Fix obsolete usage of flask.json.JSONEncoder

Flask's JSONEncoder class was removed in version 3.0 since the
Python Standard Library provides its own json library. Instead,
update the code to use either that or Flask's default JSON provider.

Flask apps don't have a `.json_encoder` property anymore, the
property is `.json`.

Author: ldionne

lnt/server/ui/app.py

@@ -46,12 +46,12 @@ def __call__(self, environ, start_response):
         return self.app(environ, start_response)
 
 
-class LNTObjectJSONEncoder(flask.json.JSONEncoder):
+class LNTObjectJSONEncoder(flask.json.provider.DefaultJSONProvider):
     """Take SQLAlchemy objects and jsonify them. If the object has an __json__
     method, use that instead."""
 
     def __init__(self, *args, **kwargs):
-        super(LNTObjectJSONEncoder, self).__init__(*args, **kwargs)
+        super().__init__(*args, **kwargs)
 
     def default(self, obj):
         if hasattr(obj, '__json__'):
@@ -74,7 +74,7 @@ def default(self, obj):
 
             return fields
 
-        return flask.json.JSONEncoder.default(self, obj)
+        return super().default(self, obj)
 
 
 class Request(flask.Request):
@@ -140,7 +140,7 @@ def create_with_instance(instance):
         # Construct the application.
         app = App(__name__)
 
-        app.json_encoder = LNTObjectJSONEncoder
+        app.json = LNTObjectJSONEncoder(app)
         # Register additional filters.
         create_jinja_environment(app.jinja_env)
 

lnt/server/ui/regression_views.py

@@ -1,6 +1,6 @@
-import flask
 import sqlalchemy
 import json
+import flask
 from flask import g
 from flask import abort
 from flask import render_template
@@ -265,7 +265,7 @@ def name(cls):
     return cls.__class__.__name__
 
 
-class LNTEncoder(flask.json.JSONEncoder):
+class LNTEncoder(json.JSONEncoder):
     """Encode all the common LNT objects."""
     def default(self, obj):
         # Most of our objects have a __json__ defined.
@@ -276,7 +276,7 @@ def default(self, obj):
             return
         if name(obj) == "SampleField":
             return obj.name
-        return flask.json.JSONEncoder.default(self, obj)
+        return flask.json.provider.DefaultJSONProvider.default(obj)
 
 
 @v4_route("/regressions/<int:id>", methods=["GET", "POST"])