Do not filter out parameters with the same name in pagination links

src/Yesod/Paginator/Widgets.hs

@@ -178,10 +178,12 @@ getUpdateGetParams
 getUpdateGetParams pageParamName = do
     params <- handlerToWidget $ reqGetParams <$> getRequest
     pure
-        $ \number ->
-              nubOn fst
-                  $ [(unPageParamName pageParamName, tshow number)]
-                  <> params
+        $ \number -> formatParams number params
+  where
+    formatParams :: Show a => a -> [(Text, Text)] -> [(Text, Text)]
+    formatParams number params =
+      let name = unPageParamName pageParamName
+      in [(name, tshow number)] <> filter ((/=) name . fst) params
 
 renderGetParams :: [(Text, Text)] -> Text
 renderGetParams [] = ""

test/Yesod/Paginator/WidgetsSpec.hs

@@ -1,56 +1,77 @@
 {-# LANGUAGE OverloadedStrings #-}
 module Yesod.Paginator.WidgetsSpec
     ( spec
-    )
-where
+    ) where
 
 import SpecHelper
 
 spec :: Spec
 spec = withApp $ do
-    describe "simple" $ it "works" $ do
-        get $ SimpleR 10 3 3
-
-        statusIs 200
-        bodyContains $ concat
-            [ "<ul class=\"pagination\">"
-            , "<li class=\"prev disabled\"><a>«</a></li>"
-            , "<li class=\"active disabled\"><a>1</a></li>"
-            , "<li class=\"next\"><a href=\"?p=2\">2</a></li>"
-            , "<li class=\"next\"><a href=\"?p=3\">3</a></li>"
-            , "<li class=\"next\"><a href=\"?p=2\">»</a></li>"
-            , "</ul>"
-            ]
-
-        request $ do
-            addGetParam "p" "3"
-            setUrl $ SimpleR 10 3 3
-
-        statusIs 200
-        bodyContains $ concat
-            [ "<ul class=\"pagination\">"
-            , "<li class=\"prev\"><a href=\"?p=2\">«</a></li>"
-            , "<li class=\"prev\"><a href=\"?p=2\">2</a></li>"
-            , "<li class=\"active disabled\"><a>3</a></li>"
-            , "<li class=\"next\"><a href=\"?p=4\">4</a></li>"
-            , "<li class=\"next\"><a href=\"?p=4\">»</a></li>"
-            , "</ul>"
-            ]
-
-        request $ do
-            addGetParam "p" "4"
-            setUrl $ SimpleR 10 3 3
-
-        statusIs 200
-        bodyContains $ concat
-            [ "<ul class=\"pagination\">"
-            , "<li class=\"prev\"><a href=\"?p=3\">«</a></li>"
-            , "<li class=\"prev\"><a href=\"?p=2\">2</a></li>"
-            , "<li class=\"prev\"><a href=\"?p=3\">3</a></li>"
-            , "<li class=\"active disabled\"><a>4</a></li>"
-            , "<li class=\"next disabled\"><a>»</a></li>"
-            , "</ul>"
-            ]
+    describe "simple" $ do
+        it "works" $ do
+            get $ SimpleR 10 3 3
+
+            statusIs 200
+            bodyContains $ concat
+                [ "<ul class=\"pagination\">"
+                , "<li class=\"prev disabled\"><a>«</a></li>"
+                , "<li class=\"active disabled\"><a>1</a></li>"
+                , "<li class=\"next\"><a href=\"?p=2\">2</a></li>"
+                , "<li class=\"next\"><a href=\"?p=3\">3</a></li>"
+                , "<li class=\"next\"><a href=\"?p=2\">»</a></li>"
+                , "</ul>"
+                ]
+
+            request $ do
+                addGetParam "p" "3"
+                setUrl $ SimpleR 10 3 3
+
+            statusIs 200
+            bodyContains $ concat
+                [ "<ul class=\"pagination\">"
+                , "<li class=\"prev\"><a href=\"?p=2\">«</a></li>"
+                , "<li class=\"prev\"><a href=\"?p=2\">2</a></li>"
+                , "<li class=\"active disabled\"><a>3</a></li>"
+                , "<li class=\"next\"><a href=\"?p=4\">4</a></li>"
+                , "<li class=\"next\"><a href=\"?p=4\">»</a></li>"
+                , "</ul>"
+                ]
+
+            request $ do
+                addGetParam "p" "4"
+                setUrl $ SimpleR 10 3 3
+
+            statusIs 200
+            bodyContains $ concat
+                [ "<ul class=\"pagination\">"
+                , "<li class=\"prev\"><a href=\"?p=3\">«</a></li>"
+                , "<li class=\"prev\"><a href=\"?p=2\">2</a></li>"
+                , "<li class=\"prev\"><a href=\"?p=3\">3</a></li>"
+                , "<li class=\"active disabled\"><a>4</a></li>"
+                , "<li class=\"next disabled\"><a>»</a></li>"
+                , "</ul>"
+                ]
+
+        it "includes all parameters with the same name" $ do
+            get $ SimpleR 10 3 3
+
+            request $ do
+                addGetParam "p" "3"
+                addGetParam "ids[]" "1"
+                addGetParam "ids[]" "2"
+                setUrl $ SimpleR 10 3 3
+
+            statusIs 200
+
+            bodyContains $ concat
+                [ "<ul class=\"pagination\">"
+                , "<li class=\"prev\"><a href=\"?p=2&amp;ids%5B%5D=2&amp;ids%5B%5D=1\">«</a></li>"
+                , "<li class=\"prev\"><a href=\"?p=2&amp;ids%5B%5D=2&amp;ids%5B%5D=1\">2</a></li>"
+                , "<li class=\"active disabled\"><a>3</a></li>"
+                , "<li class=\"next\"><a href=\"?p=4&amp;ids%5B%5D=2&amp;ids%5B%5D=1\">4</a></li>"
+                , "<li class=\"next\"><a href=\"?p=4&amp;ids%5B%5D=2&amp;ids%5B%5D=1\">»</a></li>"
+                , "</ul>"
+                ]
 
     describe "ellipsed" $ it "works" $ do
         get $ EllipsedR 10 3 3