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The situation was pretty dire.  The way in which data constructors
were handled, notably the mapping between their *source* argument types
and their *representation* argument types (after seq'ing and unpacking)
was scattered in three different places, and hard to keep in sync.

Now it is all in one place:

 * The dcRep field of a DataCon gives its representation,
   specified by a DataConRep

 * As well as having the wrapper, the DataConRep has a "boxer"
   of type DataConBoxer (defined in MkId for loopy reasons).
   The boxer used at a pattern match to reconstruct the source-level
   arguments from the rep-level bindings in the pattern match.

 * The unboxing in the wrapper and the boxing in the boxer are dual,
   and are now constructed together, by MkId.mkDataConRep. This is
   the key function of this change.

 * All the computeBoxingStrategy code in TcTyClsDcls disappears.

Much nicer.

There is a little bit of refactoring left to do; the strange
deepSplitProductType functions are now called only in WwLib, so
I moved them there, and I think they could be tidied up further.

These names end up in the ABI, and hence part of the ABI hash.
We don't want uniques in them so that we don't get spurious ABI
hash changes.

The wrapper functions can end up in interface files, and thus are
part of the ABI hash. But uniqs easily change for no good reason
when recompiling, which can lead to an ABI hash needlessly changing.

We weren't doing the binders right, and were creating NameLs
rather than NameUs for the binders of the Rule.  That gave
very funny output for T7064.

We were being inconsistent about how we tested whether dump flags
were enabled; in particular, sometimes we also checked the verbosity,
and sometimes we didn't.

This lead to oddities such as "ghc -v4" printing an "Asm code" section
which didn't contain any code, and "-v4" enabled some parts of
"-ddump-deriv" but not others.

Now all the tests use dopt, which also takes the verbosity into account
as appropriate.

Mostly d -> g (matching DynFlag -> GeneralFlag).
Also renamed if* to when*, matching the Haskell if/when names

I also removed the default values from the "Discounts and thresholds"
note: most of them were no longer up-to-date.

Along the way I added FloatSuffix to the argument parser, analogous to
IntSuffix.

All the work was done by Dan Winograd-Cort.

The main thing is that arrow comamnds now have their own
data type HsCmd (defined in HsExpr).  Previously it was
punned with the HsExpr type, which was jolly confusing,
and made it hard to do anything arrow-specific.

To make this work, we now parameterise
  * MatchGroup
  * Match
  * GRHSs, GRHS
  * StmtLR and friends
over the "body", that is the kind of thing they
enclose.  This "body" parameter can be instantiated to
either LHsExpr or LHsCmd respectively.

Everything else is really a knock-on effect; there should
be no change (yet!) in behaviour.  But it should be a sounder
basis for fixing bugs.

* Treat kind-equality constraints as *derived* equalities,
  with no evidence.  That is really what they are at the moment.

* Get rid of EvKindCast and friends.

* Postpone kind errors properly to the constraint solver
  (lots of small knock-on effects)

I moved SwapFlag to BasicTypes as well

This patch finally adds 'left' and 'right' coercions back into
GHC.  Trac #7205 gives the details.

The main change is to add a new constructor to Coercion:

  data Coercion
    = ...
    | NthCo  Int         Coercion     -- OLD, still there
    | LRCo   LeftOrRight Coercion     -- NEW

  data LeftOrRight = CLeft | CRight

Plus:
  * Similar change to TcCoercion
  * Use LRCo when decomposing AppTys
  * Coercion optimisation needs to handle left/right

The rest is just knock-on effects.

I've totally forgotten what this patch is fixing, but it's all about
getting the right source location for class methods.  It's fairly
minor, but annoying that I can't connect it with a Trac ticket

This single commit combines a lot of work done by
Thijs Alkemade <thijsalkemade@gmail.com>, plus a slew
of subsequent refactoring by Simon PJ.

The basic idea is
* Add a new expression form "_", a hole, standing for a not-yet-written expression
* Give a useful error message that
   (a) gives the type of the hole
   (b) gives the types of some enclosing value bindings that
       mention the hole

Driven by this goal I did a LOT of refactoring in TcErrors, which in turn
allows us to report enclosing value bindings for other errors, not just
holes.  (Thijs rightly did not attempt this!)

The major data type change is a new form of constraint
  data Ct = ...
    	  | CHoleCan {
    	      cc_ev       :: CtEvidence,
    	      cc_hole_ty  :: TcTauType,
    	      cc_depth    :: SubGoalDepth }

I'm still in two minds about whether this is the best plan. Another
possibility would be to have a predicate type for holes, somthing like
   class Hole a where
     holeValue :: a

It works the way it is, but there are some annoying special cases for
CHoleCan (just grep for "CHoleCan").

I've switched to passing DynFlags rather than Platform, as (a) it's
simpler to not have to extract targetPlatform in so many places, and
(b) it may be useful to have DynFlags around in future.

Pls merge to 7.6

I suppose this was a good idea for HPC, as it assumed that source code
annotations coming from a source file could only talk about the same
source file (by how Mix files are saved).

I don't see a reason why cost-centres or source annotations would want
that kind of behaviour. I introduced a flag for toggling the behaviour
per tickish.

(plus some minor refactoring, as well as making sure that the same check
applies to binary tick boxes, where they had apparently been forgotten.)

Also adds RULES and 'SPECIALIZE instance' support.

All the flags that 'ways' imply are now dynamic

Also, temporarely disable that warning for validate builds, until we
finish fixing them all.

This warning was suggested by Trac #6082, where we had
a library RULE that failed to fire because its function
was inlined too soon.

FastStrings are now always UTF8-encoded.

There's no StringTable for FastZString, but I don't think one is needed.
We only ever make a FastZString by running zEncodeFS on a FastString,
and the FastStrings are shared via the FastString StringTable, so we get
the same FastZString from the IORef.

This is a first step on the way to refactoring the FastString type.

FastBytes currently has no unique, mainly because there isn't currently
a nice way to produce them in Binary.

Also, we don't currently do the "Dictionary" thing with FastBytes in
Binary. I'm not sure whether this is important.

We can change both decisions later, but in the meantime this gets the
refactoring underway.