Generate Typeable info at definition sites

This patch implements the idea floated in Trac #9858, namely that we
should generate type-representation information at the data type
declaration site, rather than when solving a Typeable constraint.

However, this turned out quite a bit harder than I expected. I still
think it's the right thing to do, and it's done now, but it was quite
a struggle.

See particularly

 * Note [Grand plan for Typeable] in TcTypeable (which is a new module)
 * Note [The overall promotion story] in DataCon (clarifies existing stuff)

The most painful bit was that to generate Typeable instances (ie
TyConRepName bindings) for every TyCon is tricky for types in ghc-prim
etc:

 * We need to have enough data types around to *define* a TyCon
 * Many of these types are wired-in

Also, to minimise the code generated for each data type, I wanted to
generate pure data, not CAFs with unpackCString# stuff floating about.

Performance
~~~~~~~~~~~
Three perf/compiler tests start to allocate quite a bit more. This isn't
surprising, because they all allocate zillions of data types, with
practically no other code, esp. T1969

 * T3294:   GHC allocates 110% more (filed #11030 to track this)
 * T1969:   GHC allocates 30% more
 * T4801:   GHC allocates 14% more
 * T5321FD: GHC allocates 13% more
 * T783:    GHC allocates 12% more
 * T9675:   GHC allocates 12% more
 * T5642:   GHC allocates 10% more
 * T9961:   GHC allocates 6% more

 * T9203:   Program allocates 54% less

I'm treating this as acceptable. The payoff comes in Typeable-heavy
code.

Remaining to do
~~~~~~~~~~~~~~~

 * I think that "TyCon" and "Module" are over-generic names to use for
   the runtime type representations used in GHC.Typeable. Better might be
   "TrTyCon" and "TrModule". But I have not yet done this

 * Add more info the the "TyCon" e.g. source location where it was
   defined

 * Use the new "Module" type to help with Trac Trac #10068

 * It would be possible to generate TyConRepName (ie Typeable
   instances) selectively rather than all the time. We'd need to persist
   the information in interface files. Lacking a motivating reason I have
   not done this, but it would not be difficult.

Refactoring
~~~~~~~~~~~
As is so often the case, I ended up refactoring more than I intended.
In particular

 * In TyCon, a type *family* (whether type or data) is repesented by a
   FamilyTyCon
     * a algebraic data type (including data/newtype instances) is
       represented by AlgTyCon This wasn't true before; a data family
       was represented as an AlgTyCon. There are some corresponding
       changes in IfaceSyn.

     * Also get rid of the (unhelpfully named) tyConParent.

 * In TyCon define 'Promoted', isomorphic to Maybe, used when things are
   optionally promoted; and use it elsewhere in GHC.

 * Cleanup handling of knownKeyNames

 * Each TyCon, including promoted TyCons, contains its TyConRepName, if
   it has one. This is, in effect, the name of its Typeable instance.

Requires update of the haddock submodule.

Differential Revision: https://phabricator.haskell.org/D757

3 files changed, 6 insertions, 7 deletions

diff --git a/testsuite/tests/typecheck/should_fail/T5095.stderr b/testsuite/tests/typecheck/should_fail/T5095.stderr
index 46667fb8f4..a854b7ea75 100644
--- a/testsuite/tests/typecheck/should_fail/T5095.stderr
+++ b/testsuite/tests/typecheck/should_fail/T5095.stderr
@@ -6,7 +6,7 @@ T5095.hs:9:11: error:
       instance (Eq a, Eq b) => Eq (Either a b)
         -- Defined in ‘Data.Either’
       instance Eq All -- Defined in ‘Data.Monoid’
-      ...plus 35 others
+      ...plus 36 others
       ...plus one instance involving out-of-scope types
       (use -fprint-potential-instances to see them all)
     (The choice depends on the instantiation of ‘a’
diff --git a/testsuite/tests/typecheck/should_fail/tcfail072.stderr b/testsuite/tests/typecheck/should_fail/tcfail072.stderr
index 65b157332d..68d7283244 100644
--- a/testsuite/tests/typecheck/should_fail/tcfail072.stderr
+++ b/testsuite/tests/typecheck/should_fail/tcfail072.stderr
@@ -8,10 +8,10 @@ tcfail072.hs:23:13: error:
     The type variable ‘p0’ is ambiguous
     These potential instances exist:
       instance Ord Ordering -- Defined in ‘GHC.Classes’
+      instance Ord TyCon -- Defined in ‘GHC.Classes’
       instance Ord Integer
         -- Defined in ‘integer-gmp-1.0.0.0:GHC.Integer.Type’
-      instance Ord a => Ord (Maybe a) -- Defined in ‘GHC.Base’
-      ...plus 22 others
+      ...plus 23 others
       ...plus one instance involving out-of-scope types
       (use -fprint-potential-instances to see them all)
     In the expression: g A
diff --git a/testsuite/tests/typecheck/should_fail/tcfail133.stderr b/testsuite/tests/typecheck/should_fail/tcfail133.stderr
index f61320f4c1..32f73422af 100644
--- a/testsuite/tests/typecheck/should_fail/tcfail133.stderr
+++ b/testsuite/tests/typecheck/should_fail/tcfail133.stderr
@@ -7,11 +7,10 @@ tcfail133.hs:68:7: error:
     prevents the constraint ‘(Show r0)’ from being solved.
     Probable fix: use a type annotation to specify what ‘r0’ should be.
     These potential instances exist:
+      instance Show Module -- Defined in ‘GHC.Show’
       instance Show Ordering -- Defined in ‘GHC.Show’
-      instance Show Integer -- Defined in ‘GHC.Show’
-      instance (Show a, Show b, Number a, Digit b) => Show (a :@ b)
-        -- Defined at tcfail133.hs:11:54
-      ...plus 25 others
+      instance Show TrName -- Defined in ‘GHC.Show’
+      ...plus 28 others
       (use -fprint-potential-instances to see them all)
     In the expression: show
     In the expression: show $ add (One :@ Zero) (One :@ One)