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

This patch drops the file level distinction between hs-boot and hsig;
we figure out which one we are compiling based on whether or not there
is a corresponding hs file lying around.

To make the "import A" syntax continue to work for bare hs-boot
files, we also introduce hs-boot merging, which takes an A.hi-boot
and converts it to an A.hi when there is no A.hs file in scope.
This will be generalized in Backpack to merge multiple A.hi files together;
which means we can jettison the "load multiple interface files" functionality.

This works automatically for --make, but for one-shot compilation
we need a new mode: ghc --merge-requirements A will generate an A.hi/A.o
from a local A.hi-boot file; Backpack will extend this mechanism further.

Has Haddock submodule update to deal with change in msHsFilePath behavior.

    - This commit drops support for the hsig extension. Can
      we support it?  It's annoying because the finder code is
      written with the assumption that where there's an hs-boot
      file, there's always an hs file too.  To support hsig, you'd
      have to probe two locations.  Easier to just not support it.

    - #10333 affects us, modifying an hs-boot still doesn't trigger
      recomp.

    - See compiler/main/Finder.hs: this diff is very skeevy, but
      it seems to work.

    - This code cunningly doesn't drop hs-boot files from the
      "drop hs-boot files" module graph, if they don't have a
      corresponding hs file.  I have no idea if this actually is useful.

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

Test Plan: validate

Reviewers: simonpj, austin, bgamari, spinda

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D1098

1 files changed, 40 insertions, 7 deletions

diff --git a/compiler/iface/MkIface.hs b/compiler/iface/MkIface.hs
index 757bebac93..99544c4e4f 100644
--- a/compiler/iface/MkIface.hs
+++ b/compiler/iface/MkIface.hs
@@ -15,6 +15,7 @@ module MkIface (
                         -- including computing version information
 
         mkIfaceTc,
+        mkIfaceDirect,
 
         writeIfaceFile, -- Write the interface file
 
@@ -160,6 +161,35 @@ mkIface hsc_env maybe_old_fingerprint mod_details
                    warns hpc_info dir_imp_mods self_trust dependent_files
                    safe_mode 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').
@@ -357,11 +387,6 @@ mkIface_ hsc_env maybe_old_fingerprint
 
         return (errs_and_warns, Just (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
 
@@ -379,8 +404,6 @@ 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
@@ -394,6 +417,16 @@ 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