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sx/examples/1202-ffi-cc-c-large-aggregate.sx
agra cd5b958d19 comptime compiler-API: Phase 1 foundation + Phase 2.1 weld plan
Introduce the welded comptime `compiler` library (`#library "compiler"` +
`abi(.zig) extern compiler`), per design/comptime-compiler-api.md, and unify
`callconv(...)` into the new `abi(...)` annotation.

abi(...) replaces callconv(...):
- New ABI enum { default, c, zig, pure }; `abi(.c|.zig|.pure)` parses in the
  postfix slot before extern/export (and standalone). `kw_callconv` -> `kw_abi`.
- Migrated 52 sx files, the call-convention-mismatch diagnostic, and docs
  (readme/specs) from `callconv(.c)` to `abi(.c)`.

Phase 1 — welded compiler library (parse -> registry -> validation -> bridge):
- `abi(.zig) extern compiler` parses on fn decls (carries abi/extern_lib) and
  struct decls (StructDecl.abi/extern_lib).
- `#library "compiler"` is the comptime-only internal surface — never dlopen'd.
- src/ir/compiler_lib.zig: the binding registry (the safety boundary). `Field`
  welded to StructInfo.Field with layout baked from the real Zig type
  (@offsetOf/@sizeOf); `findType`/`findFn`. Welded structs are layout-validated
  at registration (field set + total size) as a header checked against the impl.
- Host-call bridge: a `fn abi(.zig) extern compiler` dispatches under the
  comptime interp to its registered Zig handler (intern/text_of round-trip),
  never dlsym. IR Function.compiler_welded; validated in declareFunction.
- Comptime-only enforcement: a runtime call to a welded fn is a clean
  build-gating error (emitCall), not an undefined-symbol link failure.

Phase 2.1 — byte-layout weld foundation:
- Decision: full byte-layout weld (sx struct laid out byte-identically to the
  bound Zig type). Registered StructInfo (first non-natural / Zig-reordered
  layout). `computeWeldPlan` — pure offset-ordered element plan + padding +
  sx-field->LLVM-element remap; unit-tested. Emit/interp wiring is the next
  sub-step (2.2+, see current/CHECKPOINT-COMPILER-API.md).

Examples: 0625/0626 (welded struct + fn round-trip), 1183/1184/1185
(layout-mismatch, unexported-fn, runtime-call diagnostics).
2026-06-17 13:31:11 +03:00

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// Regression test for issue-0025 path A.
//
// sx functions declared with `abi(.c)` that take a composite > 16 bytes
// by value must marshal the arg through `ptr byval(<T>)` per AAPCS64 / SysV
// AArch64: the caller copies the struct to an alloca, passes the alloca
// pointer with a `byval(<T>)` attribute, and the callee's entry block loads
// the struct back from the pointer.
//
// Before the fix, abiCoerceParamType returned the raw LLVM struct type for
// >16-byte composites (TODO at src/ir/emit_llvm.zig:2793), so the C ABI
// promise was silently violated whenever sx-emitted C-callable code
// interoperated with a real C caller.
#import "modules/std.sx";
Wide :: struct {
a: i64;
b: i64;
c: i64;
d: i64;
}
accept_c :: (w: Wide) -> i64 abi(.c) {
w.a + w.b + w.c + w.d
}
main :: () -> i32 {
w := Wide.{ a = 1, b = 10, c = 100, d = 1000 };
if accept_c(w) != 1111 { return 1; }
0
}