G004-wit-bindgen-cpp-emits-invalid-resource-handle-trapping-unknown-handle

[xiaozzzZZzzz240]

wit-bindgen-cpp generates invalid resource handles for variant/list<option> params, causing an 'unknown handle index' trap in wasmtime

Reproduction of a wit-bindgen-cpp handle-management defect where C++ components pass invalid resource handles across the component boundary, aborting execution in wasmtime with 'unknown handle index'.

Environment

component	version
OS	macOS 15.7 (Darwin 24.6.0), x86_64
wasmtime	wasmtime 41.0.0 (3dda91692 2026-01-20)
jco	1.16.1 (source checkout, tag jco-v1.16.1)
Node.js	v22.22.2
wac	wac-cli 0.8.1
wasi-sdk	27.0 (wasm32-wasip2-clang/clang++)

Steps to reproduce

The full chain is: compile the guest sources into a provider component and a consumer component, compose them with wac, then run the composed component. Prebuilt copies of every artifact are included (components/provider.wasm, components/consumer.wasm, composed.wasm), so you can also skip straight to step 5.

Github repo:https://github.com/xiaozzzZZzzz240/G004-wit-bindgen-cpp-emits-invalid-resource-handle-trapping-unknown-handle

1. Clone this repository:

   git clone <THIS_REPO_URL>
   cd <THIS_REPO_DIR>

2. Compile the provider component from the JavaScript sources in src/provider-JavaScript/ (toolchain versions in the table above; the WIT package is in wit/):

   jco componentize src/provider-JavaScript/world2-sbtyzmep_generated.js --wit wit --world-name world2-sbtyzmep --disable http fetch-event --out components/provider.wasm

3. Compile the consumer component from the C++ sources in src/consumer-Cpp/:

   wasm32-wasip2-clang++ -std=c++23 -fno-exceptions -o components/consumer.wasm -mexec-model=reactor src/consumer-Cpp/world2b-dthcw81x_generated.cpp src/consumer-Cpp/world2b_dthcw81x.cpp src/consumer-Cpp/world2b_dthcw81x_component_type.o

4. Compose the two components into one runnable component with wac 0.8.1:

   wac plug components/consumer.wasm --plug components/provider.wasm -o composed.wasm

5. Run the composed component with wasmtime 41.0.0:

   wasmtime run composed.wasm

Expected result

This test case intentionally performs an invalid resource-handle operation at the very end, so the expected behavior is: print the prefix below, then trap cleanly with invalid handle.

"resinst0"
"resinst0"
"bar"
"c2"
true
true
ok(some(c2(some(resource("temres63")))))
((resource("temres64"), "p"), "beta")
"c2"
true
true
"bar"
c0(1)
[some(c1([resource("temres13")]))]
"c1"
true
"temres99"
trap(invalid handle)

(jco on the same file also fails (rc=1), but its output diverges from this reference as well; see Notes below — it is raw differential data, not confirming evidence for this expected output.)

Actual result

Under wasmtime the same composed.wasm exits with rc=1. stdout:

"resinst0"
"resinst0"
"bar"
"c2"
true
true
ok(some(c2(some(resource("temres63")))))
((resource("temres64"), "p"), "beta")
"c2"
true
true
"bar"

stderr:

Error: failed to run main module `/Users/myuser/WASM/myProject/Wasm_component_testing/mycode/execute/reportrepo/G004-wit-bindgen-cpp-emits-invalid-resource-handle-unknown-handle-index/composed.wasm`

Caused by:
    0: failed to invoke `run` function
    1: error while executing at wasm backtrace:
           0:    0x858 - <unknown>!<wasm function 20>
           1: 0xd1c000 - wit-component:shim!indirect-mydefined:package3hl16smu1p/itf-sn3qxkhktg-f-cph90o7
           2: 0xcc4053 - consumer.wasm!mydefined::package3hl16smu1p::itf_sn3qxkhktg::FCph90o7(mydefined::package3hl16smu1p::itf_sn3qxkhktg::Varnl7r84, std::__2::span<std::__2::optional<mydefined::package3hl16smu1p::itf_sn3qxkhktg::Varnl7r84>, 4294967295ul>)
           3: 0xcbdf75 - consumer.wasm!exports::wasi::cli::run::Run()
           4: 0xcc428a - consumer.wasm!__wasm_export_wasiX3AcliX2FrunX400X2E2X2E0X23run
       note: using the `WASMTIME_BACKTRACE_DETAILS=1` environment variable may show more debugging information
    2: unknown handle index 3852

Notes

• Differential evidence — jco on the exact same file: rc=1

"resinst0"
"temres2"
"bar"
"c2"
true
true
ok(some(c2(some(resource("temres63")))))
((resource("temres64"), "p"), "beta")
"c2"
true
true
"bar"

--- stderr ---
can't access property "rep", repTable.get(...) is undefined
Stack:
  export_itfSn3qxkhktg$fCph90o7@/var/folders/ng/263gml_52h33wsbthhfjjr980000gn/T/ca0ba5338ca2/sources/initializer.js:12460:33

Redirecting call to abort() to mozalloc_abort

RuntimeError: unreachable
    at wasm://wasm/03286172:wasm-function[12489]:0x885e22
    at wasm://wasm/03286172:wasm-function[4582]:0x1abd23
    at mydefined:package3hl16smu1p/itf-sn3qxkhktg#f-cph90o7 (wasm://wasm/03286172:wasm-function[12711]:0x89d478)
    at wasm://wasm/11dbd7b2:wasm-function[23]:0x8a1
    at wit-component:shim.indirect-mydefined:package3hl16smu1p/itf-sn3qxkhktg-f-cph90o7 (wasm://wasm/wit-component:shim-786761ae:wasm-function[3]:0x124)
    at consumer.wasm.mydefined::package3hl16smu1p::itf_sn3qxkhktg::FCph90o7(mydefined::package3hl16smu1p::itf_sn3qxkhktg::Varnl7r84, std::__2::span<std::__2::optional<mydefined::package3hl16smu1p::itf_sn3qxkhktg::Varnl7r84>, 4294967295ul>) (wasm://wasm/consumer.wasm-0016dc16:wasm-function[251]:0x6f64)
    at consumer.wasm.exports::wasi::cli::run::Run() (wasm://wasm/consumer.wasm-0016dc16:wasm-function[19]:0xe86)
    at consumer.wasm.__wasm_export_wasiX3AcliX2FrunX400X2E2X2E0X23run (wasm://wasm/consumer.wasm-0016dc16:wasm-function[258]:0x719b)
    at Object.run (file:///private/var/folders/ng/263gml_52h33wsbthhfjjr980000gn/T/ARsKAl/composed.js:30578:13)
    at file:///private/var/folders/ng/263gml_52h33wsbthhfjjr980000gn/T/ARsKAl/_run.js:14:15