The Backpack patch.

Summary:
This patch implements Backpack for GHC.  It's a big patch but I've tried quite
hard to keep things, by-in-large, self-contained.

The user facing specification for Backpack can be found at:

    https://github.com/ezyang/ghc-proposals/blob/backpack/proposals/0000-backpack.rst

A guide to the implementation can be found at:

    https://github.com/ezyang/ghc-proposals/blob/backpack-impl/proposals/0000-backpack-impl.rst

Has a submodule update for Cabal, as well as a submodule update
for filepath to handle more strict checking of cabal-version.

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

Test Plan: validate

Reviewers: simonpj, austin, simonmar, bgamari, goldfire

Subscribers: thomie, mpickering

Differential Revision: https://phabricator.haskell.org/D1482

2 files changed, 19 insertions, 30 deletions

diff --git a/compiler/rename/RnEnv.hs b/compiler/rename/RnEnv.hs
index b1cb7fe064..d41e9ef48e 100644
--- a/compiler/rename/RnEnv.hs
+++ b/compiler/rename/RnEnv.hs
@@ -208,40 +208,16 @@ newTopSrcBinder (L loc rdr_name)
                 -- module name, we we get a confusing "M.T is not in scope" error later
 
         ; stage <- getStage
-        ; env <- getGblEnv
         ; if isBrackStage stage then
                 -- We are inside a TH bracket, so make an *Internal* name
                 -- See Note [Top-level Names in Template Haskell decl quotes] in RnNames
              do { uniq <- newUnique
                 ; return (mkInternalName uniq (rdrNameOcc rdr_name) loc) }
-          else case tcg_impl_rdr_env env of
-            Just gr ->
-                -- We're compiling --sig-of, so resolve with respect to this
-                -- module.
-                -- See Note [Signature parameters in TcGblEnv and DynFlags]
-             do { case lookupGlobalRdrEnv gr (rdrNameOcc rdr_name) of
-                    -- Be sure to override the loc so that we get accurate
-                    -- information later
-                    [GRE{ gre_name = n }] -> do
-                      -- NB: Just adding this line will not work:
-                      --    addUsedGRE True gre
-                      -- see Note [Signature lazy interface loading] for
-                      -- more details.
-                      return (setNameLoc n loc)
-                    _ -> do
-                      { -- NB: cannot use reportUnboundName rdr_name
-                        -- because it looks up in the wrong RdrEnv
-                        -- ToDo: more helpful error messages
-                      ; addErr (unknownNameErr (pprNonVarNameSpace
-                            (occNameSpace (rdrNameOcc rdr_name))) rdr_name)
-                      ; return (mkUnboundNameRdr rdr_name)
-                      }
-                }
-            Nothing ->
-                -- Normal case
+          else
              do { this_mod <- getModule
                 ; traceRn (text "newTopSrcBinder" <+> (ppr this_mod $$ ppr rdr_name $$ ppr loc))
-                ; newGlobalBinder this_mod (rdrNameOcc rdr_name) loc } }
+                ; newGlobalBinder this_mod (rdrNameOcc rdr_name) loc }
+        }
 
 {-
 *********************************************************
@@ -1216,6 +1192,14 @@ data HsSigCtxt
   | RoleAnnotCtxt NameSet    -- A role annotation, with the names of all types
                              -- in the group
 
+instance Outputable HsSigCtxt where
+    ppr (TopSigCtxt ns) = text "TopSigCtxt" <+> ppr ns
+    ppr (LocalBindCtxt ns) = text "LocalBindCtxt" <+> ppr ns
+    ppr (ClsDeclCtxt n) = text "ClsDeclCtxt" <+> ppr n
+    ppr (InstDeclCtxt ns) = text "InstDeclCtxt" <+> ppr ns
+    ppr (HsBootCtxt ns) = text "HsBootCtxt" <+> ppr ns
+    ppr (RoleAnnotCtxt ns) = text "RoleAnnotCtxt" <+> ppr ns
+
 lookupSigOccRn :: HsSigCtxt
                -> Sig RdrName
                -> Located RdrName -> RnM (Located Name)
@@ -1398,7 +1382,7 @@ lookupFixity is a bit strange.
 * Nested local fixity decls are put in the local fixity env, which we
   find with getFixtyEnv
 
-* Imported fixities are found in the HIT or PIT
+* Imported fixities are found in the PIT
 
 * Top-level fixity decls in this module may be for Names that are
     either  Global         (constructors, class operations)
diff --git a/compiler/rename/RnNames.hs b/compiler/rename/RnNames.hs
index 6b4942f41f..e1258a3d0d 100644
--- a/compiler/rename/RnNames.hs
+++ b/compiler/rename/RnNames.hs
@@ -12,6 +12,7 @@ module RnNames (
         gresFromAvails,
         calculateAvails,
         reportUnusedNames,
+        plusAvail,
         checkConName
     ) where
 
@@ -153,7 +154,10 @@ with yes we have gone with no for now.
 rnImports :: [LImportDecl RdrName]
           -> RnM ([LImportDecl Name], GlobalRdrEnv, ImportAvails, AnyHpcUsage)
 rnImports imports = do
-    this_mod <- getModule
+    tcg_env <- getGblEnv
+    -- NB: want an identity module here, because it's OK for a signature
+    -- module to import from its implementor
+    let this_mod = tcg_mod tcg_env
     let (source, ordinary) = partition is_source_import imports
         is_source_import d = ideclSource (unLoc d)
     stuff1 <- mapAndReportM (rnImportDecl this_mod) ordinary
@@ -811,7 +815,8 @@ filterImports iface decl_spec (Just (want_hiding, L l import_items))
         -- NB: the AvailTC can have fields as well as data constructors (Trac #12127)
         combine (name1, a1@(AvailTC p1 _ _), mp1)
                 (name2, a2@(AvailTC p2 _ _), mp2)
-          = ASSERT( name1 == name2 && isNothing mp1 && isNothing mp2 )
+          = ASSERT2( name1 == name2 && isNothing mp1 && isNothing mp2
+                   , ppr name1 <+> ppr name2 <+> ppr mp1 <+> ppr mp2 )
             if p1 == name1 then (name1, a1, Just p2)
                            else (name1, a2, Just p1)
         combine x y = pprPanic "filterImports/combine" (ppr x $$ ppr y)