throw UnboundLocalError when accessing loop variables outside static …

…for loops (#613)

python/taichi/lang/impl.py

@@ -301,7 +301,7 @@ def static(x, *xs):
   import taichi as ti
   assert get_runtime(
   ).inside_kernel, 'ti.static can only be used inside Taichi kernels'
-  if isinstance(x, (bool, int, float, range, list, tuple, ti.ndrange, ti.GroupedNDRange)):
+  if isinstance(x, (bool, int, float, range, list, tuple, enumerate, ti.ndrange, ti.GroupedNDRange)):
     return x
   elif isinstance(x, ti.lang.expr.Expr) and x.ptr.is_global_var():
     return x

python/taichi/lang/transformer.py

@@ -1,5 +1,6 @@
 import ast
 from .util import to_taichi_type
+import copy
 
 
 class TaichiSyntaxError(Exception):
@@ -328,7 +329,15 @@ def visit_For(self, node):
       node = ast.copy_location(t, node)
       return self.visit(node) # further translate as a range for
     elif is_static_for:
-      return node
+      t = self.parse_stmt('if 1: pass; del a')
+      t.body[0] = node
+      target = copy.deepcopy(node.target)
+      target.ctx = ast.Del()
+      if isinstance(target, ast.Tuple):
+        for tar in target.elts:
+          tar.ctx = ast.Del()
+      t.body[1].targets = [target]
+      return t
     elif is_range_for:
       loop_var = node.target.id
       self.check_loop_var(loop_var)

tests/python/test_lang.py

@@ -113,3 +113,25 @@ def test():
 
   for i in range(n):
     assert val[i] == i + 45
+
+@ti.must_throw(UnboundLocalError)
+@ti.host_arch_only
+def test_loop_var_life():
+  @ti.kernel
+  def test():
+    for i in ti.static(range(8)):
+      pass
+    print(i)
+
+  test()
+
+@ti.must_throw(UnboundLocalError)
+@ti.host_arch_only
+def test_loop_var_life_double_iters():
+  @ti.kernel
+  def test():
+    for i, v in ti.static(enumerate(range(8))):
+      pass
+    print(i)
+
+  test()