Fix wire codec for multi-level extensible record chains

extra/Lamdera/Wire3/Decoder.hs

@@ -417,10 +417,11 @@ decoderForType ifaces cname tipe =
                      in decoderForType ifaces cname extendedRecord
                     Nothing -> normalDecoder
                 _ ->
-                  -- Resolve extensible records through TAlias chains,
+                  -- Resolve extensible records through TAlias chains (possibly multi-level),
                   -- e.g. Color = ColorValue { red, green, blue, alpha }
-                  case resolveTvar tvars_ tipe of
-                    TAlias _ _ _ (Filled (TRecord fieldMap Nothing)) ->
+                  -- or   Concrete = Level2 { field } where Level2 = Level1 { ... }
+                  case resolveToRecord (resolveTvar tvars_ tipe) of
+                    Just (TRecord fieldMap Nothing) ->
                       let fields = fieldMap & fieldsToList & List.sortOn (\(name, field) -> name)
                       in decodeRecord ifaces cname fields
                     _ -> normalDecoder

extra/Lamdera/Wire3/Encoder.hs

@@ -366,12 +366,13 @@ inlineIfRecordOrCall depth ifaces cname tipe tvars aType =
             Nothing -> normalEncoder
 
         _ ->
-          -- Resolve extensible records through TAlias chains,
+          -- Resolve extensible records through TAlias chains (possibly multi-level),
           -- e.g. Color = ColorValue { red, green, blue, alpha }
-          case resolveTvar tvars tipe of
-            TAlias _ _ _ (Filled extendedRecord@(TRecord _ Nothing)) ->
+          -- or   Concrete = Level2 { field } where Level2 = Level1 { ... }
+          case resolveToRecord (resolveTvar tvars tipe) of
+            Just extendedRecord ->
               deepEncoderForType depth ifaces cname extendedRecord
-            _ -> normalEncoder
+            Nothing -> normalEncoder
     Filled _ -> normalEncoder
 
 {-| Called for encoding tvar type values, i.e.

extra/Lamdera/Wire3/Helpers.hs

@@ -212,6 +212,23 @@ resolvedRecordFieldMapM fieldMap extensibleName tvarMap =
     Nothing -> Nothing
 
 
+{-| Recursively resolve TAlias chains until we find a TRecord.
+Used by Encoder/Decoder to handle multi-level extensible record chains,
+e.g. Level2 compatible = Level1 { compatible | field2 : Int }
+     Concrete = Level2 { concreteField : Bool }
+
+A single resolveTvar call may produce TAlias _ _ _ (Filled (TAlias _ _ _ (Filled (TRecord ...))))
+which requires peeling off multiple layers.
+-}
+resolveToRecord :: Type -> Maybe Type
+resolveToRecord tipe =
+  case tipe of
+    record@(TRecord _ Nothing) -> Just record
+    TAlias _ _ tvars (Filled inner) ->
+      resolveToRecord (resolveTvar tvars inner)
+    _ -> Nothing
+
+
 resolveFieldMap tipe tvarMap =
   case tipe of
     TRecord fieldMapExtended maybeNameExtended ->

test/Test/Wire.hs

@@ -131,6 +131,7 @@ wire = do
             , "src/Test/Wire_Unsupported.elm"
             , "src/Test/Wire_Unconstructable.elm"
             , "src/Test/Wire_Union_ForeignRecordAlias.elm"
+            , "src/Test/Wire_Record_Extensible6_TwoLevel.elm"
             ]
 
       let

test/scenario-alltypes/src/Test/Wire_Record_Extensible6_TwoLevel.elm

@@ -0,0 +1,148 @@
+module Test.Wire_Record_Extensible6_TwoLevel exposing (..)
+
+import Bytes.Decode
+import Bytes.Encode
+import Lamdera.Wire3
+
+
+{-| Multi-level extensible record chains where an extensible record
+extends another extensible record before being concretely filled.
+
+This pattern is used by packages like elm-css where Length extends
+LengthOrAutoOrCoverOrContain.
+-}
+
+
+
+-- Two-level chain: Level2 extends Level1, then Concrete fills it in
+
+
+type alias Level1 compatible =
+    { compatible | level1Field : String }
+
+
+expected_w3_encode_Level1 : ({ compatible | level1Field : String.String } -> Lamdera.Wire3.Encoder) -> Level1 compatible -> Lamdera.Wire3.Encoder
+expected_w3_encode_Level1 w3_x_c_compatible =
+    w3_x_c_compatible
+
+
+expected_w3_decode_Level1 w3_x_c_compatible =
+    w3_x_c_compatible
+
+
+type alias Level2 compatible =
+    Level1 { compatible | level2Field : Int }
+
+
+expected_w3_encode_Level2 : ({ compatible | level1Field : String.String, level2Field : Int } -> Lamdera.Wire3.Encoder) -> Level2 compatible -> Lamdera.Wire3.Encoder
+expected_w3_encode_Level2 w3_x_c_compatible =
+    w3_x_c_compatible
+
+
+expected_w3_decode_Level2 w3_x_c_compatible =
+    w3_x_c_compatible
+
+
+type alias TwoLevelConcrete =
+    Level2 { concreteField : Bool }
+
+
+expected_w3_encode_TwoLevelConcrete : TwoLevelConcrete -> Lamdera.Wire3.Encoder
+expected_w3_encode_TwoLevelConcrete =
+    \w3_rec_var0 ->
+        Lamdera.Wire3.encodeSequenceWithoutLength
+            [ Lamdera.Wire3.encodeBool w3_rec_var0.concreteField
+            , Lamdera.Wire3.encodeString w3_rec_var0.level1Field
+            , Lamdera.Wire3.encodeInt w3_rec_var0.level2Field
+            ]
+
+
+expected_w3_decode_TwoLevelConcrete =
+    Lamdera.Wire3.succeedDecode
+        (\concreteField0 level1Field0 level2Field0 -> { concreteField = concreteField0, level1Field = level1Field0, level2Field = level2Field0 })
+        |> Lamdera.Wire3.andMapDecode Lamdera.Wire3.decodeBool
+        |> Lamdera.Wire3.andMapDecode Lamdera.Wire3.decodeString
+        |> Lamdera.Wire3.andMapDecode Lamdera.Wire3.decodeInt
+
+
+
+-- Three-level chain
+
+
+type alias Level3 compatible =
+    Level2 { compatible | level3Field : Float }
+
+
+expected_w3_encode_Level3 : ({ compatible | level1Field : String.String, level2Field : Int, level3Field : Float } -> Lamdera.Wire3.Encoder) -> Level3 compatible -> Lamdera.Wire3.Encoder
+expected_w3_encode_Level3 w3_x_c_compatible =
+    w3_x_c_compatible
+
+
+expected_w3_decode_Level3 w3_x_c_compatible =
+    w3_x_c_compatible
+
+
+type alias ThreeLevelConcrete =
+    Level3 { deepField : Char }
+
+
+expected_w3_encode_ThreeLevelConcrete : ThreeLevelConcrete -> Lamdera.Wire3.Encoder
+expected_w3_encode_ThreeLevelConcrete =
+    \w3_rec_var0 ->
+        Lamdera.Wire3.encodeSequenceWithoutLength
+            [ Lamdera.Wire3.encodeChar w3_rec_var0.deepField
+            , Lamdera.Wire3.encodeString w3_rec_var0.level1Field
+            , Lamdera.Wire3.encodeInt w3_rec_var0.level2Field
+            , Lamdera.Wire3.encodeFloat w3_rec_var0.level3Field
+            ]
+
+
+expected_w3_decode_ThreeLevelConcrete =
+    Lamdera.Wire3.succeedDecode
+        (\deepField0 level1Field0 level2Field0 level3Field0 -> { deepField = deepField0, level1Field = level1Field0, level2Field = level2Field0, level3Field = level3Field0 })
+        |> Lamdera.Wire3.andMapDecode Lamdera.Wire3.decodeChar
+        |> Lamdera.Wire3.andMapDecode Lamdera.Wire3.decodeString
+        |> Lamdera.Wire3.andMapDecode Lamdera.Wire3.decodeInt
+        |> Lamdera.Wire3.andMapDecode Lamdera.Wire3.decodeFloat
+
+
+
+-- Union wrapping two-level concrete types
+
+
+type TwoLevelUnion
+    = WrapTwoLevel TwoLevelConcrete
+    | WrapThreeLevel ThreeLevelConcrete
+    | NoWrap
+
+
+expected_w3_encode_TwoLevelUnion : TwoLevelUnion -> Lamdera.Wire3.Encoder
+expected_w3_encode_TwoLevelUnion w3v =
+    case w3v of
+        NoWrap ->
+            Bytes.Encode.unsignedInt8 0
+
+        WrapThreeLevel v0 ->
+            Lamdera.Wire3.encodeSequenceWithoutLength [ Bytes.Encode.unsignedInt8 1, w3_encode_ThreeLevelConcrete v0 ]
+
+        WrapTwoLevel v0 ->
+            Lamdera.Wire3.encodeSequenceWithoutLength [ Bytes.Encode.unsignedInt8 2, w3_encode_TwoLevelConcrete v0 ]
+
+
+expected_w3_decode_TwoLevelUnion =
+    Bytes.Decode.unsignedInt8
+        |> Lamdera.Wire3.andThenDecode
+            (\w3v ->
+                case w3v of
+                    0 ->
+                        Lamdera.Wire3.succeedDecode NoWrap
+
+                    1 ->
+                        Lamdera.Wire3.succeedDecode WrapThreeLevel |> Lamdera.Wire3.andMapDecode w3_decode_ThreeLevelConcrete
+
+                    2 ->
+                        Lamdera.Wire3.succeedDecode WrapTwoLevel |> Lamdera.Wire3.andMapDecode w3_decode_TwoLevelConcrete
+
+                    _ ->
+                        Lamdera.Wire3.failDecode
+            )