Fix inference for globals.

artiq/compiler/asttyped.py

@@ -18,7 +18,7 @@ class scoped(object):
     :ivar typing_env: (dict with string keys and :class:`.types.Type` values)
         map of variable names to variable types
     :ivar globals_in_scope: (set of string keys)
-        list of variables resolved as globals
+        set of variables resolved as globals
     """
 
 # Typed versions of untyped nodes

artiq/compiler/transforms/asttyped_rewriter.py

@@ -151,8 +151,8 @@ class LocalExtractor(algorithm.Visitor):
                continue
 
             self.global_.add(name)
-            self._assignable(name)
-            self.env_stack[1][name] = self.typing_env[name]
+            if name in self.env_stack[1]:
+                self.typing_env[name] = self.env_stack[1][name]
 
     def visit_Nonlocal(self, node):
         for name, loc in zip(node.names, node.name_locs):

lit-test/compiler/inferencer/scoping.py

@@ -1,8 +1,9 @@
 # RUN: %python -m artiq.compiler.testbench.inferencer %s >%t
 # RUN: OutputCheck %s --file-to-check=%t
 
+# CHECK-L: []:list(elt=int(width='a))
+x = []
+
 def f():
     global x
-    x = 1
-# CHECK-L: [x:int(width='a)]
-[x]
+    x[0] = 1