compiler: support methods defined on singleton instances.

Fixes #638.

artiq/compiler/embedding.py

@@ -561,7 +561,11 @@ class StitchingInferencer(Inferencer):
         # of having the host-to-ARTIQ mapping code in only one place and
         # also immediately getting proper diagnostics on type errors.
         attr_value = getattr(object_value, attr_name)
-        if inspect.ismethod(attr_value) and types.is_instance(object_type):
+        if (inspect.ismethod(attr_value) and
+                types.is_instance(object_type) and
+                # Check that the method is indeed defined on the class,
+                # and not just this instance.
+                hasattr(type(attr_value), attr_name)):
             # In cases like:
             #     class c:
             #         @kernel

artiq/test/lit/embedding/method_on_instance.py

@@ -0,0 +1,22 @@
+# RUN: %python -m artiq.compiler.testbench.embedding %s
+
+from artiq.language.core import *
+from artiq.language.types import *
+
+class a:
+    def foo(self, x):
+        print(x)
+
+class b:
+    def __init__(self):
+        self.obj = a()
+        self.meth = self.obj.foo
+
+    @kernel
+    def run(self):
+        self.meth(1)
+
+bi = b()
+@kernel
+def entrypoint():
+    bi.run()