new debug/test preserve context implementation

docs/config.rst

@@ -126,14 +126,6 @@ The following configuration values are used internally by Flask:
 
     Default: ``None``
 
-.. py:data:: PRESERVE_CONTEXT_ON_EXCEPTION
-
-    Don't pop the request context when an exception occurs. If not set, this
-    is true if ``DEBUG`` is true. This allows debuggers to introspect the
-    request data on errors, and should normally not need to be set directly.
-
-    Default: ``None``
-
 .. py:data:: TRAP_HTTP_EXCEPTIONS
 
     If there is no handler for an ``HTTPException``-type exception, re-raise it
@@ -392,6 +384,9 @@ The following configuration values are used internally by Flask:
 
     Added :data:`MAX_COOKIE_SIZE` to control a warning from Werkzeug.
 
+.. versionchanged:: 2.2
+    Removed ``PRESERVE_CONTEXT_ON_EXCEPTION``.
+
 
 Configuring from Python Files
 -----------------------------

docs/reqcontext.rst

@@ -219,25 +219,6 @@ sent:
     :meth:`~Flask.teardown_request` functions are called.
 
 
-Context Preservation on Error
------------------------------
-
-At the end of a request, the request context is popped and all data
-associated with it is destroyed. If an error occurs during development,
-it is useful to delay destroying the data for debugging purposes.
-
-When the development server is running in development mode (the
-``--env`` option is set to ``'development'``), the error and data will
-be preserved and shown in the interactive debugger.
-
-This behavior can be controlled with the
-:data:`PRESERVE_CONTEXT_ON_EXCEPTION` config. As described above, it
-defaults to ``True`` in the development environment.
-
-Do not enable :data:`PRESERVE_CONTEXT_ON_EXCEPTION` in production, as it
-will cause your application to leak memory on exceptions.
-
-
 .. _notes-on-proxies:
 
 Notes On Proxies