Convert interface file loading errors into proper diagnosticswip/interface-loading-errs

This patch converts all the errors to do with loading interface files
into proper structured diagnostics.

* DriverMessage: Sometimes in the driver we attempt to load an interface
  file so we embed the IfaceMessage into the DriverMessage.
* TcRnMessage: Most the time we are loading interface files during
  typechecking, so we embed the IfaceMessage

This patch also removes the TcRnInterfaceLookupError constructor which
is superceded by the IfaceMessage, which is now structured compared to
just storing an SDoc before.

1 files changed, 10 insertions, 4 deletions

diff --git a/compiler/GHC/Iface/Recomp.hs b/compiler/GHC/Iface/Recomp.hs
index 2e1150910b..b0e668f0e6 100644
--- a/compiler/GHC/Iface/Recomp.hs
+++ b/compiler/GHC/Iface/Recomp.hs
@@ -83,6 +83,7 @@ import GHC.List (uncons)
 import Data.Ord
 import Data.Containers.ListUtils
 import Data.Bifunctor
+import GHC.Iface.Errors.Ppr
 
 {-
   -----------------------------------------------
@@ -292,8 +293,13 @@ check_old_iface hsc_env mod_summary maybe_iface
              read_result <- readIface read_dflags ncu (ms_mod mod_summary) iface_path
              case read_result of
                  Failed err -> do
-                     trace_if logger (text "FYI: cannot read old interface file:" $$ nest 4 err)
-                     trace_hi_diffs logger (text "Old interface file was invalid:" $$ nest 4 err)
+                     let msg = readInterfaceErrorDiagnostic err
+                     trace_if logger
+                       $ vcat [ text "FYI: cannot read old interface file:"
+                              , nest 4 msg ]
+                     trace_hi_diffs logger $
+                       vcat [ text "Old interface file was invalid:"
+                            , nest 4 msg ]
                      return Nothing
                  Succeeded iface -> do
                      trace_if logger (text "Read the interface file" <+> text iface_path)
@@ -1323,7 +1329,7 @@ getOrphanHashes hsc_env mods = do
     dflags     = hsc_dflags hsc_env
     ctx        = initSDocContext dflags defaultUserStyle
     get_orph_hash mod = do
-          iface <- initIfaceLoad hsc_env . withException ctx
+          iface <- initIfaceLoad hsc_env . withIfaceErr ctx
                             $ loadInterface (text "getOrphanHashes") mod ImportBySystem
           return (mi_orphan_hash (mi_final_exts iface))
 
@@ -1618,7 +1624,7 @@ mkHashFun hsc_env eps name
                       -- requirements; we didn't do any /real/ typechecking
                       -- so there's no guarantee everything is loaded.
                       -- Kind of a heinous hack.
-                      initIfaceLoad hsc_env . withException ctx
+                      initIfaceLoad hsc_env . withIfaceErr ctx
                           $ withoutDynamicNow
                             -- If you try and load interfaces when dynamic-too
                             -- enabled then it attempts to load the dyn_hi and hi