compiler: unbreak subscripts for bytes values (#714).

artiq/compiler/builtins.py

@@ -285,15 +285,13 @@ def is_exception(typ, name=None):
             typ.name == name
 
 def is_iterable(typ):
-    typ = typ.find()
-    return isinstance(typ, types.TMono) and \
-        typ.name in ('list', 'array', 'range')
+    return is_listish(typ) or is_range(typ)
 
 def get_iterable_elt(typ):
-    if is_iterable(typ):
-        return typ.find()["elt"].find()
-    elif is_str(typ) or is_bytes(typ):
+    if is_str(typ) or is_bytes(typ):
         return TInt(types.TValue(8))
+    elif is_iterable(typ):
+        return typ.find()["elt"].find()
     else:
         assert False
 

artiq/compiler/transforms/inferencer.py

@@ -180,7 +180,10 @@ class Inferencer(algorithm.Visitor):
                 self.engine.process(diag)
 
     def _unify_iterable(self, element, collection):
-        if builtins.is_iterable(collection.type):
+        if builtins.is_bytes(collection.type):
+            self._unify(element.type, builtins.TInt(),
+                        element.loc, None)
+        elif builtins.is_iterable(collection.type):
             rhs_type = collection.type.find()
             rhs_wrapped_lhs_type = types.TMono(rhs_type.name, {"elt": element.type})
             self._unify(rhs_wrapped_lhs_type, rhs_type,

artiq/test/lit/integration/subscript.py

@@ -17,3 +17,7 @@ assert lst[0:3:2] == [0, 2]
 lst = [0, 0, 0, 0, 0]
 lst[0:5:2] = [1, 2, 3]
 assert lst == [1, 0, 2, 0, 3]
+
+byt = b"abc"
+assert byt[0] == 97
+assert byt[1] == 98