Make record selectors into ordinary functions

This biggish patch addresses Trac #2670.  The main effect is to make
record selectors into ordinary functions, whose unfoldings appear in
interface files, in contrast to their previous existence as magic
"implicit Ids".  This means that the usual machinery of optimisation,
analysis, and inlining applies to them, which was failing before when
the selector was somewhat complicated.  (Which it can be when
strictness annotations, unboxing annotations, and GADTs are involved.)

The change involves the following points

* Changes in Var.lhs to the representation of Var.  Now a LocalId can
  have an IdDetails as well as a GlobalId.  In particular, the
  information that an Id is a record selector is kept in the
  IdDetails.  While compiling the current module, the record selector
  *must* be a LocalId, so that it participates properly in compilation
  (free variables etc).

  This led me to change the (hidden) representation of Var, so that there
  is now only one constructor for Id, not two.

* The IdDetails is persisted into interface files, so that an
  importing module can see which Ids are records selectors.

* In TcTyClDecls, we generate the record-selector bindings in renamed,
  but not typechecked form.  In this way, we can get the typechecker
  to add all the types and so on, which is jolly helpful especially
  when GADTs or type families are involved.  Just like derived
  instance declarations.

  This is the big new chunk of 180 lines of code (much of which is
  commentary).  A call to the same function, mkAuxBinds, is needed in
  TcInstDcls for associated types.

* The typechecker therefore has to pin the correct IdDetails on to 
  the record selector, when it typechecks it.  There was a neat way
  to do this, by adding a new sort of signature to HsBinds.Sig, namely
  IdSig.  This contains an Id (with the correct Name, Type, and IdDetails);
  the type checker uses it as the binder for the final binding.  This
  worked out rather easily.

* Record selectors are no longer "implicit ids", which entails changes to
     IfaceSyn.ifaceDeclSubBndrs
     HscTypes.implicitTyThings
     TidyPgm.getImplicitBinds
  (These three functions must agree.)

* MkId.mkRecordSelectorId is deleted entirely, some 300+ lines (incl
  comments) of very error prone code.  Happy days.

* A TyCon no longer contains the list of record selectors: 
  algTcSelIds is gone

The renamer is unaffected, including the way that import and export of
record selectors is handled.

Other small things

* IfaceSyn.ifaceDeclSubBndrs had a fragile test for whether a data
  constructor had a wrapper.  I've replaced that with an explicit flag
  in the interface file. More robust I hope.

* I renamed isIdVar to isId, which touched a few otherwise-unrelated files.

1 files changed, 4 insertions, 4 deletions

diff --git a/compiler/stranal/WwLib.lhs b/compiler/stranal/WwLib.lhs
index 0bde744385..a7050dc0d0 100644
--- a/compiler/stranal/WwLib.lhs
+++ b/compiler/stranal/WwLib.lhs
@@ -23,7 +23,7 @@ import TysWiredIn	( tupleCon )
 import Type
 import Coercion         ( mkSymCoercion, splitNewTypeRepCo_maybe )
 import BasicTypes	( Boxity(..) )
-import Var              ( Var, isIdVar )
+import Var              ( Var, isId )
 import UniqSupply
 import Unique
 import Util		( zipWithEqual )
@@ -127,13 +127,13 @@ mkWwBodies fun_ty demands res_info one_shots
         -- Don't do CPR if the worker doesn't have any value arguments
         -- Then the worker is just a constant, so we don't want to unbox it.
 	; (wrap_fn_cpr, work_fn_cpr,  _cpr_res_ty)
-	       <- if any isIdVar work_args then
+	       <- if any isId work_args then
 	             mkWWcpr res_ty res_info
 	          else
 	             return (id, id, res_ty)
 
 	; let (work_lam_args, work_call_args) = mkWorkerArgs work_args res_ty
-	; return ([idNewDemandInfo v | v <- work_call_args, isIdVar v],
+	; return ([idNewDemandInfo v | v <- work_call_args, isId v],
                   Note InlineMe . wrap_fn_args . wrap_fn_cpr . wrap_fn_str . applyToVars work_call_args . Var,
                   mkLams work_lam_args. work_fn_str . work_fn_cpr . work_fn_args) }
         -- We use an INLINE unconditionally, even if the wrapper turns out to be
@@ -169,7 +169,7 @@ mkWorkerArgs :: [Var]
 	     -> ([Var],	-- Lambda bound args
 		 [Var])	-- Args at call site
 mkWorkerArgs args res_ty
-    | any isIdVar args || not (isUnLiftedType res_ty)
+    | any isId args || not (isUnLiftedType res_ty)
     = (args, args)
     | otherwise	
     = (args ++ [voidArgId], args ++ [realWorldPrimId])