From 8ae7187c55d952bf413da97dcd5a6d33cbd7421c Mon Sep 17 00:00:00 2001
From: giles <giles.bradshaw@rose-ash.com>
Date: Sat, 9 May 2026 17:01:31 +0000
Subject: [PATCH] js-on-sx: for-in walks proto chain with shadowing, stops at
 native prototypes

---
 lib/js/runtime.sx   | 36 ++++++++++++++++++++++++++++++++++++
 lib/js/transpile.sx |  2 +-
 plans/js-on-sx.md   |  2 ++
 3 files changed, 39 insertions(+), 1 deletion(-)

diff --git a/lib/js/runtime.sx b/lib/js/runtime.sx
index 6a64cafa..5717ccbf 100644
--- a/lib/js/runtime.sx
+++ b/lib/js/runtime.sx
@@ -3844,6 +3844,42 @@
     (k)
     (or (= k "__js_order__") (= k "__proto__"))))
 
+(define
+  js-for-in-keys
+  (fn
+    (o)
+    (let
+      ((result (list)))
+      (begin (js-for-in-walk o result) result))))
+
+(define
+  js-for-in-walk
+  (fn
+    (o acc)
+    (cond
+      ((not (dict? o)) nil)
+      ((= o (get Object "prototype")) nil)
+      ((= o (get Array "prototype")) nil)
+      ((= o (get Number "prototype")) nil)
+      ((= o (get String "prototype")) nil)
+      ((= o (get Boolean "prototype")) nil)
+      ((= o (get Date "prototype")) nil)
+      ((= o (get RegExp "prototype")) nil)
+      ((= o (get Map "prototype")) nil)
+      ((= o (get Set "prototype")) nil)
+      ((= o (get js-function-global "prototype")) nil)
+      (else
+        (let
+          ((own (js-object-keys o)))
+          (begin
+            (for-each
+              (fn (k) (if (contains? acc k) nil (append! acc k)))
+              own)
+            (cond
+              ((contains? (keys o) "__proto__")
+                (js-for-in-walk (get o "__proto__") acc))
+              (else nil))))))))
+
 (define
   js-object-keys
   (fn
diff --git a/lib/js/transpile.sx b/lib/js/transpile.sx
index 1a9b1a73..d9ccfb3d 100644
--- a/lib/js/transpile.sx
+++ b/lib/js/transpile.sx
@@ -948,7 +948,7 @@
                 (if
                   (= iter-kind "of")
                   (list (js-sym "js-iterable-to-list") iter-sx)
-                  (list (js-sym "js-object-keys") iter-sx))))
+                  (list (js-sym "js-for-in-keys") iter-sx))))
             (list
               (js-sym "for-each")
               (list
diff --git a/plans/js-on-sx.md b/plans/js-on-sx.md
index 06e63d0b..d8739734 100644
--- a/plans/js-on-sx.md
+++ b/plans/js-on-sx.md
@@ -158,6 +158,8 @@ Each item: implement → tests → update progress. Mark `[x]` when tests green.
 
 Append-only record of completed iterations. Loop writes one line per iteration: date, what was done, test count delta.
 
+- 2026-05-09 — **`for…in` walks the prototype chain (with shadowing) but stops at native prototypes.** Was using `js-object-keys` which only returns own enumerable keys, so `for (k in instance)` only saw the instance's own properties — not inherited ones from `FACTORY.prototype`. Per spec, for-in walks the entire chain and yields each unique enumerable key once. Added `js-for-in-keys` + `js-for-in-walk` that iterate the chain, deduping via `contains?`. Stops at `Object.prototype` / `Array.prototype` / etc. since those carry "non-enumerable" methods we don't track property-attribute-wise — without this guard, `for (k in {})` would enumerate `toString`/`valueOf`/etc. Result: language/statements/for-in 10/30 → 12/30. Object 30/30, Array 18/30 unchanged. conformance.sh: 148/148.
+
 - 2026-05-09 — **Parser swallows label declarations + accepts optional ident on `break`/`continue`.** Was rejecting `outer: while (...) { break outer; }` at parse time. Per spec, labels are valid syntax and target unwinding to the labeled enclosing loop. Added a parser branch for `<ident> ':' <stmt>` that just parses through to the inner statement (label is dropped; the runtime treats unlabeled `break`/`continue` the same way for the common case where the inner loop is the target). Also extended `break`/`continue` to optionally consume a trailing ident. Result: language/statements/while 14/30 → 16/30, for 27/30 → 28/30. labeled itself dropped 6/15 → 4/15 because we now accept some sources that should be parse errors (e.g. `label: let x;` is a SyntaxError per spec) — net positive across the suite. Object 30/30, Array 18/30 unchanged. conformance.sh: 148/148.
 
 - 2026-05-09 — **`new function(){...}(args)` and `new f(...rest)` now parse and execute.** Two fixes for `new` expression handling: (1) `jp-parse-new-primary` didn't accept the `function` keyword as a primary, so `new function(){...}` raised "Unexpected token after new"; added a branch that mirrors `jp-parse-async-tail` for the function-expression case. (2) `js-transpile-new` always built the args via `js-args` regardless of spread, so `new f(1, ...[])` failed at transpile with "unknown AST tag: js-spread"; now uses `js-array-spread-build` when any arg is a spread, matching what `js-transpile-args` does for regular calls. Result: language/expressions/new 16/30 → 19/30. Object 30/30, Array 18/30, language/expressions/call 21/30 unchanged. conformance.sh: 148/148.