test: pseudo.Type.DecodeRLP()

libevm/pseudo/reflect.go

@@ -0,0 +1,32 @@
+// Copyright 2024 the libevm authors.
+//
+// The libevm additions to go-ethereum are free software: you can redistribute
+// them and/or modify them under the terms of the GNU Lesser General Public License
+// as published by the Free Software Foundation, either version 3 of the License,
+// or (at your option) any later version.
+//
+// The libevm additions are distributed in the hope that they will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser
+// General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see
+// <http://www.gnu.org/licenses/>.
+
+package pseudo
+
+import "reflect"
+
+// Reflection is used as a last resort in pseudo types so is limited to this
+// file to avoid being seen as the norm. If you are adding to this file, please
+// try to achieve the same results with type parameters.
+
+func (c *concrete[T]) ensureNonNilPointer() {
+	v := reflect.ValueOf(c.val)
+	if v.Kind() != reflect.Pointer || !v.IsNil() {
+		return
+	}
+	el := v.Type().Elem()
+	c.val = reflect.New(el).Interface().(T) //nolint:forcetypeassert // Invariant scoped to the last few lines of code so simple to verify
+}

libevm/pseudo/rlp_test.go

@@ -59,10 +59,16 @@ func TestRLPEquivalence(t *testing.T) {
 			require.NoErrorf(t, err, "rlp.EncodeToBytes(%T)", hdr)
 
 			typ := pseudo.From(hdr).Type
-			got, err := rlp.EncodeToBytes(typ)
+			gotRLP, err := rlp.EncodeToBytes(typ)
 			require.NoErrorf(t, err, "rlp.EncodeToBytes(%T)", typ)
 
-			require.Equalf(t, want, got, "RLP encoding of %T (canonical) vs %T (under test)", hdr, typ)
+			require.Equalf(t, want, gotRLP, "RLP encoding of %T (canonical) vs %T (under test)", hdr, typ)
+
+			t.Run("decode", func(t *testing.T) {
+				pseudo := pseudo.Zero[*types.Header]()
+				require.NoError(t, rlp.DecodeBytes(gotRLP, pseudo.Type))
+				require.Equal(t, hdr, pseudo.Value.Get())
+			})
 		})
 	}
 }

libevm/pseudo/type.go

@@ -233,9 +233,6 @@ func (c *concrete[T]) UnmarshalJSON(b []byte) error {
 func (c *concrete[T]) EncodeRLP(w io.Writer) error { return rlp.Encode(w, c.val) }
 
 func (c *concrete[T]) DecodeRLP(s *rlp.Stream) error {
-	if _, _, err := s.Kind(); err != nil {
-		// DO NOT MERGE: is calling Kind() a necessary step?
-		return err
-	}
+	c.ensureNonNilPointer()
 	return s.Decode(c.val)
 }