test: Paginated ToJSON/ToSchema

primer-service/src/Primer/Pagination.hs

@@ -6,13 +6,13 @@
 module Primer.Pagination (
   PaginationParams,
   Pagination (..),
-  Paginated,
+  -- Constructor and field accessors of Pagination exported for testing
+  Paginated (..),
   -- 'Positive' is abstract. Do not export its constructor.
   Positive (getPositive),
   mkPositive,
   pagedDefaultClamp,
   -- the following are exposed for testing
-  meta,
   PaginatedMeta (PM),
   totalItems,
   pageSize,
@@ -21,7 +21,6 @@ module Primer.Pagination (
   thisPage,
   nextPage,
   lastPage,
-  items,
   getNonNeg,
   NonNeg,
   mkNonNeg,
@@ -36,7 +35,9 @@ import Optics ((?~))
 import Primer.Database (
   OffsetLimit (OL, limit, offset),
   Page (Page, pageContents, total),
+  Session,
  )
+import Primer.OpenAPI ()
 import Servant (
   DefaultErrorFormatters,
   ErrorFormatters,
@@ -132,11 +133,21 @@ data Paginated a = Paginated
   { meta :: PaginatedMeta
   , items :: [a]
   }
-  deriving (Generic)
+  deriving (Generic, Show)
 
-instance ToJSON a => ToJSON (Paginated a)
-instance FromJSON a => FromJSON (Paginated a)
-instance ToSchema a => ToSchema (Paginated a)
+-- We may well need more instances than just Paginated Session in the future.
+-- However, giving polymorphic `instance To... (Paginated a)` can generate
+-- a schema inconsistent with the ToJSON for some 'a'.
+-- This happens because aeson and openapi3 differ in their special handling
+-- for lists (e.g. to serialise strings as strings rather than arrays of
+-- characters). In particular the instance for 'Paginated Char' is broken.
+-- See https://github.com/biocad/openapi3/issues/58
+-- We prefer to explicitly list the particular instances we need, rather
+-- than having a known broken polymorphic instance, even if we expect to
+-- never hit the broken case.
+instance ToJSON (Paginated Session)
+instance FromJSON (Paginated Session)
+instance ToSchema (Paginated Session)
 
 -- Used solely for nice bounds in schema
 newtype NonNeg = NonNeg Int

primer-service/test/Tests/OpenAPI.hs

@@ -34,7 +34,7 @@ import Primer.Gen.Core.Raw (
   genValConName,
  )
 import Primer.OpenAPI ()
-import Primer.Pagination (NonNeg, PaginatedMeta (..), Positive, mkNonNeg, mkPositive)
+import Primer.Pagination (NonNeg, Paginated (Paginated), PaginatedMeta (..), Positive, mkNonNeg, mkPositive)
 import Primer.Server (openAPIInfo)
 import Tasty (Property, property)
 import Test.Tasty (TestTree, testGroup)
@@ -178,3 +178,6 @@ genPaginatedMeta = do
 
 tasty_PaginatedMeta :: Property
 tasty_PaginatedMeta = testToJSON genPaginatedMeta
+
+tasty_Paginated :: Property
+tasty_Paginated = testToJSON $ Paginated <$> genPaginatedMeta <*> G.list (R.linear 0 10) genSession