Further wibbles to moving dependency analysis back to renamer; fixes ghci failures

Wibbles to the big HsBinds reorg

MERGE TO STABLE if poss

Make the "root main" Id :Main.main into an *implicit* Id, whose parent is
Main.main.  What that means is that the "root main" Id won't be emitted
into the interface file.  Which has not been causing a problem in practice
but is clearly wrong -- there were two 'main's in the interface file.

WARNING: this is a big commit.  You might want 
	to wait a few days before updating, in case I've 
	broken something.

	However, if any of the changes are what you wanted,
	please check it out and test!

This commit does three main things:

1. A re-organisation of the way that GHC handles bindings in HsSyn.
   This has been a bit of a mess for quite a while.  The key new
   types are

	-- Bindings for a let or where clause
	data HsLocalBinds id
	  = HsValBinds (HsValBinds id)
	  | HsIPBinds  (HsIPBinds id)
	  | EmptyLocalBinds

	-- Value bindings (not implicit parameters)
	data HsValBinds id
	  = ValBindsIn  -- Before typechecking
		(LHsBinds id) [LSig id]	-- Not dependency analysed
					-- Recursive by default

	  | ValBindsOut	-- After typechecking
		[(RecFlag, LHsBinds id)]-- Dependency analysed

2. Implement Mark Jones's idea of increasing polymoprhism
   by using type signatures to cut the strongly-connected components
   of a recursive group.  As a consequence, GHC no longer insists
   on the contexts of the type signatures of a recursive group
   being identical.

   This drove a significant change: the renamer no longer does dependency
   analysis.  Instead, it attaches a free-variable set to each binding,
   so that the type checker can do the dep anal.  Reason: the typechecker
   needs to do *two* analyses:
	one to find the true mutually-recursive groups
		(which we need so we can build the right CoreSyn)
	one to find the groups in which to typecheck, taking
		account of type signatures

3. Implement non-ground SPECIALISE pragmas, as promised, and as
   requested by Remi and Ross.  Certainly, this should fix the 
   current problem with GHC, namely that if you have
	g :: Eq a => a -> b -> b
   then you can now specialise thus
	SPECIALISE g :: Int -> b -> b
    (This didn't use to work.)

   However, it goes further than that.  For example:
	f :: (Eq a, Ix b) => a -> b -> b
   then you can make a partial specialisation
	SPECIALISE f :: (Eq a) => a -> Int -> Int

    In principle, you can specialise f to *any* type that is
    "less polymorphic" (in the sense of subsumption) than f's 
    actual type.  Such as
	SPECIALISE f :: Eq a => [a] -> Int -> Int
    But I haven't tested that.

    I implemented this by doing the specialisation in the typechecker
    and desugarer, rather than leaving around the strange SpecPragmaIds,
    for the specialiser to find.  Indeed, SpecPragmaIds have vanished 
    altogether (hooray).

    Pragmas in general are handled more tidily.  There's a new
    data type HsBinds.Prag, which lives in an AbsBinds, and carries
    pragma info from the typechecker to the desugarer.


Smaller things

- The loop in the renamer goes via RnExpr, instead of RnSource.
  (That makes it more like the type checker.)

- I fixed the thing that was causing 'check_tc' warnings to be 
  emitted.

Relax the restrictions on conflicting packages.  This should address
many of the traps that people have been falling into with the current
package story.

Now, a local module can shadow a module in an exposed package, as long
as the package is not otherwise required by the program.  GHC checks
for conflicts when it knows the dependencies of the module being
compiled.

Also, we now check for module conflicts in exposed packages only when
importing a module: if an import can be satisfied from multiple
packages, that's an error.  It's not possible to prevent GHC from
starting by installing packages now (unless you install another base
package).

It seems to be possible to confuse GHCi by having a local module
shadowing a package module that goes away and comes back again.  I
think it's nearly right, but strange happenings have been observed.

I'll try to merge this into the STABLE branch.

Re-implement GHCi's :info and :browse commands in terms of TyThings
rather than IfaceSyn.

The GHC API now exposes its internal types for Haskell entities:
TyCons, Classes, DataCons, Ids and Instances (collectively known as
TyThings), so we can inspect these directly to pretty-print
information about an entity.  Previously the internal representations
were converted to IfaceSyn for passing to InteractiveUI, but we can
now remove that code.

Some of the new code comes via Visual Haskell, but I've changed it
around a lot to fix various dark corners and properly print things
like GADTs.

The pretty-printing interfaces for TyThings are exposed by a new
module PprTyThing, which is implemented purely in terms of the GHC API
(and is probably a good source of sample code).  Visual Haskell should
be able to use the functions exported by this module directly.

Lots of new goodies are exported by the GHC module, mainly for
inspecting TyThings.

Fix some reporting of errors in the GHC API: errors during the
downsweep were thrown as exceptions; now they're reported via the
(Messages->IO ()) callback in the same way as other errors.

getModuleInfo no longer prints anything on stdout.  It does ignore
error messages and return Nothing, however - we should fix this and
return the error messages at some point.

The ErrMsg type can now be thrown as an exception.  This can be a
convenient alternative if collecting multiple error messages isn't
required.  We do this in the downsweep now.

Yet another wibble to the GHCi top-level interaction story; avoid dup error messages

Further GHCi wibbles

a) Don't print the value of a 'let'
b) Only one error message for 'print id'

Comments and type sig only

Further wibble to preceding GHCi commit

Wibble to preceding GHCi commit

Improve the GHCi interaction

		Merge to STABLE?

This fix addresses Sourceforge #1156554 "GHCi: No instance for (Show (IO ()))",
and simultaneously improves the top-level interaction in two other ways:

- Only one error can show up (previously there could be two)

- If an I/O action gives a Showable result, the result is printed
  (provided it isn't ()).  So
	prompt> return 4
  prints 4, rather than nothing

- For command-line 'let' and 'x<-e' forms, if exactly one variable
  is bound, we print its value if it is Showable and not ()
	prompt> let x = 4
	4
	prompt> x <- return 5
	5

Make sure the default methods are in scope
	in a Template Haskell splice

		Merge to STABLE

This was just a typo really; in TcRnDriver.tcTopSrcDecls there were two
tcl_envs, but one had a different name so we got the less up-to-date one.

Fixes SourceForge item #1194808

TH_spliceInst tests it.

Report instances correctly in GHCi

Make GHC.modInfoPrintUnqualified work for package modules too.  Also
refactor a bit: move mkExportEnv from TcRnDriver up to GHC which is
the only use of it.

getModuleInfo now does something reasonable for package modules.

Improve generation of 'duplicate import' warnings.
This involved changing (actually simplifying) the
definition of RdrName.ImportSpec.

I'm not sure whether this one merits merging or not.
Perhaps worth a try.

Fix the test for duplicate local bindings, so that it works with
Template Haskell.  Pre-TH, all the local bindings came into scope
at once, but with TH they come into scope in groups, and we must
check for conflict with existing local bindings.

	MERGE TO STABLE

In the :i command for ghci, load the interface files for
the home module of every in-scope type or class. That way
we are sure to see all their instance declarations.

	MERGE TO STABLE branch

Wibbles to new hs-boot instance story

The boot dfunid should be a LocalId

Further stage-2 wibbles

This big commit does several things at once (aeroplane hacking)
which change the format of interface files.  

	So you'll need to recompile your libraries!

1. The "stupid theta" of a newtype declaration
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Retain the "stupid theta" in a newtype declaration.
For some reason this was being discarded, and putting it
back in meant changing TyCon and IfaceSyn slightly.
   

2. Overlap flags travel with the instance
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Arrange that the ability to support overlap and incoherence
is a property of the *instance declaration* rather than the
module that imports the instance decl.  This allows a library
writer to define overlapping instance decls without the
library client having to know.  

The implementation is that in an Instance we store the
overlap flag, and preseve that across interface files


3. Nuke the "instnce pool" and "rule pool"
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
A major tidy-up and simplification of the way that instances
and rules are sucked in from interface files.  Up till now
an instance decl has been held in a "pool" until its "gates" 
(a set of Names) are in play, when the instance is typechecked
and added to the InstEnv in the ExternalPackageState.  
This is complicated and error-prone; it's easy to suck in 
too few (and miss an instance) or too many (and thereby be
forced to suck in its type constructors, etc).

Now, as we load an instance from an interface files, we 
put it straight in the InstEnv... but the Instance we put in
the InstEnv has some Names (the "rough-match" names) that 
can be used on lookup to say "this Instance can't match".
The detailed dfun is only read lazily, and the rough-match
thing meansn it is'nt poked on until it has a chance of
being needed.

This simply continues the successful idea for Ids, whereby
they are loaded straightaway into the TypeEnv, but their
TyThing is a lazy thunk, not poked on until the thing is looked
up.

Just the same idea applies to Rules.

On the way, I made CoreRule and Instance into full-blown records
with lots of info, with the same kind of key status as TyCon or 
DataCon or Class.  And got rid of IdCoreRule altogether.   
It's all much more solid and uniform, but it meant touching
a *lot* of modules.


4. Allow instance decls in hs-boot files
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Allowing instance decls in hs-boot files is jolly useful, becuase
in a big mutually-recursive bunch of data types, you want to give
the instances with the data type declarations.  To achieve this

* The hs-boot file makes a provisional name for the dict-fun, something
  like $fx9.

* When checking the "mother module", we check that the instance
  declarations line up (by type) and generate bindings for the 
  boot dfuns, such as
	$fx9 = $f2
  where $f2 is the dfun generated by the mother module

* In doing this I decided that it's cleaner to have DFunIds get their
  final External Name at birth.  To do that they need a stable OccName,
  so I have an integer-valued dfun-name-supply in the TcM monad.
  That keeps it simple.

This feature is hardly tested yet.


5. Tidy up tidying, and Iface file generation
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
main/TidyPgm now has two entry points:

  simpleTidyPgm is for hi-boot files, when typechecking only
  (not yet implemented), and potentially when compiling without -O.
  It ignores the bindings, and generates a nice small TypeEnv.

  optTidyPgm is the normal case: compiling with -O.  It generates a
  TypeEnv rich in IdInfo

MkIface.mkIface now only generates a ModIface.  A separate
procedure, MkIface.writeIfaceFile, writes the file out to disk.

Support for returning the renamed syntax from checkModule (untested).

Significant clean-up of the handling of hi-boot files. 
Previously, when compling A.hs, we loaded A.hi-boot, and
it went into the External Package Table.  It was strange
but it worked.  This tidy up stops it going anywhere;
it's just read in, and typechecked into a ModDetails.

All this was on the way to improving the handling of
instances in hs-boot files, something Chris Ryder wanted.
I think they work quite sensibly now.  

If I've got all this right (have not had a chance to
fully test it) we can merge it into STABLE.

Wibble to ghci

GHC API work:

  - add parseName :: Session -> String -> IO [Name]
  - make lookupName look up in the global type environment

  - add data ModuleInfo
  - add a few ModuleInfo-related functions
  - add getModuleInfo :: Session -> Module -> IO ModuleInfo

More stage2 wibbles

This commit combines three overlapping things:

1.  Make rebindable syntax work for do-notation. The idea
    here is that, in particular, (>>=) can have a type that
    has class constraints on its argument types, e.g.
       (>>=) :: (Foo m, Baz a) => m a -> (a -> m b) -> m b
    The consequence is that a BindStmt and ExprStmt must have
    individual evidence attached -- previously it was one
    batch of evidence for the entire Do
    
    Sadly, we can't do this for MDo, because we use bind at
    a polymorphic type (to tie the knot), so we still use one
    blob of evidence (now in the HsStmtContext) for MDo.
    
    For arrow syntax, the evidence is in the HsCmd.
    
    For list comprehensions, it's all built-in anyway.
    
    So the evidence on a BindStmt is only used for ordinary
    do-notation.

2.  Tidy up HsSyn.  In particular:

	- Eliminate a few "Out" forms, which we can manage
	without (e.g. 

	- It ought to be the case that the type checker only
	decorates the syntax tree, but doesn't change one
	construct into another.  That wasn't true for NPat,
	LitPat, NPlusKPat, so I've fixed that.

	- Eliminate ResultStmts from Stmt.  They always had
	to be the last Stmt, which led to awkward pattern
	matching in some places; and the benefits didn't seem
	to outweigh the costs.  Now each construct that uses
	[Stmt] has a result expression too (e.g. GRHS).


3.  Make 'deriving( Ix )' generate a binding for unsafeIndex,
    rather than for index.  This is loads more efficient.

    (This item only affects TcGenDeriv, but some of point (2)
    also affects TcGenDeriv, so it has to be in one commit.)

Tweaks to get the GHC sources through Haddock.  Doesn't quite work
yet, because Haddock complains about the recursive modules.  Haddock
needs to understand SOURCE imports (it can probably just ignore them
as a first attempt).

A start on the GHC API:

Flesh out the GHC module so that it can replace CompManager.  Now, the
clients that used CompManager consume the GHC API instead (namely
Main, DriverMkDepend, and InteractiveUI).  Main is significantly
cleaner as a result.

The interface needs more work: in particular, getInfo returns results
in the form of IfaceDecls but we want to use full HsSyn and
Id/DataCon/Class across the boundary instead.

The interfaces for inspecting loaded modules are not yet implemented.

Flags cleanup.

Basically the purpose of this commit is to move more of the compiler's
global state into DynFlags, which is moving in the direction we need
to go for the GHC API which can have multiple active sessions
supported by a single GHC instance.

Before:

$ grep 'global_var' */*hs | wc -l
     78

After:

$ grep 'global_var' */*hs | wc -l
     27

Well, it's an improvement.  Most of what's left won't really affect
our ability to host multiple sessions.

Lots of static flags have become dynamic flags (yay!).  Notably lots
of flags that we used to think of as "driver" flags, like -I and -L,
are now dynamic.  The most notable static flags left behind are the
"way" flags, eg. -prof.  It would be nice to fix this, but it isn't
urgent.

On the way, lots of cleanup has happened.  Everything related to
static and dynamic flags lives in StaticFlags and DynFlags
respectively, and they share a common command-line parser library in
CmdLineParser.  The flags related to modes (--makde, --interactive
etc.) are now private to the front end: in fact private to Main
itself, for now.

Buglet in compiling hs-boot files
	We should make GlobalIds not LocalIds

	Merge to STABLE

Print full instances in ghci; merge

Missing commit from the module A export list commit

Arrange that when seeking instance decls in GHCi, in response
to a :info command, we only print ones whose types are in scope
unqualified.  This eliminates an alarmingly long list when
simply typing ':info Show', say.

On the way, I reorganised a bit.  GHCi printing happens by
converting a TyThing to an IfaceDecl, and printing that.
I now arrange to generate unqualifed IfaceExtNames directly
during this conversion, based on what is in scope.  Previously
it was done during the pretty-printing part via the UserStyle.
But this is nicer.

Make sure that the interactive context can see home-package instances;
I forgot to do this when making tcRnModule find the appropriate intances
(TcRnDriver rev 1.91)

This was causing SourceForge [ghc-Bugs-1106171].

--------------------------------------------
          Replace hi-boot files with hs-boot files
  	--------------------------------------------

This major commit completely re-organises the way that recursive modules
are dealt with.

  * It should have NO EFFECT if you do not use recursive modules

  * It is a BREAKING CHANGE if you do

====== Warning: .hi-file format has changed, so if you are
======		updating into an existing HEAD build, you'll
======		need to make clean and re-make


The details:  [documentation still to be done]

* Recursive loops are now broken with Foo.hs-boot (or Foo.lhs-boot),
  not Foo.hi-boot

* An hs-boot files is a proper source file.  It is compiled just like
  a regular Haskell source file:
	ghc Foo.hs		generates Foo.hi, Foo.o
	ghc Foo.hs-boot		generates Foo.hi-boot, Foo.o-boot

* hs-boot files are precisely a subset of Haskell. In particular:
	- they have the same import, export, and scoping rules
	- errors (such as kind errors) in hs-boot files are checked
  You do *not* need to mention the "original" name of something in
  an hs-boot file, any more than you do in any other Haskell module.

* The Foo.hi-boot file generated by compiling Foo.hs-boot is a machine-
  generated interface file, in precisely the same format as Foo.hi

* When compiling Foo.hs, its exports are checked for compatibility with
  Foo.hi-boot (previously generated by compiling Foo.hs-boot)

* The dependency analyser (ghc -M) knows about Foo.hs-boot files, and
  generates appropriate dependencies.  For regular source files it
  generates
	Foo.o : Foo.hs
	Foo.o : Baz.hi		-- Foo.hs imports Baz
	Foo.o : Bog.hi-boot	-- Foo.hs source-imports Bog

  For a hs-boot file it generates similar dependencies
	Bog.o-boot : Bog.hs-boot
	Bog.o-boot : Nib.hi	-- Bog.hs-boto imports Nib

* ghc -M is also enhanced to use the compilation manager dependency
  chasing, so that
	ghc -M Main
  will usually do the job.  No need to enumerate all the source files.

* The -c flag is no longer a "compiler mode". It simply means "omit the
  link step", and synonymous with -no-link.

Don't try to run finalizers at program exit.  This turned out to be
hard if not impossible to do in general, so now we don't attempt it at
all.

The Main.main wrapper, previously called runIO and now called
runMainIO, flushes stdout and stderr before exiting.  This should
catch most cases where programs rely on Handles being flushed at
program exit, but note that now if you simply drop a Handle in your
program, there's no guarantee it'll be flushed on exit.  If the
punters complain enough, I suppose we could implement a global
Handle table and flush them all at exit... I'd rather not do this if
possible, though.  Better to teach people to close their Handles
properly.