Revert "Unify hsig and hs-boot; add preliminary "hs-boot" merging."

Summary:
This reverts commit 06d46b1e4507e09eb2a7a04998a92610c8dc6277.

This also has a Haddock submodule update.

Test Plan: validate

Reviewers: simonpj, austin, bgamari

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D1475

16 files changed, 179 insertions, 317 deletions

diff --git a/compiler/deSugar/Desugar.hs b/compiler/deSugar/Desugar.hs
index 77834e0160..4235c5c3d1 100644
--- a/compiler/deSugar/Desugar.hs
+++ b/compiler/deSugar/Desugar.hs
@@ -296,7 +296,7 @@ deSugar hsc_env
               hpcInfo    = emptyHpcInfo other_hpc_info
 
         ; (binds_cvr, ds_hpc_info, modBreaks)
-                         <- if not (isHsBoot hsc_src)
+                         <- if not (isHsBootOrSig hsc_src)
                               then addTicksToBinds dflags mod mod_loc export_set
                                           (typeEnvTyCons type_env) binds
                               else return (binds, hpcInfo, emptyModBreaks)
diff --git a/compiler/iface/LoadIface.hs b/compiler/iface/LoadIface.hs
index d2e16c67cb..48acd8dd28 100644
--- a/compiler/iface/LoadIface.hs
+++ b/compiler/iface/LoadIface.hs
@@ -897,7 +897,7 @@ pprModIface iface
         ]
   where
     pp_hsc_src HsBootFile = ptext (sLit "[boot]")
-    pp_hsc_src HsBootMerge = ptext (sLit "[merge]")
+    pp_hsc_src HsigFile = ptext (sLit "[hsig]")
     pp_hsc_src HsSrcFile = Outputable.empty
 
 {-
diff --git a/compiler/iface/MkIface.hs b/compiler/iface/MkIface.hs
index a8d0344e77..98b8830e01 100644
--- a/compiler/iface/MkIface.hs
+++ b/compiler/iface/MkIface.hs
@@ -13,7 +13,6 @@ module MkIface (
                         -- including computing version information
 
         mkIfaceTc,
-        mkIfaceDirect,
 
         writeIfaceFile, -- Write the interface file
 
@@ -154,35 +153,6 @@ mkIface hsc_env maybe_old_fingerprint mod_details
                    warns hpc_info self_trust
                    safe_mode usages mod_details
 
--- | Make an interface from a manually constructed 'ModIface'.  We use
--- this when we are merging 'ModIface's.  We assume that the 'ModIface'
--- has accurate entries but not accurate fingerprint information (so,
--- like @intermediate_iface@ in 'mkIface_'.)
-mkIfaceDirect :: HscEnv
-              -> Maybe Fingerprint
-              -> ModIface
-              -> IO (ModIface, Bool)
-mkIfaceDirect hsc_env maybe_old_fingerprint iface0 = do
-    -- Sort some things to make sure we're deterministic
-    let intermediate_iface = iface0 {
-            mi_exports   = mkIfaceExports (mi_exports iface0),
-            mi_insts     = sortBy cmp_inst     (mi_insts iface0),
-            mi_fam_insts = sortBy cmp_fam_inst (mi_fam_insts iface0),
-            mi_rules     = sortBy cmp_rule     (mi_rules iface0)
-        }
-        dflags = hsc_dflags hsc_env
-    (final_iface, no_change_at_all)
-          <- {-# SCC "versioninfo" #-}
-                   addFingerprints hsc_env maybe_old_fingerprint
-                                   intermediate_iface
-                                   (map snd (mi_decls iface0))
-
-    -- Debug printing
-    dumpIfSet_dyn dflags Opt_D_dump_hi "FINAL INTERFACE"
-                  (pprModIface final_iface)
-
-    return (final_iface, no_change_at_all)
-
 -- | 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').
@@ -320,6 +290,11 @@ mkIface_ hsc_env maybe_old_fingerprint
 
     return (final_iface, no_change_at_all)
   where
+     cmp_rule     = comparing ifRuleName
+     -- Compare these lexicographically by OccName, *not* by unique,
+     -- because the latter is not stable across compilations:
+     cmp_inst     = comparing (nameOccName . ifDFun)
+     cmp_fam_inst = comparing (nameOccName . ifFamInstTcName)
 
      dflags = hsc_dflags hsc_env
 
@@ -337,6 +312,8 @@ mkIface_ hsc_env maybe_old_fingerprint
      deliberatelyOmitted :: String -> a
      deliberatelyOmitted x = panic ("Deliberately omitted: " ++ x)
 
+     ifFamInstTcName = ifFamInstFam
+
      flattenVectInfo (VectInfo { vectInfoVar            = vVar
                                , vectInfoTyCon          = vTyCon
                                , vectInfoParallelVars     = vParallelVars
@@ -350,16 +327,6 @@ mkIface_ hsc_env maybe_old_fingerprint
        , ifaceVectInfoParallelTyCons = nameSetElems vParallelTyCons
        }
 
-cmp_rule :: IfaceRule -> IfaceRule -> Ordering
-cmp_rule     = comparing ifRuleName
--- Compare these lexicographically by OccName, *not* by unique,
--- because the latter is not stable across compilations:
-cmp_inst :: IfaceClsInst -> IfaceClsInst -> Ordering
-cmp_inst     = comparing (nameOccName . ifDFun)
-
-cmp_fam_inst :: IfaceFamInst -> IfaceFamInst -> Ordering
-cmp_fam_inst = comparing (nameOccName . ifFamInstFam)
-
 -----------------------------
 writeIfaceFile :: DynFlags -> FilePath -> ModIface -> IO ()
 writeIfaceFile dflags hi_file_path new_iface
diff --git a/compiler/main/DriverMkDepend.hs b/compiler/main/DriverMkDepend.hs
index 1541d95c62..611d3964c5 100644
--- a/compiler/main/DriverMkDepend.hs
+++ b/compiler/main/DriverMkDepend.hs
@@ -197,9 +197,9 @@ processDeps dflags _ _ _ _ (CyclicSCC nodes)
     throwGhcExceptionIO (ProgramError (showSDoc dflags $ GHC.cyclicModuleErr nodes))
 
 processDeps dflags hsc_env excl_mods root hdl (AcyclicSCC node)
-  | Just src_file <- msHsFilePath node
   = do  { let extra_suffixes = depSuffixes dflags
               include_pkg_deps = depIncludePkgDeps dflags
+              src_file  = msHsFilePath node
               obj_file  = msObjFilePath node
               obj_files = insertSuffixes obj_file extra_suffixes
 
@@ -233,10 +233,6 @@ processDeps dflags hsc_env excl_mods root hdl (AcyclicSCC node)
         ; do_imps False (ms_imps node)
         }
 
-  | otherwise
-  = ASSERT( ms_hsc_src node == HsBootMerge )
-    panic "HsBootMerge not supported in DriverMkDepend yet"
-
 
 findDependency  :: HscEnv
                 -> SrcSpan
diff --git a/compiler/main/DriverPhases.hs b/compiler/main/DriverPhases.hs
index f079212112..ff6f8b8ab1 100644
--- a/compiler/main/DriverPhases.hs
+++ b/compiler/main/DriverPhases.hs
@@ -10,7 +10,7 @@
 -----------------------------------------------------------------------------
 
 module DriverPhases (
-   HscSource(..), isHsBoot, hscSourceString,
+   HscSource(..), isHsBootOrSig, hscSourceString,
    Phase(..),
    happensBefore, eqPhase, anyHsc, isStopLn,
    startPhase,
@@ -22,10 +22,12 @@ module DriverPhases (
    isCishSuffix,
    isDynLibSuffix,
    isHaskellUserSrcSuffix,
+   isHaskellSigSuffix,
    isSourceSuffix,
 
    isHaskellishFilename,
    isHaskellSrcFilename,
+   isHaskellSigFilename,
    isObjectFilename,
    isCishFilename,
    isDynLibFilename,
@@ -58,51 +60,63 @@ import Binary
 
 -- Note [HscSource types]
 -- ~~~~~~~~~~~~~~~~~~~~~~
--- There are two types of source file for user-written Haskell code:
+-- There are three types of source file for Haskell code:
 --
 --      * HsSrcFile is an ordinary hs file which contains code,
 --
---      * HsBootFile is an hs-boot file.  Within a unit, it can
---        be used to break recursive module imports, in which case there's an
---        HsSrcFile associated with it.  However, externally, it can
---        also be used to specify the *requirements* of a package,
---        in which case there is an HsBootMerge associated with it.
+--      * HsBootFile is an hs-boot file, which is used to break
+--        recursive module imports (there will always be an
+--        HsSrcFile associated with it), and
 --
--- An HsBootMerge is a "fake" source file, which is constructed
--- by collecting up non-recursive HsBootFiles into a single interface.
--- HsBootMerges get an hi and o file, and are treated as "non-boot"
--- sources.
+--      * HsigFile is an hsig file, which contains only type
+--        signatures and is used to specify signatures for
+--        modules.
+--
+-- Syntactically, hs-boot files and hsig files are quite similar: they
+-- only include type signatures and must be associated with an
+-- actual HsSrcFile.  isHsBootOrSig allows us to abstract over code
+-- which is indifferent to which.  However, there are some important
+-- differences, mostly owing to the fact that hsigs are proper
+-- modules (you `import Sig` directly) whereas HsBootFiles are
+-- temporary placeholders (you `import {-# SOURCE #-} Mod).
+-- When we finish compiling the true implementation of an hs-boot,
+-- we replace the HomeModInfo with the real HsSrcFile.  An HsigFile, on the
+-- other hand, is never replaced (in particular, we *cannot* use the
+-- HomeModInfo of the original HsSrcFile backing the signature, since it
+-- will export too many symbols.)
+--
+-- Additionally, while HsSrcFile is the only Haskell file
+-- which has *code*, we do generate .o files for HsigFile, because
+-- this is how the recompilation checker figures out if a file
+-- needs to be recompiled.  These are fake object files which
+-- should NOT be linked against.
 
 data HscSource
-   = HsSrcFile | HsBootFile | HsBootMerge
+   = HsSrcFile | HsBootFile | HsigFile
      deriving( Eq, Ord, Show )
         -- Ord needed for the finite maps we build in CompManager
 
-instance Outputable HscSource where
-    ppr HsSrcFile = text "HsSrcFile"
-    ppr HsBootFile = text "HsBootFile"
-    ppr HsBootMerge = text "HsBootMerge"
-
 instance Binary HscSource where
     put_ bh HsSrcFile = putByte bh 0
     put_ bh HsBootFile = putByte bh 1
-    put_ bh HsBootMerge = putByte bh 2
+    put_ bh HsigFile = putByte bh 2
     get bh = do
         h <- getByte bh
         case h of
             0 -> return HsSrcFile
             1 -> return HsBootFile
-            _ -> return HsBootMerge
+            _ -> return HsigFile
 
 hscSourceString :: HscSource -> String
 hscSourceString HsSrcFile   = ""
 hscSourceString HsBootFile  = "[boot]"
-hscSourceString HsBootMerge = "[merge]"
+hscSourceString HsigFile    = "[sig]"
 
-isHsBoot :: HscSource -> Bool
-isHsBoot HsBootFile  = True
-isHsBoot HsSrcFile   = False
-isHsBoot HsBootMerge = False
+-- See Note [isHsBootOrSig]
+isHsBootOrSig :: HscSource -> Bool
+isHsBootOrSig HsBootFile = True
+isHsBootOrSig HsigFile   = True
+isHsBootOrSig _          = False
 
 data Phase
         = Unlit HscSource
@@ -218,8 +232,10 @@ nextPhase dflags p
 startPhase :: String -> Phase
 startPhase "lhs"      = Unlit HsSrcFile
 startPhase "lhs-boot" = Unlit HsBootFile
+startPhase "lhsig"    = Unlit HsigFile
 startPhase "hs"       = Cpp   HsSrcFile
 startPhase "hs-boot"  = Cpp   HsBootFile
+startPhase "hsig"     = Cpp   HsigFile
 startPhase "hscpp"    = HsPp  HsSrcFile
 startPhase "hspp"     = Hsc   HsSrcFile
 startPhase "hc"       = HCc
@@ -248,9 +264,7 @@ startPhase _          = StopLn     -- all unknown file types
 phaseInputExt :: Phase -> String
 phaseInputExt (Unlit HsSrcFile)   = "lhs"
 phaseInputExt (Unlit HsBootFile)  = "lhs-boot"
-phaseInputExt (Unlit HsBootMerge) = panic "phaseInputExt: Unlit HsBootMerge"
-        -- You can't Unlit an HsBootMerge, because there's no source
-        -- file to Unlit!
+phaseInputExt (Unlit HsigFile)    = "lhsig"
 phaseInputExt (Cpp   _)           = "lpp"       -- intermediate only
 phaseInputExt (HsPp  _)           = "hscpp"     -- intermediate only
 phaseInputExt (Hsc   _)           = "hspp"      -- intermediate only
@@ -275,7 +289,7 @@ phaseInputExt MergeStub           = "o"
 phaseInputExt StopLn              = "o"
 
 haskellish_src_suffixes, haskellish_suffixes, cish_suffixes,
-    haskellish_user_src_suffixes
+    haskellish_user_src_suffixes, haskellish_sig_suffixes
  :: [String]
 -- When a file with an extension in the haskellish_src_suffixes group is
 -- loaded in --make mode, its imports will be loaded too.
@@ -286,7 +300,9 @@ haskellish_suffixes          = haskellish_src_suffixes ++
 cish_suffixes                = [ "c", "cpp", "C", "cc", "cxx", "s", "S", "ll", "bc", "lm_s", "m", "M", "mm" ]
 
 -- Will not be deleted as temp files:
-haskellish_user_src_suffixes = [ "hs", "lhs", "hs-boot", "lhs-boot" ]
+haskellish_user_src_suffixes =
+  haskellish_sig_suffixes ++ [ "hs", "lhs", "hs-boot", "lhs-boot" ]
+haskellish_sig_suffixes      = [ "hsig", "lhsig" ]
 
 objish_suffixes :: Platform -> [String]
 -- Use the appropriate suffix for the system on which
@@ -302,9 +318,10 @@ dynlib_suffixes platform = case platformOS platform of
   _         -> ["so"]
 
 isHaskellishSuffix, isHaskellSrcSuffix, isCishSuffix,
-    isHaskellUserSrcSuffix
+    isHaskellUserSrcSuffix, isHaskellSigSuffix
  :: String -> Bool
 isHaskellishSuffix     s = s `elem` haskellish_suffixes
+isHaskellSigSuffix     s = s `elem` haskellish_sig_suffixes
 isHaskellSrcSuffix     s = s `elem` haskellish_src_suffixes
 isCishSuffix           s = s `elem` cish_suffixes
 isHaskellUserSrcSuffix s = s `elem` haskellish_user_src_suffixes
@@ -317,7 +334,7 @@ isSourceSuffix :: String -> Bool
 isSourceSuffix suff  = isHaskellishSuffix suff || isCishSuffix suff
 
 isHaskellishFilename, isHaskellSrcFilename, isCishFilename,
-    isHaskellUserSrcFilename, isSourceFilename
+    isHaskellUserSrcFilename, isSourceFilename, isHaskellSigFilename
  :: FilePath -> Bool
 -- takeExtension return .foo, so we drop 1 to get rid of the .
 isHaskellishFilename     f = isHaskellishSuffix     (drop 1 $ takeExtension f)
@@ -325,6 +342,7 @@ isHaskellSrcFilename     f = isHaskellSrcSuffix     (drop 1 $ takeExtension f)
 isCishFilename           f = isCishSuffix           (drop 1 $ takeExtension f)
 isHaskellUserSrcFilename f = isHaskellUserSrcSuffix (drop 1 $ takeExtension f)
 isSourceFilename         f = isSourceSuffix         (drop 1 $ takeExtension f)
+isHaskellSigFilename     f = isHaskellSigSuffix     (drop 1 $ takeExtension f)
 
 isObjectFilename, isDynLibFilename :: Platform -> FilePath -> Bool
 isObjectFilename platform f = isObjectSuffix platform (drop 1 $ takeExtension f)
diff --git a/compiler/main/DriverPipeline.hs b/compiler/main/DriverPipeline.hs
index a1d36a6b54..2e6bac81b8 100644
--- a/compiler/main/DriverPipeline.hs
+++ b/compiler/main/DriverPipeline.hs
@@ -13,7 +13,7 @@
 module DriverPipeline (
         -- Run a series of compilation steps in a pipeline, for a
         -- collection of source files.
-   oneShot, compileFile, mergeRequirement,
+   oneShot, compileFile,
 
         -- Interfaces for the batch-mode driver
    linkBinary,
@@ -23,9 +23,6 @@ module DriverPipeline (
    compileOne, compileOne',
    link,
 
-        -- Misc utility
-   makeMergeRequirementSummary,
-
         -- Exports for hooks to override runPhase and link
    PhasePlus(..), CompPipeline(..), PipeEnv(..), PipeState(..),
    phaseOutputFilename, getPipeState, getPipeEnv,
@@ -73,7 +70,6 @@ import System.IO
 import Control.Monad
 import Data.List        ( isSuffixOf )
 import Data.Maybe
-import Data.Time
 import Data.Version
 
 -- ---------------------------------------------------------------------------
@@ -133,6 +129,22 @@ compileOne' m_tc_result mHscMessage
             hsc_env0 summary mod_index nmods mb_old_iface maybe_old_linkable
             source_modified0
  = do
+   let dflags0     = ms_hspp_opts summary
+       this_mod    = ms_mod summary
+       src_flavour = ms_hsc_src summary
+       location    = ms_location summary
+       input_fnpp  = ms_hspp_file summary
+       mod_graph   = hsc_mod_graph hsc_env0
+       needsTH     = any (xopt Opt_TemplateHaskell . ms_hspp_opts) mod_graph
+       needsQQ     = any (xopt Opt_QuasiQuotes     . ms_hspp_opts) mod_graph
+       needsLinker = needsTH || needsQQ
+       isDynWay    = any (== WayDyn) (ways dflags0)
+       isProfWay   = any (== WayProf) (ways dflags0)
+   -- #8180 - when using TemplateHaskell, switch on -dynamic-too so
+   -- the linker can correctly load the object files.
+   let dflags1 = if needsLinker && dynamicGhc && not isDynWay && not isProfWay
+                  then gopt_set dflags0 Opt_BuildDynamicToo
+                  else dflags0
 
    debugTraceMsg dflags1 2 (text "compile: input file" <+> text input_fnpp)
 
@@ -146,7 +158,7 @@ compileOne' m_tc_result mHscMessage
             ASSERT( isJust maybe_old_linkable || isNoLink (ghcLink dflags) )
             return hmi0 { hm_linkable = maybe_old_linkable }
         (HscNotGeneratingCode, HscNothing) ->
-            let mb_linkable = if isHsBoot src_flavour
+            let mb_linkable = if isHsBootOrSig src_flavour
                                 then Nothing
                                 -- TODO: Questionable.
                                 else Just (LM (ms_hs_date summary) this_mod [])
@@ -158,10 +170,10 @@ compileOne' m_tc_result mHscMessage
         (HscUpdateBoot, _) -> do
             touchObjectFile dflags object_filename
             return hmi0
-        (HscUpdateBootMerge, HscInterpreted) ->
+        (HscUpdateSig, HscInterpreted) ->
             let linkable = LM (ms_hs_date summary) this_mod []
             in return hmi0 { hm_linkable = Just linkable }
-        (HscUpdateBootMerge, _) -> do
+        (HscUpdateSig, _) -> do
             output_fn <- getOutputFilename next_phase
                             Temporary basename dflags next_phase (Just location)
 
@@ -171,7 +183,7 @@ compileOne' m_tc_result mHscMessage
             _ <- runPipeline StopLn hsc_env
                               (output_fn,
                                Just (HscOut src_flavour
-                                            mod_name HscUpdateBootMerge))
+                                            mod_name HscUpdateSig))
                               (Just basename)
                               Persistent
                               (Just location)
@@ -218,7 +230,6 @@ compileOne' m_tc_result mHscMessage
  where dflags0     = ms_hspp_opts summary
        location    = ms_location summary
        input_fn    = expectJust "compile:hs" (ml_hs_file location)
-       input_fnpp  = ms_hspp_file summary
        mod_graph   = hsc_mod_graph hsc_env0
        needsTH     = any (xopt Opt_TemplateHaskell . ms_hspp_opts) mod_graph
        needsQQ     = any (xopt Opt_QuasiQuotes     . ms_hspp_opts) mod_graph
@@ -228,7 +239,6 @@ compileOne' m_tc_result mHscMessage
 
 
        src_flavour = ms_hsc_src summary
-       this_mod = ms_mod summary
        mod_name = ms_mod_name summary
        next_phase = hscPostBackendPhase dflags src_flavour hsc_lang
        object_filename = ml_obj_file location
@@ -489,50 +499,6 @@ oneShot hsc_env stop_phase srcs = do
   o_files <- mapM (compileFile hsc_env stop_phase) srcs
   doLink (hsc_dflags hsc_env) stop_phase o_files
 
--- | Constructs a 'ModSummary' for a "signature merge" node.
--- This is a simplified construction function which only checks
--- for a local hs-boot file.
-makeMergeRequirementSummary :: HscEnv -> Bool -> ModuleName -> IO ModSummary
-makeMergeRequirementSummary hsc_env obj_allowed mod_name = do
-    let dflags = hsc_dflags hsc_env
-    location <- liftIO $ mkHomeModLocation2 dflags mod_name
-                         (moduleNameSlashes mod_name) (hiSuf dflags)
-    obj_timestamp <-
-         if isObjectTarget (hscTarget dflags) || obj_allowed -- bug #1205
-             then liftIO $ modificationTimeIfExists (ml_obj_file location)
-             else return Nothing
-    r <- findHomeModule hsc_env mod_name
-    let has_local_boot = case r of
-                            Found _ _ -> True
-                            _ -> False
-    src_timestamp <- case obj_timestamp of
-                        Just date -> return date
-                        Nothing -> getCurrentTime -- something fake
-    return ModSummary {
-            ms_mod = mkModule (thisPackage dflags) mod_name,
-            ms_hsc_src = HsBootMerge,
-            ms_location = location,
-            ms_hs_date = src_timestamp,
-            ms_obj_date = obj_timestamp,
-            ms_iface_date = Nothing,
-            -- TODO: fill this in with all the imports eventually
-            ms_srcimps = [],
-            ms_textual_imps = [],
-            ms_merge_imps = (has_local_boot, []),
-            ms_hspp_file = "FAKE",
-            ms_hspp_opts = dflags,
-            ms_hspp_buf = Nothing
-            }
-
--- | Top-level entry point for @ghc -merge-requirement ModName@.
-mergeRequirement :: HscEnv -> ModuleName -> IO ()
-mergeRequirement hsc_env mod_name = do
-    mod_summary <- makeMergeRequirementSummary hsc_env True mod_name
-    -- Based off of GhcMake handling
-    _ <- liftIO $ compileOne' Nothing Nothing hsc_env mod_summary 1 1 Nothing
-                              Nothing SourceUnmodified
-    return ()
-
 compileFile :: HscEnv -> Phase -> (FilePath, Maybe Phase) -> IO FilePath
 compileFile hsc_env stop_phase (src, mb_phase) = do
    exists <- doesFileExist src
@@ -1014,8 +980,7 @@ runPhase (RealPhase (Hsc src_flavour)) input_fn dflags0
                                         ms_obj_date  = Nothing,
                                         ms_iface_date   = Nothing,
                                         ms_textual_imps = imps,
-                                        ms_srcimps      = src_imps,
-                                        ms_merge_imps = (False, []) }
+                                        ms_srcimps      = src_imps }
 
   -- run the compiler!
         let msg hsc_env _ what _ = oneShotMsg hsc_env what
@@ -1048,7 +1013,7 @@ runPhase (HscOut src_flavour mod_name result) _ dflags = do
                    -- stamp file for the benefit of Make
                    liftIO $ touchObjectFile dflags o_file
                    return (RealPhase StopLn, o_file)
-            HscUpdateBootMerge ->
+            HscUpdateSig ->
                 do -- We need to create a REAL but empty .o file
                    -- because we are going to attempt to put it in a library
                    PipeState{hsc_env=hsc_env'} <- getPipeState
@@ -2211,7 +2176,7 @@ writeInterfaceOnlyMode dflags =
 -- | What phase to run after one of the backend code generators has run
 hscPostBackendPhase :: DynFlags -> HscSource -> HscTarget -> Phase
 hscPostBackendPhase _ HsBootFile _    =  StopLn
-hscPostBackendPhase _ HsBootMerge _    =  StopLn
+hscPostBackendPhase _ HsigFile _      =  StopLn
 hscPostBackendPhase dflags _ hsc_lang =
   case hsc_lang of
         HscC -> HCc
diff --git a/compiler/main/Finder.hs b/compiler/main/Finder.hs
index 1ccf33f668..c6bbd7583f 100644
--- a/compiler/main/Finder.hs
+++ b/compiler/main/Finder.hs
@@ -228,11 +228,8 @@ findHomeModule hsc_env mod_name =
      source_exts =
       [ ("hs",   mkHomeModLocationSearched dflags mod_name "hs")
       , ("lhs",  mkHomeModLocationSearched dflags mod_name "lhs")
-      -- TODO: This is a giant hack!  If we find an hs-boot file,
-      -- pretend that there's an hs file here too, even if there isn't.
-      -- GhcMake will know what to do next.
-      , ("hs-boot",   mkHomeModLocationSearched dflags mod_name "hs")
-      , ("lhs-boot",  mkHomeModLocationSearched dflags mod_name "lhs")
+      , ("hsig",  mkHomeModLocationSearched dflags mod_name "hsig")
+      , ("lhsig",  mkHomeModLocationSearched dflags mod_name "lhsig")
       ]
 
      hi_exts = [ (hisuf,                mkHiOnlyModLocation dflags hisuf)
@@ -253,6 +250,7 @@ findHomeModule hsc_env mod_name =
         then return (Found (error "GHC.Prim ModLocation") mod)
         else searchPathExts home_path mod exts
 
+
 -- | Search for a module in external packages only.
 findPackageModule :: HscEnv -> Module -> IO FindResult
 findPackageModule hsc_env mod = do
diff --git a/compiler/main/GHC.hs b/compiler/main/GHC.hs
index f64796069f..fa1c2f0beb 100644
--- a/compiler/main/GHC.hs
+++ b/compiler/main/GHC.hs
@@ -988,7 +988,7 @@ compileCore simplify fn = do
    _ <- load LoadAllTargets
    -- Then find dependencies
    modGraph <- depanal [] True
-   case find ((== Just fn) . msHsFilePath) modGraph of
+   case find ((== fn) . msHsFilePath) modGraph of
      Just modSummary -> do
        -- Now we have the module name;
        -- parse, typecheck and desugar the module
diff --git a/compiler/main/GhcMake.hs b/compiler/main/GhcMake.hs
index 65df44b83d..06cd082d13 100644
--- a/compiler/main/GhcMake.hs
+++ b/compiler/main/GhcMake.hs
@@ -1424,7 +1424,7 @@ reachableBackwards mod summaries
   = [ ms | (ms,_,_) <- reachableG (transposeG graph) root ]
   where -- the rest just sets up the graph:
         (graph, lookup_node) = moduleGraphNodes False summaries
-        root  = expectJust "reachableBackwards" (lookup_node IsBoot mod)
+        root  = expectJust "reachableBackwards" (lookup_node HsBootFile mod)
 
 -- ---------------------------------------------------------------------------
 --
@@ -1463,8 +1463,7 @@ topSortModuleGraph drop_hs_boot_nodes summaries mb_root_mod
             -- the specified module.  We do this by building a graph with
             -- the full set of nodes, and determining the reachable set from
             -- the specified node.
-            let root | Just node <- lookup_node NotBoot root_mod
-                     , graph `hasVertexG` node = node
+            let root | Just node <- lookup_node HsSrcFile root_mod, graph `hasVertexG` node = node
                      | otherwise = throwGhcException (ProgramError "module does not exist")
             in graphFromEdgedVertices (seq root (reachableG graph root))
 
@@ -1477,48 +1476,36 @@ summaryNodeSummary :: SummaryNode -> ModSummary
 summaryNodeSummary (s, _, _) = s
 
 moduleGraphNodes :: Bool -> [ModSummary]
-  -> (Graph SummaryNode, IsBoot -> ModuleName -> Maybe SummaryNode)
+  -> (Graph SummaryNode, HscSource -> ModuleName -> Maybe SummaryNode)
 moduleGraphNodes drop_hs_boot_nodes summaries = (graphFromEdgedVertices nodes, lookup_node)
   where
     numbered_summaries = zip summaries [1..]
 
-    lookup_node :: IsBoot -> ModuleName -> Maybe SummaryNode
-    lookup_node is_boot mod = Map.lookup (mod, is_boot) node_map
+    lookup_node :: HscSource -> ModuleName -> Maybe SummaryNode
+    lookup_node hs_src mod = Map.lookup (mod, hscSourceToIsBoot hs_src) node_map
 
-    lookup_key :: IsBoot -> ModuleName -> Maybe Int
-    lookup_key is_boot mod = fmap summaryNodeKey (lookup_node is_boot mod)
+    lookup_key :: HscSource -> ModuleName -> Maybe Int
+    lookup_key hs_src mod = fmap summaryNodeKey (lookup_node hs_src mod)
 
     node_map :: NodeMap SummaryNode
     node_map = Map.fromList [ ((moduleName (ms_mod s),
                                 hscSourceToIsBoot (ms_hsc_src s)), node)
                             | node@(s, _, _) <- nodes ]
 
-    hasImplSet :: Set.Set ModuleName
-    hasImplSet = Set.fromList [ ms_mod_name s
-                              | s <- summaries, ms_hsc_src s == HsSrcFile ]
-
-    hasImpl :: ModuleName -> Bool
-    hasImpl modname = modname `Set.member` hasImplSet
-
     -- We use integers as the keys for the SCC algorithm
     nodes :: [SummaryNode]
     nodes = [ (s, key, out_keys)
             | (s, key) <- numbered_summaries
              -- Drop the hi-boot ones if told to do so
-            , not (isBootSummary s && hasImpl (ms_mod_name s)
-                                   && drop_hs_boot_nodes)
-            , let out_keys
-                    = out_edge_keys IsBoot  (map unLoc (ms_home_srcimps s)) ++
-                      out_edge_keys NotBoot (map unLoc (ms_home_imps s)) ++
-                      (if fst (ms_merge_imps s)
-                        then out_edge_keys IsBoot [moduleName (ms_mod s)]
-                        else []) ++
-                      (-- see [boot-edges] below
-                       if drop_hs_boot_nodes || ms_hsc_src s /= HsSrcFile
-                       then []
-                       else case lookup_key IsBoot (ms_mod_name s) of
-                             Nothing -> []
-                             Just k  -> [k]) ]
+            , not (isBootSummary s && drop_hs_boot_nodes)
+            , let out_keys = out_edge_keys hs_boot_key (map unLoc (ms_home_srcimps s)) ++
+                             out_edge_keys HsSrcFile   (map unLoc (ms_home_imps s)) ++
+                             (-- see [boot-edges] below
+                              if drop_hs_boot_nodes || ms_hsc_src s == HsBootFile
+                              then []
+                              else case lookup_key HsBootFile (ms_mod_name s) of
+                                    Nothing -> []
+                                    Just k  -> [k]) ]
 
     -- [boot-edges] if this is a .hs and there is an equivalent
     -- .hs-boot, add a link from the former to the latter.  This
@@ -1528,13 +1515,12 @@ moduleGraphNodes drop_hs_boot_nodes summaries = (graphFromEdgedVertices nodes, l
     -- the .hs, and so the HomePackageTable will always have the
     -- most up to date information.
 
-    out_edge_keys :: IsBoot -> [ModuleName] -> [Int]
-    out_edge_keys hi_boot ms = mapMaybe (lookup_out_edge_key hi_boot) ms
+    -- Drop hs-boot nodes by using HsSrcFile as the key
+    hs_boot_key | drop_hs_boot_nodes = HsSrcFile
+                | otherwise          = HsBootFile
 
-    lookup_out_edge_key :: IsBoot -> ModuleName -> Maybe Int
-    lookup_out_edge_key hi_boot m
-        | hasImpl m, drop_hs_boot_nodes = lookup_key NotBoot m
-        | otherwise                     = lookup_key hi_boot m
+    out_edge_keys :: HscSource -> [ModuleName] -> [Int]
+    out_edge_keys hi_boot ms = mapMaybe (lookup_key hi_boot) ms
         -- If we want keep_hi_boot_nodes, then we do lookup_key with
         -- IsBoot; else NotBoot
 
@@ -1623,7 +1609,7 @@ downsweep hsc_env old_summaries excl_mods allow_dup_roots
         -- dependency on what-ever the signature's implementation is.
         -- (But not when we're type checking!)
         calcDeps summ
-          | HsBootFile <- ms_hsc_src summ
+          | HsigFile <- ms_hsc_src summ
           , Just m <- getSigOf (hsc_dflags hsc_env) (moduleName (ms_mod summ))
           , moduleUnitId m == thisPackage (hsc_dflags hsc_env)
                       = (noLoc (moduleName m), NotBoot) : msDeps summ
@@ -1707,16 +1693,10 @@ mkRootMap summaries = Map.insertListWith (flip (++))
 -- modules always contains B.hs if it contains B.hs-boot.
 -- Remember, this pass isn't doing the topological sort.  It's
 -- just gathering the list of all relevant ModSummaries
---
--- NB: for signatures, (m,NotBoot) is "special"; the Haskell file
--- may not exist; we just synthesize it ourselves.
 msDeps :: ModSummary -> [(Located ModuleName, IsBoot)]
 msDeps s =
     concat [ [(m,IsBoot), (m,NotBoot)] | m <- ms_home_srcimps s ]
         ++ [ (m,NotBoot) | m <- ms_home_imps s ]
-        ++ if fst (ms_merge_imps s)
-            then [ (noLoc (moduleName (ms_mod s)), IsBoot) ]
-            else []
 
 home_imps :: [(Maybe FastString, Located ModuleName)] -> [Located ModuleName]
 home_imps imps = [ lmodname |  (mb_pkg, lmodname) <- imps,
@@ -1798,6 +1778,8 @@ summariseFile hsc_env old_summaries file mb_phase obj_allowed maybe_buf
     new_summary src_timestamp = do
         let dflags = hsc_dflags hsc_env
 
+        let hsc_src = if isHaskellSigFilename file then HsigFile else HsSrcFile
+
         (dflags', hspp_fn, buf)
             <- preprocessFile hsc_env file mb_phase maybe_buf
 
@@ -1820,16 +1802,12 @@ summariseFile hsc_env old_summaries file mb_phase obj_allowed maybe_buf
 
         hi_timestamp <- maybeGetIfaceDate dflags location
 
-        return (ModSummary { ms_mod = mod,
-                             ms_hsc_src = if "boot" `isSuffixOf` file
-                                            then HsBootFile
-                                            else HsSrcFile,
+        return (ModSummary { ms_mod = mod, ms_hsc_src = hsc_src,
                              ms_location = location,
                              ms_hspp_file = hspp_fn,
                              ms_hspp_opts = dflags',
                              ms_hspp_buf  = Just buf,
                              ms_srcimps = srcimps, ms_textual_imps = the_imps,
-                             ms_merge_imps = (False, []),
                              ms_hs_date = src_timestamp,
                              ms_iface_date = hi_timestamp,
                              ms_obj_date = obj_timestamp })
@@ -1875,17 +1853,6 @@ summariseModule hsc_env old_summary_map is_boot (L loc wanted_mod)
                    Left e | isDoesNotExistError e -> find_it
                           | otherwise             -> ioError e
 
-  | NotBoot <- is_boot
-  , Just _ <- getSigOf dflags wanted_mod
-  = do mod_summary0 <- makeMergeRequirementSummary hsc_env
-                                                   obj_allowed
-                                                   wanted_mod
-       hi_timestamp <- maybeGetIfaceDate dflags (ms_location mod_summary0)
-       let mod_summary = mod_summary0 {
-            ms_iface_date = hi_timestamp
-            }
-       return (Just (Right mod_summary))
-
   | otherwise  = find_it
   where
     dflags = hsc_dflags hsc_env
@@ -1948,10 +1915,17 @@ summariseModule hsc_env old_summary_map is_boot (L loc wanted_mod)
         (dflags', hspp_fn, buf) <- preprocessFile hsc_env src_fn Nothing maybe_buf
         (srcimps, the_imps, L mod_loc mod_name) <- getImports dflags' buf hspp_fn src_fn
 
-        let hsc_src =
-                case is_boot of
-                    IsBoot  -> HsBootFile
-                    NotBoot -> HsSrcFile
+        -- NB: Despite the fact that is_boot is a top-level parameter, we
+        -- don't actually know coming into this function what the HscSource
+        -- of the module in question is.  This is because we may be processing
+        -- this module because another module in the graph imported it: in this
+        -- case, we know if it's a boot or not because of the {-# SOURCE #-}
+        -- annotation, but we don't know if it's a signature or a regular
+        -- module until we actually look it up on the filesystem.
+        let hsc_src = case is_boot of
+                IsBoot -> HsBootFile
+                _ | isHaskellSigFilename src_fn -> HsigFile
+                  | otherwise -> HsSrcFile
 
         when (mod_name /= wanted_mod) $
                 throwOneError $ mkPlainErrMsg dflags' mod_loc $
@@ -1976,7 +1950,6 @@ summariseModule hsc_env old_summary_map is_boot (L loc wanted_mod)
                               ms_hspp_buf  = Just buf,
                               ms_srcimps      = srcimps,
                               ms_textual_imps = the_imps,
-                              ms_merge_imps = (False, []),
                               ms_hs_date   = src_timestamp,
                               ms_iface_date = hi_timestamp,
                               ms_obj_date  = obj_timestamp })))
@@ -2082,6 +2055,4 @@ cyclicModuleErr mss
 
     ppr_ms :: ModSummary -> SDoc
     ppr_ms ms = quotes (ppr (moduleName (ms_mod ms))) <+>
-                case msHsFilePath ms of
-                    Just path -> parens (text path)
-                    Nothing -> empty
+                (parens (text (msHsFilePath ms)))
diff --git a/compiler/main/HscMain.hs b/compiler/main/HscMain.hs
index 1bc37bd7aa..401f049f2b 100644
--- a/compiler/main/HscMain.hs
+++ b/compiler/main/HscMain.hs
@@ -99,12 +99,12 @@ import {- Kind parts of -} Type         ( Kind )
 import CoreLint         ( lintInteractiveExpr )
 import VarEnv           ( emptyTidyEnv )
 import THNames          ( templateHaskellNames )
+import Panic
 import ConLike
 
 import GHC.Exts
 #endif
 
-import Panic
 import Module
 import Packages
 import RdrName
@@ -118,8 +118,7 @@ import TcRnDriver
 import TcIface          ( typecheckIface )
 import TcRnMonad
 import IfaceEnv         ( initNameCache )
-import LoadIface        ( ifaceStats, initExternalPackageState
-                        , findAndReadIface )
+import LoadIface        ( ifaceStats, initExternalPackageState )
 import PrelInfo
 import MkIface
 import Desugar
@@ -607,9 +606,6 @@ genericHscFrontend mod_summary =
 
 genericHscFrontend' :: ModSummary -> Hsc FrontendResult
 genericHscFrontend' mod_summary
-    | ms_hsc_src mod_summary == HsBootMerge
-    = FrontendInterface `fmap` hscMergeFrontEnd mod_summary
-    | otherwise
     = FrontendTypecheck `fmap` hscFileFrontEnd mod_summary
 
 --------------------------------------------------------------
@@ -661,32 +657,9 @@ hscIncrementalCompile always_do_basic_recompilation_check m_tc_result
                        ms_hsc_src mod_summary == HsSrcFile
                        then finish              hsc_env mod_summary tc_result mb_old_hash
                        else finishTypecheckOnly hsc_env mod_summary tc_result mb_old_hash
-                FrontendInterface raw_iface ->
-                            finishMerge         hsc_env mod_summary raw_iface mb_old_hash
             liftIO $ hscMaybeWriteIface dflags (hm_iface hmi) no_change mod_summary
             return (status, hmi)
 
--- Generates and writes out the final interface for an hs-boot merge.
-finishMerge :: HscEnv
-            -> ModSummary
-            -> ModIface
-            -> Maybe Fingerprint
-            -> Hsc (HscStatus, HomeModInfo, Bool)
-finishMerge hsc_env summary iface0 mb_old_hash = do
-    MASSERT( ms_hsc_src summary == HsBootMerge )
-    (iface, changed) <- liftIO $ mkIfaceDirect hsc_env mb_old_hash iface0
-    details <- liftIO $ genModDetails hsc_env iface
-    let dflags = hsc_dflags hsc_env
-        hsc_status =
-            case hscTarget dflags of
-                HscNothing -> HscNotGeneratingCode
-                _ -> HscUpdateBootMerge
-    return (hsc_status,
-            HomeModInfo{ hm_details  = details,
-                         hm_iface    = iface,
-                         hm_linkable = Nothing },
-            changed)
-
 -- Generates and writes out the final interface for a typecheck.
 finishTypecheckOnly :: HscEnv
               -> ModSummary
@@ -695,12 +668,12 @@ finishTypecheckOnly :: HscEnv
               -> Hsc (HscStatus, HomeModInfo, Bool)
 finishTypecheckOnly hsc_env summary tc_result mb_old_hash = do
     let dflags = hsc_dflags hsc_env
-    MASSERT( hscTarget dflags == HscNothing || ms_hsc_src summary == HsBootFile )
     (iface, changed, details) <- liftIO $ hscSimpleIface hsc_env tc_result mb_old_hash
     let hsc_status =
           case (hscTarget dflags, ms_hsc_src summary) of
             (HscNothing, _) -> HscNotGeneratingCode
             (_, HsBootFile) -> HscUpdateBoot
+            (_, HsigFile) -> HscUpdateSig
             _ -> panic "finishTypecheckOnly"
     return (hsc_status,
             HomeModInfo{ hm_details  = details,
@@ -789,46 +762,10 @@ batchMsg hsc_env mod_index recomp mod_summary =
 -- FrontEnds
 --------------------------------------------------------------
 
--- | Given an 'HsBootMerge' 'ModSummary', merges all @hs-boot@ files
--- under this module name into a composite, publically visible 'ModIface'.
-hscMergeFrontEnd :: ModSummary -> Hsc ModIface
-hscMergeFrontEnd mod_summary = do
-    hsc_env <- getHscEnv
-    MASSERT( ms_hsc_src mod_summary == HsBootMerge )
-    let dflags = hsc_dflags hsc_env
-    -- TODO: actually merge in signatures from external packages.
-    -- Grovel in HPT if necessary
-    -- TODO: replace with 'computeInterface'
-    let hpt = hsc_HPT hsc_env
-    -- TODO multiple mods
-    let name = moduleName (ms_mod mod_summary)
-        mod = mkModule (thisPackage dflags) name
-        is_boot = True
-    iface0 <- case lookupHptByModule hpt mod of
-        Just hm -> return (hm_iface hm)
-        Nothing -> do
-            mb_iface0 <- liftIO . initIfaceCheck hsc_env
-                    $ findAndReadIface (text "merge-requirements")
-                                       mod is_boot
-            case mb_iface0 of
-                Succeeded (i, _) -> return i
-                Failed err -> liftIO $ throwGhcExceptionIO
-                                (ProgramError (showSDoc dflags err))
-    let iface = iface0 {
-                    mi_hsc_src = HsBootMerge,
-                    -- TODO: mkDependencies doublecheck
-                    mi_deps = (mi_deps iface0) {
-                        dep_mods = (name, is_boot)
-                                 : dep_mods (mi_deps iface0)
-                      }
-                    }
-    return iface
-
 -- | Given a 'ModSummary', parses and typechecks it, returning the
 -- 'TcGblEnv' resulting from type-checking.
 hscFileFrontEnd :: ModSummary -> Hsc TcGblEnv
 hscFileFrontEnd mod_summary = do
-    MASSERT( ms_hsc_src mod_summary == HsBootFile || ms_hsc_src mod_summary == HsSrcFile )
     hpm <- hscParse' mod_summary
     hsc_env <- getHscEnv
     tcg_env <- tcRnModule' hsc_env mod_summary False hpm
diff --git a/compiler/main/HscTypes.hs b/compiler/main/HscTypes.hs
index 362164eba4..cb0d2841b7 100644
--- a/compiler/main/HscTypes.hs
+++ b/compiler/main/HscTypes.hs
@@ -29,7 +29,7 @@ module HscTypes (
 
         -- * Information about the module being compiled
         -- (re-exported from DriverPhases)
-        HscSource(..), isHsBoot, hscSourceString,
+        HscSource(..), isHsBootOrSig, hscSourceString,
 
 
         -- * State relating to modules in this package
@@ -162,7 +162,7 @@ import PatSyn
 import PrelNames        ( gHC_PRIM, ioTyConName, printName, mkInteractiveModule )
 import Packages hiding  ( Version(..) )
 import DynFlags
-import DriverPhases     ( Phase, HscSource(..), isHsBoot, hscSourceString )
+import DriverPhases     ( Phase, HscSource(..), isHsBootOrSig, hscSourceString )
 import BasicTypes
 import IfaceSyn
 import CoreSyn          ( CoreRule, CoreVect )
@@ -202,7 +202,7 @@ data HscStatus
     = HscNotGeneratingCode
     | HscUpToDate
     | HscUpdateBoot
-    | HscUpdateBootMerge
+    | HscUpdateSig
     | HscRecomp CgGuts ModSummary
 
 -- -----------------------------------------------------------------------------
@@ -2410,8 +2410,6 @@ data ModSummary
           -- ^ Source imports of the module
         ms_textual_imps :: [(Maybe FastString, Located ModuleName)],
           -- ^ Non-source imports of the module from the module *text*
-        ms_merge_imps   :: (Bool, [Module]),
-          -- ^ Non-textual imports computed for HsBootMerge
         ms_hspp_file    :: FilePath,
           -- ^ Filename of preprocessed source file
         ms_hspp_opts    :: DynFlags,
@@ -2441,10 +2439,8 @@ ms_imps ms =
 -- The ModLocation is stable over successive up-sweeps in GHCi, wheres
 -- the ms_hs_date and imports can, of course, change
 
-msHsFilePath :: ModSummary -> Maybe FilePath
-msHsFilePath  ms = ml_hs_file  (ms_location ms)
-
-msHiFilePath, msObjFilePath :: ModSummary -> FilePath
+msHsFilePath, msHiFilePath, msObjFilePath :: ModSummary -> FilePath
+msHsFilePath  ms = expectJust "msHsFilePath" (ml_hs_file  (ms_location ms))
 msHiFilePath  ms = ml_hi_file  (ms_location ms)
 msObjFilePath ms = ml_obj_file (ms_location ms)
 
@@ -2459,10 +2455,7 @@ instance Outputable ModSummary where
                           text "ms_mod =" <+> ppr (ms_mod ms)
                                 <> text (hscSourceString (ms_hsc_src ms)) <> comma,
                           text "ms_textual_imps =" <+> ppr (ms_textual_imps ms),
-                          text "ms_srcimps =" <+> ppr (ms_srcimps ms),
-                          if not (null (snd (ms_merge_imps ms)))
-                            then text "ms_merge_imps =" <+> ppr (ms_merge_imps ms)
-                            else empty]),
+                          text "ms_srcimps =" <+> ppr (ms_srcimps ms)]),
              char '}'
             ]
 
@@ -2470,20 +2463,29 @@ showModMsg :: DynFlags -> HscTarget -> Bool -> ModSummary -> String
 showModMsg dflags target recomp mod_summary
   = showSDoc dflags $
         hsep [text (mod_str ++ replicate (max 0 (16 - length mod_str)) ' '),
-              char '(',
-              case msHsFilePath mod_summary of
-                Just path -> text (normalise path) <> comma
-                Nothing -> text "nothing" <> comma,
+              char '(', text (normalise $ msHsFilePath mod_summary) <> comma,
               case target of
                   HscInterpreted | recomp
                              -> text "interpreted"
                   HscNothing -> text "nothing"
-                  _ -> text (normalise $ msObjFilePath mod_summary),
+                  _ | HsigFile == ms_hsc_src mod_summary -> text "nothing"
+                    | otherwise -> text (normalise $ msObjFilePath mod_summary),
               char ')']
  where
     mod     = moduleName (ms_mod mod_summary)
     mod_str = showPpr dflags mod
-                ++ hscSourceString (ms_hsc_src mod_summary)
+                ++ hscSourceString' dflags mod (ms_hsc_src mod_summary)
+
+-- | Variant of hscSourceString which prints more information for signatures.
+-- This can't live in DriverPhases because this would cause a module loop.
+hscSourceString' :: DynFlags -> ModuleName -> HscSource -> String
+hscSourceString' _ _ HsSrcFile   = ""
+hscSourceString' _ _ HsBootFile  = "[boot]"
+hscSourceString' dflags mod HsigFile =
+     "[" ++ (maybe "abstract sig"
+               (("sig of "++).showPpr dflags)
+               (getSigOf dflags mod)) ++ "]"
+    -- NB: -sig-of could be missing if we're just typechecking
 
 {-
 ************************************************************************
diff --git a/compiler/typecheck/TcBinds.hs b/compiler/typecheck/TcBinds.hs
index 3115179c2f..ccf8202847 100644
--- a/compiler/typecheck/TcBinds.hs
+++ b/compiler/typecheck/TcBinds.hs
@@ -21,7 +21,7 @@ import {-# SOURCE #-} TcExpr  ( tcMonoExpr )
 import {-# SOURCE #-} TcPatSyn ( tcInferPatSynDecl, tcCheckPatSynDecl, tcPatSynBuilderBind )
 import DynFlags
 import HsSyn
-import HscTypes( isHsBoot )
+import HscTypes( isHsBootOrSig )
 import TcRnMonad
 import TcEnv
 import TcUnify
@@ -74,7 +74,7 @@ import Data.List (partition)
 
 addTypecheckedBinds :: TcGblEnv -> [LHsBinds Id] -> TcGblEnv
 addTypecheckedBinds tcg_env binds
-  | isHsBoot (tcg_src tcg_env) = tcg_env
+  | isHsBootOrSig (tcg_src tcg_env) = tcg_env
     -- Do not add the code for record-selector bindings
     -- when compiling hs-boot files
   | otherwise = tcg_env { tcg_binds = foldr unionBags
diff --git a/compiler/typecheck/TcInstDcls.hs b/compiler/typecheck/TcInstDcls.hs
index ef0c4b6c8f..06cb42715a 100644
--- a/compiler/typecheck/TcInstDcls.hs
+++ b/compiler/typecheck/TcInstDcls.hs
@@ -49,7 +49,7 @@ import BasicTypes
 import DynFlags
 import ErrUtils
 import FastString
-import HscTypes ( isHsBoot )
+import HscTypes ( isHsBootOrSig )
 import Id
 import MkId
 import Name
@@ -441,7 +441,7 @@ tcInstDecls1 tycl_decls inst_decls deriv_decls
     typeable_err i =
       setSrcSpan (getSrcSpan (iSpec i)) $
         do env <- getGblEnv
-           if isHsBoot (tcg_src env)
+           if isHsBootOrSig (tcg_src env)
              then
                do warn <- woptM Opt_WarnDerivingTypeable
                   when warn $ addWarnTc $ vcat
diff --git a/compiler/typecheck/TcRnDriver.hs b/compiler/typecheck/TcRnDriver.hs
index 1987354dbd..1b2a8d993e 100644
--- a/compiler/typecheck/TcRnDriver.hs
+++ b/compiler/typecheck/TcRnDriver.hs
@@ -164,12 +164,8 @@ tcRnSignature dflags hsc_src
  = do { tcg_env <- getGblEnv ;
         case tcg_sig_of tcg_env of {
           Just sof
-           | hsc_src /= HsBootFile -> do
-                { modname <- fmap moduleName getModule
-                ; addErr (text "Found -sig-of entry for" <+> ppr modname
-                                <+> text "which is not hs-boot." $$
-                          text "Try removing" <+> ppr modname <+>
-                          text "from -sig-of")
+           | hsc_src /= HsigFile -> do
+                { addErr (ptext (sLit "Illegal -sig-of specified for non hsig"))
                 ; return tcg_env
                 }
            | otherwise -> do
@@ -183,7 +179,15 @@ tcRnSignature dflags hsc_src
                 , tcg_imports = tcg_imports tcg_env `plusImportAvails` avails
                 })
             } ;
-          Nothing -> return tcg_env
+          Nothing
+             | HsigFile <- hsc_src
+             , HscNothing <- hscTarget dflags -> do
+                { return tcg_env
+                }
+             | HsigFile <- hsc_src -> do
+                { addErr (ptext (sLit "Missing -sig-of for hsig"))
+                ; failM }
+             | otherwise -> return tcg_env
         }
       }
 
@@ -319,7 +323,7 @@ tcRnModuleTcRnM hsc_env hsc_src
 
                 -- Rename and type check the declarations
         traceRn (text "rn1a") ;
-        tcg_env <- if isHsBoot hsc_src then
+        tcg_env <- if isHsBootOrSig hsc_src then
                         tcRnHsBootDecls hsc_src local_decls
                    else
                         {-# SCC "tcRnSrcDecls" #-}
@@ -675,9 +679,9 @@ tcRnHsBootDecls hsc_src decls
                 -- are written into the interface file.
         ; let { type_env0 = tcg_type_env gbl_env
               ; type_env1 = extendTypeEnvWithIds type_env0 val_ids
-              -- Don't add the dictionaries for non-recursive case, we don't
-              -- actually want to /define/ the instance, just an export list
-              ; type_env2 | Just _ <- tcg_impl_rdr_env gbl_env = type_env1
+              -- Don't add the dictionaries for hsig, we don't actually want
+              -- to /define/ the instance
+              ; type_env2 | HsigFile <- hsc_src = type_env1
                           | otherwise = extendTypeEnvWithIds type_env1 dfun_ids
               ; dfun_ids = map iDFunId inst_infos
               }
@@ -687,9 +691,14 @@ tcRnHsBootDecls hsc_src decls
    ; traceTc "boot" (ppr lie); return gbl_env }
 
 badBootDecl :: HscSource -> String -> Located decl -> TcM ()
-badBootDecl _hsc_src what (L loc _)
+badBootDecl hsc_src what (L loc _)
   = addErrAt loc (char 'A' <+> text what
-      <+> text "declaration is not (currently) allowed in a hs-boot file")
+      <+> ptext (sLit "declaration is not (currently) allowed in a")
+      <+> (case hsc_src of
+            HsBootFile -> ptext (sLit "hs-boot")
+            HsigFile -> ptext (sLit "hsig")
+            _ -> panic "badBootDecl: should be an hsig or hs-boot file")
+      <+> ptext (sLit "file"))
 
 {-
 Once we've typechecked the body of the module, we want to compare what
@@ -1064,7 +1073,7 @@ emptyRnEnv2 = mkRnEnv2 emptyInScopeSet
 missingBootThing :: Bool -> Name -> String -> SDoc
 missingBootThing is_boot name what
   = quotes (ppr name) <+> ptext (sLit "is exported by the")
-    <+> (if is_boot then ptext (sLit "hs-boot") else ptext (sLit "signature"))
+    <+> (if is_boot then ptext (sLit "hs-boot") else ptext (sLit "hsig"))
     <+> ptext (sLit "file, but not")
     <+> text what <+> ptext (sLit "the module")
 
@@ -1074,11 +1083,11 @@ bootMisMatch is_boot extra_info real_thing boot_thing
           ptext (sLit "has conflicting definitions in the module"),
           ptext (sLit "and its") <+>
             (if is_boot then ptext (sLit "hs-boot file")
-                       else ptext (sLit "signature file")),
+                       else ptext (sLit "hsig file")),
           ptext (sLit "Main module:") <+> PprTyThing.pprTyThing real_thing,
           (if is_boot
             then ptext (sLit "Boot file:  ")
-            else ptext (sLit "Signature file: "))
+            else ptext (sLit "Hsig file: "))
             <+> PprTyThing.pprTyThing boot_thing,
           extra_info]
 
@@ -1086,7 +1095,7 @@ instMisMatch :: Bool -> ClsInst -> SDoc
 instMisMatch is_boot inst
   = hang (ppr inst)
        2 (ptext (sLit "is defined in the") <+>
-        (if is_boot then ptext (sLit "hs-boot") else ptext (sLit "signature"))
+        (if is_boot then ptext (sLit "hs-boot") else ptext (sLit "hsig"))
        <+> ptext (sLit "file, but not in the module itself"))
 
 {-
diff --git a/compiler/typecheck/TcRnMonad.hs b/compiler/typecheck/TcRnMonad.hs
index 3ad4677742..5544254311 100644
--- a/compiler/typecheck/TcRnMonad.hs
+++ b/compiler/typecheck/TcRnMonad.hs
@@ -608,7 +608,7 @@ getInteractivePrintName :: TcRn Name
 getInteractivePrintName = do { hsc <- getTopEnv; return (ic_int_print $ hsc_IC hsc) }
 
 tcIsHsBootOrSig :: TcRn Bool
-tcIsHsBootOrSig = do { env <- getGblEnv; return (isHsBoot (tcg_src env)) }
+tcIsHsBootOrSig = do { env <- getGblEnv; return (isHsBootOrSig (tcg_src env)) }
 
 tcSelfBootInfo :: TcRn SelfBootInfo
 tcSelfBootInfo = do { env <- getGblEnv; return (tcg_self_boot env) }
diff --git a/compiler/typecheck/TcRnTypes.hs b/compiler/typecheck/TcRnTypes.hs
index f4cfa4f780..d81727a41d 100644
--- a/compiler/typecheck/TcRnTypes.hs
+++ b/compiler/typecheck/TcRnTypes.hs
@@ -341,7 +341,6 @@ data DsMetaVal
 -- to have a TcGblEnv which is only defined here.
 data FrontendResult
         = FrontendTypecheck TcGblEnv
-        | FrontendInterface ModIface
 
 -- | 'TcGblEnv' describes the top-level of the module at the
 -- point at which the typechecker is finished work.