BridgeJS: Lower imported optional stack parameters fully on the stack - #802
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An imported optional whose payload is stack-only ([T]?, [String: V]?, @js struct?) used a hybrid convention: the isSome flag crossed as a wasm i32 parameter while the payload was conditionally pushed onto the shared stacks. Optional returns and optional array elements of the same types already travel entirely on the stacks: payload first, then a 0/1 flag on the i32 stack. This lowers those parameters the same way. The Swift thunk pushes the payload (if some) followed by the flag, the wasm signature carries no argument for the parameter, and the JS handler pops the flag before conditionally lifting the payload, through the same fragment already used for optional returns and elements. The hybrid shape was the last parameter category that both passed a wasm argument and pushed stack data, which is what enabled the argument transposition fixed in swiftwasm#794. Every stack-touching parameter is now flagless and reverse-ordered, matching returns and elements. All other optional parameter ABIs (scalars, strings, JSObject, closures, enums, heap objects) are unchanged.
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kateinoigakukun
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Overview
Imported optional parameters with stack-only payloads (
[T]?,[String: V]?,@JS struct?) used a hybrid convention: theisSomeflag crossed as a wasmi32argument while the payload went on the shared stacks. Optional returns and optional array elements of the same types already put both on the stacks.This lowers those parameters the same way. The wasm signature carries no argument for them; JS pops the flag and conditionally lifts, through the same fragment as optional returns. Scalars, strings,
JSObject, closures, enums and heap objects keep their current optional ABIs, as do all exported signatures.This also removes the mixed parameter representation that caused the argument-order bug fixed in #794. Optional stack-based values now use the same stack-only representation as other stack-based parameters.
Test plan
make unittest