Implement exception reraising from the guard handler

src/common.cpp

@@ -702,6 +702,50 @@ Result<StackFrame> StackFrame::attach(const StackFrame& frame) const {
   return StackFrame(TRY(MkGcRoot(pod)));
 }
 
+Result<Value> StackFrame::unwind(const Value& val, uint64_t start_from) const {
+  StackFrame cur = TRY(copy());
+
+  uint64_t depth = 0;
+  while (true) {
+    if (cur.guard() && depth >= start_from) {
+      auto state = TRY(cur.get(1));
+      if (!state.is<Int64>()) return ERROR(TypeMismatch);
+      auto state_int = state.to<Int64>()->value();
+
+      if (state_int <= 1) {
+        auto detached_stack = TRY(detach(depth - 1));
+
+        auto new_cont = TRY(Continuation::create(val, detached_stack));
+
+        cur = TRY(cur.set(1, Value(TRY(Int64::create((int64_t)1)))));
+        cur = TRY(cur.set(2, Value(std::move(new_cont))));
+        return Value(std::move(cur));
+      }
+    }
+
+    auto parent = TRY(cur.parent());
+    if (parent.is<Nil>()) break;
+
+    cur = TRY(parent.to<StackFrame>()->copy());
+    ++depth;
+  }
+  return Value(TRY(Nil::create()));
+}
+
+Result<uint64_t> StackFrame::depth() const {
+  StackFrame cur = TRY(copy());
+
+  uint64_t depth = 1;
+  while (true) {
+    auto parent = TRY(cur.parent());
+    if (parent.is<Nil>()) break;
+
+    cur = TRY(parent.to<StackFrame>()->copy());
+    ++depth;
+  }
+  return depth;
+}
+
 Result<StackFrame> StackFrame::set_guard(bool guard) const {
   uint64_t size = _value->size;
   auto pod = TRY(arena_alloc<PodStackFrame>(sizeof(OffPtr<PodObject>) * size));

src/common.hpp

@@ -1168,6 +1168,9 @@ class StackFrame : public Object {
   Result<StackFrame> detach(uint64_t depth) const;
   Result<StackFrame> attach(const StackFrame& frame) const;
 
+  Result<Value> unwind(const Value& val, uint64_t start_from = 0) const;
+  Result<uint64_t> depth() const;
+
   Result<StackFrame> set_guard(bool guard = true) const;
 
   virtual Result<Value> copy_value() const final;

src/stdlib.cpp

@@ -406,6 +406,61 @@ Result<StackFrame> stdlib_raise(const StackFrame& stack) {
   return ERROR_OBJ(Raise, cont);
 }
 
+Result<StackFrame> stdlib_reraise(const StackFrame& stack) {
+  auto stack_size = TRY(stack.size());
+
+  auto params = TRY(stack.get(0));
+  auto size = TRY(params.size());
+  if (size != 1) return ERROR(ArgumentCountMismatch);
+
+  auto cont_val = TRY(params.get(0));
+
+  if (!cont_val.is<Continuation>()) return ERROR(TypeMismatch);
+
+  Continuation& cont = *cont_val.to<Continuation>();
+  StackFrame cont_stack = TRY(cont.frame());
+
+  StackFrame cur = TRY(stack.copy());
+
+  uint64_t depth = 0;
+
+  while (true) {
+    if (cur.guard()) {
+      auto state = TRY(cur.get(1));
+      if (!state.is<Int64>()) return ERROR(TypeMismatch);
+      auto state_int = state.to<Int64>()->value();
+
+      if (state_int > 1) {
+        auto val = TRY(cont.value());
+        auto remaining_stack = TRY(stack.detach(depth - 1));
+
+        Value fun = TRY(params.get(0));
+        cur = TRY(cur.set(1, Value(TRY(Int64::create((int64_t)0)))));
+        cur = TRY(cur.set(2, Value(std::move(fun))));
+        cur = TRY(cur.settop(3));
+
+        cur = TRY(remaining_stack.attach(cur));
+        cur = TRY(cont_stack.attach(cur));
+
+        uint64_t start_from = depth + TRY(cont_stack.depth()) + 1;
+
+        auto res = TRY(cur.unwind(val, start_from));
+        if (res.is<StackFrame>())
+          return res.to<StackFrame>()->copy();
+        else
+          break;
+      }
+    }
+
+    auto parent = TRY(cur.parent());
+    if (parent.is<Nil>()) break;
+
+    cur = TRY(parent.to<StackFrame>()->copy());
+    ++depth;
+  }
+  return ERROR_OBJ(Raise, cont_val);
+}
+
 Result<StackFrame> stdlib_task(const StackFrame& stack) {
   auto params = TRY(stack.get(0));
   Array& params_array = *params.to<Array>();
@@ -588,6 +643,7 @@ static StdlibFunctionEntry function_entries[] = {
     STDLIB_FUNCTION(map, Map),
     STDLIB_FUNCTION(error, Error),
     STDLIB_FUNCTION(raise, Raise),
+    STDLIB_FUNCTION(reraise, Reraise),
     STDLIB_FUNCTION(task, Task),
     STDLIB_FUNCTION(guard, Guard),
     STDLIB_FUNCTION(serialize, Serialize),

src/stdlib.hpp

@@ -22,6 +22,7 @@ enum class StdlibFunctionId : uint64_t {
   Map,
   Error,
   Raise,
+  Reraise,
   Task,
   Guard,
   Serialize,

src/vm.cpp

@@ -303,35 +303,10 @@ Result<void> VM::step_bytecode() {
 }
 
 Result<Value> VM::unwind(const Continuation& cont) {
-  StackFrame cur = TRY(cont.frame());
+  auto val = TRY(cont.value());
+  auto cont_stack = TRY(cont.frame());
 
-  uint64_t depth = 0;
-  while (true) {
-    if (cur.guard()) {
-      auto state = TRY(cur.get(1));
-      if (!state.is<Int64>()) return ERROR(TypeMismatch);
-      auto state_int = state.to<Int64>()->value();
-
-      if (state_int <= 1) {
-        auto val = TRY(cont.value());
-        auto cont_stack = TRY(cont.frame());
-        cont_stack = TRY(cont_stack.detach(depth - 1));
-
-        auto new_cont = TRY(Continuation::create(val, cont_stack));
-
-        cur = TRY(cur.set(1, Value(TRY(Int64::create((int64_t)1)))));
-        cur = TRY(cur.set(2, Value(std::move(new_cont))));
-        return Value(std::move(cur));
-      }
-    }
-
-    auto parent = TRY(cur.parent());
-    if (parent.is<Nil>()) break;
-
-    cur = TRY(parent.to<StackFrame>()->copy());
-    ++depth;
-  }
-  return Value(TRY(Nil::create()));
+  return cont_stack.unwind(val);
 }
 
 Result<StackFrame> VM::handle_raise(const Continuation& cont) {