capi exceptions fixes

We got away with sloppy exception clearing in some places, since
raiseExcHelper would end up calling typeCall which would re-throw
the capi exception that hadn't been cleared.

Now that typeCall doesn't do that (which is fine), those bugs got
exposed.

src/runtime/builtin_modules/builtins.cpp

@@ -248,7 +248,7 @@ Box* open(Box* arg1, Box* arg2, Box* arg3) {
 extern "C" Box* chr(Box* arg) {
     i64 n = PyInt_AsLong(arg);
     if (n == -1 && PyErr_Occurred())
-        raiseExcHelper(TypeError, "an integer is required");
+        throwCAPIException();
 
     if (n < 0 || n >= 256) {
         raiseExcHelper(ValueError, "chr() arg not in range(256)");

src/runtime/descr.cpp

@@ -347,6 +347,9 @@ Box* BoxedMethodDescriptor::callInternal(BoxedFunctionBase* f, CallRewriteArgs*
         RELEASE_ASSERT(0, "0x%x", call_flags);
     }
 
+    if (!rtn)
+        throwCAPIException();
+
     rewrite_args->rewriter->call(true, (void*)checkAndThrowCAPIException);
     rewrite_args->out_rtn = r_rtn;
     rewrite_args->out_success = true;

src/runtime/iterators.cpp

@@ -44,8 +44,10 @@ public:
         Box* next = PyIter_Next(iterator);
         if (next)
             value = next;
-        else
+        else {
+            checkAndThrowCAPIException();
             *this = *end();
+        }
     }
 
     Box* getValue() override { return value; }

src/runtime/list.cpp

@@ -101,7 +101,7 @@ extern "C" Box* listPop(BoxedList* self, Box* idx) {
 
     int64_t n = PyInt_AsSsize_t(idx);
     if (n == -1 && PyErr_Occurred())
-        raiseExcHelper(TypeError, "an integer is required");
+        throwCAPIException();
 
     if (n < 0)
         n = self->size + n;

src/runtime/objmodel.cpp

@@ -3515,6 +3515,7 @@ Box* callCLFunc(CLFunction* f, CallRewriteArgs* rewrite_args, int num_output_arg
     ASSERT(chosen_cf->spec->rtn_type->isFitBy(r->cls), "%s (%p) was supposed to return %s, but gave a %s",
            g.func_addr_registry.getFuncNameAtAddress(chosen_cf->code, true, NULL).c_str(), chosen_cf->code,
            chosen_cf->spec->rtn_type->debugName().c_str(), r->cls->tp_name);
+    assert(!PyErr_Occurred());
 
     return r;
 }

src/runtime/stacktrace.cpp

@@ -47,6 +47,7 @@ void showBacktrace() {
 }
 
 void raiseExc(Box* exc_obj) {
+    assert(!PyErr_Occurred());
     throw ExcInfo(exc_obj->cls, exc_obj, None);
 }
 
@@ -56,6 +57,7 @@ void raiseSyntaxError(const char* msg, int lineno, int col_offset, llvm::StringR
     Box* exc = runtimeCall(SyntaxError, ArgPassSpec(1), boxString(msg), NULL, NULL, NULL, NULL);
 
     auto tb = new BoxedTraceback(LineInfo(lineno, col_offset, file, func), None);
+    assert(!PyErr_Occurred());
     throw ExcInfo(exc->cls, exc, tb);
 }
 
@@ -175,6 +177,7 @@ extern "C" void raise0() {
         raiseExcHelper(TypeError, "exceptions must be old-style classes or derived from BaseException, not NoneType");
 
     exc_info->reraise = true;
+    assert(!PyErr_Occurred());
     throw * exc_info;
 }
 
@@ -256,6 +259,7 @@ extern "C" void raise3(Box* arg0, Box* arg1, Box* arg2) {
     auto exc_info = excInfoForRaise(arg0, arg1, arg2);
 
     exc_info.reraise = reraise;
+    assert(!PyErr_Occurred());
     throw exc_info;
 }