compiler: don't crash printing locations of specialized functions.

Fixes #987.

artiq/compiler/embedding.py

@@ -749,6 +749,11 @@ class Stitcher:
                               quote_function=self._quote_function)
 
     def _function_loc(self, function):
+        if isinstance(function, SpecializedFunction):
+            function = function.host_function
+        if hasattr(function, 'artiq_embedded'):
+            function = function.artiq_embedded.function
+
         filename = function.__code__.co_filename
         line     = function.__code__.co_firstlineno
         name     = function.__code__.co_name

artiq/test/lit/embedding/error_specialized_annot.py

@@ -0,0 +1,19 @@
+# RUN: %python -m artiq.compiler.testbench.embedding +diag %s 2>%t
+# RUN: OutputCheck %s --file-to-check=%t
+
+from artiq.experiment import *
+
+class c():
+# CHECK-L: ${LINE:+2}: error: type annotation for argument 'x', 'None', is not an ARTIQ type
+    @kernel
+    def hello(self, x: None):
+        pass
+
+    @kernel
+    def run(self):
+        self.hello(2)
+
+i = c()
+@kernel
+def entrypoint():
+    i.run()