GitLab

'import' syntax is seperate from ':module' syntax

GHCi was building its GlobalRdrEnv wrongly, so that the
gre_par field was bogus.  That in turn fooled the renamer.
The fix is easy: use the right function!  Namely, call
RnNames.gresFromAvail rather than availsToNameSet.

The main purpose of this patch is to add a bunch of new rules
to the coercion optimiser.  They are documented in the (revised)
Appendix of the System FC paper.  

Some code has moved about:

- OptCoercion is now a separate module, mainly because it
  now uses tcMatchTy, which is defined in Unify, so OptCoercion
  must live higehr up in the hierarchy

- Functions that manipulate Kinds has moved from 
  Type.lhs to Coercion.lhs.  Reason: the function typeKind
  now needs to call coercionKind.  And in any case, a Kind is
  a flavour of Type, so it builds on top of Type; indeed Coercions
  and Kinds are both flavours of Type.

  This change required fiddling with a number of imports, hence
  the one-line changes to otherwise-unrelated modules

- The representation of CoTyCons in TyCon has changed.   Instead of
  an extensional representation (a kind checker) there is now an
  intensional representation (namely TyCon.CoTyConDesc).  This was
  needed for one of the new coercion optimisations.

We were keeping things as Int, and then converting them to Word16 at
the last minute, when really they ought to have been Word16 all along.

It turns out we can easily support breakpoints on expressions with
unlifted types, by translating 

  case tick# of _ -> e

into

  let f = \s . case tick# of _ -> e 
  in  f realWorld#

instead of just a plain let-binding.  This is the same trick that GHC
uses for abstracting join points of unlifted type.

In #2845, GHC has eta-expanded the tick expression, changing the
result type from IO a to (# State#, a #), which was the reason the
tick was suddenly being ignored.  By supporting ticks on unlifted
expressions we can make it work again, although some confusion might
arise because _result will no longer be available (it now has
unboxed-tuple type, so we can't bind it in the environment).  The
underlying problem here is that GHC does transformations like
eta-expanding the tick expressions, and there's nothing we can do to
prevent that.

The problem is that we install the client's CWD before calling
runStmt, but runStmt has to load modules before running the code.  We
need to install the CWD just before running the code instead, which
means it has to be done inside runStmt (and resume).

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.

Ifdefs for whether we had extensible exceptions or not were spreading
through GHC's source, and things would only have got worse for the next
2-3 years, so instead we now use an implementation of extensible
exceptions built on top of the old exception type.

      
      - Ticket #1995: Unsoundness with newtypes
      - Ticket #2475: "Can't unify" error when stopped at an exception
      
      In addition this patch adds the following:
      
      - Unfailingness: RTTI cannot panic anymore. 
        In case of failure, it recovers gracefully by returning the "I know nothing" type
      - A -ddump-rtti flag

TopHandler now uses the new extensible exceptions module, so we
need to interact with it using the new types.

Switching to boxyUnify should be enough to fix this.

We were doing lots of cons'ing and tail'ing without forcing the tails,
so were building up lots of thunks.

These fix these failures:
   break008(ghci)
   break009(ghci)
   break026(ghci)
   ghci.prog009(ghci)
   ghci025(ghci)
   print007(ghci)
   prog001(ghci)
   prog002(ghci)
   prog003(ghci)
at least some of which have this symptom:
    Exception: expectJust prune

using the new block-inheriting forkIO (#1048)

This patch implements three new features:
* view patterns (syntax: expression -> pat in a pattern)
* working versions of record wildcards and record puns
See the manual for detailed descriptions.

Other minor observable changes:
* There is a check prohibiting local fixity declarations
  when the variable being fixed is not defined in the same let
* The warn-unused-binds option now reports warnings for do and mdo stmts

Implementation notes: 

* The pattern renamer is now in its own module, RnPat, and the
implementation is now in a CPS style so that the correct context is
delivered to pattern expressions.

* These features required a fairly major upheaval to the renamer.
Whereas the old version used to collect up all the bindings from a let
(or top-level, or recursive do statement, ...) and put them into scope
before renaming anything, the new version does the collection as it
renames.  This allows us to do the right thing with record wildcard
patterns (which need to be expanded to see what names should be
collected), and it allows us to implement the desired semantics for view
patterns in lets.  This change had a bunch of domino effects brought on
by fiddling with the top-level renaming.

* Prior to this patch, there was a tricky bug in mkRecordSelId in HEAD,
which did not maintain the invariant necessary for loadDecl.  See note
[Tricky iface loop] for details.

    
    This flag works like -fbreak-on-exception, but only stops
    on uncaught exceptions.

In fact hs-boot files had nothing to do with it: the problem was that
GHCi would forget the breakpoint information for a module that had
been reloaded but not recompiled.  It's amazing that we never noticed
this before.

The ModBreaks were in the ModDetails, which was the wrong place.  When
we avoid recompiling a module, ModDetails is regenerated from ModIface
by typecheckIface, and at that point it has no idea what the ModBreaks
should be, so typecheckIface made it empty.  The right place for the
ModBreaks to go is with the Linkable, which is retained when
compilation is avoided.  So now I've placed the ModBreaks in with the
CompiledByteCode, which also makes it clear that only byte-code
modules have breakpoints.

This fixes break022/break023

Older GHCs can't parse OPTIONS_GHC.
This also changes the URL referenced for the -w options from
WorkingConventions#Warnings to CodingStyle#Warnings for the compiler
modules.