swc-project/swc · critical

Should be serializable

Error message

Should be serializable

What it means

Host import behind a plugin's source-map position lookup (span/char-pos -> `PartialLoc`). It builds a `PartialLoc` (optional source-file name, line, col, col_display) and CBOR-encodes it for the guest; encode failure panics. All fields are plain integers and an Option<String>, so a healthy runtime cannot fail here - the panic means the host/guest plugin boundary is broken (swc_core schema divergence or memory corruption).

Source

Thrown at crates/swc_plugin_runner/src/imported_fn/source_map.rs:62

    env: &SourceMapHostEnvironment,
    byte_pos: u32,
    should_include_source_file: i32,
    allocated_ret_ptr: u32,
) -> u32 {
    let original_loc = env.source_map.lock().lookup_char_pos(BytePos(byte_pos));
    let ret = VersionedSerializable::new(PartialLoc {
        source_file: if should_include_source_file == 0 {
            None
        } else {
            Some(original_loc.file)
        },
        line: original_loc.line,
        col: original_loc.col.0,
        col_display: original_loc.col_display,
    });

    let serialized_loc_bytes =
        PluginSerializedBytes::try_serialize(&ret).expect("Should be serializable");

    allocate_return_values_into_guest(caller, allocated_ret_ptr, &serialized_loc_bytes);
    1
}

#[cfg_attr(debug_assertions, tracing::instrument(level = "info", skip_all))]
pub fn doctest_offset_line_proxy(
    _caller: &mut dyn runtime::Caller<'_>,
    env: &SourceMapHostEnvironment,
    orig: u32,
) -> u32 {
    env.source_map.lock().doctest_offset_line(orig as usize) as u32
}

#[allow(clippy::too_many_arguments)]
#[cfg_attr(debug_assertions, tracing::instrument(level = "info", skip_all))]
pub fn merge_spans_proxy(
    caller: &mut dyn runtime::Caller<'_>,

View on GitHub (pinned to 5176682b65)

Solutions

1. Rebuild the plugin with the swc_core version matching the installed @swc/core
2. Upgrade @swc/core and plugins together
3. Disable sourcemap-dependent plugin features as a stopgap
4. Report upstream with versions if the crash remains on matched builds

Example fix

# before
# @swc/core@new + source-map plugin wasm built on swc_core@old

# after
# rebuild plugin: cargo update -p swc_core --precise <host version> && cargo build-wasi --release

assertPluginHostAligned(pluginName, coreVersion); // sourcemap-lookup plugins included

// contain native panics: run transform in a worker, retry without plugins on crash

When it happens

Trigger: A wasm plugin performs source-map position lookups while its swc_core bindings and the host runner disagree on the CBOR schema, or the runner's encoder hits an internal error.

Common situations: Source-map-heavy plugins (error-formatters, coverage tools) run against an @swc/core newer/older than the plugin binary was built for.

Related errors

• Should be serializable
• Should be serializable
• Should able to be deserialized into string
• Should able to deserialize
• Should able to read memory from given ptr

AI-assisted analysis of swc-project/swc@5176682b65 (2026-08-17). Data as JSON: /api/errors/1e0a6ce352534843. Report an issue: GitHub.