Can't write to StorageMap when benchmarking, EncodeLike is not implemented for any type even if it's the same in pallet

Question

I have the following StorageMap defined in my pallet:

#[pallet::storage]
pub(super) type Signatures<T: Config> = StorageMap<
    _,
    Blake2_128Concat,
    T::Hash,
    BoundedBTreeMap<Public, BoundedVec<u8, T::SignatureLength>, T::MaxAuthorities>,
>;

and in the benchmarks:

benchmarks!{
test_add{
    type CustomMap= BoundedBTreeMap<sp_core::sr25519::Public, BoundedVec<u8, ConstU32<64>>, ConstU32<32>>;
        let mut custom : CustomMap= BoundedBTreeMap::new();
        let id = H256::default();// using a concrete type also wouldn't work
        let hash = T::Hash::default();
     }:{
 Signatures::<T>::insert(hash, custom);
}

} it gives me the following error:

 error[E0277]: the trait bound `frame_support::BoundedBTreeMap<sp_core::sr25519::Public, frame_support::BoundedVec<u8, ConstU32<64>>, ConstU32<32>>: EncodeL
ike<frame_support::BoundedBTreeMap<sp_core::sr25519::Public, frame_support::BoundedVec<u8, <T as pallet::Config>::SignatureLength>, <T as pallet::Config>::
MaxAuthorities>>` is not satisfied
     --> /home/test/projects/custom/pallet/src/benchmarking.rs:70:46
      |
  70  |             Signatures::<T>::insert(hash, custom);
      |             ----------------------           ^^^^^^ the trait `EncodeLike<frame_support::BoundedBTreeMap<sp_core::sr25519::Public, frame_support::Bou
ndedVec<u8, <T as pallet::Config>::SignatureLength>, <T as pallet::Config>::MaxAuthorities>>` is not implemented for `frame_support::BoundedBTreeMap<sp_cor
e::sr25519::Public, frame_support::BoundedVec<u8, ConstU32<64>>, ConstU32<32>>`

even though the same code is executed perfectly in the pallet with no errors.

Answer 1

I think the problem is that you are using ConstU32<64> instead of the config constant T::SignatureLength (same for the other parameter). It is not correct and lead to problems when benchmarking your pallet later on.
For the hash type: you need to require it to have a Default in the config trait and then do T::Hash::default(). You can obviously not use concrete types here, since benchmarks are generic over the pallet config trait. But you could additionally require them to be From<H256> for benchmarking only by putting a where_clause on the benchmark.

In your case you can probably let the Rust compiler guess the type like this:

benchmarks!{
test_add{
        let mut custom = BoundedBTreeMap::new();
        let id = H256::default();// using a concrete type also wouldn't work
        let hash = T::Hash::default();
     }:{
 Signatures::<T>::insert(hash, custom);
}

Or if you really want to type it, then create a type alias with something like SignatureOf<T> for example like in the Alliance pallet and use that.
If this does not answer your question the please provide source code. Otherwise it is not possible to debug.