Raise AutoGraph error if variable is created inside a loop body.

PiperOrigin-RevId: 209775953

2 files changed, 36 insertions, 0 deletions

diff --git a/tensorflow/contrib/autograph/converters/control_flow.py b/tensorflow/contrib/autograph/converters/control_flow.py
index 5a5a6ad63a..f7dd3183b0 100644
--- a/tensorflow/contrib/autograph/converters/control_flow.py
+++ b/tensorflow/contrib/autograph/converters/control_flow.py
@@ -95,6 +95,18 @@ class ControlFlowTransformer(converter.Base):
       return 'no variables'
     return ', '.join(map(str, symbol_set))
 
+  def _validate_no_live_vars_created(self, node):
+    body_scope = anno.getanno(node, annos.NodeAnno.BODY_SCOPE)
+    live_vars_out = anno.getanno(node, anno.Static.LIVE_VARS_OUT)
+    live_vars_created_in_body = live_vars_out & body_scope.created
+    if live_vars_created_in_body:
+      raise ValueError(
+          'The following variables are created inside the loop and used later:'
+          '\n%s\n'
+          'Variables must be declared outside loops because loops may not'
+          ' necessarily execute.' % self._fmt_symbol_list(
+              live_vars_created_in_body))
+
   def visit_If(self, node):
     node = self.generic_visit(node)
 
@@ -197,6 +209,8 @@ class ControlFlowTransformer(converter.Base):
   def visit_While(self, node):
     self.generic_visit(node)
 
+    self._validate_no_live_vars_created(node)
+
     body_scope = anno.getanno(node, annos.NodeAnno.BODY_SCOPE)
     body_closure = body_scope.modified - body_scope.created
     all_referenced = body_scope.referenced
@@ -262,6 +276,8 @@ class ControlFlowTransformer(converter.Base):
   def visit_For(self, node):
     self.generic_visit(node)
 
+    self._validate_no_live_vars_created(node)
+
     body_scope = anno.getanno(node, annos.NodeAnno.BODY_SCOPE)
     body_closure = body_scope.modified - body_scope.created
     all_referenced = body_scope.referenced
diff --git a/tensorflow/contrib/autograph/converters/control_flow_test.py b/tensorflow/contrib/autograph/converters/control_flow_test.py
index 6cb907f69a..02bc00dbc8 100644
--- a/tensorflow/contrib/autograph/converters/control_flow_test.py
+++ b/tensorflow/contrib/autograph/converters/control_flow_test.py
@@ -57,6 +57,17 @@ class ControlFlowTest(converter_testing.TestCase):
 
     self.assertTransformedResult(test_fn, constant_op.constant(5), 0)
 
+  def test_while_variable_defined_in_body(self):
+    def bad_while_loop(n):
+      while n > 0:
+        n -= 1
+        s = n
+      return s
+
+    node, ctx = self.prepare(bad_while_loop, {})
+    with self.assertRaises(transformer.AutographParseError):
+      control_flow.transform(node, ctx)
+
   def test_if_basic(self):
 
     def test_fn(n):
@@ -196,6 +207,15 @@ class ControlFlowTest(converter_testing.TestCase):
       self.assertEqual(result.test_fn(5), 10)
       self.assertEqual(eval_count[0], 1)
 
+  def test_for_variable_defined_in_body(self):
+    def bad_for_loop(n):
+      for i in range(n):
+        s = i
+      return s
+
+    node, ctx = self.prepare(bad_for_loop, {})
+    with self.assertRaises(transformer.AutographParseError):
+      control_flow.transform(node, ctx)
 
 if __name__ == '__main__':
   test.main()