HS: js-block return values + worker stub test

Parser: parse-js-block extracts raw JS source by character positions.
Compiler: js-block AST → hs-js-exec call, stores result in it.
Runtime: hs-js-exec creates JS Function, handles promise rejection.
Test runner: host-new-function/host-promise-state natives + promise monkey-patch.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

lib/hyperscript/compiler.sx

@@ -2268,6 +2268,25 @@
                   (list (quote hs-halt!) (quote event) (nth ast 1)))
                 ((= head (quote focus!))
                   (list (quote dom-focus) (hs-to-sx (nth ast 1))))
+                ((= head (quote js-block))
+                  (let
+                    ((params (nth ast 1)) (js-src (nth ast 2)))
+                    (let
+                      ((bound-syms (map (fn (p) (make-symbol p)) params)))
+                      (list
+                        (quote let)
+                        (list
+                          (list
+                            (quote __hs-js)
+                            (list
+                              (quote hs-js-exec)
+                              (cons (quote list) params)
+                              js-src
+                              (cons (quote list) bound-syms))))
+                        (list
+                          (quote begin)
+                          (list (quote set!) (quote it) (quote __hs-js))
+                          (quote __hs-js))))))
                 (true ast)))))))))
 
 ;; ── Convenience: source → SX ─────────────────────────────────

lib/hyperscript/parser.sx

@@ -2506,6 +2506,33 @@
           (let
             ((target (cond ((at-end?) (list (quote beingTold))) ((and (= (tp-type) "keyword") (or (= (tp-val) "then") (= (tp-val) "end"))) (list (quote beingTold))) (true (parse-expr)))))
             (list (quote close-element) target))))
+      (define
+        parse-js-block
+        (fn
+          ()
+          (let
+            ((params (if (= (tp-type) "paren-open") (do (adv!) (define collect-params! (fn (acc) (cond ((or (at-end?) (= (tp-type) "paren-close")) (do (when (= (tp-type) "paren-close") (adv!)) acc)) ((= (tp-type) "comma") (do (adv!) (collect-params! acc))) (true (let ((pname (tp-val))) (do (adv!) (collect-params! (append acc pname)))))))) (collect-params! (list))) (list))))
+            (let
+              ((js-start (cur-start)))
+              (define
+                skip-to-end!
+                (fn
+                  ()
+                  (if
+                    (or
+                      (at-end?)
+                      (and (= (tp-type) "keyword") (= (tp-val) "end")))
+                    nil
+                    (do (adv!) (skip-to-end!)))))
+              (skip-to-end!)
+              (let
+                ((js-end (cur-start)))
+                (let
+                  ((js-src (substring src js-start js-end)))
+                  (when
+                    (and (= (tp-type) "keyword") (= (tp-val) "end"))
+                    (adv!))
+                  (list (quote js-block) params js-src)))))))
       (define
         parse-cmd
         (fn
@@ -2655,6 +2682,8 @@
                 (do (adv!) (list (quote continue))))
               ((and (= typ "keyword") (or (= val "exit") (= val "halt")))
                 (do (adv!) (list (quote exit))))
+              ((and (= typ "keyword") (= val "js"))
+                (do (adv!) (parse-js-block)))
               (true (parse-expr))))))
       (define
         parse-cmd-list
@@ -2710,7 +2739,8 @@
                 (= v "close")
                 (= v "pick")
                 (= v "ask")
-                (= v "answer"))))
+                (= v "answer")
+                (= v "js"))))
           (define
             cl-collect
             (fn

lib/hyperscript/runtime.sx

@@ -2588,3 +2588,21 @@
           node
           (walk (hs-node-get node (first keys)) (rest keys)))))
     (hs-line-for (walk (hs-parse-ast src-str) path))))
+
+(define
+  hs-js-exec
+  (fn
+    (param-names js-src bound-args)
+    (let
+      ((js-fn (host-new-function param-names js-src)))
+      (let
+        ((result (host-call-fn js-fn bound-args)))
+        (if
+          (= (host-typeof result) "promise")
+          (let
+            ((state (host-promise-state result)))
+            (if
+              (and state (= (host-get state "ok") false))
+              (raise (host-get state "value"))
+              (if state (host-get state "value") result)))
+          result)))))

shared/static/wasm/sx/hs-compiler.sx

@@ -2268,6 +2268,25 @@
                   (list (quote hs-halt!) (quote event) (nth ast 1)))
                 ((= head (quote focus!))
                   (list (quote dom-focus) (hs-to-sx (nth ast 1))))
+                ((= head (quote js-block))
+                  (let
+                    ((params (nth ast 1)) (js-src (nth ast 2)))
+                    (let
+                      ((bound-syms (map (fn (p) (make-symbol p)) params)))
+                      (list
+                        (quote let)
+                        (list
+                          (list
+                            (quote __hs-js)
+                            (list
+                              (quote hs-js-exec)
+                              (cons (quote list) params)
+                              js-src
+                              (cons (quote list) bound-syms))))
+                        (list
+                          (quote begin)
+                          (list (quote set!) (quote it) (quote __hs-js))
+                          (quote __hs-js))))))
                 (true ast)))))))))
 
 ;; ── Convenience: source → SX ─────────────────────────────────

shared/static/wasm/sx/hs-parser.sx

@@ -2506,6 +2506,33 @@
           (let
             ((target (cond ((at-end?) (list (quote beingTold))) ((and (= (tp-type) "keyword") (or (= (tp-val) "then") (= (tp-val) "end"))) (list (quote beingTold))) (true (parse-expr)))))
             (list (quote close-element) target))))
+      (define
+        parse-js-block
+        (fn
+          ()
+          (let
+            ((params (if (= (tp-type) "paren-open") (do (adv!) (define collect-params! (fn (acc) (cond ((or (at-end?) (= (tp-type) "paren-close")) (do (when (= (tp-type) "paren-close") (adv!)) acc)) ((= (tp-type) "comma") (do (adv!) (collect-params! acc))) (true (let ((pname (tp-val))) (do (adv!) (collect-params! (append acc pname)))))))) (collect-params! (list))) (list))))
+            (let
+              ((js-start (cur-start)))
+              (define
+                skip-to-end!
+                (fn
+                  ()
+                  (if
+                    (or
+                      (at-end?)
+                      (and (= (tp-type) "keyword") (= (tp-val) "end")))
+                    nil
+                    (do (adv!) (skip-to-end!)))))
+              (skip-to-end!)
+              (let
+                ((js-end (cur-start)))
+                (let
+                  ((js-src (substring src js-start js-end)))
+                  (when
+                    (and (= (tp-type) "keyword") (= (tp-val) "end"))
+                    (adv!))
+                  (list (quote js-block) params js-src)))))))
       (define
         parse-cmd
         (fn
@@ -2655,6 +2682,8 @@
                 (do (adv!) (list (quote continue))))
               ((and (= typ "keyword") (or (= val "exit") (= val "halt")))
                 (do (adv!) (list (quote exit))))
+              ((and (= typ "keyword") (= val "js"))
+                (do (adv!) (parse-js-block)))
               (true (parse-expr))))))
       (define
         parse-cmd-list
@@ -2710,7 +2739,8 @@
                 (= v "close")
                 (= v "pick")
                 (= v "ask")
-                (= v "answer"))))
+                (= v "answer")
+                (= v "js"))))
           (define
             cl-collect
             (fn

shared/static/wasm/sx/hs-runtime.sx

@@ -2588,3 +2588,21 @@
           node
           (walk (hs-node-get node (first keys)) (rest keys)))))
     (hs-line-for (walk (hs-parse-ast src-str) path))))
+
+(define
+  hs-js-exec
+  (fn
+    (param-names js-src bound-args)
+    (let
+      ((js-fn (host-new-function param-names js-src)))
+      (let
+        ((result (host-call-fn js-fn bound-args)))
+        (if
+          (= (host-typeof result) "promise")
+          (let
+            ((state (host-promise-state result)))
+            (if
+              (and state (= (host-get state "ok") false))
+              (raise (host-get state "value"))
+              (if state (host-get state "value") result)))
+          result)))))

spec/tests/test-hyperscript-behavioral.sx

@@ -13636,5 +13636,12 @@ end")
 ;; ── worker (1 tests) ──
 (defsuite "hs-upstream-worker"
   (deftest "raises a helpful error when the worker plugin is not installed"
-    (error "SKIP (untranslated): raises a helpful error when the worker plugin is not installed"))
+    (hs-cleanup!)
+    (let ((caught nil))
+      (guard (_e (true (set! caught (str _e))))
+        (hs-compile "worker MyWorker def noop() end end"))
+      (assert (not (nil? caught)))
+      (assert (string-contains? caught "worker plugin"))
+      (assert (string-contains? caught "hyperscript.org/features/worker")))
+  )
 )

tests/hs-run-filtered.js

@@ -568,6 +568,41 @@ K.registerNative('host-to-list',([obj])=>{try{return[...obj];}catch(e){return[];
 K.registerNative('host-await',a=>{});
 K.registerNative('load-library!',()=>false);
 
+// ── JS block execution support ─────────────────────────────────
+// Track promise states for synchronous introspection in hs-js-exec
+const _promiseStates = new WeakMap();
+const _origPReject = Promise.reject.bind(Promise);
+const _origPResolve = Promise.resolve.bind(Promise);
+Promise.reject = function(v) {
+  const p = _origPReject(v);
+  _promiseStates.set(p, {ok: false, value: v});
+  p.catch(() => {}); // suppress unhandled rejection warning
+  return p;
+};
+Promise.resolve = function(v) {
+  if (v && typeof v === 'object' && typeof v.then === 'function') return _origPResolve(v);
+  const p = _origPResolve(v);
+  _promiseStates.set(p, {ok: true, value: v});
+  return p;
+};
+
+K.registerNative('host-new-function', a => {
+  const paramList = a[0];
+  const src = a[1];
+  const params = paramList && paramList._type === 'list' && paramList.items
+    ? Array.from(paramList.items)
+    : Array.isArray(paramList) ? paramList : [];
+  try { return new Function(...params, src); } catch(e) { return null; }
+});
+
+K.registerNative('host-promise-state', a => {
+  const p = a[0];
+  if (!p || typeof p.then !== 'function') return null;
+  const s = _promiseStates.get(p);
+  if (!s) return null;
+  return {ok: s.ok, value: s.value};
+});
+
 let _testDeadline = 0;
 // Mock fetch routes
 const _fetchRoutes = {

tests/playwright/generate-sx-tests.py

@@ -155,6 +155,15 @@ MANUAL_TEST_BODIES = {
         '      (assert-contains "foo" _names)',
         '      (assert-contains "bar" _values))',
     ],
+    "raises a helpful error when the worker plugin is not installed": [
+        '    (hs-cleanup!)',
+        '    (let ((caught nil))',
+        '      (guard (_e (true (set! caught (str _e))))',
+        '        (hs-compile "worker MyWorker def noop() end end"))',
+        '      (assert (not (nil? caught)))',
+        '      (assert (string-contains? caught "worker plugin"))',
+        '      (assert (string-contains? caught "hyperscript.org/features/worker")))',
+    ],
 }