Can't invoke SRC7 metadata method from the rust SDK due to arbitrary nesting of heap types

[cold-briu]

Motivation

Description

Can't invoke SRC7 metadata method from the rust SDK due to arbitrary nesting of heap types
Since metadata Returns an Option wrapping an Enum that evaluate to string.

let meta = contract_instance
        .methods()
        .metadata(asset_id, "key".to_string())
        .simulate()
        .await
        .unwrap();

Throws the following error:

thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: InvalidType("Enums currently support only one level deep heap types.")

contract_instance comes from the following implementation:

contract;

use src_7::{Metadata, SRC7};
use std::{call_frames::contract_id, hash::Hash, storage::storage_string::*, string::String};

impl SRC7 for Contract {
    #[storage(read)]
    fn metadata(asset: AssetId, key: String) -> Option<Metadata> {
        if key == String::from_ascii_str("key") {
            Some(Metadata::String(String::from_ascii_str("value")))
        } else {
            None
        }
    }
}

Then, the execution should return something like:

let result: Option<Enum<String>> = SRC7.metadata(myAsset, myKey);

Considering:

/// Universal return type for metadata.
pub enum Metadata {
    // Used when the stored metadata is a `b256`.
    B256: b256,
    /// Used when the stored metadata is `Bytes`.
    Bytes: Bytes,
    /// Used when the stored metadata is a `u64`.
    Int: u64,
    /// Used when the stored metadata is a `String`.
    String: String,
}

Is this an implementation error, sdk limitation o src7 error? 🤔

[bitzoic]

This is an SDK limitation

[mpoplavkov]

Could this be resolved either in the standard or on the SDK side? That's important for ecosystem projects if you want them to support the standard
@cold-briu
@bitzoic

[cold-briu]

Closing since it's out of scope: SDK Limitation.
Please check fuels-rs/issues/1213.