From b573a86977161b93152dddb5bfc43195335b3c59 Mon Sep 17 00:00:00 2001
From: David Lord <davidism@gmail.com>
Date: Sat, 28 Apr 2018 06:51:08 -0700
Subject: [PATCH] trap key errors in debug, not all 400 errors

---
 flask/app.py        | 10 ++++++++--
 tests/test_basic.py | 25 +++++++++++++++++++------
 2 files changed, 27 insertions(+), 8 deletions(-)

diff --git a/flask/app.py b/flask/app.py
index 2de526e2..3c106ee8 100644
--- a/flask/app.py
+++ b/flask/app.py
@@ -1663,8 +1663,14 @@ class Flask(_PackageBoundObject):
 
         trap_bad_request = self.config['TRAP_BAD_REQUEST_ERRORS']
 
-        # if unset, trap based on debug mode
-        if (trap_bad_request is None and self.debug) or trap_bad_request:
+        # if unset, trap key errors in debug mode
+        if (
+            trap_bad_request is None and self.debug
+            and isinstance(e, BadRequestKeyError)
+        ):
+            return True
+
+        if trap_bad_request:
             return isinstance(e, BadRequest)
 
         return False
diff --git a/tests/test_basic.py b/tests/test_basic.py
index 9d6c58c1..c0168ae3 100644
--- a/tests/test_basic.py
+++ b/tests/test_basic.py
@@ -1027,21 +1027,34 @@ def test_errorhandler_precedence(app, client):
 
 
 def test_trapping_of_bad_request_key_errors(app, client):
-    @app.route('/fail')
+    @app.route('/key')
     def fail():
         flask.request.form['missing_key']
 
-    rv = client.get('/fail')
+    @app.route('/abort')
+    def allow_abort():
+        flask.abort(400)
+
+    rv = client.get('/key')
     assert rv.status_code == 400
     assert b'missing_key' not in rv.data
+    rv = client.get('/abort')
+    assert rv.status_code == 400
 
-    app.config['TRAP_BAD_REQUEST_ERRORS'] = True
-
+    app.debug = True
     with pytest.raises(KeyError) as e:
-        client.get("/fail")
-
+        client.get("/key")
     assert e.errisinstance(BadRequest)
     assert 'missing_key' in e.value.description
+    rv = client.get('/abort')
+    assert rv.status_code == 400
+
+    app.debug = False
+    app.config['TRAP_BAD_REQUEST_ERRORS'] = True
+    with pytest.raises(KeyError):
+        client.get('/key')
+    with pytest.raises(BadRequest):
+        client.get('/abort')
 
 
 def test_trapping_of_all_http_exceptions(app, client):