ffi M1.1 (first pass): id / Class / SEL / BOOL type aliases

Adds named stand-ins for the three opaque Obj-C runtime types
and Apple's signed-char boolean to library/modules/std/objc.sx:

  id    :: *void;   // any Obj-C instance pointer
  Class :: *void;   // a class object pointer
  SEL   :: *void;   // a registered selector
  BOOL  :: s8;      // Apple's signed-char boolean (NOT sx's bool)

All resolve to their underlying type at the LLVM layer — no
runtime cost — but make foreign-class declarations read closer
to Objective-C source. The header's old caveat about lacking
type aliases is gone.

141-objc-type-aliases.sx exercises the aliases against the real
macOS Obj-C runtime: alloc/init an NSObject, fetch its class
via objc_getClass, sel_registerName a SEL, then call
'isKindOfClass:' returning BOOL=1. Non-macOS paths print the
same line to keep the snapshot stable.

DEFERRED (M1.1.b, follow-up): 'Class(T)' parameterization with
#extends-aware covariance, and 'instancetype' per-decl
substitution. Both require compiler-level type-check support
beyond plain stdlib aliases.

170 examples pass (+1).

current/CHECKPOINT-FFI.md

@@ -6,7 +6,38 @@ add a test and make it pass — that's two commits).
 
 ## Last completed step
 
-**issue-0043 closed — `#foreign` C-variadic tail via `args: ..T`.**
+**M1.0 — Expression-bodied function declarations**
+(3 commits: `6c95b2a`, `4a048d3`, `86c1127`).
+
+sx's `=>` body form (already used in lambdas) now spans every
+function-declaration position: top-level, struct method, AND
+`#objc_class` member method. The parser extension is a single
+arm in `parseForeignClassDecl` ([src/parser.zig:1262]) that
+mirrors the existing `parseFnDecl` arrow handling.
+
+Three commits, FFI cadence:
+- `6c95b2a` ffi M1.0 (1/3): lock in passing top-level + struct-method form
+  (`examples/139-expression-bodied-fn.sx`).
+- `4a048d3` ffi M1.0 (2/3, xfail): `=>` body inside `#objc_class` member
+  captured as parser error (`examples/140-expression-bodied-objc-method.sx`).
+- `86c1127` ffi M1.0 (3/3): parser extension, 140 flips green.
+
+169 examples pass (+2 from M1.0). `zig build test` green.
+
+This is the first milestone of the **6-month Obj-C FFI roadmap**
+saved at `~/.claude/plans/lets-see-options-for-merry-dijkstra.md`.
+The roadmap covers: M1 language precursors + typed `Class(T)` +
+class-synthesis foundation; M2 declarative class sugar (properties,
+class constants, `#extends` chaining); M3 retire
+`uikit_register_classes`; M4 ARC + autoreleasepool; M5 closure↔block
+bridge; M6 auto-import + production hardening. Resolved design
+questions: per-instance allocator at `alloc()`, directive-statement
+`#extends`/`#implements` syntax, refcount inherited from NSObject.
+Four design questions still open (see roadmap).
+
+---
+
+**Prior landing — issue-0043 closed: `#foreign` C-variadic tail via `args: ..T`.**
 A trailing variadic param on a `#foreign` declaration now maps to the
 C calling convention's `...` instead of sx's slice-packing path. Drops
 the existing per-arity shim pattern (`__log_2i :: (prio, tag, fmt, a:
@@ -145,14 +176,30 @@ plus 2 codegen fixes surfaced along the way.**
 
 ## Current state
 
-- 97/97 regression tests pass (was 86 at start of FFI work; +11 net,
-  factoring in the `examples/issue-0036.sx` → `101-ffi-medium-struct.sx`
-  promotion).
-- `tests/cross_compile.sh` runs clean (empty tuple list).
-- Chess Android build + iOS-sim build both clean. emit_llvm.zig sret
-  + struct↔array changes don't regress either.
-- ABI coverage matrix locked in for all four C-ABI aggregate slots
-  (≤8 B int, 9..16 B int, 16 B HFA, >16 B byval+sret).
+- 169/169 example tests pass; `zig build test` green.
+- Phase 3.0/3.1/3.2 (Obj-C DSL dispatch + selector mangling +
+  selector override + uikit.sx C1-C5 cluster migrations) all
+  landed. M1.0 (expression-bodied functions) just landed.
+- Chess on macOS / iOS-sim / Android all build and run.
+- Active forward plan: 6-month Obj-C FFI roadmap at
+  `~/.claude/plans/lets-see-options-for-merry-dijkstra.md`.
+
+## Next step (M1.1 — Foreign type aliases)
+
+Introduce sx-side typed aliases for the Obj-C primitives that
+today are `*void`: `Class(T)` (phantom-parameterized), `id`, `SEL`,
+`BOOL`, `instancetype`. Per the roadmap, the load-bearing piece
+is `Class(T)`: a phantom-typed pointer alias enabling type-safe
+factory returns like
+`layerClass :: Class(CALayer) = CAEAGLLayer.class();` (the M2.1(a)
+class-constant form). Plain `Class` ⇒ `Class(NSObject)` sugar.
+`Cls.class()` returns `Class(Cls)`. Covariant on `#extends`.
+
+Files to touch: [src/parser.zig](../src/parser.zig) (parser
+support for `Class(T)` type syntax),
+[src/ir/lower.zig](../src/ir/lower.zig) (alias resolution +
+covariance check). LLVM layer unchanged — these are phantom-typed,
+underlying representation stays `*void`.
 
 ## Phase 1B complete (1.6–1.14)
 

examples/141-objc-type-aliases.sx

@@ -0,0 +1,47 @@
+// M1.1 — Obj-C primitive type aliases.
+//
+// `id`, `Class`, `SEL`, `BOOL` from `modules/std/objc.sx` stand in
+// for the three opaque Obj-C runtime types and Apple's signed-char
+// boolean. They resolve to `*void` / `s8` at the LLVM layer — no
+// runtime cost — but make foreign-class and call-site declarations
+// read closer to Objective-C source.
+//
+// `Class(T)` parameterization (phantom T, `#extends`-aware
+// covariance) is deferred to a follow-up; for now plain `Class`
+// is the only form and assignments are not checked against the
+// referent's class hierarchy.
+
+#import "modules/std.sx";
+#import "modules/compiler.sx";
+#import "modules/std/objc.sx";
+
+// Foreign-class declaration using the aliases at param/return positions.
+NSObjectAlias :: #foreign #objc_class("NSObject") {
+    alloc :: () -> *Self;
+    init  :: (self: *Self) -> *Self;
+    isKindOfClass :: (self: *Self, cls: Class) -> BOOL;
+}
+
+main :: () -> s32 {
+    inline if OS == .macos {
+        // id - any Obj-C instance pointer.
+        nsobj : id = NSObjectAlias.alloc().init();
+
+        // Class - the runtime class object.
+        ns_cls : Class = objc_getClass("NSObject".ptr);
+
+        // SEL - registered selector.
+        sel : SEL = sel_registerName("alloc".ptr);
+        _ = sel;
+
+        // BOOL - Apple's signed-char boolean. Cast the *Self into
+        // a *NSObjectAlias for the method call.
+        obj : *NSObjectAlias = xx nsobj;
+        flag : BOOL = obj.isKindOfClass(ns_cls);
+        print("isKindOfClass: {}\n", flag);  // 1 (true)
+    }
+    inline if OS != .macos {
+        print("isKindOfClass: 1\n");  // skip — runtime not present
+    }
+    0;
+}

library/modules/std/objc.sx

@@ -1,9 +1,5 @@
 // Obj-C runtime FFI primitives.
 //
-// `*void` stands in for the Obj-C `id`/`Class`/`SEL` types. There's no
-// sx-level type alias yet, so naming discipline at call sites is the only
-// thing keeping them apart.
-//
 // objc_msgSend has the standard ARM64 calling convention (no varargs path).
 // Each call site must invoke through a function pointer of the *exact*
 // argument and return shape. The idiom:
@@ -11,6 +7,28 @@
 //     msg_fn : (recv: *void, sel: *void, arg: [*]u8) -> *void = xx objc_msgSend;
 //     result := msg_fn(receiver, selector, c_string);
 
+// ─── Obj-C primitive type aliases ───────────────────────────────────────
+// Named stand-ins for the three opaque Obj-C runtime types. They all
+// resolve to `*void` at the LLVM layer (no runtime cost) but improve
+// readability in foreign-class declarations and call sites.
+//
+//   id    — any Obj-C instance pointer
+//   Class — a class object pointer
+//   SEL   — a registered selector
+//
+// `Class(T)` parameterization (phantom-typed, with `#extends`-aware
+// covariance) is a follow-up — needs compiler-level type-check support.
+// For now, `Class` alone is the only form; assignments are not checked
+// against the referent's class hierarchy.
+id    :: *void;
+Class :: *void;
+SEL   :: *void;
+
+// Apple's `BOOL` is a signed char (NOT sx's built-in `bool`, which is
+// LLVM `i1`). Obj-C method signatures that take or return `BOOL` cross
+// the FFI boundary as `s8`.
+BOOL :: s8;
+
 // On macOS libobjc is auto-loaded by libSystem; on iOS it isn't, so we
 // link it explicitly. Foundation registers NSString etc. with the runtime,
 // also auto-loaded on macOS and required as an explicit framework on iOS.

tests/expected/141-objc-type-aliases.exit

@@ -0,0 +1 @@
+0

tests/expected/141-objc-type-aliases.txt

@@ -0,0 +1 @@
+isKindOfClass: 1