Change from throwing a Box* to an ExcInfo triple

ExcInfo is a triple of exc_type, exc_value, exc_traceback -
analogous to Python's sys.exc_info().  Previously, we were just
throwing exc_value.

I still don't understand all the rules for when type(exc_value)
is not necessarily exc_type.  But this also makes it easier to
pass exc_traceback around, and should make it possible to make
our handling more consistent.

This commit just changes the runtime; the generated code currently
still expects a Box* to be thrown and will crash.

src/capi/object.cpp

@@ -39,8 +39,8 @@ extern "C" PyObject* _PyObject_Str(PyObject* v) noexcept {
 
     try {
         return str(v);
-    } catch (Box* b) {
-        PyErr_SetObject(b->cls, b);
+    } catch (ExcInfo e) {
+        setCAPIException(e);
         return NULL;
     }
 }
@@ -79,8 +79,8 @@ extern "C" PyObject* PyObject_GetAttrString(PyObject* o, const char* attr) noexc
 
     try {
         return getattr(o, attr);
-    } catch (Box* b) {
-        PyErr_SetObject(b->cls, b);
+    } catch (ExcInfo e) {
+        setCAPIException(e);
         return NULL;
     }
 }

src/capi/typeobject.cpp

@@ -484,8 +484,8 @@ static PyObject* call_maybe(PyObject* o, const char* name, PyObject** nameobj, c
 PyObject* slot_tp_repr(PyObject* self) noexcept {
     try {
         return repr(self);
-    } catch (Box* e) {
-        PyErr_SetObject(e->cls, e);
+    } catch (ExcInfo e) {
+        setCAPIException(e);
         return NULL;
     }
 }
@@ -493,8 +493,8 @@ PyObject* slot_tp_repr(PyObject* self) noexcept {
 PyObject* slot_tp_str(PyObject* self) noexcept {
     try {
         return str(self);
-    } catch (Box* e) {
-        PyErr_SetObject(e->cls, e);
+    } catch (ExcInfo e) {
+        setCAPIException(e);
         return NULL;
     }
 }
@@ -542,8 +542,8 @@ PyObject* slot_tp_call(PyObject* self, PyObject* args, PyObject* kwds) noexcept
 
         // TODO: runtime ICs?
         return runtimeCall(self, ArgPassSpec(0, 0, true, true), args, kwds, NULL, NULL, NULL);
-    } catch (Box* e) {
-        PyErr_SetObject(e->cls, e);
+    } catch (ExcInfo e) {
+        setCAPIException(e);
         return NULL;
     }
 }
@@ -631,8 +631,8 @@ static PyObject* slot_tp_new(PyTypeObject* self, PyObject* args, PyObject* kwds)
         new_attr = processDescriptor(new_attr, None, self);
 
         return runtimeCall(new_attr, ArgPassSpec(1, 0, true, true), self, args, kwds, NULL, NULL);
-    } catch (Box* e) {
-        PyErr_SetObject(e->cls, e);
+    } catch (ExcInfo e) {
+        setCAPIException(e);
         return NULL;
     }
 }
@@ -660,8 +660,8 @@ static int slot_tp_init(PyObject* self, PyObject* args, PyObject* kwds) noexcept
 PyObject* slot_sq_item(PyObject* self, Py_ssize_t i) noexcept {
     try {
         return getitem(self, boxInt(i));
-    } catch (Box* e) {
-        PyErr_SetObject(e->cls, e);
+    } catch (ExcInfo e) {
+        setCAPIException(e);
         return NULL;
     }
 }
@@ -1781,7 +1781,7 @@ extern "C" int PyType_Ready(PyTypeObject* cls) noexcept {
 
     try {
         add_operators(cls);
-    } catch (Box* b) {
+    } catch (ExcInfo e) {
         abort();
     }
 

src/codegen/ast_interpreter.cpp

@@ -123,7 +123,7 @@ private:
     SymMap sym_table;
     CFGBlock* next_block, *current_block;
     AST_stmt* current_inst;
-    Box* last_exception;
+    ExcInfo last_exception;
     BoxedClosure* passed_closure, *created_closure;
     BoxedGenerator* generator;
     unsigned edgecount;
@@ -224,7 +224,7 @@ void gatherInterpreterRoots(GCVisitor* visitor) {
 
 ASTInterpreter::ASTInterpreter(CompiledFunction* compiled_function)
     : compiled_func(compiled_function), source_info(compiled_function->clfunc->source), scope_info(0), next_block(0),
-      current_block(0), current_inst(0), last_exception(0), passed_closure(0), created_closure(0), generator(0),
+      current_block(0), current_inst(0), last_exception(NULL, NULL, NULL), passed_closure(0), created_closure(0), generator(0),
       edgecount(0) {
 
     CLFunction* f = compiled_function->clfunc;
@@ -506,9 +506,9 @@ Value ASTInterpreter::visit_invoke(AST_Invoke* node) {
     try {
         v = visit_stmt(node->stmt);
         next_block = node->normal_dest;
-    } catch (Box* b) {
+    } catch (ExcInfo e) {
         next_block = node->exc_dest;
-        last_exception = b;
+        last_exception = e;
     }
 
     return v;
@@ -561,8 +561,10 @@ Value ASTInterpreter::visit_langPrimitive(AST_LangPrimitive* node) {
     } else if (node->opcode == AST_LangPrimitive::NONE) {
         v = None;
     } else if (node->opcode == AST_LangPrimitive::LANDINGPAD) {
-        v = last_exception;
-        last_exception = nullptr;
+        abort();
+        // Have to figure out how to represent landingpads
+        //v = last_exception;
+        //last_exception = nullptr;
     } else if (node->opcode == AST_LangPrimitive::ISINSTANCE) {
         assert(node->args.size() == 3);
         Value obj = visit_expr(node->args[0]);

src/core/types.h

@@ -469,6 +469,14 @@ public:
     LineInfo(int line, int column, const std::string& file, const std::string& func)
         : line(line), column(column), file(file), func(func) {}
 };
+
+struct ExcInfo {
+    Box* type, *value, *traceback;
+
+    ExcInfo(Box* type, Box* value, Box* traceback) : type(type), value(value), traceback(traceback) {}
+    bool matches(BoxedClass* cls) const;
+};
+
 }
 
 #endif

src/gc/collector.h

@@ -42,6 +42,7 @@ public:
     void operator=(Box* b) { value = b; }
 
     operator Box*() { return value; }
+    Box* operator->() { return value; }
 };
 
 void runCollection();

src/jit.cpp

@@ -150,12 +150,12 @@ int main(int argc, char** argv) {
 
         try {
             main_module = createAndRunModule("__main__", fn);
-        } catch (Box* b) {
-            if (isInstance(b, SystemExit)) {
+        } catch (ExcInfo e) {
+            if (e.matches(SystemExit)) {
                 printf("Warning: ignoring SystemExit code\n");
                 return 1;
             } else {
-                std::string msg = formatException(b);
+                std::string msg = formatException(e.value);
                 printLastTraceback();
                 fprintf(stderr, "%s\n", msg.c_str());
                 return 1;
@@ -222,12 +222,12 @@ int main(int argc, char** argv) {
 
                 try {
                     compileAndRunModule(m, main_module);
-                } catch (Box* b) {
-                    if (isInstance(b, SystemExit)) {
+                } catch (ExcInfo e) {
+                    if (e.matches(SystemExit)) {
                         printf("Warning: ignoring SystemExit code\n");
                         return 1;
                     } else {
-                        std::string msg = formatException(b);
+                        std::string msg = formatException(e.value);
                         printLastTraceback();
                         fprintf(stderr, "%s\n", msg.c_str());
                     }

src/runtime/builtin_modules/builtins.cpp

@@ -446,8 +446,8 @@ Box* hasattr(Box* obj, Box* _str) {
     Box* attr;
     try {
         attr = getattrInternal(obj, str->s, NULL);
-    } catch (Box* e) {
-        if (isSubclass(e->cls, Exception))
+    } catch (ExcInfo e) {
+        if (e.matches(Exception))
             return False;
         throw;
     }
@@ -623,7 +623,7 @@ extern "C" PyObject* PyErr_NewException(char* name, PyObject* _base, PyObject* d
         // TODO Not sure if this should be called here
         fixup_slot_dispatchers(cls);
         return cls;
-    } catch (Box* e) {
+    } catch (ExcInfo e) {
         abort();
     }
 }

src/runtime/builtin_modules/sys.cpp

@@ -82,7 +82,7 @@ extern "C" int PySys_SetObject(const char* name, PyObject* v) noexcept {
                 sys_module->delattr(name, NULL);
         } else
             sys_module->setattr(name, v, NULL);
-    } catch (Box* b) {
+    } catch (ExcInfo e) {
         abort();
     }
     return 0;

src/runtime/builtin_modules/thread.cpp

@@ -31,8 +31,8 @@ static void* thread_start(Box* target, Box* varargs, Box* kwargs) {
 
     try {
         runtimeCall(target, ArgPassSpec(0, 0, true, kwargs != NULL), varargs, kwargs, NULL, NULL, NULL);
-    } catch (Box* b) {
-        std::string msg = formatException(b);
+    } catch (ExcInfo e) {
+        std::string msg = formatException(e.value);
         printLastTraceback();
         fprintf(stderr, "%s\n", msg.c_str());
     }

src/runtime/capi.cpp

@@ -158,7 +158,7 @@ extern "C" PyObject* PyObject_CallObject(PyObject* obj, PyObject* args) noexcept
     try {
         Box* r = runtimeCall(obj, ArgPassSpec(0, 0, true, false), args, NULL, NULL, NULL, NULL);
         return r;
-    } catch (Box* b) {
+    } catch (ExcInfo e) {
         Py_FatalError("unimplemented");
     }
 }
@@ -174,8 +174,8 @@ extern "C" PyObject* _PyObject_CallMethod_SizeT(PyObject* o, char* name, char* f
 extern "C" Py_ssize_t PyObject_Size(PyObject* o) noexcept {
     try {
         return len(o)->n;
-    } catch (Box* b) {
-        PyErr_SetObject(b->cls, b);
+    } catch (ExcInfo e) {
+        setCAPIException(e);
         return -1;
     }
 }
@@ -183,8 +183,8 @@ extern "C" Py_ssize_t PyObject_Size(PyObject* o) noexcept {
 extern "C" PyObject* PyObject_GetIter(PyObject* o) noexcept {
     try {
         return getiter(o);
-    } catch (Box* b) {
-        PyErr_SetObject(b->cls, b);
+    } catch (ExcInfo e) {
+        setCAPIException(e);
         return NULL;
     }
 }
@@ -192,8 +192,8 @@ extern "C" PyObject* PyObject_GetIter(PyObject* o) noexcept {
 extern "C" PyObject* PyObject_Repr(PyObject* obj) noexcept {
     try {
         return repr(obj);
-    } catch (Box* b) {
-        PyErr_SetObject(b->cls, b);
+    } catch (ExcInfo e) {
+        setCAPIException(e);
         return NULL;
     }
 }
@@ -352,7 +352,7 @@ extern "C" PyObject* PyObject_GetAttr(PyObject* o, PyObject* attr_name) noexcept
 
     try {
         return getattr(o, static_cast<BoxedString*>(attr_name)->s.c_str());
-    } catch (Box* b) {
+    } catch (ExcInfo e) {
         Py_FatalError("unimplemented");
     }
 }
@@ -364,8 +364,8 @@ extern "C" PyObject* PyObject_GenericGetAttr(PyObject* o, PyObject* name) noexce
 extern "C" PyObject* PyObject_GetItem(PyObject* o, PyObject* key) noexcept {
     try {
         return getitem(o, key);
-    } catch (Box* b) {
-        PyErr_SetObject(b->cls, b);
+    } catch (ExcInfo e) {
+        setCAPIException(e);
         return NULL;
     }
 }
@@ -389,7 +389,7 @@ int _Py_SwappedOp[] = { Py_GT, Py_GE, Py_EQ, Py_NE, Py_LT, Py_LE };
 extern "C" long PyObject_Hash(PyObject* o) noexcept {
     try {
         return hash(o)->n;
-    } catch (Box* b) {
+    } catch (ExcInfo e) {
         Py_FatalError("unimplemented");
     }
 }
@@ -419,7 +419,7 @@ extern "C" long _Py_HashPointer(void* p) noexcept {
 extern "C" int PyObject_IsTrue(PyObject* o) noexcept {
     try {
         return nonzero(o);
-    } catch (Box* b) {
+    } catch (ExcInfo e) {
         Py_FatalError("unimplemented");
     }
 }
@@ -459,7 +459,7 @@ extern "C" PyObject* PyObject_Call(PyObject* callable_object, PyObject* args, Py
             return runtimeCall(callable_object, ArgPassSpec(0, 0, true, true), args, kw, NULL, NULL, NULL);
         else
             return runtimeCall(callable_object, ArgPassSpec(0, 0, true, false), args, NULL, NULL, NULL, NULL);
-    } catch (Box* b) {
+    } catch (ExcInfo e) {
         Py_FatalError("unimplemented");
     }
 }
@@ -496,7 +496,7 @@ extern "C" PyObject* PySequence_GetItem(PyObject* o, Py_ssize_t i) noexcept {
     try {
         // Not sure if this is really the same:
         return getitem(o, boxInt(i));
-    } catch (Box* b) {
+    } catch (ExcInfo e) {
         Py_FatalError("unimplemented");
     }
 }
@@ -505,7 +505,7 @@ extern "C" PyObject* PySequence_GetSlice(PyObject* o, Py_ssize_t i1, Py_ssize_t
     try {
         // Not sure if this is really the same:
         return getitem(o, new BoxedSlice(boxInt(i1), boxInt(i2), None));
-    } catch (Box* b) {
+    } catch (ExcInfo e) {
         Py_FatalError("unimplemented");
     }
 }
@@ -551,8 +551,8 @@ extern "C" PyObject* PyIter_Next(PyObject* iter) noexcept {
     try {
         return callattr(iter, &next_str, CallattrFlags({.cls_only = true, .null_on_nonexistent = false }),
                         ArgPassSpec(0), NULL, NULL, NULL, NULL, NULL);
-    } catch (Box* b) {
-        PyErr_SetObject(b->cls, b);
+    } catch (ExcInfo e) {
+        setCAPIException(e);
         return NULL;
     }
 }
@@ -672,6 +672,12 @@ finally:
     --tstate->recursion_depth;
 }
 
+void setCAPIException(const ExcInfo& e) {
+    cur_thread_state.curexc_type = e.type;
+    cur_thread_state.curexc_value = e.value;
+    cur_thread_state.curexc_traceback = e.traceback;
+}
+
 void checkAndThrowCAPIException() {
     Box* _type = cur_thread_state.curexc_type;
     if (!_type)
@@ -859,7 +865,7 @@ extern "C" PyObject* PyImport_Import(PyObject* module_name) noexcept {
 
     try {
         return import(-1, None, &static_cast<BoxedString*>(module_name)->s);
-    } catch (Box* e) {
+    } catch (ExcInfo e) {
         Py_FatalError("unimplemented");
     }
 }
@@ -895,7 +901,7 @@ extern "C" int PyNumber_Check(PyObject* obj) noexcept {
 extern "C" PyObject* PyNumber_Add(PyObject* lhs, PyObject* rhs) noexcept {
     try {
         return binop(lhs, rhs, AST_TYPE::Add);
-    } catch (Box* b) {
+    } catch (ExcInfo e) {
         Py_FatalError("unimplemented");
     }
 }
@@ -903,7 +909,7 @@ extern "C" PyObject* PyNumber_Add(PyObject* lhs, PyObject* rhs) noexcept {
 extern "C" PyObject* PyNumber_Subtract(PyObject* lhs, PyObject* rhs) noexcept {
     try {
         return binop(lhs, rhs, AST_TYPE::Sub);
-    } catch (Box* b) {
+    } catch (ExcInfo e) {
         Py_FatalError("unimplemented");
     }
 }
@@ -911,7 +917,7 @@ extern "C" PyObject* PyNumber_Subtract(PyObject* lhs, PyObject* rhs) noexcept {
 extern "C" PyObject* PyNumber_Multiply(PyObject* lhs, PyObject* rhs) noexcept {
     try {
         return binop(lhs, rhs, AST_TYPE::Mult);
-    } catch (Box* b) {
+    } catch (ExcInfo e) {
         Py_FatalError("unimplemented");
     }
 }
@@ -919,7 +925,7 @@ extern "C" PyObject* PyNumber_Multiply(PyObject* lhs, PyObject* rhs) noexcept {
 extern "C" PyObject* PyNumber_Divide(PyObject* lhs, PyObject* rhs) noexcept {
     try {
         return binop(lhs, rhs, AST_TYPE::Div);
-    } catch (Box* b) {
+    } catch (ExcInfo e) {
         Py_FatalError("unimplemented");
     }
 }
@@ -935,7 +941,7 @@ extern "C" PyObject* PyNumber_TrueDivide(PyObject*, PyObject*) noexcept {
 extern "C" PyObject* PyNumber_Remainder(PyObject* lhs, PyObject* rhs) noexcept {
     try {
         return binop(lhs, rhs, AST_TYPE::Mod);
-    } catch (Box* b) {
+    } catch (ExcInfo e) {
         Py_FatalError("unimplemented");
     }
 }
@@ -959,7 +965,7 @@ extern "C" PyObject* PyNumber_Positive(PyObject* o) noexcept {
 extern "C" PyObject* PyNumber_Absolute(PyObject* o) noexcept {
     try {
         return abs_(o);
-    } catch (Box* b) {
+    } catch (ExcInfo e) {
         Py_FatalError("unimplemented");
     }
 }
@@ -975,7 +981,7 @@ extern "C" PyObject* PyNumber_Lshift(PyObject*, PyObject*) noexcept {
 extern "C" PyObject* PyNumber_Rshift(PyObject* lhs, PyObject* rhs) noexcept {
     try {
         return binop(lhs, rhs, AST_TYPE::RShift);
-    } catch (Box* b) {
+    } catch (ExcInfo e) {
         Py_FatalError("unimplemented");
     }
 }
@@ -983,7 +989,7 @@ extern "C" PyObject* PyNumber_Rshift(PyObject* lhs, PyObject* rhs) noexcept {
 extern "C" PyObject* PyNumber_And(PyObject* lhs, PyObject* rhs) noexcept {
     try {
         return binop(lhs, rhs, AST_TYPE::BitAnd);
-    } catch (Box* b) {
+    } catch (ExcInfo e) {
         Py_FatalError("unimplemented");
     }
 }

src/runtime/capi.h

@@ -23,6 +23,8 @@ class BoxedModule;
 BoxedModule* importTestExtension(const std::string&);
 
 void checkAndThrowCAPIException();
+struct ExcInfo;
+void setCAPIException(const ExcInfo& e);
 }
 
 #endif

src/runtime/classobj.cpp

@@ -224,17 +224,17 @@ Box* instanceNonzero(Box* _inst) {
     Box* nonzero_func = NULL;
     try {
         nonzero_func = _instanceGetattribute(inst, boxStrConstant("__nonzero__"), false);
-    } catch (Box* b) {
-        if (!isInstance(b, AttributeError))
-            throw;
+    } catch (ExcInfo e) {
+        if (!e.matches(AttributeError))
+            throw e;
     }
 
     if (nonzero_func == NULL) {
         try {
             nonzero_func = _instanceGetattribute(inst, boxStrConstant("__len__"), false);
-        } catch (Box* b) {
-            if (!isInstance(b, AttributeError))
-                throw;
+        } catch (ExcInfo e) {
+            if (!e.matches(AttributeError))
+                throw e;
         }
     }
 

src/runtime/dict.cpp

@@ -14,6 +14,7 @@
 
 #include "runtime/dict.h"
 
+#include "capi/types.h"
 #include "core/common.h"
 #include "core/stats.h"
 #include "core/types.h"
@@ -136,8 +137,8 @@ extern "C" PyObject* PyDict_Copy(PyObject* o) noexcept {
     RELEASE_ASSERT(PyDict_Check(o), "");
     try {
         return dictCopy(static_cast<BoxedDict*>(o));
-    } catch (Box* e) {
-        PyErr_SetObject(e->cls, e);
+    } catch (ExcInfo e) {
+        setCAPIException(e);
         return NULL;
     }
 }
@@ -179,7 +180,7 @@ extern "C" int PyDict_SetItem(PyObject* mp, PyObject* _key, PyObject* _item) noe
     try {
         // TODO should demote GIL?
         setitem(b, key, item);
-    } catch (Box* b) {
+    } catch (ExcInfo e) {
         abort();
     }
     return 0;
@@ -189,7 +190,7 @@ extern "C" int PyDict_SetItemString(PyObject* mp, const char* key, PyObject* ite
     Box* key_s;
     try {
         key_s = boxStrConstant(key);
-    } catch (Box* b) {
+    } catch (ExcInfo e) {
         abort();
     }
 
@@ -200,8 +201,8 @@ extern "C" PyObject* PyDict_GetItem(PyObject* dict, PyObject* key) noexcept {
     ASSERT(dict->cls == dict_cls || dict->cls == attrwrapper_cls, "%s", getTypeName(dict)->c_str());
     try {
         return getitem(dict, key);
-    } catch (Box* b) {
-        if (isSubclass(b->cls, KeyError))
+    } catch (ExcInfo e) {
+        if (e.matches(KeyError))
             return NULL;
         abort();
     }
@@ -215,7 +216,7 @@ extern "C" PyObject* PyDict_GetItemString(PyObject* dict, const char* key) noexc
     Box* key_s;
     try {
         key_s = boxStrConstant(key);
-    } catch (Box* b) {
+    } catch (ExcInfo e) {
         abort();
     }
     return PyDict_GetItem(dict, key_s);
@@ -404,8 +405,8 @@ extern "C" int PyDict_Merge(PyObject* a, PyObject* b, int override_) noexcept {
     try {
         dictMerge(static_cast<BoxedDict*>(a), b);
         return 0;
-    } catch (Box* e) {
-        PyErr_SetObject(e->cls, e);
+    } catch (ExcInfo e) {
+        setCAPIException(e);
         return -1;
     }
 }

src/runtime/file.cpp

@@ -16,6 +16,7 @@
 #include <cstring>
 #include <sstream>
 
+#include "capi/types.h"
 #include "core/common.h"
 #include "core/stats.h"
 #include "core/types.h"
@@ -205,8 +206,8 @@ extern "C" int PyFile_WriteObject(PyObject* v, PyObject* f, int flags) noexcept
         Box* r = fileWrite(static_cast<BoxedFile*>(f), v);
         assert(r == None);
         return 0;
-    } catch (Box* b) {
-        PyErr_SetObject(b->cls, b);
+    } catch (ExcInfo e) {
+        setCAPIException(e);
         return -1;
     }
 }
@@ -271,7 +272,7 @@ extern "C" int PyObject_AsFileDescriptor(PyObject* o) noexcept {
 extern "C" int PyFile_SoftSpace(PyObject* f, int newflag) noexcept {
     try {
         return softspace(f, newflag);
-    } catch (Box* b) {
+    } catch (ExcInfo e) {
         abort();
     }
 }

src/runtime/generator.cpp

@@ -53,7 +53,7 @@ static void generatorEntry(BoxedGenerator* g) {
 
         Box** args = g->args ? &g->args->elts[0] : nullptr;
         callCLFunc(func->f, nullptr, func->f->numReceivedArgs(), func->closure, g, g->arg1, g->arg2, g->arg3, args);
-    } catch (Box* e) {
+    } catch (ExcInfo e) {
         // unhandled exception: propagate the exception to the caller
         g->exception = e;
     }
@@ -85,8 +85,8 @@ Box* generatorSend(Box* s, Box* v) {
     self->running = false;
 
     // propagate exception to the caller
-    if (self->exception)
-        raiseExc(self->exception);
+    if (self->exception.type)
+        raiseRaw(self->exception);
 
     // throw StopIteration if the generator exited
     if (self->entryExited)
@@ -99,7 +99,8 @@ Box* generatorThrow(Box* s, BoxedClass* e) {
     assert(s->cls == generator_cls);
     assert(isSubclass(e, Exception));
     BoxedGenerator* self = static_cast<BoxedGenerator*>(s);
-    self->exception = exceptionNew1(e);
+    Box* ex = exceptionNew1(e);
+    self->exception = ExcInfo(ex->cls, ex, NULL);
     return generatorSend(self, None);
 }
 
@@ -128,10 +129,10 @@ extern "C" Box* yield(BoxedGenerator* obj, Box* value) {
     threading::pushGenerator(obj, obj->stack_begin, (void*)obj->returnContext.uc_mcontext.gregs[REG_RSP]);
 
     // if the generator receives a exception from the caller we have to throw it
-    if (self->exception) {
-        Box* exception = self->exception;
-        self->exception = nullptr;
-        raiseExc(exception);
+    if (self->exception.type) {
+        ExcInfo e = self->exception;
+        self->exception = ExcInfo(NULL, NULL, NULL);
+        raiseRaw(e);
     }
     return self->returnValue;
 }
@@ -146,7 +147,7 @@ extern "C" BoxedGenerator* createGenerator(BoxedFunction* function, Box* arg1, B
 
 extern "C" BoxedGenerator::BoxedGenerator(BoxedFunction* function, Box* arg1, Box* arg2, Box* arg3, Box** args)
     : function(function), arg1(arg1), arg2(arg2), arg3(arg3), args(nullptr), entryExited(false), running(false),
-      returnValue(nullptr), exception(nullptr) {
+      returnValue(nullptr), exception(nullptr, nullptr, nullptr) {
 
     giveAttr("__name__", boxString(function->f->source->getName()));
 
@@ -214,8 +215,12 @@ extern "C" void generatorGCHandler(GCVisitor* v, Box* b) {
                                reinterpret_cast<void* const*>(&g->args->elts[num_args - 3]));
     if (g->returnValue)
         v->visit(g->returnValue);
-    if (g->exception)
-        v->visit(g->exception);
+    if (g->exception.type)
+        v->visit(g->exception.type);
+    if (g->exception.value)
+        v->visit(g->exception.value);
+    if (g->exception.traceback)
+        v->visit(g->exception.traceback);
 
     if (g->running) {
         v->visitPotentialRange((void**)&g->returnContext,

src/runtime/iterobject.cpp

@@ -17,6 +17,7 @@
 #include <cmath>
 #include <sstream>
 
+#include "capi/types.h"
 #include "core/common.h"
 #include "core/options.h"
 #include "core/stats.h"
@@ -39,7 +40,7 @@ Box* seqiterHasnext(Box* s) {
     Box* next;
     try {
         next = getitem(self->b, boxInt(self->idx));
-    } catch (Box* b) {
+    } catch (ExcInfo e) {
         return False;
     }
     self->idx++;
@@ -75,12 +76,12 @@ Box* iterwrapperHasnext(Box* s) {
     try {
         next = callattr(self->iter, &next_str, CallattrFlags({.cls_only = true, .null_on_nonexistent = false }),
                         ArgPassSpec(0), NULL, NULL, NULL, NULL, NULL);
-    } catch (Box* b) {
-        if (isSubclass(b->cls, StopIteration)) {
+    } catch (ExcInfo e) {
+        if (e.matches(StopIteration)) {
             self->next = NULL;
             return False;
         }
-        throw;
+        throw e;
     }
     self->next = next;
     return True;
@@ -99,8 +100,8 @@ Box* iterwrapperNext(Box* s) {
 extern "C" PyObject* PySeqIter_New(PyObject* seq) noexcept {
     try {
         return new BoxedSeqIter(seq);
-    } catch (Box* e) {
-        PyErr_SetObject(e->cls, e);
+    } catch (ExcInfo e) {
+        setCAPIException(e);
         return NULL;
     }
 }

src/runtime/list.cpp

@@ -18,6 +18,7 @@
 #include <cstring>
 #include <sstream>
 
+#include "capi/types.h"
 #include "core/ast.h"
 #include "core/common.h"
 #include "core/stats.h"
@@ -32,7 +33,7 @@ namespace pyston {
 extern "C" int PyList_Append(PyObject* op, PyObject* newitem) noexcept {
     try {
         listAppend(op, newitem);
-    } catch (Box* b) {
+    } catch (ExcInfo e) {
         abort();
     }
     return 0;
@@ -149,7 +150,7 @@ extern "C" PyObject* PyList_GetItem(PyObject* op, Py_ssize_t i) noexcept {
     RELEASE_ASSERT(i >= 0, ""); // unlike list.__getitem__, PyList_GetItem doesn't do index wrapping
     try {
         return listGetitemUnboxed(static_cast<BoxedList*>(op), i);
-    } catch (Box* b) {
+    } catch (ExcInfo e) {
         abort();
     }
 }
@@ -539,7 +540,7 @@ extern "C" PyObject* PyList_New(Py_ssize_t size) noexcept {
     RELEASE_ASSERT(size == 0, "");
     try {
         return new BoxedList();
-    } catch (Box* b) {
+    } catch (ExcInfo e) {
         abort();
     }
 }
@@ -622,8 +623,8 @@ extern "C" PyObject* _PyList_Extend(PyListObject* self, PyObject* b) noexcept {
 
     try {
         return listIAdd(l, b);
-    } catch (Box* b) {
-        PyErr_SetObject(b->cls, b);
+    } catch (ExcInfo e) {
+        setCAPIException(e);
         return NULL;
     }
 }
@@ -643,8 +644,8 @@ extern "C" int PyList_SetSlice(PyObject* a, Py_ssize_t ilow, Py_ssize_t ihigh, P
         else
             listDelitemSlice(l, new BoxedSlice(boxInt(ilow), boxInt(ihigh), None));
         return 0;
-    } catch (Box* b) {
-        PyErr_SetObject(b->cls, b);
+    } catch (ExcInfo e) {
+        setCAPIException(e);
         return -1;
     }
 }

src/runtime/long.cpp

@@ -94,7 +94,7 @@ extern "C" unsigned long PyLong_AsUnsignedLong(PyObject* vv) noexcept {
 
     try {
         return asUnsignedLong(l);
-    } catch (Box* e) {
+    } catch (ExcInfo e) {
         abort();
     }
 }

src/runtime/objmodel.cpp

@@ -1748,7 +1748,7 @@ extern "C" BoxedString* reprOrNull(Box* obj) {
         Box* r = repr(obj);
         assert(r->cls == str_cls); // this should be checked by repr()
         return static_cast<BoxedString*>(r);
-    } catch (Box* b) {
+    } catch (ExcInfo e) {
         return nullptr;
     }
 }
@@ -1757,7 +1757,7 @@ extern "C" BoxedString* strOrNull(Box* obj) {
     try {
         BoxedString* r = str(obj);
         return static_cast<BoxedString*>(r);
-    } catch (Box* b) {
+    } catch (ExcInfo e) {
         return nullptr;
     }
 }
@@ -3879,10 +3879,10 @@ extern "C" Box* importStar(Box* _from_module, BoxedModule* to_module) {
             Box* attr_name;
             try {
                 attr_name = runtimeCallInternal2(all_getitem, NULL, ArgPassSpec(2), all, boxInt(idx));
-            } catch (Box* b) {
-                if (b->cls == IndexError)
+            } catch (ExcInfo e) {
+                if (e.matches(IndexError))
                     break;
-                throw;
+                throw e;
             }
             idx++;
 

src/runtime/objmodel.h

@@ -34,6 +34,7 @@ class BoxedGenerator;
 extern "C" void raise0() __attribute__((__noreturn__));
 extern "C" void raise3(Box*, Box*, Box*) __attribute__((__noreturn__));
 void raiseExc(Box* exc_obj) __attribute__((__noreturn__));
+void raiseRaw(const ExcInfo& e) __attribute__((__noreturn__));
 
 // helper function for raising from the runtime:
 void raiseExcHelper(BoxedClass*, const char* fmt, ...) __attribute__((__noreturn__));
@@ -138,5 +139,7 @@ static const char* objectNewParameterTypeErrorMsg() {
         return "object.__new__() takes no parameters";
     }
 }
+
+bool exceptionMatches(const ExcInfo& e, BoxedClass* cls);
 }
 #endif

src/runtime/stacktrace.cpp

@@ -98,10 +98,10 @@ void unwindExc(Box* exc_obj) {
 static gc::GCRootHandle last_exc;
 static std::vector<const LineInfo*> last_tb;
 
-void raiseRaw(Box* exc_obj) __attribute__((__noreturn__));
-void raiseRaw(Box* exc_obj) {
+void raiseRaw(const ExcInfo& e) __attribute__((__noreturn__));
+void raiseRaw(const ExcInfo& e) {
     // Using libgcc:
-    throw exc_obj;
+    throw e;
 
     // Using libunwind
     // unwindExc(exc_obj);
@@ -112,7 +112,7 @@ void raiseExc(Box* exc_obj) {
     last_tb = std::move(entries);
     last_exc = exc_obj;
 
-    raiseRaw(exc_obj);
+    raiseRaw(ExcInfo(exc_obj->cls, exc_obj, NULL));
 }
 
 // Have a special helper function for syntax errors, since we want to include the location
@@ -125,7 +125,7 @@ void raiseSyntaxError(const char* msg, int lineno, int col_offset, const std::st
     // TODO: leaks this!
     last_tb.push_back(new LineInfo(lineno, col_offset, file, func));
 
-    raiseRaw(last_exc);
+    raiseRaw(ExcInfo(SyntaxError, last_exc, NULL));
 }
 
 static void _printTraceback(const std::vector<const LineInfo*>& tb) {
@@ -216,7 +216,12 @@ extern "C" void exit(int code) {
 }
 
 void raise0() {
-    raiseRaw(last_exc);
+    raiseRaw(ExcInfo(last_exc->cls, last_exc, NULL));
+}
+
+bool ExcInfo::matches(BoxedClass* cls) const {
+    RELEASE_ASSERT(isSubclass(this->type->cls, type_cls), "throwing old-style objects not supported yet");
+    return isSubclass(static_cast<BoxedClass*>(this->type), cls);
 }
 
 void raise3(Box* arg0, Box* arg1, Box* arg2) {

src/runtime/tuple.cpp

@@ -73,7 +73,7 @@ extern "C" PyObject* PyTuple_GetItem(PyObject* op, Py_ssize_t i) noexcept {
     RELEASE_ASSERT(i >= 0, ""); // unlike tuple.__getitem__, PyTuple_GetItem doesn't do index wrapping
     try {
         return tupleGetitemUnboxed(static_cast<BoxedTuple*>(op), i);
-    } catch (Box* b) {
+    } catch (ExcInfo e) {
         abort();
     }
 }

src/runtime/types.cpp

@@ -240,12 +240,12 @@ BoxIterator& BoxIterator::operator++() {
     } else {
         try {
             value = iter->nextIC();
-        } catch (Box* e) {
-            if ((e == StopIteration) || isSubclass(e->cls, StopIteration)) {
+        } catch (ExcInfo e) {
+            if (e.matches(StopIteration)) {
                 iter = nullptr;
                 value = nullptr;
             } else
-                throw;
+                throw e;
         }
     }
     return *this;
@@ -531,12 +531,12 @@ extern "C" Box* createUserClass(std::string* name, Box* _bases, Box* _attr_dict)
         Box* r = runtimeCall(metaclass, ArgPassSpec(3), boxStringPtr(name), _bases, _attr_dict, NULL, NULL);
         RELEASE_ASSERT(r, "");
         return r;
-    } catch (Box* b) {
+    } catch (ExcInfo e) {
         // TODO [CAPI] bad error handling...
 
-        RELEASE_ASSERT(isSubclass(b->cls, BaseException), "");
+        RELEASE_ASSERT(e.matches(BaseException), "");
 
-        Box* msg = b->getattr("message");
+        Box* msg = e.value->getattr("message");
         RELEASE_ASSERT(msg, "");
         RELEASE_ASSERT(msg->cls == str_cls, "");
 
@@ -545,7 +545,7 @@ extern "C" Box* createUserClass(std::string* name, Box* _bases, Box* _attr_dict)
                                      "    %s",
                                      PyString_AS_STRING(msg));
 
-        PyErr_Restore(b->cls, newmsg, NULL);
+        PyErr_Restore(e.type, newmsg, NULL);
         checkAndThrowCAPIException();
 
         // Should not reach here

src/runtime/types.h

@@ -557,7 +557,7 @@ public:
     bool entryExited;
     bool running;
     Box* returnValue;
-    Box* exception;
+    ExcInfo exception;
 
     ucontext_t context, returnContext;
     void* stack_begin;