Extern registry slot+arity; extern trace; vtable Array/String tests

src/backend/vm_instructions.rs

@@ -630,6 +630,14 @@ impl VM {
             nyash_args.push(arg_value.to_nyash_box());
         }
         
+        // Optional trace
+        if crate::config::env::extern_trace() {
+            if let Some(slot) = crate::runtime::extern_registry::resolve_slot(iface_name, method_name) {
+                eprintln!("[EXT] call {}.{} slot={} argc={}", iface_name, method_name, slot, nyash_args.len());
+            } else {
+                eprintln!("[EXT] call {}.{} argc={}", iface_name, method_name, nyash_args.len());
+            }
+        }
         // Route through unified plugin host (delegates to v2, handles env.* stubs)
         let host = crate::runtime::get_global_plugin_host();
         let host = host.read().map_err(|_| VMError::InvalidInstruction("Plugin host lock poisoned".into()))?;
@@ -650,6 +658,10 @@ impl VM {
                 let mut msg = String::new();
                 if strict { msg.push_str("ExternCall STRICT: unregistered or unsupported call "); } else { msg.push_str("ExternCall failed: "); }
                 msg.push_str(&format!("{}.{}", iface_name, method_name));
+                // Arity check when known
+                if let Err(detail) = crate::runtime::extern_registry::check_arity(iface_name, method_name, nyash_args.len()) {
+                    msg.push_str(&format!(" ({})", detail));
+                }
                 if let Some(spec) = crate::runtime::extern_registry::resolve(iface_name, method_name) {
                     msg.push_str(&format!(" (expected arity {}..{})", spec.min_arity, spec.max_arity));
                 } else {

src/config/env.rs

@@ -125,3 +125,4 @@ pub fn abi_strict() -> bool { std::env::var("NYASH_ABI_STRICT").ok().as_deref()
 
 // ---- ExternCall strict diagnostics ----
 pub fn extern_strict() -> bool { std::env::var("NYASH_EXTERN_STRICT").ok().as_deref() == Some("1") }
+pub fn extern_trace() -> bool { std::env::var("NYASH_EXTERN_TRACE").ok().as_deref() == Some("1") }

src/runtime/extern_registry.rs

@@ -5,20 +5,26 @@
 use once_cell::sync::Lazy;
 
 #[derive(Clone, Copy, Debug)]
-pub struct ExternSpec { pub iface: &'static str, pub method: &'static str, pub min_arity: u8, pub max_arity: u8 }
+pub struct ExternSpec {
+    pub iface: &'static str,
+    pub method: &'static str,
+    pub min_arity: u8,
+    pub max_arity: u8,
+    pub slot: Option<u16>,
+}
 
 static EXTERNS: Lazy<Vec<ExternSpec>> = Lazy::new(|| vec![
     // console
-    ExternSpec { iface: "env.console", method: "log", min_arity: 1, max_arity: 1 },
+    ExternSpec { iface: "env.console", method: "log", min_arity: 1, max_arity: 1, slot: Some(10) },
     // debug
-    ExternSpec { iface: "env.debug", method: "trace", min_arity: 1, max_arity: 255 },
+    ExternSpec { iface: "env.debug", method: "trace", min_arity: 1, max_arity: 255, slot: Some(11) },
     // runtime
-    ExternSpec { iface: "env.runtime", method: "checkpoint", min_arity: 0, max_arity: 0 },
+    ExternSpec { iface: "env.runtime", method: "checkpoint", min_arity: 0, max_arity: 0, slot: Some(12) },
     // future (scaffold)
-    ExternSpec { iface: "env.future", method: "new", min_arity: 1, max_arity: 1 },
-    ExternSpec { iface: "env.future", method: "birth", min_arity: 1, max_arity: 1 },
-    ExternSpec { iface: "env.future", method: "set", min_arity: 2, max_arity: 2 },
-    ExternSpec { iface: "env.future", method: "await", min_arity: 1, max_arity: 1 },
+    ExternSpec { iface: "env.future", method: "new", min_arity: 1, max_arity: 1, slot: Some(20) },
+    ExternSpec { iface: "env.future", method: "birth", min_arity: 1, max_arity: 1, slot: Some(20) },
+    ExternSpec { iface: "env.future", method: "set", min_arity: 2, max_arity: 2, slot: Some(21) },
+    ExternSpec { iface: "env.future", method: "await", min_arity: 1, max_arity: 1, slot: Some(22) },
 ]);
 
 pub fn resolve(iface: &str, method: &str) -> Option<ExternSpec> {
@@ -35,3 +41,15 @@ pub fn all_ifaces() -> Vec<&'static str> {
     v.sort(); v.dedup(); v
 }
 
+/// Resolve slot id for an extern call (if assigned)
+pub fn resolve_slot(iface: &str, method: &str) -> Option<u16> {
+    resolve(iface, method).and_then(|s| s.slot)
+}
+
+/// Check arity against registry; returns Ok or an explanatory error string
+pub fn check_arity(iface: &str, method: &str, argc: usize) -> Result<(), String> {
+    if let Some(s) = resolve(iface, method) {
+        if argc as u8 >= s.min_arity && argc as u8 <= s.max_arity { Ok(()) }
+        else { Err(format!("arity {} out of range {}..{}", argc, s.min_arity, s.max_arity)) }
+    } else { Err("unknown extern".to_string()) }
+}

src/tests/vtable_array_string.rs

@@ -0,0 +1,45 @@
+#[test]
+fn vtable_array_and_string_len_get_set() {
+    use crate::backend::vm::VM;
+    use crate::mir::{MirModule, MirFunction, FunctionSignature, MirInstruction, EffectMask, BasicBlockId, ConstValue, MirType};
+    std::env::set_var("NYASH_ABI_VTABLE", "1");
+
+    // Array: set(0, "x"); len(); get(0)
+    let sig = FunctionSignature { name: "main".into(), params: vec![], return_type: MirType::String, effects: EffectMask::PURE };
+    let mut f = MirFunction::new(sig, BasicBlockId::new(0));
+    let bb = f.entry_block;
+    let arr = f.next_value_id();
+    f.get_block_mut(bb).unwrap().add_instruction(MirInstruction::NewBox { dst: arr, box_type: "ArrayBox".into(), args: vec![] });
+    let idx0 = f.next_value_id();
+    f.get_block_mut(bb).unwrap().add_instruction(MirInstruction::Const { dst: idx0, value: ConstValue::Integer(0) });
+    let sval = f.next_value_id();
+    f.get_block_mut(bb).unwrap().add_instruction(MirInstruction::Const { dst: sval, value: ConstValue::String("x".into()) });
+    f.get_block_mut(bb).unwrap().add_instruction(MirInstruction::BoxCall { dst: None, box_val: arr, method: "set".into(), args: vec![idx0, sval], method_id: None, effects: EffectMask::PURE });
+    let lenv = f.next_value_id();
+    f.get_block_mut(bb).unwrap().add_instruction(MirInstruction::BoxCall { dst: Some(lenv), box_val: arr, method: "len".into(), args: vec![], method_id: None, effects: EffectMask::PURE });
+    // sanity: len should be 1 (not asserted here, just exercise path)
+    let got = f.next_value_id();
+    f.get_block_mut(bb).unwrap().add_instruction(MirInstruction::BoxCall { dst: Some(got), box_val: arr, method: "get".into(), args: vec![idx0], method_id: None, effects: EffectMask::PURE });
+    f.get_block_mut(bb).unwrap().add_instruction(MirInstruction::Return { value: Some(got) });
+    let mut m = MirModule::new("tarr".into()); m.add_function(f);
+    let mut vm = VM::new();
+    let out = vm.execute_module(&m).expect("vm exec");
+    assert_eq!(out.to_string_box().value, "x");
+
+    // String: len()
+    let sig2 = FunctionSignature { name: "main".into(), params: vec![], return_type: MirType::Integer, effects: EffectMask::PURE };
+    let mut f2 = MirFunction::new(sig2, BasicBlockId::new(0));
+    let bb2 = f2.entry_block;
+    let s = f2.next_value_id();
+    f2.get_block_mut(bb2).unwrap().add_instruction(MirInstruction::Const { dst: s, value: ConstValue::String("abc".into()) });
+    let sb = f2.next_value_id();
+    f2.get_block_mut(bb2).unwrap().add_instruction(MirInstruction::NewBox { dst: sb, box_type: "StringBox".into(), args: vec![s] });
+    let ln = f2.next_value_id();
+    f2.get_block_mut(bb2).unwrap().add_instruction(MirInstruction::BoxCall { dst: Some(ln), box_val: sb, method: "len".into(), args: vec![], method_id: None, effects: EffectMask::PURE });
+    f2.get_block_mut(bb2).unwrap().add_instruction(MirInstruction::Return { value: Some(ln) });
+    let mut m2 = MirModule::new("tstr".into()); m2.add_function(f2);
+    let mut vm2 = VM::new();
+    let out2 = vm2.execute_module(&m2).expect("vm exec");
+    assert_eq!(out2.to_string_box().value, "3");
+}
+