Deprecate sum-type tables (#1385)

* wow * Add changelog * Deprecate sum tables
yesodweb · Apr 12, 2022 · d6453cf · d6453cf
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diff --git a/persistent/ChangeLog.md b/persistent/ChangeLog.md
@@ -1,5 +1,6 @@
 # Changelog for persistent
 
+
 ## 2.14.0.0 (unreleased)
 
 * [#1386](https://github.com/yesodweb/persistent/pull/1386)
@@ -9,6 +10,10 @@
       instead.
     * Remove the `CompositeDef` constructor from `ReferenceDef` which was not
       used internally anymore.
+* [#1385](https://github.com/yesodweb/persistent/pull/1385)
+    * The support for entity-level sum types is deprecated. It adds a
+      considerable amount of complexity to the code, and the pattern is not
+      particularly good for actually supporting sum types in most databases.
 * [#1384](https://github.com/yesodweb/persistent/pull/1384)
     * Add `tabulateEntityA` to the `PersistEntity` class, allowing you to
       construct an `Entity a` by providing a function `EntityField a t -> f t`.
@@ -21,7 +26,6 @@
 * [#1374](https://github.com/yesodweb/persistent/pull/1374)
     * Increasing test coverage for errors thrown when parsing entity definitions
 
-
 ## 2.13.3.4
 
 * [#1379](https://github.com/yesodweb/persistent/pull/1379)

diff --git a/persistent/Database/Persist/Quasi.hs b/persistent/Database/Persist/Quasi.hs
@@ -667,6 +667,8 @@ import Employment as Import
 
 === Entity-level
 
+NOTE: This feature is deprecated as of version 2.14 and will be removed in 2.15 (unless there are many complaints).
+
 The
 <https://github.com/yesodweb/persistent/blob/master/persistent-test/src/SumTypeTest.hs#L35 tests for this feature>
 demonstrate their usage. Note the use of the sign @+@ in front of the entity

diff --git a/persistent/Database/Persist/TH.hs b/persistent/Database/Persist/TH.hs
@@ -1761,6 +1761,15 @@ fieldError tableName fieldName err = mconcat
 
 mkEntity :: M.Map EntityNameHS a -> EntityMap -> MkPersistSettings -> UnboundEntityDef -> Q [Dec]
 mkEntity embedEntityMap entityMap mps preDef = do
+    when (isEntitySum (unboundEntityDef preDef)) $ do
+        reportWarning $ unlines
+            [ "persistent has deprecated sum type entities as of 2.14.0.0."
+            , "We will delete support for these entities in 2.15.0.0."
+            , "If you need these, please add a comment on this GitHub issue:"
+            , ""
+            , "    https://github.com/yesodweb/persistent/issues/987"
+            ]
+
     entityDefExp <- liftAndFixKeys mps embedEntityMap entityMap preDef
     let
         entDef =

diff --git a/persistent/test/Database/Persist/TH/SumSpec.hs b/persistent/test/Database/Persist/TH/SumSpec.hs
@@ -0,0 +1,43 @@
+{-# LANGUAGE DataKinds #-}
+{-# LANGUAGE DerivingStrategies #-}
+{-# LANGUAGE FlexibleContexts #-}
+{-# LANGUAGE FlexibleInstances #-}
+{-# LANGUAGE GADTs #-}
+{-# LANGUAGE GeneralizedNewtypeDeriving #-}
+{-# LANGUAGE MultiParamTypeClasses #-}
+{-# LANGUAGE OverloadedLabels #-}
+{-# LANGUAGE PartialTypeSignatures #-}
+{-# LANGUAGE QuasiQuotes #-}
+{-# LANGUAGE StandaloneDeriving #-}
+{-# LANGUAGE TemplateHaskell #-}
+{-# LANGUAGE TypeApplications #-}
+{-# LANGUAGE TypeFamilies #-}
+{-# LANGUAGE UndecidableInstances #-}
+
+module Database.Persist.TH.SumSpec where
+
+import TemplateTestImports
+
+
+import Database.Persist.TH.MultiBlockSpec.Model
+
+share
+    [ mkPersistWith sqlSettings importDefList
+    ]
+    [persistLowerCase|
+
+What
+    name Text
+
+Lamp
+    name Text
+
++Please
+    what WhatId
+    lamp LampId
+|]
+
+spec :: Spec
+spec = do
+    it "should warn" True
+
diff --git a/persistent/test/Database/Persist/THSpec.hs b/persistent/test/Database/Persist/THSpec.hs
@@ -67,6 +67,7 @@ import qualified Database.Persist.TH.RequireOnlyPersistImportSpec as RequireOnly
 import qualified Database.Persist.TH.SharedPrimaryKeyImportedSpec as SharedPrimaryKeyImportedSpec
 import qualified Database.Persist.TH.SharedPrimaryKeySpec as SharedPrimaryKeySpec
 import qualified Database.Persist.TH.ToFromPersistValuesSpec as ToFromPersistValuesSpec
+import qualified Database.Persist.TH.SumSpec as SumSpec
 
 -- test to ensure we can have types ending in Id that don't trash the TH
 -- machinery
@@ -177,6 +178,7 @@ instance Arbitrary Address where
 
 spec :: Spec
 spec = describe "THSpec" $ do
+    describe "SumSpec" $ SumSpec.spec
     PersistWithSpec.spec
     KindEntitiesSpec.spec
     NestedSymbolsInTypeSpec.spec