Consolidate imports in getMinimalImports (#18264)

1 files changed, 22 insertions, 3 deletions

diff --git a/compiler/GHC/Rename/Names.hs b/compiler/GHC/Rename/Names.hs
index 7531913a7b..13a592423a 100644
--- a/compiler/GHC/Rename/Names.hs
+++ b/compiler/GHC/Rename/Names.hs
@@ -4,7 +4,7 @@
 Extracting imported and top-level names in scope
 -}
 
-{-# LANGUAGE CPP, NondecreasingIndentation, MultiWayIf, NamedFieldPuns #-}
+{-# LANGUAGE CPP, NondecreasingIndentation #-}
 {-# LANGUAGE FlexibleContexts #-}
 {-# LANGUAGE RankNTypes #-}
 {-# LANGUAGE ScopedTypeVariables #-}
@@ -72,7 +72,7 @@ import Data.Either      ( partitionEithers, isRight, rights )
 import Data.Map         ( Map )
 import qualified Data.Map as Map
 import Data.Ord         ( comparing )
-import Data.List        ( partition, (\\), find, sortBy )
+import Data.List        ( partition, (\\), find, sortBy, groupBy, sortOn )
 import Data.Function    ( on )
 import qualified Data.Set as S
 import System.FilePath  ((</>))
@@ -1570,7 +1570,7 @@ decls, and simply trim their import lists.  NB that
 -}
 
 getMinimalImports :: [ImportDeclUsage] -> RnM [LImportDecl GhcRn]
-getMinimalImports = mapM mk_minimal
+getMinimalImports = fmap combine . mapM mk_minimal
   where
     mk_minimal (L l decl, used_gres, unused)
       | null unused
@@ -1623,6 +1623,25 @@ getMinimalImports = mapM mk_minimal
 
           all_non_overloaded = all (not . flIsOverloaded)
 
+    combine :: [LImportDecl GhcRn] -> [LImportDecl GhcRn]
+    combine = map merge . groupBy ((==) `on` getKey) . sortOn getKey
+
+    getKey :: LImportDecl GhcRn -> (Bool, Maybe ModuleName, ModuleName)
+    getKey decl =
+      ( isImportDeclQualified . ideclQualified $ idecl -- is this qualified? (important that this be first)
+      , unLoc <$> ideclAs idecl -- what is the qualifier (inside Maybe monad)
+      , unLoc . ideclName $ idecl -- Module Name
+      )
+      where
+        idecl :: ImportDecl GhcRn
+        idecl = unLoc decl
+
+    merge :: [LImportDecl GhcRn] -> LImportDecl GhcRn
+    merge []                     = error "getMinimalImports: unexpected empty list"
+    merge decls@((L l decl) : _) = L l (decl { ideclHiding = Just (False, L l lies) })
+      where lies = concatMap (unLoc . snd) $ mapMaybe (ideclHiding . unLoc) decls
+
+
 printMinimalImports :: HscSource -> [ImportDeclUsage] -> RnM ()
 -- See Note [Printing minimal imports]
 printMinimalImports hsc_src imports_w_usage