Improve application context popping

Exceptions during teardown handling will no longer leave application
contexts lingering around.  This fixes #1767

CHANGES

@@ -77,6 +77,8 @@ Version 0.11
 - ``send_from_directory`` now raises BadRequest if the filename is invalid on
   the server OS (pull request ``#1763``).
 - Added the ``JSONIFY_MIMETYPE`` configuration variable (pull request ``#1728``).
+- Exceptions during teardown handling will no longer leave bad application
+  contexts lingering around.
 
 Version 0.10.2
 --------------

flask/ctx.py

@@ -181,11 +181,13 @@ class AppContext(object):
 
     def pop(self, exc=_sentinel):
         """Pops the app context."""
+        try:
             self._refcnt -= 1
             if self._refcnt <= 0:
                 if exc is _sentinel:
                     exc = sys.exc_info()[1]
                 self.app.do_teardown_appcontext(exc)
+        finally:
             rv = _app_ctx_stack.pop()
         assert rv is self, 'Popped wrong app context.  (%r instead of %r)' \
             % (rv, self)
@@ -341,6 +343,7 @@ class RequestContext(object):
         """
         app_ctx = self._implicit_app_ctx_stack.pop()
 
+        try:
             clear_request = False
             if not self._implicit_app_ctx_stack:
                 self.preserved = False
@@ -360,10 +363,8 @@ class RequestContext(object):
                 if request_close is not None:
                     request_close()
                 clear_request = True
-
+        finally:
             rv = _request_ctx_stack.pop()
-        assert rv is self, 'Popped wrong request context.  (%r instead of %r)' \
-            % (rv, self)
 
             # get rid of circular dependencies at the end of the request
             # so that we don't require the GC to be active.
@@ -374,6 +375,9 @@ class RequestContext(object):
             if app_ctx is not None:
                 app_ctx.pop(exc)
 
+            assert rv is self, 'Popped wrong request context.  ' \
+                '(%r instead of %r)' % (rv, self)
+
     def auto_pop(self, exc):
         if self.request.environ.get('flask._preserve_context') or \
            (exc is not None and self.app.preserve_context_on_exception):

tests/test_appctx.py

@@ -146,3 +146,25 @@ def test_context_refcounts():
     assert res.status_code == 200
     assert res.data == b''
     assert called == ['request', 'app']
+
+
+def test_clean_pop():
+    called = []
+    app = flask.Flask(__name__)
+
+    @app.teardown_request
+    def teardown_req(error=None):
+        1 / 0
+
+    @app.teardown_appcontext
+    def teardown_app(error=None):
+        called.append('TEARDOWN')
+
+    try:
+        with app.test_request_context():
+            called.append(flask.current_app.name)
+    except ZeroDivisionError:
+        pass
+
+    assert called == ['test_appctx', 'TEARDOWN']
+    assert not flask.current_app