compiler: support short form of raise.

Fixes #240.

artiq/compiler/transforms/artiq_ir_generator.py

@@ -599,7 +599,10 @@ class ARTIQIRGenerator(algorithm.Visitor):
                 self.append(ir.Reraise())
 
     def visit_Raise(self, node):
-        self.raise_exn(self.visit(node.exc), loc=self.current_loc)
+        if types.is_exn_constructor(node.exc.type):
+            self.raise_exn(self.alloc_exn(node.exc.type.instance), loc=self.current_loc)
+        else:
+            self.raise_exn(self.visit(node.exc), loc=self.current_loc)
 
     def visit_Try(self, node):
         dispatcher = self.add_block("try.dispatch")

artiq/compiler/transforms/inferencer.py

@@ -1290,20 +1290,13 @@ class Inferencer(algorithm.Visitor):
 
         if node.exc is not None:
             exc_type = node.exc.type
-            if not types.is_var(exc_type) and not builtins.is_exception(exc_type):
-                if types.is_exn_constructor(exc_type):
-                    notes = [diagnostic.Diagnostic("note",
-                        "this value is an exception constructor; use {suggestion} instead",
-                        {"suggestion": node.exc.loc.source() + "()"},
-                        node.exc.loc)]
-                else:
-                    notes = []
-
+            if types.is_exn_constructor(exc_type):
+                pass # short form
+            elif not types.is_var(exc_type) and not builtins.is_exception(exc_type):
                 diag = diagnostic.Diagnostic("error",
                     "cannot raise a value of type {type}, which is not an exception",
                     {"type": types.TypePrinter().name(exc_type)},
-                    node.loc,
-                    notes=notes)
+                    node.loc)
                 self.engine.process(diag)
 
     def visit_Assert(self, node):

artiq/test/lit/integration/raise.py

@@ -0,0 +1,8 @@
+# RUN: %python -m artiq.compiler.testbench.jit %s
+# RUN: %python %s
+# REQUIRES: exceptions
+
+try:
+    raise ValueError
+except ValueError:
+    pass