Major clean-up of HscMain.

This patch entails a major restructuring of HscMain and a small bugfix
to MkIface (which required the restructuring in HscMain).

In MkIface:

  - mkIface* no longer outputs orphan warnings directly and also no
    longer quits GHC when -Werror is set.  Instead, errors are
    reported using the common IO (Messages, Maybe result) scheme.

In HscMain:

  - Get rid of the 'Comp' monad.  This monad was mostly GhcMonad + two
    reader arguments, a ModSummary for the currently compiled module
    and a possible old interface.  The latter actually lead to a small
    space-leak since only its hash was needed (to check whether the
    newly-generated interface file was the same as the original one).

    Functions originally of type 'Comp' now only take the arguments
    that they actually need.  This leads to slighly longer argument
    lists in some places, however, it is now much easier to see what
    is actually going on.

  - Get rid of 'myParseModule'.  Rename 'parseFile' to 'hscParse'.

  - Join 'deSugarModule' and 'hscDesugar' (keeping the latter).

  - Rename 'typecheck{Rename}Module{'}' to 'hscTypecheck{Rename}'.
    One variant keeps the renamed syntax, the other doesn't.

  - Parameterise 'HscStatus', so that 'InteractiveStatus' is just a
    different parameterisation of 'HscStatus'.

  - 'hscCompile{OneShot,Batch,Nothing,Interactive}' are now
    implemented using a (local) typeclass called 'HsCompiler'.  The
    idea is to make the common structure more obvious.  Using this
    typeclass we now have two functions 'genericHscCompile' (original
    'hscCompiler') and 'genericHscRecompile' (original 'genComp')
    describing the default pipeline.  The methods of the typeclass
    describe a sort of "hook" interface (in OO-terms this would be
    called the "template method" pattern).

    One problem with this approach is that we parameterise over the
    /result/ type which, in fact, is not actually different for
    "nothing" and "batch" mode.  To avoid functional dependencies or
    associated types, we use type tags to make them artificially
    different and parameterise the type class over the result type.
    A perhaps better approach might be to use records instead.
    
  - Drop some redundant 'HscEnv' arguments.  These were likely
    different from what 'getSession' would return because during
    compilation we temporarily set the module's DynFlags as well as a
    few other fields.  We now use the 'withTempSession' combinator to
    temporarily change the 'HscEnv' and automatically restore the
    original session after the enclosed action has returned (even in
    case of exceptions).

  - Rename 'hscCompile' to 'hscGenHardCode' (since that is what it
    does).

Calls in 'GHC' and 'DriverPipeline' accordingly needed small
adaptions.

1 files changed, 10 insertions, 12 deletions

diff --git a/compiler/iface/MkIface.lhs b/compiler/iface/MkIface.lhs
index 285f17197d..97449b712b 100644
--- a/compiler/iface/MkIface.lhs
+++ b/compiler/iface/MkIface.lhs
@@ -100,7 +100,6 @@ import Control.Monad
 import Data.List
 import Data.IORef
 import System.FilePath
-import System.Exit	( exitWith, ExitCode(..) )
 \end{code}
 
 
@@ -116,8 +115,9 @@ mkIface :: HscEnv
 	-> Maybe Fingerprint	-- The old fingerprint, if we have it
 	-> ModDetails		-- The trimmed, tidied interface
 	-> ModGuts		-- Usages, deprecations, etc
-	-> IO (ModIface, 	-- The new one
-	       Bool)		-- True <=> there was an old Iface, and the 
+	-> IO (Messages,
+               Maybe (ModIface, -- The new one
+	              Bool))	-- True <=> there was an old Iface, and the
                                 --          new one is identical, so no need
                                 --          to write it
 
@@ -134,7 +134,7 @@ mkIface hsc_env maybe_old_fingerprint mod_details
         = mkIface_ hsc_env maybe_old_fingerprint
                    this_mod is_boot used_names deps rdr_env 
                    fix_env warns hpc_info dir_imp_mods mod_details
-	
+
 -- | make an interface from the results of typechecking only.  Useful
 -- for non-optimising compilation, or where we aren't generating any
 -- object code at all ('HscNothing').
@@ -142,8 +142,7 @@ mkIfaceTc :: HscEnv
           -> Maybe Fingerprint	-- The old fingerprint, if we have it
           -> ModDetails		-- gotten from mkBootModDetails, probably
           -> TcGblEnv		-- Usages, deprecations, etc
-	  -> IO (ModIface,
-	         Bool)
+	  -> IO (Messages, Maybe (ModIface, Bool))
 mkIfaceTc hsc_env maybe_old_fingerprint mod_details
   tc_result@TcGblEnv{ tcg_mod = this_mod,
                       tcg_src = hsc_src,
@@ -214,7 +213,7 @@ mkIface_ :: HscEnv -> Maybe Fingerprint -> Module -> IsBootInterface
          -> NameEnv FixItem -> Warnings -> HpcInfo
          -> ImportedMods
          -> ModDetails
-         -> IO (ModIface, Bool)
+	 -> IO (Messages, Maybe (ModIface, Bool))
 mkIface_ hsc_env maybe_old_fingerprint 
          this_mod is_boot used_names deps rdr_env fix_env src_warns hpc_info
          dir_imp_mods
@@ -305,10 +304,9 @@ mkIface_ hsc_env maybe_old_fingerprint
 	      		    	     | r <- iface_rules
 	      		   	     , isNothing (ifRuleOrph r) ]
 
-	; when (not (isEmptyBag orph_warnings))
-	       (do { printErrorsAndWarnings dflags errs_and_warns -- XXX
-	       	   ; when (errorsFound dflags errs_and_warns) 
-		          (exitWith (ExitFailure 1)) })
+	; if errorsFound dflags errs_and_warns
+            then return ( errs_and_warns, Nothing )
+            else do {
 
 -- XXX	; when (dopt Opt_D_dump_hi_diffs dflags) (printDump pp_diffs)
    
@@ -322,7 +320,7 @@ mkIface_ hsc_env maybe_old_fingerprint
                 -- with the old GlobalRdrEnv (mi_globals).
         ; let final_iface = new_iface{ mi_globals = Just rdr_env }
 
-	; return (final_iface, no_change_at_all) }
+	; return (errs_and_warns, Just (final_iface, no_change_at_all)) }}
   where
      r1 `le_rule`     r2 = ifRuleName      r1    <=    ifRuleName      r2
      i1 `le_inst`     i2 = ifDFun          i1 `le_occ` ifDFun          i2