[PlutusTx] [Builtins] Split 'FromBuiltin' and 'ToBuiltin' (#5971)

This addresses the [inconsistencies](#5547 (comment)) that we got from using the now retired `FromBuiltin`/`ToBuiltin` classes for two mutually exclusive purposes. Now we have two versions of those classes: one is used for converting builtins to Plutus Tx types and back, while the other one is for making builtins transparent/opaque within Plutus Tx. These two purposes are very similar, but also subtly different and that is explained in the docs.

plutus-core/plutus-core/src/PlutusCore/Builtin/Polymorphism.hs

@@ -8,6 +8,7 @@
 {-# LANGUAGE TypeFamilies             #-}
 {-# LANGUAGE TypeOperators            #-}
 {-# LANGUAGE UndecidableInstances     #-}
+{-# LANGUAGE UndecidableSuperClasses  #-}
 
 module PlutusCore.Builtin.Polymorphism
     ( Opaque (..)
@@ -214,7 +215,8 @@ type family AllElaboratedArgs constr x where
 -- built-in type.
 type AllBuiltinArgs
         :: forall a. (GHC.Type -> GHC.Type) -> (GHC.Type -> GHC.Constraint) -> a -> GHC.Constraint
-type AllBuiltinArgs uni constr x = AllElaboratedArgs constr (ElaborateBuiltin uni x)
+class    AllElaboratedArgs constr (ElaborateBuiltin uni x) => AllBuiltinArgs uni constr x
+instance AllElaboratedArgs constr (ElaborateBuiltin uni x) => AllBuiltinArgs uni constr x
 
 -- Custom type errors to guide the programmer adding a new built-in function.
 

plutus-ledger-api/test-plugin/Spec/Value.hs

@@ -157,7 +157,7 @@ valueToLists = ListTx.map (fmap AssocMap.toList) . AssocMap.toList . getValue
 eqValueCode :: CompiledCode Value -> CompiledCode Value -> (Bool, PLC.CountingSt)
 eqValueCode valueCode1 valueCode2 = (res, cost) where
     prog =
-        $$(compile [|| \value1 value2 -> toBuiltin ((value1 :: Value) == value2) ||])
+        $$(compile [|| \value1 value2 -> toOpaque ((value1 :: Value) == value2) ||])
             `unsafeApplyCode` valueCode1 `unsafeApplyCode` valueCode2
     (errOrRes, cost)
         = PLC.runCekNoEmit PLC.defaultCekParameters PLC.counting

plutus-tx-plugin/src/PlutusTx/Compiler/Builtins.hs

@@ -18,7 +18,7 @@ module PlutusTx.Compiler.Builtins (
     , lookupBuiltinType
     , errorFunc) where
 
-import PlutusTx.Builtins.Class qualified as Builtins
+import PlutusTx.Builtins.HasOpaque qualified as Builtins
 import PlutusTx.Builtins.Internal qualified as Builtins
 
 import PlutusTx.Compiler.Error

plutus-tx-plugin/src/PlutusTx/Compiler/Expr.hs

@@ -49,7 +49,7 @@ import PlutusTx.PIRTypes
 import PlutusTx.PLCTypes (PLCType, PLCVar)
 
 -- I feel like we shouldn't need this, we only need it to spot the special String type, which is annoying
-import PlutusTx.Builtins.Class qualified as Builtins
+import PlutusTx.Builtins.HasOpaque qualified as Builtins
 import PlutusTx.Trace
 
 import PlutusIR qualified as PIR

plutus-tx-plugin/test/Plugin/Primitives/9.6/deconstructorData2.pir.golden

@@ -247,6 +247,14 @@
             )
           )
         )
+        (termbind
+          (nonstrict)
+          (vardecl
+            `$fHasFromOpaqueBuiltinDataBuiltinData_$cfromOpaque`
+            (fun (con data) (con data))
+          )
+          (lam eta (con data) eta)
+        )
         (termbind
           (strict)
           (vardecl
@@ -271,7 +279,7 @@
         (termbind
           (nonstrict)
           (vardecl
-            `$fFromBuiltinBuiltinListList_$cfromBuiltin`
+            `$fHasFromOpaqueBuiltinListList_$cfromOpaque`
             (all
               arep
               (type)
@@ -292,7 +300,7 @@
               a
               (type)
               (lam
-                `$dFromBuiltin`
+                `$dHasFromOpaque`
                 [ [ (lam arep (type) (lam a (type) (fun arep a))) arep ] a ]
                 (let
                   (rec)
@@ -323,7 +331,7 @@
                               [
                                 [
                                   { Cons a }
-                                  [ `$dFromBuiltin` [ { head arep } l ] ]
+                                  [ `$dHasFromOpaque` [ { head arep } l ] ]
                                 ]
                                 [ go [ { tail arep } l ] ]
                               ]
@@ -347,11 +355,6 @@
           )
           (builtin fstPair)
         )
-        (termbind
-          (nonstrict)
-          (vardecl id (all a (type) (fun a a)))
-          (abs a (type) (lam x a x))
-        )
         (termbind
           (strict)
           (vardecl
@@ -405,12 +408,12 @@
                     [
                       {
                         {
-                          `$fFromBuiltinBuiltinListList_$cfromBuiltin`
+                          `$fHasFromOpaqueBuiltinListList_$cfromOpaque`
                           (con data)
                         }
                         (con data)
                       }
-                      { id (con data) }
+                      `$fHasFromOpaqueBuiltinDataBuiltinData_$cfromOpaque`
                     ]
                     a
                   ]

plutus-tx/changelog.d/20240513_014001_effectfully_split_FromBuiltin_and_ToBuiltin_into_IsBuiltin_and_IsOpaque.md

@@ -0,0 +1,5 @@
+### Changed
+
+- Split `PlutusTx.Builtins.Class` into `PlutusTx.Builtins.HasBuiltin` and `PlutusTx.Builtins.HasOpaque` in #5971:
++ Split 'FromBuiltin' into 'HasFromBuiltin' and 'HasFromOpaque'
++ Split 'ToBuiltin' into 'HasToBuiltin' and 'HasToOpaque'

plutus-tx/plutus-tx.cabal

@@ -70,7 +70,8 @@ library
     PlutusTx.Blueprint.Write
     PlutusTx.Bool
     PlutusTx.Builtins
-    PlutusTx.Builtins.Class
+    PlutusTx.Builtins.HasBuiltin
+    PlutusTx.Builtins.HasOpaque
     PlutusTx.Builtins.Internal
     PlutusTx.Code
     PlutusTx.Coverage
@@ -108,6 +109,7 @@ library
     PlutusTx.IsData.Instances
     PlutusTx.IsData.TH
     PlutusTx.Lift.Instances
+    PlutusTx.Lift.TestInstances
     PlutusTx.Lift.TH
     PlutusTx.Lift.THUtils