coredevice: do not desync kernel TCP stream on RPCReturnValueError.

And propagate the error upwards instead of trying to squeeze it
through the core device in futility.

artiq/coredevice/comm_kernel.py

@@ -524,6 +524,8 @@ class CommKernel:
             self._write_header(_H2DMsgType.RPC_REPLY)
             self._write_bytes(return_tags)
             self._send_rpc_value(bytearray(return_tags), result, result, service)
+        except RPCReturnValueError as exn:
+            raise
         except Exception as exn:
             logger.debug("rpc service: %d %r %r ! %r", service_id, args, kwargs, exn)
 

artiq/test/coredevice/test_embedding.py

@@ -3,6 +3,7 @@ from time import sleep
 
 from artiq.experiment import *
 from artiq.test.hardware_testbench import ExperimentCase
+from artiq.coredevice.comm_kernel import RPCReturnValueError
 
 
 class _Roundtrip(EnvExperiment):
@@ -96,6 +97,12 @@ class _RPCTypes(EnvExperiment):
     def return_str(self) -> TStr:
         return "foo"
 
+    def return_bytes(self) -> TBytes:
+        return b"foo"
+
+    def return_bytearray(self) -> TByteArray:
+        return bytearray(b"foo")
+
     def return_tuple(self) -> TTuple([TInt32, TInt32]):
         return (1, 2)
 
@@ -105,6 +112,9 @@ class _RPCTypes(EnvExperiment):
     def return_range(self) -> TRange32:
         return range(10)
 
+    def return_mismatch(self):
+        return b"foo"
+
     @kernel
     def run_recv(self):
         core_log(self.return_bool())
@@ -112,6 +122,8 @@ class _RPCTypes(EnvExperiment):
         core_log(self.return_int64())
         core_log(self.return_float())
         core_log(self.return_str())
+        core_log(self.return_bytes())
+        core_log(self.return_bytearray())
         core_log(self.return_tuple())
         core_log(self.return_list())
         core_log(self.return_range())
@@ -126,20 +138,31 @@ class _RPCTypes(EnvExperiment):
         self.accept(0x100000000)
         self.accept(1.0)
         self.accept("foo")
+        self.accept(b"foo")
+        self.accept(bytearray(b"foo"))
         self.accept((2, 3))
         self.accept([1, 2])
         self.accept(range(10))
         self.accept(self)
 
-    def run(self):
-        self.run_send()
-        self.run_recv()
+    @kernel
+    def run_mismatch(self):
+        self.return_mismatch()
 
 
 class RPCTypesTest(ExperimentCase):
-    def test_args(self):
+    def test_send(self):
         exp = self.create(_RPCTypes)
-        exp.run()
+        exp.run_send()
+
+    def test_recv(self):
+        exp = self.create(_RPCTypes)
+        exp.run_send()
+
+    def test_mismatch(self):
+        exp = self.create(_RPCTypes)
+        with self.assertRaises(RPCReturnValueError):
+            exp.run_mismatch()
 
 
 class _RPCCalls(EnvExperiment):