Fix undeclared variables when using strict_undefined

Visit target variable in list and dictionary comprehensions

Author: Sébastien Granjoux

doc/build/unreleased/418.rst

@@ -0,0 +1,7 @@
+.. change::
+    :tags: bug, parser
+    :tickets: 418
+
+    Fix undefined variable errors when strict_undefined is True and using
+    nested list comprehension.
+

mako/pyparser.py

@@ -93,6 +93,7 @@ def visit_FunctionDef(self, node):
     def visit_ListComp(self, node):
         if self.in_function:
             for comp in node.generators:
+                self.visit(comp.target)
                 self.visit(comp.iter)
         else:
             self.generic_visit(node)
@@ -102,6 +103,7 @@ def visit_ListComp(self, node):
     def visit_DictComp(self, node):
         if self.in_function:
             for comp in node.generators:
+                self.visit(comp.target)
                 self.visit(comp.iter)
         else:
             self.generic_visit(node)