From d82396a23fd31f5ae63bbd51a1afb60b01a57b85 Mon Sep 17 00:00:00 2001
From: Brian Carroll <brian.carroll.ireland@gmail.com>
Date: Tue, 1 Nov 2022 16:58:51 +0000
Subject: [PATCH] virtual-dom: explicit Err for UnusedViews

---
 .../virtual-dom/platform/Html/Internal.roc    | 20 ++++++++++++-------
 1 file changed, 13 insertions(+), 7 deletions(-)

diff --git a/examples/virtual-dom/platform/Html/Internal.roc b/examples/virtual-dom/platform/Html/Internal.roc
index 14639cdb9b..6cc1d853bd 100644
--- a/examples/virtual-dom/platform/Html/Internal.roc
+++ b/examples/virtual-dom/platform/Html/Internal.roc
@@ -414,30 +414,36 @@ ClientInit state : {
     staticViews: Dict HtmlId (Html state),
 }
 
-initClientApp : List U8, List Str, App state initData -> Result (ClientInit state) [ViewNotFound HtmlId, JsonError] | initData has Decoding
+initClientApp : List U8, List Str, App state initData -> Result (ClientInit state) [JsonError, ViewNotFound HtmlId, UnusedViews (List HtmlId)] | initData has Decoding
 initClientApp = \json, viewIdList, app ->
     initData <- json |> Decode.fromBytes Json.fromUtf8 |> Result.mapErr (\_ -> JsonError) |> Result.try
     state = app.initDynamic initData
     dynamicViews = app.renderDynamic state
-    unindexedViews = Dict.map dynamicViews translateStatic
-    empty = Dict.withCapacity (Dict.len unindexedViews)
-    staticViews <- indexViews viewIdList unindexedViews 0 0 empty |> Result.try
+    staticUnindexed = Dict.map dynamicViews translateStatic
+    empty = Dict.withCapacity (Dict.len staticUnindexed)
+    staticViews <- indexViews viewIdList staticUnindexed 0 0 empty |> Result.try
     Ok {
         state,
         dynamicViews,
         staticViews,
     }
 
-indexViews : List HtmlId, Dict HtmlId (Html state), Nat, Nat, Dict HtmlId (Html state) -> Result (Dict HtmlId (Html state)) [ViewNotFound HtmlId]
+indexViews : List HtmlId, Dict HtmlId (Html state), Nat, Nat, Dict HtmlId (Html state) -> Result (Dict HtmlId (Html state)) [ViewNotFound HtmlId, UnusedViews (List HtmlId)]
 indexViews = \viewIdList, unindexedViews, viewIndex, nodeIndex, indexedViews ->
     when List.get viewIdList viewIndex is
-        Err OutOfBounds -> Ok indexedViews
         Ok id ->
             view <- Dict.get unindexedViews id |> Result.mapErr (\_ -> ViewNotFound id) |> Result.try
             indexedState = indexNodes { list: List.withCapacity 1, index: nodeIndex } view
             indexedView <- List.first indexedState.list |> Result.mapErr (\_ -> ViewNotFound id) |> Result.try
             newIndexedViews = Dict.insert indexedViews id indexedView
-            indexViews viewIdList unindexedViews (viewIndex + 1) indexedState.index newIndexedViews
+            newUnindexedViews = Dict.remove unindexedViews id
+            indexViews viewIdList newUnindexedViews (viewIndex + 1) indexedState.index newIndexedViews
+
+        Err OutOfBounds ->
+            if Dict.len unindexedViews == 0 then
+                Ok indexedViews
+            else
+                Err (UnusedViews (Dict.keys unindexedViews))
 
 indexNodes : { list : List (Html state), index : Nat }, Html state -> { list : List (Html state), index : Nat }
 indexNodes = \{ list, index }, node ->