swift: Propagate all protos with synthesized impls

.golden/swiftGenericNewtypeSpec/golden

@@ -1,4 +1,4 @@
-struct LTree<A: Codable>: CaseIterable, Hashable, Codable {
+struct LTree<A: Hashable & Codable>: Hashable, Codable {
     typealias LTreeTag = Tagged<LTree, [A]>
     let value: LTreeTag
 }

.golden/swiftGenericStructSpec/golden

@@ -1,4 +1,4 @@
-struct Tree<A: Codable>: Codable {
+struct Tree<A: Hashable & Codable>: Hashable, Codable {
     var rootLabel: A
     var subForest: [Tree<A>]
 }

.golden/swiftMultipleTypeVariableSpec/golden

@@ -1,4 +1,4 @@
-struct Data<A: Codable, B: Codable>: CaseIterable, Hashable, Codable {
+struct Data<A: Hashable & Codable, B: Hashable & Codable>: CaseIterable, Hashable, Codable {
     var field0: A
     var field1: B
 }

.golden/swiftTypeVariableSpec/golden

@@ -1,3 +1,3 @@
-struct Data<A: Codable>: CaseIterable, Hashable, Codable {
+struct Data<A: Hashable & Codable>: CaseIterable, Hashable, Codable {
     var field0: A
 }

src/Moat/Pretty/Swift.hs

@@ -109,17 +109,17 @@ prettyRawValueAndProtocols Nothing ps = ": " ++ prettyProtocols ps
 prettyRawValueAndProtocols (Just ty) [] = ": " ++ prettyMoatType ty
 prettyRawValueAndProtocols (Just ty) ps = ": " ++ prettyMoatType ty ++ ", " ++ prettyProtocols ps
 
+prettyProtocol :: Protocol -> String
+prettyProtocol = \case
+  Hashable -> "Hashable"
+  Codable -> "Codable"
+  Equatable -> "Equatable"
+  OtherProtocol s -> s
+
 prettyProtocols :: [Protocol] -> String
 prettyProtocols = \case
   [] -> ""
   ps -> intercalate ", " (prettyProtocol <$> ps)
-    where
-      prettyProtocol :: Protocol -> String
-      prettyProtocol = \case
-        Hashable -> "Hashable"
-        Codable -> "Codable"
-        Equatable -> "Equatable"
-        OtherProtocol s -> s
 
 -- TODO: Need a plan to avoid @error@ in these pure functions
 {-# ANN prettyTags "HLint: ignore" #-}
@@ -269,7 +269,27 @@ onLast :: (a -> a) -> [a] -> [a]
 onLast _ [] = []
 onLast f (x : xs) = x : map f xs
 
+-- | Copy protocols from the parent type to upper bounds of generic type
+--   parameters.
+--
+--   This is needed for protocols with compiler-synthesized implementations
+--   (similar to 'deriving stock'), of which there are currently three:
+--
+--   - 'Equatable'
+--   - 'Hashable'
+--   - 'Codable'
+--
+--   See the [Swift documentation](https://docs.swift.org/swift-book/documentation/the-swift-programming-language/protocols#Adopting-a-Protocol-Using-a-Synthesized-Implementation).
 addTyVarBounds :: [String] -> [Protocol] -> [String]
-addTyVarBounds tyVars protos
-  | Codable `elem` protos = map (++ ": Codable") tyVars
-  | otherwise = tyVars
+addTyVarBounds tyVars protos =
+  let isSynthesized :: Protocol -> Bool
+      isSynthesized = \case
+        Hashable -> True
+        Codable -> True
+        Equatable -> True
+        OtherProtocol _ -> False
+      synthesizedProtos = filter isSynthesized protos
+      bounds = ": " ++ intercalate " & " (map prettyProtocol synthesizedProtos)
+   in case synthesizedProtos of
+        [] -> tyVars
+        _ -> map (++ bounds) tyVars

test/GenericNewtypeSpec.hs

@@ -16,7 +16,7 @@ mobileGenWith
   ( defaultOptions
       { dataAnnotations = [Parcelize, Serializable]
       , dataInterfaces = [Parcelable]
-      , dataProtocols = [OtherProtocol "CaseIterable", Hashable, Codable]
+      , dataProtocols = [Hashable, Codable]
       , dataRawValue = Just Str
       , generateDocComments = False
       }

test/GenericStructSpec.hs

@@ -12,7 +12,7 @@ import Prelude
 mobileGenWith
   ( defaultOptions
       { dataInterfaces = [Parcelable]
-      , dataProtocols = [Codable]
+      , dataProtocols = [Hashable, Codable]
       , generateDocComments = False
       }
   )