Refactor SrcLoc and SrcSpansrcloc

The "Unhelpful" cases are now in a separate type. This allows us to
improve various things, e.g.:
* Most of the panic's in SrcLoc are now gone
* The Lexer now works with RealSrcSpans rather than SrcSpans, i.e. it
  knows that it has real locations and thus can assume that the line
  number etc really exists
* Some of the more suspicious cases are no longer necessary, e.g.
  we no longer need this case in advanceSrcLoc:
      advanceSrcLoc loc _ = loc -- Better than nothing

More improvements can probably be made, e.g. tick locations can
probably use RealSrcSpans too.

4 files changed, 10 insertions, 4 deletions

diff --git a/compiler/rename/RnEnv.lhs b/compiler/rename/RnEnv.lhs
index c4ad95a333..b3333731c1 100644
--- a/compiler/rename/RnEnv.lhs
+++ b/compiler/rename/RnEnv.lhs
@@ -1053,7 +1053,11 @@ unknownNameSuggestErr where_look tried_rdr_name
   where
     pp_item :: (RdrName, HowInScope) -> SDoc
     pp_item (rdr, Left loc) = quotes (ppr rdr) <+>   -- Locally defined
-                              parens (ptext (sLit "line") <+> int (srcSpanStartLine loc))
+                              parens (ptext (sLit "line") <+> int (srcSpanStartLine loc'))
+        where loc' = case loc of
+                     UnhelpfulSpan _ ->
+                         panic "unknownNameSuggestErr UnhelpfulSpan"
+                     RealSrcSpan l -> l
     pp_item (rdr, Right is) = quotes (ppr rdr) <+>   -- Imported
                               parens (ptext (sLit "imported from") <+> ppr (is_mod is))
 
diff --git a/compiler/rename/RnHsDoc.hs b/compiler/rename/RnHsDoc.hs
index beb45bbfbc..9e53f49320 100644
--- a/compiler/rename/RnHsDoc.hs
+++ b/compiler/rename/RnHsDoc.hs
@@ -3,7 +3,7 @@ module RnHsDoc ( rnHsDoc, rnLHsDoc, rnMbLHsDoc ) where
 
 import TcRnTypes
 import HsSyn
-import SrcLoc      ( Located(..) )
+import SrcLoc
 
 
 rnMbLHsDoc :: Maybe LHsDocString -> RnM (Maybe LHsDocString)
diff --git a/compiler/rename/RnHsSyn.lhs b/compiler/rename/RnHsSyn.lhs
index 478ba32655..bfbcdc515f 100644
--- a/compiler/rename/RnHsSyn.lhs
+++ b/compiler/rename/RnHsSyn.lhs
@@ -22,7 +22,7 @@ import TysWiredIn       ( tupleTyCon, listTyCon, parrTyCon, charTyCon )
 import Name             ( Name, getName, isTyVarName )
 import NameSet
 import BasicTypes       ( Boxity )
-import SrcLoc           ( Located(..), unLoc )
+import SrcLoc
 \end{code}
 
 %************************************************************************
diff --git a/compiler/rename/RnNames.lhs b/compiler/rename/RnNames.lhs
index 46058c4677..3867e17693 100644
--- a/compiler/rename/RnNames.lhs
+++ b/compiler/rename/RnNames.lhs
@@ -1256,7 +1256,9 @@ warnUnusedImportDecls gbl_env
        ; ifDOptM Opt_D_dump_minimal_imports $
          printMinimalImports usage }
   where
-    explicit_import (L loc _) = isGoodSrcSpan loc
+    explicit_import (L loc _) = case loc of
+                                UnhelpfulSpan _ -> False
+                                RealSrcSpan _ -> True
         -- Filter out the implicit Prelude import
         -- which we do not want to bleat about
 \end{code}