Fix continue/break in else block behavior (#146)

Fixes: https://github.com/google/grumpy/issues/123

compiler/stmt.py

@@ -173,6 +173,8 @@ class StatementVisitor(ast.NodeVisitor):
         self._tie_target(target, value.expr)
 
   def visit_Break(self, node):
+    if not self.block.loop_stack:
+      raise util.ParseError(node, "'break' not in loop")
     self._write_py_context(node.lineno)
     self.writer.write('goto Label{}'.format(self.block.top_loop().end_label))
 
@@ -242,6 +244,8 @@ class StatementVisitor(ast.NodeVisitor):
         self.block.bind_var(self.writer, node.name, type_.expr)
 
   def visit_Continue(self, node):
+    if not self.block.loop_stack:
+      raise util.ParseError(node, "'continue' not in loop")
     self._write_py_context(node.lineno)
     self.writer.write('goto Label{}'.format(self.block.top_loop().start_label))
 
@@ -296,13 +300,13 @@ class StatementVisitor(ast.NodeVisitor):
       self._visit_each(node.body)
       self.writer.write('goto Label{}'.format(loop.start_label))
 
+    self.block.pop_loop()
     if node.orelse:
       self.writer.write_label(orelse_label)
       self._visit_each(node.orelse)
     # Avoid label "defined and not used" in case there's no break statements.
     self.writer.write('goto Label{}'.format(loop.end_label))
     self.writer.write_label(loop.end_label)
-    self.block.pop_loop()
 
   def visit_FunctionDef(self, node):
     self._write_py_context(node.lineno)

compiler/stmt_test.py

@@ -202,6 +202,16 @@ class StatementVisitorTest(unittest.TestCase):
         else:
           print 'bar'""")))
 
+  def testForElseBreakNotNested(self):
+    self.assertRaisesRegexp(
+        util.ParseError, "'continue' not in loop",
+        _ParseAndVisit, 'for i in (1,):\n  pass\nelse:\n  continue')
+
+  def testForElseContinueNotNested(self):
+    self.assertRaisesRegexp(
+        util.ParseError, "'continue' not in loop",
+        _ParseAndVisit, 'for i in (1,):\n  pass\nelse:\n  continue')
+
   def testFunctionDef(self):
     self.assertEqual((0, 'bar baz\n'), _GrumpRun(textwrap.dedent("""\
         def foo(a, b):

testing/for_test.py

@@ -51,3 +51,26 @@ for i, j in [('a', 1), ('b', 2)]:
   l.append(i)
   l.append(j)
 assert l == ['a', 1, 'b', 2]
+
+# break and continue statements in an else clause applies to the outer loop.
+# See: https://github.com/google/grumpy/issues/123
+l = []
+for i in range(2):
+  l.append(i)
+  for j in range(10, 12):
+    l.append(j)
+  else:
+    l.append(12)
+    continue
+  l.append(-1)
+assert l == [0, 10, 11, 12, 1, 10, 11, 12]
+
+l = []
+for i in range(10):
+  l.append(i)
+  for j in range(10, 12):
+    l.append(j)
+  else:
+    break
+  l.append(-1)
+assert l == [0, 10, 11]