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

3 files changed, 13 insertions, 3 deletions

diff --git a/testsuite/tests/module/all.T b/testsuite/tests/module/all.T
index c4c2fffe57..d0b37aaa33 100644
--- a/testsuite/tests/module/all.T
+++ b/testsuite/tests/module/all.T
@@ -116,7 +116,7 @@ test('mod85', normal, compile, [''])
 test('mod86', normal, compile, [''])
 test('mod87', normal, compile_fail, [''])
 test('mod88', normal, compile_fail, [''])
-test('mod89', normal, compile_fail, [''])
+test('mod89', normal, compile, [''])
 test('mod90', normal, compile_fail, [''])
 test('mod91', normal, compile_fail, [''])
 test('mod92', normal, compile, [''])
diff --git a/testsuite/tests/module/mod89.hs b/testsuite/tests/module/mod89.hs
index 2c48d65a16..1e903a0125 100644
--- a/testsuite/tests/module/mod89.hs
+++ b/testsuite/tests/module/mod89.hs
@@ -1,3 +1,5 @@
+{-# OPTIONS_GHC -Wall #-}
+
 -- !!! Sublist for non-class/tycon
 module M where
 import Prelude(map(..))
diff --git a/testsuite/tests/module/mod89.stderr b/testsuite/tests/module/mod89.stderr
index 0f956536cb..b355f3050b 100644
--- a/testsuite/tests/module/mod89.stderr
+++ b/testsuite/tests/module/mod89.stderr
@@ -1,2 +1,10 @@
-
-mod89.hs:3:16: Module ‘Prelude’ does not export ‘map(..)’
+

+mod89.hs:5:1: warning:

+    The import item ‘map(..)’ suggests that

+    ‘map’ has (in-scope) constructors or class methods,

+    but it has none

+

+mod89.hs:5:1: warning:

+    The import of ‘Prelude’ is redundant

+      except perhaps to import instances from ‘Prelude’

+    To import instances alone, use: import Prelude()