diff options
Diffstat (limited to 'compiler/iface/TcIface.hs')
| -rw-r--r-- | compiler/iface/TcIface.hs | 24 |
1 files changed, 20 insertions, 4 deletions
diff --git a/compiler/iface/TcIface.hs b/compiler/iface/TcIface.hs index 8bc0dd1110..12980475b2 100644 --- a/compiler/iface/TcIface.hs +++ b/compiler/iface/TcIface.hs @@ -1319,9 +1319,11 @@ tcIfaceGlobal name -> do -- It's defined in the module being compiled { type_env <- setLclEnv () get_type_env -- yuk ; case lookupNameEnv type_env name of - Just thing -> return thing - Nothing -> pprPanic "tcIfaceGlobal (local): not found:" - (ppr name $$ ppr type_env) } + Just thing -> return thing + Nothing -> + pprPanic "tcIfaceGlobal (local): not found" + (ifKnotErr name (if_doc env) type_env) + } ; _ -> do @@ -1337,11 +1339,25 @@ tcIfaceGlobal name Succeeded thing -> return thing }}}}} +ifKnotErr :: Name -> SDoc -> TypeEnv -> SDoc +ifKnotErr name env_doc type_env = vcat + [ text "You are in a maze of twisty little passages, all alike." + , text "While forcing the thunk for TyThing" <+> ppr name + , text "which was lazily initialized by" <+> env_doc <> text "," + , text "I tried to tie the knot, but I couldn't find" <+> ppr name + , text "in the current type environment." + , text "If you are developing GHC, please read Note [Tying the knot]" + , text "and Note [Type-checking inside the knot]." + , text "Consider rebuilding GHC with profiling for a better stack trace." + , hang (text "Contents of current type environment:") + 2 (ppr type_env) + ] + -- Note [Tying the knot] -- ~~~~~~~~~~~~~~~~~~~~~ -- The if_rec_types field is used in two situations: -- --- a) Compiling M.hs, which indiretly imports Foo.hi, which mentions M.T +-- a) Compiling M.hs, which indirectly imports Foo.hi, which mentions M.T -- Then we look up M.T in M's type environment, which is splatted into if_rec_types -- after we've built M's type envt. -- |