Thinning and renaming modules from packages on the command line.

Summary:
This patch set adds support for extra syntax on -package and related
arguments which allow you to thin and rename modules from a package.
For example, this argument:

    -package "base (Data.Bool as Bam, Data.List)"

adds two more modules into scope, Bam and Data.List, without adding
any of base's other modules to scope.

These flags are additive: so, for example, saying:

    -hide-all-packages -package base -package "base (Data.Bool as Bam)"

will provide both the normal bindings for modules in base, as well as
the module Bam.

There is also a new debug flag -ddump-mod-map which prints the state
of the module mapping database.  H = hidden, E = exposed (so for
example EH says the module in question is exported, but in a hidden
package.)

Module suggestions have been minorly overhauled to work better with reexports:
if you have -package "base (Data.Bool as Bam)" and mispell Bam, GHC
will suggest "Did you mean Bam (defined via package flags to be
base:Data.Bool)"; and generally you will get more accurate information.
Also, fix a bug where we suggest the -package flag when we really need
the -package-key flag.

NB: The renaming afforded here does *not* affect what wired in
symbols GHC generates.  (But it does affect implicit prelude!)

ToDo: add 'hiding' functionality, to make it easier to support the alternative
prelude use-case.

ToDo: Cabal support

Signed-off-by: Edward Z. Yang <ezyang@cs.stanford.edu>

Test Plan: new tests and validate

Reviewers: simonpj, simonmar, hvr, austin

Subscribers: simonmar, relrod, ezyang, carter

Differential Revision: https://phabricator.haskell.org/D113

GHC Trac Issues: #9375

2 files changed, 8 insertions, 11 deletions

diff --git a/ghc/InteractiveUI.hs b/ghc/InteractiveUI.hs
index f42d47a51d..386d4df17d 100644
--- a/ghc/InteractiveUI.hs
+++ b/ghc/InteractiveUI.hs
@@ -39,7 +39,7 @@ import HscTypes ( tyThingParent_maybe, handleFlagWarnings, getSafeMode, hsc_IC,
                   setInteractivePrintName )
 import Module
 import Name
-import Packages ( trusted, getPackageDetails, listVisibleModuleNames )
+import Packages ( trusted, getPackageDetails, listVisibleModuleNames, pprFlag )
 import PprTyThing
 import RdrName ( getGRE_NameQualifier_maybes )
 import SrcLoc
@@ -2333,15 +2333,7 @@ showPackages = do
   let pkg_flags = packageFlags dflags
   liftIO $ putStrLn $ showSDoc dflags $ vcat $
     text ("active package flags:"++if null pkg_flags then " none" else "")
-    : map showFlag pkg_flags
-  where showFlag (ExposePackage a) = text $ showArg a
-        showFlag (HidePackage     p) = text $ "  -hide-package " ++ p
-        showFlag (IgnorePackage   p) = text $ "  -ignore-package " ++ p
-        showFlag (TrustPackage    p) = text $ "  -trust " ++ p
-        showFlag (DistrustPackage p) = text $ "  -distrust " ++ p
-        showArg (PackageArg p) = "  -package " ++ p
-        showArg (PackageIdArg p) = "  -package-id " ++ p
-        showArg (PackageKeyArg p) = "  -package-key " ++ p
+    : map pprFlag pkg_flags
 
 showPaths :: GHCi ()
 showPaths = do
diff --git a/ghc/Main.hs b/ghc/Main.hs
index 2bb156c5b9..70dde39824 100644
--- a/ghc/Main.hs
+++ b/ghc/Main.hs
@@ -33,7 +33,7 @@ import InteractiveUI    ( interactiveUI, ghciWelcomeMsg, defaultGhciSettings )
 import Config
 import Constants
 import HscTypes
-import Packages         ( dumpPackages, simpleDumpPackages )
+import Packages         ( dumpPackages, simpleDumpPackages, pprModuleMap )
 import DriverPhases
 import BasicTypes       ( failed )
 import StaticFlags
@@ -217,6 +217,11 @@ main' postLoadMode dflags0 args flagWarnings = do
   when (verbosity dflags6 >= 3) $ do
         liftIO $ hPutStrLn stderr ("Hsc static flags: " ++ unwords staticFlags)
 
+
+  when (dopt Opt_D_dump_mod_map dflags6) . liftIO $
+    printInfoForUser (dflags6 { pprCols = 200 })
+                     (pkgQual dflags6) (pprModuleMap dflags6)
+
         ---------------- Final sanity checking -----------
   liftIO $ checkOptions postLoadMode dflags6 srcs objs