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

1 files changed, 1 insertions, 10 deletions

diff --git a/compiler/main/HscMain.hs b/compiler/main/HscMain.hs
index 0acbdff8a5..5ae104b1da 100644
--- a/compiler/main/HscMain.hs
+++ b/compiler/main/HscMain.hs
@@ -90,9 +90,7 @@ import BasicTypes       ( HValue )
 import ByteCodeGen      ( byteCodeGen, coreExprToBCOs )
 import Linker
 import CoreTidy         ( tidyExpr )
-import Type             ( Type )
-import PrelNames
-import {- Kind parts of -} Type         ( Kind )
+import Type             ( Type, Kind )
 import CoreLint         ( lintInteractiveExpr )
 import VarEnv           ( emptyTidyEnv )
 import Panic
@@ -101,7 +99,6 @@ import ConLike
 import GHC.Exts
 #endif
 
-import DsMeta           ( templateHaskellNames )
 import Module
 import Packages
 import RdrName
@@ -192,12 +189,6 @@ newHscEnv dflags = do
                      hsc_type_env_var = Nothing }
 
 
-knownKeyNames :: [Name]      -- Put here to avoid loops involving DsMeta,
-knownKeyNames =              -- where templateHaskellNames are defined
-    map getName wiredInThings
-        ++ basicKnownKeyNames
-        ++ templateHaskellNames
-
 -- -----------------------------------------------------------------------------
 
 getWarnings :: Hsc WarningMessages