63bd9f1..a29b758a42 100644
--- a/testsuite/tests/typecheck/should_fail/tcfail213.stderr
+++ b/testsuite/tests/typecheck/should_fail/tcfail213.stderr
@@ -1,7 +1,7 @@
-
-tcfail213.hs:8:1:
-    Illegal constraint ‘F a’ in a superclass/instance context
-      (Use UndecidableInstances to permit this)
-    In the context: F a
-    While checking the super-classes of class ‘C’
-    In the class declaration for ‘C’
+

+tcfail213.hs:8:1: error:

+    Illegal constraint ‘F a’ in a superclass context

+      (Use UndecidableInstances to permit this)

+    In the context: F a

+    While checking the super-classes of class ‘C’

+    In the class declaration for ‘C’

diff --git a/testsuite/tests/typecheck/should_fail/tcfail214.stderr b/testsuite/tests/typecheck/should_fail/tcfail214.stderr
index 5520a3eff1..a2741b876b 100644
--- a/testsuite/tests/typecheck/should_fail/tcfail214.stderr
+++ b/testsuite/tests/typecheck/should_fail/tcfail214.stderr
@@ -1,7 +1,5 @@
-
-tcfail214.hs:9:10:
-    Illegal constraint ‘F a’ in a superclass/instance context
-      (Use UndecidableInstances to permit this)
-    In the context: F a
-    While checking an instance declaration
-    In the instance declaration for ‘C [a]’
+

+tcfail214.hs:9:10: error:

+    The constraint ‘F a’ is no smaller than the instance head

+    (Use UndecidableInstances to permit this)

+    In the instance declaration for ‘C [a]’

diff --git a/testsuite/tests/typecheck/should_fail/tcfail220.hsig b/testsuite/tests/typecheck/should_fail/tcfail220.hsig
index 129bae368c..560fc317a6 100644
--- a/testsuite/tests/typecheck/should_fail/tcfail220.hsig
+++ b/testsuite/tests/typecheck/should_fail/tcfail220.hsig
@@ -1,5 +1,4 @@
 {-# LANGUAGE NoImplicitPrelude #-}
 module ShouldFail where
 
-data Bool a b c d = False
 data Maybe a b = Nothing
diff --git a/testsuite/tests/typecheck/should_fail/tcfail220.stderr b/testsuite/tests/typecheck/should_fail/tcfail220.stderr
index 6a4e87382d..432dc4c1a3 100644
--- a/testsuite/tests/typecheck/should_fail/tcfail220.stderr
+++ b/testsuite/tests/typecheck/should_fail/tcfail220.stderr
@@ -1,17 +1,9 @@
-[1 of 1] Compiling ShouldFail[sig of Prelude] ( tcfail220.hsig, nothing )
-
-tcfail220.hsig:4:1: error:
-    Type constructor ‘Bool’ has conflicting definitions in the module
-    and its hsig file
-    Main module: data Bool = False | True
-    Hsig file:  type role Bool phantom phantom phantom phantom
-                data Bool a b c d = False
-    The types have different kinds
-
-tcfail220.hsig:5:1: error:
-    Type constructor ‘Maybe’ has conflicting definitions in the module
-    and its hsig file
-    Main module: data Maybe a = Nothing | Just a
-    Hsig file:  type role Maybe phantom phantom
-                data Maybe a b = Nothing
-    The types have different kinds
+[1 of 1] Compiling ShouldFail[sig of Prelude] ( tcfail220.hsig, nothing )

+

+tcfail220.hsig:4:1: error:

+    Type constructor ‘Maybe’ has conflicting definitions in the module

+    and its hsig file

+    Main module: data Maybe a = Nothing | Just a

+    Hsig file:  type role Maybe phantom phantom

+                data Maybe a b = Nothing

+    The types have different kinds