[project @ 2002-01-08 17:31:30 by simonmar]

Fix a problem which lead to home-package instances ending up in the
package instance table in GHCi, which results in strange duplicate
instance errors when reloading modules.  See the comments for details.

diff --git a/ghc/compiler/typecheck/TcInstDcls.lhs b/ghc/compiler/typecheck/TcInstDcls.lhs
index bf79e5c..f6e6a99 100644 (file)
--- a/ghc/compiler/typecheck/TcInstDcls.lhs
+++ b/ghc/compiler/typecheck/TcInstDcls.lhs
@@ -33,7 +33,7 @@ import TcType         ( mkClassPred, mkTyVarTy, mkTyVarTys, tcSplitForAllTys,
 import Inst            ( InstOrigin(..), newDicts, instToId,
                          LIE, mkLIE, emptyLIE, plusLIE, plusLIEs )
 import TcDeriv         ( tcDeriving )
-import TcEnv           ( TcEnv, tcExtendGlobalValEnv, 
+import TcEnv           ( TcEnv, tcExtendGlobalValEnv, isLocalThing,
                          tcExtendTyVarEnvForMeths, tcLookupId, tcLookupClass,
                          InstInfo(..), pprInstInfo, simpleInstInfoTyCon, 
                          simpleInstInfoTy, newDFunName
@@ -172,33 +172,49 @@ tcInstDecls1 inst_env0 prs hst unf_env get_fixity this_mod decls
        inst_decls = [inst_decl | InstD inst_decl <- decls]     
        tycl_decls = [decl      | TyClD decl <- decls]
        clas_decls = filter isClassDecl tycl_decls
-       (imported_inst_ds, local_inst_ds) = partition isIfaceInstDecl inst_decls
+       (iface_inst_ds, local_inst_ds) = partition isIfaceInstDecl inst_decls
     in
        -- (1) Do the ordinary instance declarations
     mapNF_Tc tcLocalInstDecl1 local_inst_ds            `thenNF_Tc` \ local_inst_infos ->
-    mapNF_Tc tcImportedInstDecl1 imported_inst_ds      `thenNF_Tc` \ imported_dfuns ->
+    mapNF_Tc tcImportedInstDecl1 iface_inst_ds         `thenNF_Tc` \ iface_dfuns ->
 
        -- (2) Instances from generic class declarations
     getGenericInstances clas_decls             `thenTc` \ generic_inst_info -> 
 
        -- Next, construct the instance environment so far, consisting of
-       --      a) cached non-home-package InstEnv (gotten from pcs)    pcs_insts pcs
+       --      a) cached non-home-package InstEnv (gotten from pcs)    inst_env0
        --      b) imported instance decls (not in the home package)    inst_env1
-       --      c) other modules in this package (gotten from hst)      inst_env2
-       --      d) local instance decls                                 inst_env3
-       --      e) generic instances                                    inst_env4
+       --      c) imported instance decls (from this module)           inst_env2
+       --      c) other modules in this package (gotten from hst)      inst_env3
+       --      d) local instance decls                                 inst_env4
+       --      e) generic instances                                    inst_env5
        -- The result of (b) replaces the cached InstEnv in the PCS
+       --
+       -- Note that iface_dfuns may contain not only insts that we demand-loaded
+       -- from package interface files, but also instances from the current module
+       -- in the case where we are loading this module's interface file in GHCi,
+       -- so we partition the iface_dfuns into package instances and local instances
+       -- below so that we don't end up with home package instances in the PCS.
+       --
+       -- There can't be any instance declarations from the home
+       -- package other than from the current module (with the
+       -- compilation manager) because they are loaded explicitly by
+       -- the compilation manager.  The partition is really only
+       -- necessary when we're under control of the compilation
+       -- manager.
     let
        local_inst_info = catMaybes local_inst_infos
+       (local_iface_dfuns, pkg_iface_dfuns) = partition (isLocalThing this_mod) iface_dfuns
        hst_dfuns       = foldModuleEnv ((++) . md_insts) [] hst
     in 
 
 --    pprTrace "tcInstDecls" (vcat [ppr imported_dfuns, ppr hst_dfuns]) $
 
-    addInstDFuns inst_env0 imported_dfuns      `thenNF_Tc` \ inst_env1 ->
+    addInstDFuns inst_env0 pkg_iface_dfuns     `thenNF_Tc` \ inst_env1 ->
     addInstDFuns inst_env1 hst_dfuns           `thenNF_Tc` \ inst_env2 ->
-    addInstInfos inst_env2 local_inst_info     `thenNF_Tc` \ inst_env3 ->
-    addInstInfos inst_env3 generic_inst_info   `thenNF_Tc` \ inst_env4 ->
+    addInstDFuns inst_env2 local_iface_dfuns   `thenNF_Tc` \ inst_env3 ->
+    addInstInfos inst_env3 local_inst_info     `thenNF_Tc` \ inst_env4 ->
+    addInstInfos inst_env4 generic_inst_info   `thenNF_Tc` \ inst_env5 ->
 
        -- (3) Compute instances from "deriving" clauses; 
        --     note that we only do derivings for things in this module;