Implement reraise correctly: don't destroy the parent frame

src/error.cpp

@@ -63,6 +63,8 @@ const char* errname(ErrorCode errcode) {
       return "runtime-error";
     case ErrorCode::Raise:
       return "raise";
+    case ErrorCode::Reraise:
+      return "reraise";
     case ErrorCode::TaskFailed:
       return "task-failed";
   }

src/error.hpp

@@ -23,6 +23,7 @@ enum class ErrorCode {
   SyntaxError,
   RuntimeError,
   Raise,
+  Reraise,
   TaskFailed,
 };
 

src/stdlib.cpp

@@ -417,48 +417,9 @@ Result<StackFrame> stdlib_reraise(const StackFrame& stack) {
 
   if (!cont_val.is<Continuation>()) return ERROR(TypeMismatch);
 
-  Continuation& cont = *cont_val.to<Continuation>();
-  StackFrame cont_stack = TRY(cont.frame());
+  auto new_cont = Value(TRY(Continuation::create(cont_val, stack)));
 
-  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);
+  return ERROR_OBJ(Reraise, new_cont);
 }
 
 Result<StackFrame> stdlib_task(const StackFrame& stack) {

src/vm.cpp

@@ -302,17 +302,16 @@ Result<void> VM::step_bytecode() {
   return Result<void>();
 }
 
-Result<Value> VM::unwind(const Continuation& cont) {
+Result<Value> VM::unwind(const Continuation& cont, uint64_t start_from) {
   auto val = TRY(cont.value());
   auto cont_stack = TRY(cont.frame());
 
-  return cont_stack.unwind(val);
+  return cont_stack.unwind(val, start_from);
 }
 
-Result<StackFrame> VM::handle_raise(const Continuation& cont) {
-  // TODO: this should do proper stack unwinding
-
-  auto unwind_res = TRY(unwind(cont));
+Result<StackFrame> VM::handle_raise(const Continuation& cont,
+                                    uint64_t start_from) {
+  auto unwind_res = TRY(unwind(cont, start_from));
 
   if (!unwind_res.is<Nil>()) {
     auto new_stack = TRY(unwind_res.to<StackFrame>()->copy());
@@ -358,6 +357,59 @@ Result<StackFrame> VM::handle_raise(const Continuation& cont) {
   return ERROR(TypeMismatch);
 }
 
+Result<StackFrame> VM::handle_reraise(const Continuation& parent_cont) {
+  auto stack = TRY(parent_cont.frame());
+  auto cont_val = TRY(parent_cont.value());
+
+  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));
+
+        auto params = TRY(cur.get(0));
+        Value fun = TRY(params.get(0));
+        cur = TRY(cur.set(1, Value(TRY(Int64::create((int64_t)0)))));
+        cur = TRY(cur.settop(2));
+
+        cur = TRY(cont_stack.attach(cur));
+
+        uint64_t start_from = TRY(cont_stack.depth()) + 1;
+
+        auto res = TRY(cur.unwind(val, start_from));
+        if (res.is<StackFrame>()) {
+          return res.to<StackFrame>()->copy();
+        } else {
+          auto new_cont = TRY(Continuation::create(val, cur));
+          return handle_raise(new_cont, start_from);
+        }
+      }
+    }
+
+    auto parent = TRY(cur.parent());
+    if (parent.is<Nil>()) break;
+
+    cur = TRY(parent.to<StackFrame>()->copy());
+    ++depth;
+  }
+
+  auto new_cont = TRY(Continuation::create(TRY(cont.value()), stack));
+  return handle_raise(new_cont, 0);
+}
+
 Result<void> VM::step_native() {
   auto fun = TRY(_stack.fun());
   if (!fun.is<StdlibFunction>()) return ERROR(TypeMismatch);
@@ -392,6 +444,12 @@ Result<void> VM::step() {
         return Result<void>();
       }
     }
+    if (res.error() == ErrorCode::Reraise) {
+      if (obj.is<Continuation>()) {
+        _stack = TRY(handle_reraise(*obj.to<Continuation>()));
+        return Result<void>();
+      }
+    }
 
     auto cont = TRY(Continuation::create(obj, _stack));
     _stack = TRY(handle_raise(cont));

src/vm.hpp

@@ -63,8 +63,10 @@ class VM {
   Result<void> vm_global_load(Opcode& oc);
   Result<void> vm_global_store(Opcode& oc);
 
-  Result<Value> unwind(const Continuation& cont);
-  Result<StackFrame> handle_raise(const Continuation& cont);
+  Result<Value> unwind(const Continuation& cont, uint64_t start_from = 0);
+  Result<StackFrame> handle_raise(const Continuation& cont,
+                                  uint64_t start_from = 0);
+  Result<StackFrame> handle_reraise(const Continuation& cont);
 
   Result<Value> get(bool is_const, uint64_t idx);
   Result<Value> getconst(uint64_t idx);