Implement Default for DefaultGateSerializer and DefaultGeneratorSerializer (#1531)

* Implement Default for DefaultGateSerializer and DefaultGeneratorSerializer

* Apply comments

* Update doc

* Clippy

plonky2/examples/square_root.rs

@@ -66,6 +66,7 @@ impl<F: RichField + Extendable<D>, const D: usize> SimpleGenerator<F, D>
     }
 }
 
+#[derive(Default)]
 pub struct CustomGeneratorSerializer<C: GenericConfig<D>, const D: usize> {
     pub _phantom: PhantomData<C>,
 }
@@ -131,9 +132,7 @@ fn main() -> Result<()> {
     // Test serialization
     {
         let gate_serializer = DefaultGateSerializer;
-        let generator_serializer = CustomGeneratorSerializer {
-            _phantom: PhantomData::<C>,
-        };
+        let generator_serializer = CustomGeneratorSerializer::<C, D>::default();
 
         let data_bytes = data
             .to_bytes(&gate_serializer, &generator_serializer)

plonky2/src/plonk/config.rs

@@ -106,7 +106,7 @@ pub trait GenericConfig<const D: usize>:
 }
 
 /// Configuration using Poseidon over the Goldilocks field.
-#[derive(Debug, Copy, Clone, Eq, PartialEq, Serialize)]
+#[derive(Debug, Copy, Clone, Default, Eq, PartialEq, Serialize)]
 pub struct PoseidonGoldilocksConfig;
 impl GenericConfig<2> for PoseidonGoldilocksConfig {
     type F = GoldilocksField;
@@ -116,7 +116,7 @@ impl GenericConfig<2> for PoseidonGoldilocksConfig {
 }
 
 /// Configuration using truncated Keccak over the Goldilocks field.
-#[derive(Debug, Copy, Clone, Eq, PartialEq)]
+#[derive(Debug, Copy, Clone, Default, Eq, PartialEq)]
 pub struct KeccakGoldilocksConfig;
 impl GenericConfig<2> for KeccakGoldilocksConfig {
     type F = GoldilocksField;

plonky2/src/util/serialization/gate_serialization.rs

@@ -114,6 +114,15 @@ pub mod default {
     use crate::hash::hash_types::RichField;
     use crate::util::serialization::GateSerializer;
 
+    /// A gate serializer that can be used to serialize all default gates supported
+    /// by the `plonky2` library.
+    /// Being a unit struct, it can be simply called as
+    /// ```rust
+    /// use plonky2::util::serialization::DefaultGateSerializer;
+    /// let gate_serializer = DefaultGateSerializer;
+    /// ```
+    /// Applications using custom gates should define their own serializer implementing
+    /// the `GateSerializer` trait. This can be easily done through the `impl_gate_serializer` macro.
     pub struct DefaultGateSerializer;
     impl<F: RichField + Extendable<D>, const D: usize> GateSerializer<F, D> for DefaultGateSerializer {
         impl_gate_serializer! {

plonky2/src/util/serialization/generator_serialization.rs

@@ -127,6 +127,20 @@ pub mod default {
     use crate::recursion::dummy_circuit::DummyProofGenerator;
     use crate::util::serialization::WitnessGeneratorSerializer;
 
+    /// A generator serializer that can be used to serialize all default generators supported
+    /// by the `plonky2` library. It can simply be called as
+    /// ```rust
+    /// use plonky2::util::serialization::DefaultGeneratorSerializer;
+    /// use plonky2::plonk::config::PoseidonGoldilocksConfig;
+    ///
+    /// const D: usize = 2;
+    /// type C = PoseidonGoldilocksConfig;
+    /// let generator_serializer = DefaultGeneratorSerializer::<C, D>::default();
+    /// ```
+    /// Applications using custom generators should define their own serializer implementing
+    /// the `WitnessGeneratorSerializer` trait. This can be easily done through the
+    /// `impl_generator_serializer` macro.
+    #[derive(Default)]
     pub struct DefaultGeneratorSerializer<C: GenericConfig<D>, const D: usize> {
         pub _phantom: PhantomData<C>,
     }