From b92b2e6c743c8b09744c9c9788046c719cc38eab Mon Sep 17 00:00:00 2001
From: Jimmy Jia <tesrin@gmail.com>
Date: Thu, 1 Nov 2018 16:41:53 -0400
Subject: [PATCH 1/2] Do not handle RoutingExceptions with app error handlers

---
 flask/app.py                     | 9 ++++++++-
 tests/test_user_error_handler.py | 5 +++++
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/flask/app.py b/flask/app.py
index 49a025cd..8d193656 100644
--- a/flask/app.py
+++ b/flask/app.py
@@ -20,7 +20,8 @@ from threading import Lock
 from werkzeug.datastructures import Headers, ImmutableDict
 from werkzeug.exceptions import BadRequest, BadRequestKeyError, HTTPException, \
     InternalServerError, MethodNotAllowed, default_exceptions
-from werkzeug.routing import BuildError, Map, RequestRedirect, Rule
+from werkzeug.routing import BuildError, Map, RequestRedirect, \
+    RoutingException, Rule
 
 from . import cli, json
 from ._compat import integer_types, reraise, string_types, text_type
@@ -1638,6 +1639,12 @@ class Flask(_PackageBoundObject):
         if e.code is None:
             return e
 
+        # RoutingExceptions such as RequestRedirects are special exceptions
+        # used to trigger routing actions such as redirects, and also behave
+        # like proxy exceptions. We return these unchanged as well.
+        if isinstance(e, RoutingException):
+            return e
+
         handler = self._find_error_handler(e)
         if handler is None:
             return e
diff --git a/tests/test_user_error_handler.py b/tests/test_user_error_handler.py
index 18d5f277..4e52485c 100644
--- a/tests/test_user_error_handler.py
+++ b/tests/test_user_error_handler.py
@@ -184,6 +184,10 @@ def test_default_error_handler():
     def forbidden():
         raise Forbidden()
 
+    @app.route('/slash/')
+    def slash():
+        return ''
+
     app.register_blueprint(bp, url_prefix='/bp')
 
     c = app.test_client()
@@ -191,5 +195,6 @@ def test_default_error_handler():
     assert c.get('/bp/forbidden').data == b'bp-forbidden'
     assert c.get('/undefined').data == b'default'
     assert c.get('/forbidden').data == b'forbidden'
+    assert c.get('/slash').location.endswith('/slash/')
 
 

From 662ce2151d0f17d592133eeecdc8d7e6676db811 Mon Sep 17 00:00:00 2001
From: David Lord <davidism@gmail.com>
Date: Mon, 7 Jan 2019 09:52:54 -0800
Subject: [PATCH 2/2] add changelog for GH-2986

---
 CHANGES.rst                      |  5 +++++
 flask/app.py                     | 16 +++++++++++++---
 tests/test_user_error_handler.py |  9 ++++-----
 3 files changed, 22 insertions(+), 8 deletions(-)

diff --git a/CHANGES.rst b/CHANGES.rst
index cb1e6239..bdf0c896 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -19,11 +19,16 @@ Unreleased
     Python version. (`#2825`_)
 -   :func:`send_file` handles an ``attachment_filename`` that is a
     native Python 2 string (bytes) with UTF-8 coded bytes. (`#2933`_)
+-   A catch-all error handler registered for ``HTTPException`` will not
+    handle ``RoutingExcpetion``, which is used internally during
+    routing. This fixes the unexpected behavior that had been introduced
+    in 1.0. (`#2986`_)
 
 .. _#2766: https://github.com/pallets/flask/issues/2766
 .. _#2765: https://github.com/pallets/flask/pull/2765
 .. _#2825: https://github.com/pallets/flask/pull/2825
 .. _#2933: https://github.com/pallets/flask/issues/2933
+.. _#2986: https://github.com/pallets/flask/pull/2986
 
 
 Version 1.0.2
diff --git a/flask/app.py b/flask/app.py
index 8d193656..c570a95b 100644
--- a/flask/app.py
+++ b/flask/app.py
@@ -1632,6 +1632,16 @@ class Flask(_PackageBoundObject):
         registered error handlers and fall back to returning the
         exception as response.
 
+        .. versionchanged:: 1.0.3
+            ``RoutingException``, used internally for actions such as
+             slash redirects during routing, is not passed to error
+             handlers.
+
+        .. versionchanged:: 1.0
+            Exceptions are looked up by code *and* by MRO, so
+            ``HTTPExcpetion`` subclasses can be handled with a catch-all
+            handler for the base ``HTTPException``.
+
         .. versionadded:: 0.3
         """
         # Proxy exceptions don't have error codes.  We want to always return
@@ -1639,9 +1649,9 @@ class Flask(_PackageBoundObject):
         if e.code is None:
             return e
 
-        # RoutingExceptions such as RequestRedirects are special exceptions
-        # used to trigger routing actions such as redirects, and also behave
-        # like proxy exceptions. We return these unchanged as well.
+        # RoutingExceptions are used internally to trigger routing
+        # actions, such as slash redirects raising RequestRedirect. They
+        # are not raised or handled in user code.
         if isinstance(e, RoutingException):
             return e
 
diff --git a/tests/test_user_error_handler.py b/tests/test_user_error_handler.py
index 4e52485c..f4a08f58 100644
--- a/tests/test_user_error_handler.py
+++ b/tests/test_user_error_handler.py
@@ -184,9 +184,9 @@ def test_default_error_handler():
     def forbidden():
         raise Forbidden()
 
-    @app.route('/slash/')
+    @app.route("/slash/")
     def slash():
-        return ''
+        return "slash"
 
     app.register_blueprint(bp, url_prefix='/bp')
 
@@ -195,6 +195,5 @@ def test_default_error_handler():
     assert c.get('/bp/forbidden').data == b'bp-forbidden'
     assert c.get('/undefined').data == b'default'
     assert c.get('/forbidden').data == b'forbidden'
-    assert c.get('/slash').location.endswith('/slash/')
-
-
+    # Don't handle RequestRedirect raised when adding slash.
+    assert c.get("/slash", follow_redirects=True).data == b"slash"