`inst.method(args)` on a value typed as a foreign-class alias
(`Activity :: #jni_class("android/app/Activity") { getWindow ::
(self: *Self) -> *Window; }` etc.) now lowers to `jni_msg_send`
with descriptor auto-derived from the sx signature, env from the
enclosing `#jni_env` scope (lexical-direct via 2.16b), and slot
interning re-used from Phase 1C.
Touch surface:
- `Lowering` gains `foreign_class_map: StringHashMap(*const
ForeignClassDecl)` populated in `scanDecls` + `lowerDecls`.
- New `registerForeignClassDecl` records each declared alias; the
type-bridge fallback already interns the alias as a 0-field
struct, so `*Activity` resolves cleanly through `getStructTypeName`.
- New `lowerForeignMethodCall` looks up the method in
`ForeignClassDecl.members`, derives the descriptor via
`jni_descriptor.deriveMethod` (with a `ClassRegistry` built from
`foreign_class_map`), and emits `jni_msg_send` directly. Filters
by runtime — `jni_class`/`jni_interface` lower; `objc_class` etc.
surface a clear "not yet supported" diagnostic until Phase 3/4.
- `lowerCall`'s method-dispatch arm inserts the foreign-class
check before the standard struct-method resolution.
JNI descriptor derivation gains `*void → Ljava/lang/Object;` (the
opaque-jobject convention) — common when sx code doesn't have a
precise Java type for the value. Locked in with a unit test.
IR snapshot at `tests/expected/ffi-jni-class-08-call.ir` shows the
full lowering: env from the enclosing fn param, target from the
foreign-class arg, slot-interned `(class, method, sig)` cache
pair, jni_msg_send to `CallObjectMethod` (slot 34). Mangled slot
names `@SX_JNI_CLS_getWindow____Ljava_lang_Object_` confirm the
derived descriptor.
129/129 examples + 16 jni_descriptor unit tests green.
`act.getWindow()` on `act: *Activity` (where `Activity ::
#jni_class("android/app/Activity") { getWindow :: ... }`) should
lower to `#jni_call(*void)(act, "getWindow", "()Ljava/lang/Object;")`
(omitted-env form picking up env from the enclosing `#jni_env`
scope via 2.16b's lexical-direct path). Today's sema reports
"unresolved: 'getWindow'" because foreign-class members aren't
yet wired into the method-resolution path.
The make-green follow-up needs:
- sema: register `ForeignClassDecl.members` so method names
resolve on foreign-class receivers (or suppress the unresolved
fallback for them).
- lower: build a `foreign_class_map` in scan pass; new arm in
`lowerCall`'s method-dispatch site emits a synthetic
`FfiIntrinsicCall { kind: jni_call, args: [target, "name",
"(sig)Ret", method_args...] }` with the descriptor derived via
`jni_descriptor.deriveMethod`.
- type system: `*Activity` resolution path so `inferExprType`
on the receiver returns a known type (likely register foreign
classes as synthetic 0-field structs reusing the struct-type
machinery).
Larger session needed — pausing here at the xfail.
