handle trailing comma in import list properly

Author: kokobd

ghcide/src/Development/IDE/Plugin/CodeAction/ExactPrint.hs

@@ -529,12 +529,16 @@ addCommaInImportList :: Monad m =>
   -> m [LocatedAn AnnListItem a]
 addCommaInImportList lies x = do
   let hasSibling = not (null lies)
+      (EpAnn _ lastItem _) = let (L item _) = last lies in ann (item)
+      isTrailingCommaAnn (AddCommaAnn _) = True
+      isTrailingCommaAnn _ = False
+      lastItemHasTrailingComma = any isTrailingCommaAnn (lann_trailing lastItem)
   -- Add the space before the comma
   x <- pure $ setEntryDP x (SameLine $ if hasSibling then 1 else 0)
 
   -- Add the comma (if needed)
   let
-    fixLast = if hasSibling then first addComma else id
+    fixLast = if hasSibling && not lastItemHasTrailingComma then first addComma else id
     lies' = over _last fixLast lies ++ [x]
 
   pure lies'

ghcide/test/exe/Main.hs

@@ -1882,6 +1882,28 @@ extendImportTests = testGroup "extend import actions"
                     , "               )"
                     , "main = print (stuffA, stuffB)"
                     ])
+        , testSession "extend multi line import with trailing comma" $ template
+            [("ModuleA.hs", T.unlines
+                    [ "module ModuleA where"
+                    , "stuffA :: Double"
+                    , "stuffA = 0.00750"
+                    , "stuffB :: Integer"
+                    , "stuffB = 123"
+                    ])]
+            ("ModuleB.hs", T.unlines
+                    [ "module ModuleB where"
+                    , "import ModuleA (stuffB,"
+                    , "               )"
+                    , "main = print (stuffA, stuffB)"
+                    ])
+            (Range (Position 3 17) (Position 3 18))
+            ["Add stuffA to the import list of ModuleA"]
+            (T.unlines
+                    [ "module ModuleB where"
+                    , "import ModuleA (stuffB, stuffA"
+                    , "               )"
+                    , "main = print (stuffA, stuffB)"
+                    ])
         , testSession "extend single line import with method within class" $ template
             [("ModuleA.hs", T.unlines
                     [ "module ModuleA where"