Fix bug with exception variable reuse in deferred node.

See #1748 (comment)

Author: Guido van Rossum

mypy/checker.py

@@ -1712,7 +1712,8 @@ def visit_try_without_finally(self, s: TryStmt, try_frame: bool) -> None:
                                           'accept outside except: blocks even in '
                                           'python 2)'.format(s.vars[i].name))
                             var = cast(Var, s.vars[i].node)
-                            var.type = DeletedType(source=source)
+                            if not self.current_node_deferred:
+                                var.type = DeletedType(source=source)
                             self.binder.cleanse(s.vars[i])
             if s.else_body:
                 self.accept(s.else_body)

test-data/unit/check-statements.test

@@ -687,6 +687,17 @@ e = 1 # E: Assignment to variable 'e' outside except: block
 e = E1() # E: Assignment to variable 'e' outside except: block
 [builtins fixtures/exception.pyi]
 
+[case testExceptionVariableReuseInDeferredNode]
+def f(*a: BaseException) -> int:
+    x
+    try: pass
+    except BaseException as err: pass
+    try: pass
+    except BaseException as err: f(err)
+x = f()
+[builtins fixtures/exception.pyi]
+
+
 [case testArbitraryExpressionAsExceptionType]
 import typing
 a = BaseException