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.

4 files changed, 12 insertions, 12 deletions

diff --git a/compiler/simplCore/CSE.lhs b/compiler/simplCore/CSE.lhs
index 9b90220155..d4aef90725 100644
--- a/compiler/simplCore/CSE.lhs
+++ b/compiler/simplCore/CSE.lhs
@@ -342,7 +342,7 @@ extendSubst (CS cs in_scope sub) x y = CS cs in_scope (extendVarEnv sub x y)
 addBinder :: CSEnv -> Id -> (CSEnv, Id)
 addBinder (CS cs in_scope sub) v
   | not (v `elemInScopeSet` in_scope) = (CS cs (extendInScopeSet in_scope v)  sub,		       v)
-  | isIdVar v			      = (CS cs (extendInScopeSet in_scope v') (extendVarEnv sub v v'), v')
+  | isId v			      = (CS cs (extendInScopeSet in_scope v') (extendVarEnv sub v v'), v')
   | otherwise			      = WARN( True, ppr v )
 				        (CS emptyUFM in_scope		      sub,		       v)
 	-- This last case is the unusual situation where we have shadowing of
diff --git a/compiler/simplCore/FloatIn.lhs b/compiler/simplCore/FloatIn.lhs
index 1146c77031..36e3d4de70 100644
--- a/compiler/simplCore/FloatIn.lhs
+++ b/compiler/simplCore/FloatIn.lhs
@@ -373,7 +373,7 @@ noFloatIntoRhs (AnnLam b _)   	    = not (is_one_shot b)
 noFloatIntoRhs rhs = exprIsHNF (deAnnotate' rhs)	-- We'd just float right back out again...
 
 is_one_shot :: Var -> Bool
-is_one_shot b = isIdVar b && isOneShotBndr b
+is_one_shot b = isId b && isOneShotBndr b
 \end{code}
 
 
diff --git a/compiler/simplCore/SetLevels.lhs b/compiler/simplCore/SetLevels.lhs
index 270ce17095..6f48272a9f 100644
--- a/compiler/simplCore/SetLevels.lhs
+++ b/compiler/simplCore/SetLevels.lhs
@@ -525,7 +525,7 @@ lvlBind top_lvl ctxt_lvl env (AnnRec pairs)
        new_rhss <- mapM (lvlExpr ctxt_lvl new_env) rhss
        return (Rec ([TB b dest_lvl | b <- new_bndrs] `zip` new_rhss), new_env)
 
-  | isSingleton pairs && count isIdVar abs_vars > 1
+  | isSingleton pairs && count isId abs_vars > 1
   = do	-- Special case for self recursion where there are
 	-- several variables carried around: build a local loop:	
 	--	poly_f = \abs_vars. \lam_vars . letrec f = \lam_vars. rhs in f lam_vars
@@ -605,7 +605,7 @@ lvlLamBndrs lvl bndrs
 	[] bndrs
   where
     go old_lvl bumped_major rev_lvld_bndrs (bndr:bndrs)
-	| isIdVar bndr &&		-- Go to the next major level if this is a value binder,
+	| isId bndr &&	    		-- Go to the next major level if this is a value binder,
 	  not bumped_major && 		-- and we havn't already gone to the next level (one jump per group)
 	  not (isOneShotLambda bndr)	-- and it isn't a one-shot lambda
 	= go new_lvl True (TB bndr new_lvl : rev_lvld_bndrs) bndrs
@@ -647,7 +647,7 @@ isFunction :: CoreExprWithFVs -> Bool
 -- We may only want to do this if there are sufficiently few free 
 -- variables.  We certainly only want to do it for values, and not for
 -- constructors.  So the simple thing is just to look for lambdas
-isFunction (_, AnnLam b e) | isIdVar b = True
+isFunction (_, AnnLam b e) | isId b    = True
                            | otherwise = isFunction e
 isFunction (_, AnnNote _ e)            = isFunction e
 isFunction _                           = False
@@ -765,10 +765,10 @@ maxIdLevel (_, lvl_env,_,id_env) var_set
 						Nothing		   -> [in_var])
 
     max_out out_var lvl 
-	| isIdVar out_var = case lookupVarEnv lvl_env out_var of
+	| isId out_var = case lookupVarEnv lvl_env out_var of
 				Just lvl' -> maxLvl lvl' lvl
 				Nothing   -> lvl 
-	| otherwise       = lvl	-- Ignore tyvars in *maxIdLevel*
+	| otherwise    = lvl	-- Ignore tyvars in *maxIdLevel*
 
 lookupVar :: LevelEnv -> Id -> LevelledExpr
 lookupVar (_, _, _, id_env) v = case lookupVarEnv id_env v of
@@ -808,7 +808,7 @@ abstractVars dest_lvl (_, lvl_env, _, id_env) fvs
 
 	-- We are going to lambda-abstract, so nuke any IdInfo,
 	-- and add the tyvars of the Id (if necessary)
-    zap v | isIdVar v = WARN( workerExists (idWorkerInfo v) ||
+    zap v | isId v = WARN( workerExists (idWorkerInfo v) ||
 		           not (isEmptySpecInfo (idSpecialisation v)),
 		           text "absVarsOf: discarding info on" <+> ppr v )
 		     setIdInfo v vanillaIdInfo
@@ -823,7 +823,7 @@ absVarsOf :: IdEnv ([Var], LevelledExpr) -> Var -> [Var]
 	--	we must look in x's type
 	-- And similarly if x is a coercion variable.
 absVarsOf id_env v 
-  | isIdVar v = [av2 | av1 <- lookup_avs v
+  | isId v    = [av2 | av1 <- lookup_avs v
 		     , av2 <- add_tyvars av1]
   | isCoVar v = add_tyvars v
   | otherwise = [v]
@@ -871,7 +871,7 @@ cloneVar :: TopLevelFlag -> LevelEnv -> Id -> Level -> Level -> LvlM (LevelEnv,
 cloneVar TopLevel env v _ _
   = return (env, v)	-- Don't clone top level things
 cloneVar NotTopLevel env@(_,_,subst,_) v ctxt_lvl dest_lvl
-  = ASSERT( isIdVar v ) do
+  = ASSERT( isId v ) do
     us <- getUniqueSupplyM
     let
       (subst', v1) = cloneIdBndr subst us v
@@ -883,7 +883,7 @@ cloneRecVars :: TopLevelFlag -> LevelEnv -> [Id] -> Level -> Level -> LvlM (Leve
 cloneRecVars TopLevel env vs _ _
   = return (env, vs)	-- Don't clone top level things
 cloneRecVars NotTopLevel env@(_,_,subst,_) vs ctxt_lvl dest_lvl
-  = ASSERT( all isIdVar vs ) do
+  = ASSERT( all isId vs ) do
     us <- getUniqueSupplyM
     let
       (subst', vs1) = cloneRecIdBndrs subst us vs
diff --git a/compiler/simplCore/SimplCore.lhs b/compiler/simplCore/SimplCore.lhs
index 98ef348be7..d6aecc4b39 100644
--- a/compiler/simplCore/SimplCore.lhs
+++ b/compiler/simplCore/SimplCore.lhs
@@ -43,7 +43,7 @@ import FloatOut		( floatOutwards )
 import FamInstEnv
 import Id
 import DataCon
-import TyCon		( tyConSelIds, tyConDataCons )
+import TyCon		( tyConDataCons )
 import Class		( classSelIds )
 import BasicTypes       ( CompilerPhase, isActive )
 import VarSet