`stellar contract invoke` panics when contract function returns spec type `SC_SPEC_TYPE_VAL`

[leighmcculloch]

What version are you using?

stellar-cli 25.1.0

What did you do?

When a Soroban contract function has return type Val (which maps to SC_SPEC_TYPE_VAL in the contract spec), and the function returns Bool(false), calling the function via stellar contract invoke panics.

Minimal reproducing contract:

#![no_std]

use soroban_sdk::{contract, contractimpl, Env, Val};

#[contract]
pub struct BoolFalseContract;

#[contractimpl]
impl BoolFalseContract {
    pub fn retval(_env: Env) -> Val {
        Val::from_bool(false).into()
    }
}

Cargo.toml:

[package]
name = "bool_false_poc"
version = "0.1.0"
edition = "2021"
publish = false

[lib]
crate-type = ["cdylib"]

[dependencies]
soroban-sdk = "25.1.0"

[dev-dependencies]
soroban-sdk = { version = "25.1.0", features = ["testutils"] }

[profile.release]
opt-level = "z"
overflow-checks = true
debug = 0
strip = "symbols"
debug-assertions = false
panic = "abort"
codegen-units = 1
lto = true

Steps to reproduce:

# Build the contract
cargo build --release --target wasm32-unknown-unknown

# Deploy to local network
stellar contract deploy \
  --wasm target/wasm32-unknown-unknown/release/bool_false_poc.wasm \
  --source deployer --network local --alias bool-false-poc

# Invoke the function — this panics
stellar contract invoke --id bool-false-poc --source deployer --network local -- retval

What did you expect to see?

The CLI should successfully display the return value, e.g.:

false

What did you see instead?

The CLI panics with:

thread 'main' panicked at 'not yet implemented: Bool(false,) doesn't have a matching Val'

Notes

• The contract itself executes correctly — the issue is purely in the CLI's result formatting
• All non-Void ScVal variants are affected when the spec type is SC_SPEC_TYPE_VAL, not just Bool
• A fix would need to handle ScType::Val for all ScVal variants, likely by recursively inferring the concrete type from the value itself

[Kanasjnr]

@leighmcculloch is this available to work on? i would love to take it