feat: expose native extension features to Shen Batteries

boot.lua

@@ -1586,6 +1586,30 @@ local function initialise()
   local r
   local fn = P.F["shen.initialise"]
   if fn then r = fn() end
+  -- Initialise the Shen Batteries feature registry from capabilities detected
+  -- by native extension installers.  The Batteries module loader asks the
+  -- port for `(shen.x.features.current)` before loading a module; leaving the
+  -- registry unbound makes that query fail even though the extension API is
+  -- otherwise available.  Keep this derived from backend globals so
+  -- SHEN_X_SHA256=pure (and ports without native backends) advertise no host
+  -- capability while retaining the portable implementation.
+  if P.F["shen.x.features.current"] then
+    local detected = {}
+    local function add_backend(global, feature)
+      local backend = P.GLOBALS[global]
+      if backend == R.intern("host") then
+        detected[#detected + 1] = R.intern(feature)
+      end
+    end
+    add_backend("shen.x.*sha256-backend*", "shen.x/sha256-host")
+    add_backend("shen.x.*zmq-backend*", "shen.x/zmq-host")
+    -- The community extension's `features.initialise` additionally hooks the
+    -- legacy macro registration API (`shen.set-lambda-form-entry`), which is
+    -- not present in the refreshed 41.2 kernel.  Seed its backing global
+    -- directly; `features.current` is the stable API consumed by Batteries
+    -- and `features.add` can still extend this list later.
+    P.GLOBALS["shen.x.features.*features*"] = R.from_table(detected)
+  end
   -- Register the lua.* interop entries in Shen's own arity/lambda-form
   -- tables (needs the *property-vector* the kernel just created).
   require("lua_interop").post_initialise()

scripts/run-tests.lua

@@ -34,6 +34,7 @@ local specs = {
   "test/engine_spec.lua",
   "test/error_robustness_spec.lua",
   "test/eval_order_spec.lua",
+  "test/features_spec.lua",
   "test/interop_spec.lua",
   "test/io_spec.lua",
   "test/jit_spec.lua",

test/features_spec.lua

@@ -0,0 +1,40 @@
+-- Shen Batteries feature bridge (including shen-extensions capabilities).
+--
+--   luajit test/features_spec.lua
+local shen = require("shen")
+shen.boot{ quiet = true }
+local R = require("runtime")
+local P = shen.prims
+
+local npass, nfail = 0, 0
+local function check(cond, name)
+  if cond then npass = npass + 1
+  else nfail = nfail + 1; io.write("FAIL: ", name, "\n") end
+end
+
+local function names(xs)
+  local out = {}
+  while R.is_cons(xs) do
+    out[tostring(xs[1])] = true
+    xs = xs[2]
+  end
+  return out
+end
+
+local ok, current = pcall(shen.call, "shen.x.features.current")
+check(ok, "features.current is callable after boot")
+if ok then
+  local have = names(current)
+  local backend = P.GLOBALS["shen.x.*sha256-backend*"]
+  if backend == R.intern("host") then
+    check(have["shen.x/sha256-host"] == true,
+      "host SHA-256 backend is advertised to Batteries")
+  else
+    check(have["shen.x/sha256-host"] ~= true,
+      "non-host SHA-256 backend is not advertised as host")
+  end
+  check(not have["shen.x/zmq-host"], "unsupported ZMQ backend is not advertised")
+end
+
+io.write(string.format("features_spec: %d pass, %d fail\n", npass, nfail))
+os.exit(nfail == 0 and 0 or 1)