Use hie files as source of truth for name source spans.

Since we started reusing `.hi` files, this exposes a bug where definitions
aren't available since a bad source span from the `.hi` file gets put into
the NameCache. We rectify by ensuring the span in the NameCache always matches
the one from the `.hie` file.

This has surfaced because an interaction between the commit which uses `.hi`
instead of retypechecking and the change to use the shared global NameCache
to read `.hie` files.

src-ghc86/Development/IDE/GHC/HieBin.hs

@@ -339,7 +339,12 @@ fromHieName :: NameCache -> HieName -> (NameCache, Name)
 fromHieName nc (ExternalName mod occ span) =
     let cache = nsNames nc
     in case lookupOrigNameCache cache mod occ of
-         Just name -> (nc, name)
+         Just name
+           | nameSrcSpan name == span -> (nc, name)
+           | otherwise ->
+             let name' = setNameLoc name span
+                 new_cache = extendNameCache cache mod occ name'
+             in ( nc{ nsNames = new_cache }, name' )
          Nothing ->
            let (uniq, us) = takeUniqFromSupply (nsUniqs nc)
                name       = mkExternalName uniq mod occ span