[wtholliday]

Summary

An extern that returns a tuple, struct, array, enum or f32x4 now receives a trailing output pointer and returns void:

extern fn host_pair(x: i32) -> (i32, i32)

void host_pair(void* ctx, int32_t x, int32_t* out);

• One ABI rule, every backend. TypeID::extern_returns_via_pointer in src/types.rs is the single definition; Cranelift, LLVM, VM and stack codegen all use it. Previously each backend had its own predicate and they had already drifted (f32x4 was by-value on Cranelift/LLVM and by-pointer on VM/stack, so no one host function worked everywhere).
• f32x4 goes through the pointer as four floats on all backends. Vector return registers are not portable and libffi cannot marshal them. Cranelift and LLVM reload the vector after the call.
• Checker validates extern signatures. Return types no backend can marshal (function types, i8/u8/u32) and parameter types outside bool, i32, f32, f64, slices and references are rejected at check time with a message listing the supported set. Previously a struct or f32x4 parameter compiled on the JIT but panicked in VM codegen.
• Output slot is 16-byte aligned on Cranelift and LLVM, since the host stores through it as int32_t* / float* / double*.
• VM codegen checks the libffi argument budget at compile time instead of panicking on the first call.
• lyte.h documents the rule, including supported parameter types, enums (int32_t* out) and f32x4 (float* out).

Tests

• compiler.rs: one shared runner per backend and assert_extern_all_backends; tuple, struct, array, enum and f32x4 each run the identical program and host function on VM, stack, Cranelift and LLVM.
• New golden tests tests/cases/checker/extern_fn_ret_type.lyte and extern_fn_param_type.lyte for the checker errors; tests/cases/extern_tuple_ret.lyte covers all five by-pointer kinds in check mode.
• cargo test --workspace passes with default features, and cargo test -p lyte -p lyte-cli --features llvm passes against LLVM 19.1.7.

🤖 Generated with Claude Code