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vados-cosmonic merged 2 commits into from
Aug 14, 2026
Merged

feat(bindgen): disable trapped instances #1872

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7e12926
feat(bindgen): detect and disable component after trap
vados-cosmonic Aug 14, 2026
8dc0379
test(transpile): increase transpile code char limit
vados-cosmonic Aug 14, 2026
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23 changes: 23 additions & 0 deletions crates/js-component-bindgen/src/function_bindgen.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1576,6 +1576,14 @@ impl Bindgen for FunctionBindgen<'_> {

Instruction::CallWasm { name, sig } => {
let debug_log_fn = self.intrinsic(Intrinsic::DebugLog);
let get_component_state = self.intrinsic(Intrinsic::Component(
ComponentIntrinsic::GetOrCreateAsyncState,
));
let component_idx_expr = self
.component_state
.as_ref()
.map(|state| state.get_js_exprs().component_idx)
.unwrap_or_else(|| "-1".into());
let has_post_return = self.post_return.is_some();
let is_async = self.is_async;
uwriteln!(
Expand All @@ -1594,6 +1602,13 @@ impl Bindgen for FunctionBindgen<'_> {
// (if we're calling into wasm then we know it was not)
uwriteln!(self.src, "const hostProvided = false;");

// Argument validation and lowering happen before this instruction. Only
// disable the instance once execution is about to enter the component.
uwriteln!(
self.src,
"{get_component_state}({component_idx_expr}).throwIfTrapped();"
);

// Inject machinery for starting a 'current' task
// (this will define the 'task' variable)
self.start_current_task(inst);
Expand Down Expand Up @@ -1689,6 +1704,7 @@ impl Bindgen for FunctionBindgen<'_> {
taskID: task.id(),
err,
}});
{get_component_state}({component_idx_expr}).markTrapped(err);
task.setErrored(err);
task.reject(err);
task.exit();
Expand All @@ -1706,6 +1722,7 @@ impl Bindgen for FunctionBindgen<'_> {
taskID: task.id(),
err,
}});
{get_component_state}({component_idx_expr}).markTrapped(err);
task.setErrored(err);
task.reject(err);
task.exit();
Expand Down Expand Up @@ -1791,6 +1808,9 @@ impl Bindgen for FunctionBindgen<'_> {
// Call to an imported interface (normally provided by the host)
Instruction::CallInterface { func, async_ } => {
let debug_log_fn = self.intrinsic(Intrinsic::DebugLog);
let get_component_state = self.intrinsic(Intrinsic::Component(
ComponentIntrinsic::GetOrCreateAsyncState,
));
let start_current_task_fn = self.intrinsic(Intrinsic::AsyncTask(
AsyncTaskIntrinsic::CreateNewCurrentTask,
));
Expand Down Expand Up @@ -1935,6 +1955,7 @@ impl Bindgen for FunctionBindgen<'_> {
subtaskID: task.getParentSubtask()?.id(),
err,
}});
{get_component_state}({component_idx_expr}).markTrapped(err);
task.setErrored(err);
task.reject(err);
task.exit();
Expand All @@ -1953,6 +1974,7 @@ impl Bindgen for FunctionBindgen<'_> {
subtaskID: task.getParentSubtask()?.id(),
err,
}});
{get_component_state}({component_idx_expr}).markTrapped(err);
task.setErrored(err);
task.reject(err);
task.exit();
Expand Down Expand Up @@ -2016,6 +2038,7 @@ impl Bindgen for FunctionBindgen<'_> {
try {{
ret = {{ tag: 'ok', val: {call} }};
}} catch (e) {{
if ({get_component_state}({component_idx_expr}).markTrapped(e)) {{ throw e; }}
ret = {{ tag: 'err', val: {err_payload}(e) }};
}}
"#,
Expand Down
15 changes: 15 additions & 0 deletions crates/js-component-bindgen/src/intrinsics/component.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -136,6 +136,7 @@ impl ComponentIntrinsic {
let promise_with_resolvers_fn = Intrinsic::PromiseWithResolversPonyfill.name();
let stream_readable_end_class =
Intrinsic::AsyncStream(AsyncStreamIntrinsic::StreamReadableEndClass).name();
let trap_error_class = Intrinsic::TrapError.name();

output.push_str(&format!(
r#"
Expand All @@ -161,6 +162,7 @@ impl ComponentIntrinsic {
#suspendedTasksByTaskID = new Map();
#suspendedTaskIDs = [];
#errored = null;
#trapped = null;

#backpressure = 0;
#backpressureWaiters = 0n;
Expand Down Expand Up @@ -197,6 +199,19 @@ impl ComponentIntrinsic {
this.#errored = err;
}}

markTrapped(err) {{
if (!(err instanceof {trap_error_class} || err instanceof WebAssembly.RuntimeError)) {{
return false;
}}
{debug_log_fn}('[{component_async_state_class}#markTrapped()] component trapped', {{ err, componentIdx: this.#componentIdx }});
if (this.#trapped === null) {{ this.#trapped = err; }}
return true;
}}

throwIfTrapped() {{
if (this.#trapped !== null) {{ throw this.#trapped; }}
}}

callingSyncImport(val) {{
if (val === undefined) {{ return this.#callingAsyncImport; }}
if (typeof val !== 'boolean') {{ throw new TypeError('invalid setting for async import'); }}
Expand Down
7 changes: 4 additions & 3 deletions crates/js-component-bindgen/src/intrinsics/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1409,9 +1409,10 @@ pub fn render_intrinsics(args: RenderIntrinsicsArgs) -> Source {
if args.intrinsics.contains(&Intrinsic::Component(
ComponentIntrinsic::ComponentAsyncStateClass,
)) {
args.intrinsics.extend([&Intrinsic::AsyncStream(
AsyncStreamIntrinsic::GlobalStreamMap,
)]);
args.intrinsics.extend([
&Intrinsic::TrapError,
&Intrinsic::AsyncStream(AsyncStreamIntrinsic::GlobalStreamMap),
]);
}

if args
Expand Down
6 changes: 3 additions & 3 deletions docs/src/advanced/detecting-traps.md
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Original file line number Diff line number Diff line change
Expand Up @@ -4,8 +4,8 @@ While some errors are represented at the WIT type level and expected, some inter
may cause a component instance to [trap][wiki-trap]. Jco-generated bindings report the
component-model traps they detect with the exported `_util.TrapError` class.

**After an instance has trapped, the component instance should no longer be used,
and any subsequent use (successful or otherwise) is undefined behavior**.
After an instance has trapped, Jco marks the component instance as unusable. Any subsequent
call throws the original trap without re-entering the component.

To detect these traps, use the `_util.TrapError` class:

Expand All @@ -21,7 +21,7 @@ try {
} catch (err) {
if (err instanceof _util.TrapError) {
console.error(`TRAP: ${err}`);
// avoid continuing to use the instance
// The instance is now disabled and cannot be called again.
} else {
// Other exceptions are unexpected and should be handled separately.
throw err;
Expand Down
2 changes: 1 addition & 1 deletion packages/jco-transpile/test/transpile.ts
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Expand Up @@ -11,7 +11,7 @@ import { readComponentBytes } from './helpers.js';
// - (2025/02/04) increased due to stabilization changes for async tasks
// - (2025/12/16) increased due to additional async impl
// - (2026/07/02) increased due to async launch (and actually enabling the tests)
const FLAVORFUL_WASM_TRANSPILED_CODE_CHAR_LIMIT = 185_000;
const FLAVORFUL_WASM_TRANSPILED_CODE_CHAR_LIMIT = 190_000;

suite('Transpile', async () => {
const flavorfulWasmBytes = await readComponentBytes(
Expand Down