wasmerio/wasmer · error · anyhow::Error

unsupported Wasm C API import version: {version:?}

Error message

unsupported Wasm C API import version: {version:?}

What it means

Wasmer's Wasm C API imports layer only supports version V0 of the Wasm C API. When a module (or embedder) declares a C API import version that is not compatible with V0, validate_supported bails with this error before any imports are registered. It is a forward-compatibility guard against newer/unknown C API versions.

Source

Thrown at lib/c-api-imports/src/lib.rs:131

        Self {
            version: module_wasm_c_api_version_used(module),
            imported_memory_type,
            imported_table_type,
            resolve_module_sync,
            func_env: None,
        }
    }

    fn needs_imports(&self) -> bool {
        self.version.is_some()
    }

    fn validate_supported(&self) -> Result<()> {
        if let Some(version) = self.version
            && !WasmCAPIVersion::V0.is_compatible_with(version)
        {
            bail!("unsupported Wasm C API import version: {version:?}");
        }
        Ok(())
    }

    fn register_imports(&mut self, store: &mut StoreMut<'_>, io: &mut Imports) -> Result<()> {
        self.validate_supported()?;
        if self.version.is_none() {
            return Ok(());
        }

        let func_env = FunctionEnv::new(
            &mut *store,
            WasmCapiEnv {
                resolve_module_sync: self.resolve_module_sync.clone(),
                ..WasmCapiEnv::default()
            },
        );
        self.func_env = Some(func_env.clone());

View on GitHub (pinned to 8c4b9ee9d3)

Solutions

1. Set the C API import version to V0 (or leave it as None to use the default)
2. Rebuild/upgrade the embedding code so both sides agree on the V0 C API revision
3. Upgrade Wasmer to a release that supports the requested C API version, if one exists

Example fix

// before
let imports = WasmCApiImports::default().version(WasmCAPIVersion::V2);
// after
let imports = WasmCApiImports::default().version(WasmCAPIVersion::V0);

if let Some(v) = imports.version() {
    if !wasm_c_api_imports::WasmCAPIVersion::V0.is_compatible_with(v) {
        return Err(format!("unsupported C API version {v:?}; use V0"));
    }
}

fn is_supported_version(v: Option<WasmCAPIVersion>) -> bool {
    v.map_or(true, |v| WasmCAPIVersion::V0.is_compatible_with(v))
}

match result {
    Err(e) if e.to_string().contains("unsupported Wasm C API import version") => retry_with_v0(),
    other => other?,
}

When it happens

Trigger: Calling add_imports/register_imports on a WasmCApiImports instance whose `version` field is set to Some(v) where WasmCAPIVersion::V0.is_compatible_with(v) is false (e.g. a newer C API version enum value).

Common situations: Using a wasm-c-api header/SDK newer than the Wasmer build; embedding Wasmer behind a C API shim built against a different spec revision; misconfigured import builder passing an explicit version.

Related errors

• env.memory import for Wasm C API module is not a memory
• env.__indirect_function_table import for Wasm C API module i
• unimplemented operator {operator:?}
• `wasm_valtype_kind: argument is a null pointer
• not a `sys` backend!

AI-assisted analysis of wasmerio/wasmer@8c4b9ee9d3 (2026-09-01). Data as JSON: /api/errors/bdd9fa1689afd105. Report an issue: GitHub.