Move Iface.Load errors into Iface.Errors module

This commit moves the error-related functions in `GHC.Iface.Load` into
a brand new module called `GHC.Iface.Errors`. This will avoid boot files
and circular dependencies in the context of #18516, in the
pretty-printing modules.

3 files changed, 341 insertions, 320 deletions

diff --git a/compiler/GHC/Iface/Errors.hs b/compiler/GHC/Iface/Errors.hs
new file mode 100644
index 0000000000..6cfa09f99d
--- /dev/null
+++ b/compiler/GHC/Iface/Errors.hs
@@ -0,0 +1,335 @@
+
+{-# LANGUAGE FlexibleContexts #-}
+
+module GHC.Iface.Errors
+  ( badIfaceFile
+  , hiModuleNameMismatchWarn
+  , homeModError
+  , cannotFindInterface
+  , cantFindInstalledErr
+  , cannotFindModule
+  , cantFindErr
+  -- * Utility functions
+  , mayShowLocations
+  ) where
+
+import GHC.Platform.Profile
+import GHC.Platform.Ways
+import GHC.Utils.Panic.Plain
+import GHC.Data.FastString
+import GHC.Driver.Session
+import GHC.Driver.Env.Types
+import GHC.Data.Maybe
+import GHC.Prelude
+import GHC.Unit
+import GHC.Unit.Env
+import GHC.Unit.Finder.Types
+import GHC.Unit.State
+import GHC.Utils.Outputable as Outputable
+
+
+badIfaceFile :: String -> SDoc -> SDoc
+badIfaceFile file err
+  = vcat [text "Bad interface file:" <+> text file,
+          nest 4 err]
+
+hiModuleNameMismatchWarn :: Module -> Module -> SDoc
+hiModuleNameMismatchWarn requested_mod read_mod
+ | moduleUnit requested_mod == moduleUnit read_mod =
+    sep [text "Interface file contains module" <+> quotes (ppr read_mod) <> comma,
+         text "but we were expecting module" <+> quotes (ppr requested_mod),
+         sep [text "Probable cause: the source code which generated interface file",
+             text "has an incompatible module name"
+            ]
+        ]
+ | otherwise =
+  -- ToDo: This will fail to have enough qualification when the package IDs
+  -- are the same
+  withPprStyle (mkUserStyle alwaysQualify AllTheWay) $
+    -- we want the Modules below to be qualified with package names,
+    -- so reset the PrintUnqualified setting.
+    hsep [ text "Something is amiss; requested module "
+         , ppr requested_mod
+         , text "differs from name found in the interface file"
+         , ppr read_mod
+         , parens (text "if these names look the same, try again with -dppr-debug")
+         ]
+
+homeModError :: InstalledModule -> ModLocation -> SDoc
+-- See Note [Home module load error]
+homeModError mod location
+  = text "attempting to use module " <> quotes (ppr mod)
+    <> (case ml_hs_file location of
+           Just file -> space <> parens (text file)
+           Nothing   -> Outputable.empty)
+    <+> text "which is not loaded"
+
+
+-- -----------------------------------------------------------------------------
+-- Error messages
+
+cannotFindInterface :: UnitState -> HomeUnit -> Profile -> ([FilePath] -> SDoc) -> ModuleName -> InstalledFindResult -> SDoc
+cannotFindInterface = cantFindInstalledErr (sLit "Failed to load interface for")
+                                           (sLit "Ambiguous interface for")
+
+cantFindInstalledErr
+    :: PtrString
+    -> PtrString
+    -> UnitState
+    -> HomeUnit
+    -> Profile
+    -> ([FilePath] -> SDoc)
+    -> ModuleName
+    -> InstalledFindResult
+    -> SDoc
+cantFindInstalledErr cannot_find _ unit_state home_unit profile tried_these mod_name find_result
+  = ptext cannot_find <+> quotes (ppr mod_name)
+    $$ more_info
+  where
+    build_tag  = waysBuildTag (profileWays profile)
+
+    more_info
+      = case find_result of
+            InstalledNoPackage pkg
+                -> text "no unit id matching" <+> quotes (ppr pkg) <+>
+                   text "was found" $$ looks_like_srcpkgid pkg
+
+            InstalledNotFound files mb_pkg
+                | Just pkg <- mb_pkg, not (isHomeUnitId home_unit pkg)
+                -> not_found_in_package pkg files
+
+                | null files
+                -> text "It is not a module in the current program, or in any known package."
+
+                | otherwise
+                -> tried_these files
+
+            _ -> panic "cantFindInstalledErr"
+
+    looks_like_srcpkgid :: UnitId -> SDoc
+    looks_like_srcpkgid pk
+     -- Unsafely coerce a unit id (i.e. an installed package component
+     -- identifier) into a PackageId and see if it means anything.
+     | (pkg:pkgs) <- searchPackageId unit_state (PackageId (unitIdFS pk))
+     = parens (text "This unit ID looks like the source package ID;" $$
+       text "the real unit ID is" <+> quotes (ftext (unitIdFS (unitId pkg))) $$
+       (if null pkgs then Outputable.empty
+        else text "and" <+> int (length pkgs) <+> text "other candidates"))
+     -- Todo: also check if it looks like a package name!
+     | otherwise = Outputable.empty
+
+    not_found_in_package pkg files
+       | build_tag /= ""
+       = let
+            build = if build_tag == "p" then "profiling"
+                                        else "\"" ++ build_tag ++ "\""
+         in
+         text "Perhaps you haven't installed the " <> text build <>
+         text " libraries for package " <> quotes (ppr pkg) <> char '?' $$
+         tried_these files
+
+       | otherwise
+       = text "There are files missing in the " <> quotes (ppr pkg) <>
+         text " package," $$
+         text "try running 'ghc-pkg check'." $$
+         tried_these files
+
+mayShowLocations :: DynFlags -> [FilePath] -> SDoc
+mayShowLocations dflags files
+    | null files = Outputable.empty
+    | verbosity dflags < 3 =
+          text "Use -v (or `:set -v` in ghci) " <>
+              text "to see a list of the files searched for."
+    | otherwise =
+          hang (text "Locations searched:") 2 $ vcat (map text files)
+
+cannotFindModule :: HscEnv -> ModuleName -> FindResult -> SDoc
+cannotFindModule hsc_env = cannotFindModule'
+    (hsc_dflags   hsc_env)
+    (hsc_unit_env hsc_env)
+    (targetProfile (hsc_dflags hsc_env))
+
+
+cannotFindModule' :: DynFlags -> UnitEnv -> Profile -> ModuleName -> FindResult -> SDoc
+cannotFindModule' dflags unit_env profile mod res = pprWithUnitState (ue_units unit_env) $
+  cantFindErr (gopt Opt_BuildingCabalPackage dflags)
+              (sLit cannotFindMsg)
+              (sLit "Ambiguous module name")
+              unit_env
+              profile
+              (mayShowLocations dflags)
+              mod
+              res
+  where
+    cannotFindMsg =
+      case res of
+        NotFound { fr_mods_hidden = hidden_mods
+                 , fr_pkgs_hidden = hidden_pkgs
+                 , fr_unusables = unusables }
+          | not (null hidden_mods && null hidden_pkgs && null unusables)
+          -> "Could not load module"
+        _ -> "Could not find module"
+
+cantFindErr
+    :: Bool -- ^ Using Cabal?
+    -> PtrString
+    -> PtrString
+    -> UnitEnv
+    -> Profile
+    -> ([FilePath] -> SDoc)
+    -> ModuleName
+    -> FindResult
+    -> SDoc
+cantFindErr _ _ multiple_found _ _ _ mod_name (FoundMultiple mods)
+  | Just pkgs <- unambiguousPackages
+  = hang (ptext multiple_found <+> quotes (ppr mod_name) <> colon) 2 (
+       sep [text "it was found in multiple packages:",
+                hsep (map ppr pkgs) ]
+    )
+  | otherwise
+  = hang (ptext multiple_found <+> quotes (ppr mod_name) <> colon) 2 (
+       vcat (map pprMod mods)
+    )
+  where
+    unambiguousPackages = foldl' unambiguousPackage (Just []) mods
+    unambiguousPackage (Just xs) (m, ModOrigin (Just _) _ _ _)
+        = Just (moduleUnit m : xs)
+    unambiguousPackage _ _ = Nothing
+
+    pprMod (m, o) = text "it is bound as" <+> ppr m <+>
+                                text "by" <+> pprOrigin m o
+    pprOrigin _ ModHidden = panic "cantFindErr: bound by mod hidden"
+    pprOrigin _ (ModUnusable _) = panic "cantFindErr: bound by mod unusable"
+    pprOrigin m (ModOrigin e res _ f) = sep $ punctuate comma (
+      if e == Just True
+          then [text "package" <+> ppr (moduleUnit m)]
+          else [] ++
+      map ((text "a reexport in package" <+>)
+                .ppr.mkUnit) res ++
+      if f then [text "a package flag"] else []
+      )
+
+cantFindErr using_cabal cannot_find _ unit_env profile tried_these mod_name find_result
+  = ptext cannot_find <+> quotes (ppr mod_name)
+    $$ more_info
+  where
+    mhome_unit = ue_home_unit unit_env
+    more_info
+      = case find_result of
+            NoPackage pkg
+                -> text "no unit id matching" <+> quotes (ppr pkg) <+>
+                   text "was found"
+
+            NotFound { fr_paths = files, fr_pkg = mb_pkg
+                     , fr_mods_hidden = mod_hiddens, fr_pkgs_hidden = pkg_hiddens
+                     , fr_unusables = unusables, fr_suggestions = suggest }
+                | Just pkg <- mb_pkg
+                , Nothing <- mhome_unit           -- no home-unit
+                -> not_found_in_package pkg files
+
+                | Just pkg <- mb_pkg
+                , Just home_unit <- mhome_unit    -- there is a home-unit but the
+                , not (isHomeUnit home_unit pkg)  -- module isn't from it
+                -> not_found_in_package pkg files
+
+                | not (null suggest)
+                -> pp_suggestions suggest $$ tried_these files
+
+                | null files && null mod_hiddens &&
+                  null pkg_hiddens && null unusables
+                -> text "It is not a module in the current program, or in any known package."
+
+                | otherwise
+                -> vcat (map pkg_hidden pkg_hiddens) $$
+                   vcat (map mod_hidden mod_hiddens) $$
+                   vcat (map unusable unusables) $$
+                   tried_these files
+
+            _ -> panic "cantFindErr"
+
+    build_tag = waysBuildTag (profileWays profile)
+
+    not_found_in_package pkg files
+       | build_tag /= ""
+       = let
+            build = if build_tag == "p" then "profiling"
+                                        else "\"" ++ build_tag ++ "\""
+         in
+         text "Perhaps you haven't installed the " <> text build <>
+         text " libraries for package " <> quotes (ppr pkg) <> char '?' $$
+         tried_these files
+
+       | otherwise
+       = text "There are files missing in the " <> quotes (ppr pkg) <>
+         text " package," $$
+         text "try running 'ghc-pkg check'." $$
+         tried_these files
+
+    pkg_hidden :: Unit -> SDoc
+    pkg_hidden uid =
+        text "It is a member of the hidden package"
+        <+> quotes (ppr uid)
+        --FIXME: we don't really want to show the unit id here we should
+        -- show the source package id or installed package id if it's ambiguous
+        <> dot $$ pkg_hidden_hint uid
+
+    pkg_hidden_hint uid
+     | using_cabal
+        = let pkg = expectJust "pkg_hidden" (lookupUnit (ue_units unit_env) uid)
+           in text "Perhaps you need to add" <+>
+              quotes (ppr (unitPackageName pkg)) <+>
+              text "to the build-depends in your .cabal file."
+     | Just pkg <- lookupUnit (ue_units unit_env) uid
+         = text "You can run" <+>
+           quotes (text ":set -package " <> ppr (unitPackageName pkg)) <+>
+           text "to expose it." $$
+           text "(Note: this unloads all the modules in the current scope.)"
+     | otherwise = Outputable.empty
+
+    mod_hidden pkg =
+        text "it is a hidden module in the package" <+> quotes (ppr pkg)
+
+    unusable (pkg, reason)
+      = text "It is a member of the package"
+      <+> quotes (ppr pkg)
+      $$ pprReason (text "which is") reason
+
+    pp_suggestions :: [ModuleSuggestion] -> SDoc
+    pp_suggestions sugs
+      | null sugs = Outputable.empty
+      | otherwise = hang (text "Perhaps you meant")
+                       2 (vcat (map pp_sugg sugs))
+
+    -- NB: Prefer the *original* location, and then reexports, and then
+    -- package flags when making suggestions.  ToDo: if the original package
+    -- also has a reexport, prefer that one
+    pp_sugg (SuggestVisible m mod o) = ppr m <+> provenance o
+      where provenance ModHidden = Outputable.empty
+            provenance (ModUnusable _) = Outputable.empty
+            provenance (ModOrigin{ fromOrigUnit = e,
+                                   fromExposedReexport = res,
+                                   fromPackageFlag = f })
+              | Just True <- e
+                 = parens (text "from" <+> ppr (moduleUnit mod))
+              | f && moduleName mod == m
+                 = parens (text "from" <+> ppr (moduleUnit mod))
+              | (pkg:_) <- res
+                 = parens (text "from" <+> ppr (mkUnit pkg)
+                    <> comma <+> text "reexporting" <+> ppr mod)
+              | f
+                 = parens (text "defined via package flags to be"
+                    <+> ppr mod)
+              | otherwise = Outputable.empty
+    pp_sugg (SuggestHidden m mod o) = ppr m <+> provenance o
+      where provenance ModHidden =  Outputable.empty
+            provenance (ModUnusable _) = Outputable.empty
+            provenance (ModOrigin{ fromOrigUnit = e,
+                                   fromHiddenReexport = rhs })
+              | Just False <- e
+                 = parens (text "needs flag -package-id"
+                    <+> ppr (moduleUnit mod))
+              | (pkg:_) <- rhs
+                 = parens (text "needs flag -package-id"
+                    <+> ppr (mkUnit pkg))
+              | otherwise = Outputable.empty
+
diff --git a/compiler/GHC/Iface/Load.hs b/compiler/GHC/Iface/Load.hs
index d2d3e858e9..b52498129f 100644
--- a/compiler/GHC/Iface/Load.hs
+++ b/compiler/GHC/Iface/Load.hs
@@ -32,14 +32,12 @@ module GHC.Iface.Load (
         pprModIfaceSimple,
         ifaceStats, pprModIface, showIface,
 
-        cannotFindModule
+        module Iface_Errors -- avoids boot files in Ppr modules
    ) where
 
 #include "HsVersions.h"
 
 import GHC.Prelude
-import GHC.Platform.Ways
-import GHC.Platform.Profile
 
 import {-# SOURCE #-} GHC.IfaceToCore
    ( tcIfaceDecls, tcIfaceRules, tcIfaceInst, tcIfaceFamInst
@@ -57,6 +55,7 @@ import GHC.Iface.Ext.Fields
 import GHC.Iface.Binary
 import GHC.Iface.Rename
 import GHC.Iface.Env
+import GHC.Iface.Errors as Iface_Errors
 
 import GHC.Tc.Utils.Monad
 
@@ -105,13 +104,12 @@ import GHC.Unit.State
 import GHC.Unit.Home
 import GHC.Unit.Home.ModInfo
 import GHC.Unit.Finder
-import GHC.Unit.Env
+import GHC.Unit.Env ( ue_hpt )
 
 import GHC.Data.Maybe
 import GHC.Data.FastString
 
 import Control.Monad
-import Control.Exception
 import Data.Map ( toList )
 import System.FilePath
 import System.Directory
@@ -709,7 +707,7 @@ computeInterface hsc_env doc_str hi_boot_file mod0 = do
           Succeeded (iface0, path) ->
             rnModIface hsc_env (instUnitInsts (moduleUnit indef)) Nothing iface0 >>= \case
               Right x   -> return (Succeeded (x, path))
-              Left errs -> throwIO . mkSrcErr $ errs
+              Left errs -> throwErrors errs
           Failed err -> return (Failed err)
       (mod, _) -> find_iface mod
 
@@ -909,7 +907,7 @@ findAndReadIface logger name_cache fc hooks unit_state home_unit dflags doc_str
                                       unit_state
                                       home_unit
                                       profile
-                                      (may_show_locations dflags)
+                                      (Iface_Errors.mayShowLocations dflags)
                                       (moduleName mod)
                                       err
 
@@ -1227,316 +1225,3 @@ pprExtensibleFields (ExtensibleFields fs) = vcat . map pprField $ toList fs
   where
     pprField (name, (BinData size _data)) = text name <+> text "-" <+> ppr size <+> text "bytes"
 
-{-
-*********************************************************
-*                                                       *
-\subsection{Errors}
-*                                                       *
-*********************************************************
--}
-
-badIfaceFile :: String -> SDoc -> SDoc
-badIfaceFile file err
-  = vcat [text "Bad interface file:" <+> text file,
-          nest 4 err]
-
-hiModuleNameMismatchWarn :: Module -> Module -> SDoc
-hiModuleNameMismatchWarn requested_mod read_mod
- | moduleUnit requested_mod == moduleUnit read_mod =
-    sep [text "Interface file contains module" <+> quotes (ppr read_mod) <> comma,
-         text "but we were expecting module" <+> quotes (ppr requested_mod),
-         sep [text "Probable cause: the source code which generated interface file",
-             text "has an incompatible module name"
-            ]
-        ]
- | otherwise =
-  -- ToDo: This will fail to have enough qualification when the package IDs
-  -- are the same
-  withPprStyle (mkUserStyle alwaysQualify AllTheWay) $
-    -- we want the Modules below to be qualified with package names,
-    -- so reset the PrintUnqualified setting.
-    hsep [ text "Something is amiss; requested module "
-         , ppr requested_mod
-         , text "differs from name found in the interface file"
-         , ppr read_mod
-         , parens (text "if these names look the same, try again with -dppr-debug")
-         ]
-
-homeModError :: InstalledModule -> ModLocation -> SDoc
--- See Note [Home module load error]
-homeModError mod location
-  = text "attempting to use module " <> quotes (ppr mod)
-    <> (case ml_hs_file location of
-           Just file -> space <> parens (text file)
-           Nothing   -> Outputable.empty)
-    <+> text "which is not loaded"
-
-
--- -----------------------------------------------------------------------------
--- Error messages
-
-cannotFindInterface :: UnitState -> HomeUnit -> Profile -> ([FilePath] -> SDoc) -> ModuleName -> InstalledFindResult -> SDoc
-cannotFindInterface = cantFindInstalledErr (sLit "Failed to load interface for")
-                                           (sLit "Ambiguous interface for")
-
-cantFindInstalledErr
-    :: PtrString
-    -> PtrString
-    -> UnitState
-    -> HomeUnit
-    -> Profile
-    -> ([FilePath] -> SDoc)
-    -> ModuleName
-    -> InstalledFindResult
-    -> SDoc
-cantFindInstalledErr cannot_find _ unit_state home_unit profile tried_these mod_name find_result
-  = ptext cannot_find <+> quotes (ppr mod_name)
-    $$ more_info
-  where
-    build_tag  = waysBuildTag (profileWays profile)
-
-    more_info
-      = case find_result of
-            InstalledNoPackage pkg
-                -> text "no unit id matching" <+> quotes (ppr pkg) <+>
-                   text "was found" $$ looks_like_srcpkgid pkg
-
-            InstalledNotFound files mb_pkg
-                | Just pkg <- mb_pkg, not (isHomeUnitId home_unit pkg)
-                -> not_found_in_package pkg files
-
-                | null files
-                -> text "It is not a module in the current program, or in any known package."
-
-                | otherwise
-                -> tried_these files
-
-            _ -> panic "cantFindInstalledErr"
-
-    looks_like_srcpkgid :: UnitId -> SDoc
-    looks_like_srcpkgid pk
-     -- Unsafely coerce a unit id (i.e. an installed package component
-     -- identifier) into a PackageId and see if it means anything.
-     | (pkg:pkgs) <- searchPackageId unit_state (PackageId (unitIdFS pk))
-     = parens (text "This unit ID looks like the source package ID;" $$
-       text "the real unit ID is" <+> quotes (ftext (unitIdFS (unitId pkg))) $$
-       (if null pkgs then Outputable.empty
-        else text "and" <+> int (length pkgs) <+> text "other candidates"))
-     -- Todo: also check if it looks like a package name!
-     | otherwise = Outputable.empty
-
-    not_found_in_package pkg files
-       | build_tag /= ""
-       = let
-            build = if build_tag == "p" then "profiling"
-                                        else "\"" ++ build_tag ++ "\""
-         in
-         text "Perhaps you haven't installed the " <> text build <>
-         text " libraries for package " <> quotes (ppr pkg) <> char '?' $$
-         tried_these files
-
-       | otherwise
-       = text "There are files missing in the " <> quotes (ppr pkg) <>
-         text " package," $$
-         text "try running 'ghc-pkg check'." $$
-         tried_these files
-
-may_show_locations :: DynFlags -> [FilePath] -> SDoc
-may_show_locations dflags files
-    | null files = Outputable.empty
-    | verbosity dflags < 3 =
-          text "Use -v (or `:set -v` in ghci) " <>
-              text "to see a list of the files searched for."
-    | otherwise =
-          hang (text "Locations searched:") 2 $ vcat (map text files)
-
-cannotFindModule :: HscEnv -> ModuleName -> FindResult -> SDoc
-cannotFindModule hsc_env = cannotFindModule'
-    (hsc_dflags   hsc_env)
-    (hsc_unit_env hsc_env)
-    (targetProfile (hsc_dflags hsc_env))
-
-
-cannotFindModule' :: DynFlags -> UnitEnv -> Profile -> ModuleName -> FindResult -> SDoc
-cannotFindModule' dflags unit_env profile mod res = pprWithUnitState (ue_units unit_env) $
-  cantFindErr (gopt Opt_BuildingCabalPackage dflags)
-              (sLit cannotFindMsg)
-              (sLit "Ambiguous module name")
-              unit_env
-              profile
-              (may_show_locations dflags)
-              mod
-              res
-  where
-    cannotFindMsg =
-      case res of
-        NotFound { fr_mods_hidden = hidden_mods
-                 , fr_pkgs_hidden = hidden_pkgs
-                 , fr_unusables = unusables }
-          | not (null hidden_mods && null hidden_pkgs && null unusables)
-          -> "Could not load module"
-        _ -> "Could not find module"
-
-cantFindErr
-    :: Bool -- ^ Using Cabal?
-    -> PtrString
-    -> PtrString
-    -> UnitEnv
-    -> Profile
-    -> ([FilePath] -> SDoc)
-    -> ModuleName
-    -> FindResult
-    -> SDoc
-cantFindErr _ _ multiple_found _ _ _ mod_name (FoundMultiple mods)
-  | Just pkgs <- unambiguousPackages
-  = hang (ptext multiple_found <+> quotes (ppr mod_name) <> colon) 2 (
-       sep [text "it was found in multiple packages:",
-                hsep (map ppr pkgs) ]
-    )
-  | otherwise
-  = hang (ptext multiple_found <+> quotes (ppr mod_name) <> colon) 2 (
-       vcat (map pprMod mods)
-    )
-  where
-    unambiguousPackages = foldl' unambiguousPackage (Just []) mods
-    unambiguousPackage (Just xs) (m, ModOrigin (Just _) _ _ _)
-        = Just (moduleUnit m : xs)
-    unambiguousPackage _ _ = Nothing
-
-    pprMod (m, o) = text "it is bound as" <+> ppr m <+>
-                                text "by" <+> pprOrigin m o
-    pprOrigin _ ModHidden = panic "cantFindErr: bound by mod hidden"
-    pprOrigin _ (ModUnusable _) = panic "cantFindErr: bound by mod unusable"
-    pprOrigin m (ModOrigin e res _ f) = sep $ punctuate comma (
-      if e == Just True
-          then [text "package" <+> ppr (moduleUnit m)]
-          else [] ++
-      map ((text "a reexport in package" <+>)
-                .ppr.mkUnit) res ++
-      if f then [text "a package flag"] else []
-      )
-
-cantFindErr using_cabal cannot_find _ unit_env profile tried_these mod_name find_result
-  = ptext cannot_find <+> quotes (ppr mod_name)
-    $$ more_info
-  where
-    mhome_unit = ue_home_unit unit_env
-    more_info
-      = case find_result of
-            NoPackage pkg
-                -> text "no unit id matching" <+> quotes (ppr pkg) <+>
-                   text "was found"
-
-            NotFound { fr_paths = files, fr_pkg = mb_pkg
-                     , fr_mods_hidden = mod_hiddens, fr_pkgs_hidden = pkg_hiddens
-                     , fr_unusables = unusables, fr_suggestions = suggest }
-                | Just pkg <- mb_pkg
-                , Nothing <- mhome_unit           -- no home-unit
-                -> not_found_in_package pkg files
-
-                | Just pkg <- mb_pkg
-                , Just home_unit <- mhome_unit    -- there is a home-unit but the
-                , not (isHomeUnit home_unit pkg)  -- module isn't from it
-                -> not_found_in_package pkg files
-
-                | not (null suggest)
-                -> pp_suggestions suggest $$ tried_these files
-
-                | null files && null mod_hiddens &&
-                  null pkg_hiddens && null unusables
-                -> text "It is not a module in the current program, or in any known package."
-
-                | otherwise
-                -> vcat (map pkg_hidden pkg_hiddens) $$
-                   vcat (map mod_hidden mod_hiddens) $$
-                   vcat (map unusable unusables) $$
-                   tried_these files
-
-            _ -> panic "cantFindErr"
-
-    build_tag = waysBuildTag (profileWays profile)
-
-    not_found_in_package pkg files
-       | build_tag /= ""
-       = let
-            build = if build_tag == "p" then "profiling"
-                                        else "\"" ++ build_tag ++ "\""
-         in
-         text "Perhaps you haven't installed the " <> text build <>
-         text " libraries for package " <> quotes (ppr pkg) <> char '?' $$
-         tried_these files
-
-       | otherwise
-       = text "There are files missing in the " <> quotes (ppr pkg) <>
-         text " package," $$
-         text "try running 'ghc-pkg check'." $$
-         tried_these files
-
-    pkg_hidden :: Unit -> SDoc
-    pkg_hidden uid =
-        text "It is a member of the hidden package"
-        <+> quotes (ppr uid)
-        --FIXME: we don't really want to show the unit id here we should
-        -- show the source package id or installed package id if it's ambiguous
-        <> dot $$ pkg_hidden_hint uid
-
-    pkg_hidden_hint uid
-     | using_cabal
-        = let pkg = expectJust "pkg_hidden" (lookupUnit (ue_units unit_env) uid)
-           in text "Perhaps you need to add" <+>
-              quotes (ppr (unitPackageName pkg)) <+>
-              text "to the build-depends in your .cabal file."
-     | Just pkg <- lookupUnit (ue_units unit_env) uid
-         = text "You can run" <+>
-           quotes (text ":set -package " <> ppr (unitPackageName pkg)) <+>
-           text "to expose it." $$
-           text "(Note: this unloads all the modules in the current scope.)"
-     | otherwise = Outputable.empty
-
-    mod_hidden pkg =
-        text "it is a hidden module in the package" <+> quotes (ppr pkg)
-
-    unusable (pkg, reason)
-      = text "It is a member of the package"
-      <+> quotes (ppr pkg)
-      $$ pprReason (text "which is") reason
-
-    pp_suggestions :: [ModuleSuggestion] -> SDoc
-    pp_suggestions sugs
-      | null sugs = Outputable.empty
-      | otherwise = hang (text "Perhaps you meant")
-                       2 (vcat (map pp_sugg sugs))
-
-    -- NB: Prefer the *original* location, and then reexports, and then
-    -- package flags when making suggestions.  ToDo: if the original package
-    -- also has a reexport, prefer that one
-    pp_sugg (SuggestVisible m mod o) = ppr m <+> provenance o
-      where provenance ModHidden = Outputable.empty
-            provenance (ModUnusable _) = Outputable.empty
-            provenance (ModOrigin{ fromOrigUnit = e,
-                                   fromExposedReexport = res,
-                                   fromPackageFlag = f })
-              | Just True <- e
-                 = parens (text "from" <+> ppr (moduleUnit mod))
-              | f && moduleName mod == m
-                 = parens (text "from" <+> ppr (moduleUnit mod))
-              | (pkg:_) <- res
-                 = parens (text "from" <+> ppr (mkUnit pkg)
-                    <> comma <+> text "reexporting" <+> ppr mod)
-              | f
-                 = parens (text "defined via package flags to be"
-                    <+> ppr mod)
-              | otherwise = Outputable.empty
-    pp_sugg (SuggestHidden m mod o) = ppr m <+> provenance o
-      where provenance ModHidden =  Outputable.empty
-            provenance (ModUnusable _) = Outputable.empty
-            provenance (ModOrigin{ fromOrigUnit = e,
-                                   fromHiddenReexport = rhs })
-              | Just False <- e
-                 = parens (text "needs flag -package-id"
-                    <+> ppr (moduleUnit mod))
-              | (pkg:_) <- rhs
-                 = parens (text "needs flag -package-id"
-                    <+> ppr (mkUnit pkg))
-              | otherwise = Outputable.empty
-
diff --git a/compiler/ghc.cabal.in b/compiler/ghc.cabal.in
index 29137a146f..4178b9d0f6 100644
--- a/compiler/ghc.cabal.in
+++ b/compiler/ghc.cabal.in
@@ -438,6 +438,7 @@ Library
         GHC.Hs.Utils
         GHC.Iface.Binary
         GHC.Iface.Env
+        GHC.Iface.Errors
         GHC.Iface.Ext.Ast
         GHC.Iface.Ext.Binary
         GHC.Iface.Ext.Debug