ServerFnError<TargetErr> should impl From<ServerFnError<SourceErr>> where TargetErr: From<SourceErr>

[nicolas-guichard]

Last one in my series of proposed improvements to ServerFnError: we could provide a conversion from ServerFnError<OldCustErr> to ServerFnError<NewCustErr> if NewCustErr: From<OldCustErr>. Something like:

impl<OldCustErr, NewCustErr: OldCustErr> From<ServerFnError<OldCustErr>> for ServerFnError<NewCustErr> {
    fn from(value: ServerFnError<NoCustomError>) -> Self {
        match self {
            ServerFnError::<OldCustErr>::WrappedServerError(o) => ServerFnError::<NewCustErr>::WrappedServerError(o.into()),
            ServerFnError::<OldCustErr>::Registration(s) => ServerFnError::<NewCustErr>::Registration(s),
            ServerFnError::<OldCustErr>::Request(s) => ServerFnError::<NewCustErr>::Request(s),
            ServerFnError::<OldCustErr>::Response(s) => ServerFnError::<NewCustErr>::Response(s),
            ServerFnError::<OldCustErr>::ServerError(s) => ServerFnError::<NewCustErr>::ServerError(s),
            ServerFnError::<OldCustErr>::Deserialization(s) => ServerFnError::<NewCustErr>::Deserialization(s),
            ServerFnError::<OldCustErr>::Serialization(s) => ServerFnError::<NewCustErr>::Serialization(s),
            ServerFnError::<OldCustErr>::Args(s) => ServerFnError::<NewCustErr>::Args(s),
            ServerFnError::<OldCustErr>::MissingArg(s) => ServerFnError::<NewCustErr>::MissingArg(s),
        }
    }
}

The typical use-case I have is helper functions that can fail in one or two ways, shared by multiple server functions that can also fail in other ways.

[gbj]

Again, feel free to make a PR if the compiler will actually allow this.

[benwis]

This one also conflicts with an existing trait, this time in convert

   Compiling server_fn v0.7.0-rc1 (/celCluster/projects/leptos/server_fn)
error[E0119]: conflicting implementations of trait `std::convert::From<ServerFnError<_>>` for type `ServerFnError<_>`
   --> server_fn/src/error.rs:197:1
    |
197 | impl<OldCustErr, NewCustErr: From<OldCustErr>> From<ServerFnError<OldCustErr>> for ServerFnError<NewCustErr...
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = note: conflicting implementation in crate `core`:
            - impl<T> std::convert::From<T> for T;