harness: validate actual result shape against declared arity - #236
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assert_return with an empty expected list never inspected the actual value: compareValues short-circuited to a vacuous pass, and invoke collapsed the raw return by declared arity, discarding it for arity 0 and casting unchecked for 2+. A spurious result from an arity-0 export passed silently. Extract the collapse into collapseResultsByArity (value-mapping.ts), which validates the observed shape against the declared arity per the runtime's convention (resultsToHost, runtime/src/exec/boundary.ts): arity 0 requires undefined, arity 1 requires non-undefined (a ComponentValue is never undefined; arrays stay legal — a single list<T> result IS an array, the deliberate deviation from the issue text), and arity n>=2 requires an array of exactly n. compareValues now rejects a non-undefined actual when nothing is expected. Error messages use a bigint-safe describe helper (JSON.stringify throws on lifted i64s). Unit coverage in harness/tests/value_mapping_test.ts; the arity-0 spurious-result path is untestable end-to-end (it requires a broken runtime), which is why the collapse is a pure exported function. Fixes #188
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Fixes #188.
assert_returnwith an empty expected list never inspected the actual value: two stacked layers discarded it independently —compareValuesshort-circuited to a vacuous pass whenexpectedwas empty, andinvokecollapsed the raw return by declared arity, discarding it for arity 0 and castingraw as unknown[]unchecked for 2+.Changes
collapseResultsByArity(new,harness/src/value-mapping.ts): pure collapse+validate of the raw invoke return against the declared arity, per the runtime's convention (resultsToHost,runtime/src/exec/boundary.ts):rawmust beundefinedrawmust not beundefined(aComponentValueis neverundefined—runtime/src/cabi/types.ts). Deliberate deviation from the issue's suggested fix: arrays stay legal at arity 1, because a singlelist<T>/tuple result IS a JS array — disambiguating that from N results is exactly whycomputeExportAritiesexists.rawmust be an array of exactly that lengthRuntimeExecutor.invokeuses it; a shape mismatch now fails the command loudly.compareValueswith emptyexpectednow requiresactual === undefinedinstead of passing vacuously.JSON.stringifythrows on lifted i64 bigints).harness/tests/value_mapping_test.ts(14 tests), including pins for the bigint-safe messages and the arity-1-array non-throw.The collapse is a pure exported function because the arity-0 spurious-result path cannot be exercised end-to-end — producing one requires a broken runtime.
Gates
just conformance— pass (1257 passed, 0 failed, 112 pre-existing xfail; all 88 harness tests green). No latent runtime bug surfaced by the stricter checks.just sched-seeds— pass (seeds 1 and 4242).