[commit: ghc] master: Fix #12064 by making IfaceClass typechecking more lazy. (8f6d292)

[git at git.haskell.org]

Repository : ssh://git@git.haskell.org/ghc

On branch  : master
Link       : http://ghc.haskell.org/trac/ghc/changeset/8f6d292746217f1fa9f645ff8d191943af1c5771/ghc

>---------------------------------------------------------------

commit 8f6d292746217f1fa9f645ff8d191943af1c5771
Author: Edward Z. Yang <ezyang at cs.stanford.edu>
Date:   Sun May 15 16:13:51 2016 -0700

    Fix #12064 by making IfaceClass typechecking more lazy.
    
    Summary:
    Comes with a test based off of prog006.
    
    Signed-off-by: Edward Z. Yang <ezyang at cs.stanford.edu>
    
    Test Plan: validate
    
    Reviewers: simonpj, austin, bgamari
    
    Subscribers: thomie
    
    Differential Revision: https://phabricator.haskell.org/D2221
    
    GHC Trac Issues: #12064


>---------------------------------------------------------------

8f6d292746217f1fa9f645ff8d191943af1c5771
 compiler/iface/TcIface.hs                           | 21 ++++++++++++---------
 compiler/typecheck/TcRnDriver.hs                    |  2 +-
 testsuite/tests/typecheck/should_compile/T12064.hs  |  4 ++++
 .../tests/typecheck/should_compile/T12064.hs-boot   |  2 ++
 testsuite/tests/typecheck/should_compile/T12064a.hs |  4 ++++
 testsuite/tests/typecheck/should_compile/all.T      |  2 ++
 6 files changed, 25 insertions(+), 10 deletions(-)

diff --git a/compiler/iface/TcIface.hs b/compiler/iface/TcIface.hs
index 320594c..a6486f3 100644
--- a/compiler/iface/TcIface.hs
+++ b/compiler/iface/TcIface.hs
@@ -426,20 +426,23 @@ tc_iface_decl _parent ignore_prags
    tc_sig :: IfaceClassOp -> IfL TcMethInfo
    tc_sig (IfaceClassOp occ rdr_ty dm)
      = do { op_name <- lookupIfaceTop occ
-          ; ~(op_ty, dm') <- forkM (mk_op_doc op_name rdr_ty) $
-                             do { ty <- tcIfaceType rdr_ty
-                                ; dm' <- tc_dm dm
-                                ; return (ty, dm') }
+          ; let doc = mk_op_doc op_name rdr_ty
+          ; op_ty <- forkM (doc <+> text "ty") $ tcIfaceType rdr_ty
                 -- Must be done lazily for just the same reason as the
                 -- type of a data con; to avoid sucking in types that
                 -- it mentions unless it's necessary to do so
+          ; dm'   <- tc_dm doc dm
           ; return (op_name, op_ty, dm') }
 
-   tc_dm :: Maybe (DefMethSpec IfaceType) -> IfL (Maybe (DefMethSpec Type))
-   tc_dm Nothing               = return Nothing
-   tc_dm (Just VanillaDM)      = return (Just VanillaDM)
-   tc_dm (Just (GenericDM ty)) = do { ty' <- tcIfaceType ty
-                                    ; return (Just (GenericDM ty')) }
+   tc_dm :: SDoc
+         -> Maybe (DefMethSpec IfaceType)
+         -> IfL (Maybe (DefMethSpec Type))
+   tc_dm _   Nothing               = return Nothing
+   tc_dm _   (Just VanillaDM)      = return (Just VanillaDM)
+   tc_dm doc (Just (GenericDM ty))
+        = do { -- Must be done lazily to avoid sucking in types
+             ; ty' <- forkM (doc <+> text "dm") $ tcIfaceType ty
+             ; return (Just (GenericDM ty')) }
 
    tc_at cls (IfaceAT tc_decl if_def)
      = do ATyCon tc <- tc_iface_decl (Just cls) ignore_prags tc_decl
diff --git a/compiler/typecheck/TcRnDriver.hs b/compiler/typecheck/TcRnDriver.hs
index 5e83305..c6865f5 100644
--- a/compiler/typecheck/TcRnDriver.hs
+++ b/compiler/typecheck/TcRnDriver.hs
@@ -363,7 +363,7 @@ tcRnModuleTcRnM hsc_env hsc_src
             Nothing -> return tcg_env) ;
 
         -- The new type env is already available to stuff slurped from
-        -- interface files, via TcEnv.updateGlobalTypeEnv
+        -- interface files, via TcEnv.setGlobalTypeEnv
         -- It's important that this includes the stuff in checkHiBootIface,
         -- because the latter might add new bindings for boot_dfuns,
         -- which may be mentioned in imported unfoldings
diff --git a/testsuite/tests/typecheck/should_compile/T12064.hs b/testsuite/tests/typecheck/should_compile/T12064.hs
new file mode 100644
index 0000000..0c3d1b3
--- /dev/null
+++ b/testsuite/tests/typecheck/should_compile/T12064.hs
@@ -0,0 +1,4 @@
+{-# LANGUAGE ExistentialQuantification #-}
+module T12064 where
+import T12064a
+data D = forall n. K n => DCon n
diff --git a/testsuite/tests/typecheck/should_compile/T12064.hs-boot b/testsuite/tests/typecheck/should_compile/T12064.hs-boot
new file mode 100644
index 0000000..4536cf3
--- /dev/null
+++ b/testsuite/tests/typecheck/should_compile/T12064.hs-boot
@@ -0,0 +1,2 @@
+module T12064 where
+data D
diff --git a/testsuite/tests/typecheck/should_compile/T12064a.hs b/testsuite/tests/typecheck/should_compile/T12064a.hs
new file mode 100644
index 0000000..381edfc
--- /dev/null
+++ b/testsuite/tests/typecheck/should_compile/T12064a.hs
@@ -0,0 +1,4 @@
+module T12064a where
+import {-# SOURCE #-} T12064
+class K a where
+  kfun :: D -> a
diff --git a/testsuite/tests/typecheck/should_compile/all.T b/testsuite/tests/typecheck/should_compile/all.T
index e58feae..0f43d00 100644
--- a/testsuite/tests/typecheck/should_compile/all.T
+++ b/testsuite/tests/typecheck/should_compile/all.T
@@ -515,3 +515,5 @@ test('T11811', normal, compile, [''])
 test('T11793', normal, compile, [''])
 test('T11348', normal, compile, [''])
 test('T11947', normal, compile, [''])
+test('T12064', extra_clean(['T12064.hi-boot', 'T12064.o-boot', 'T11062a.hi', 'T11062a.o']),
+     multimod_compile, ['T12064', '-v0'])