Merge pull request #2035 from plotly/fix-debugger-html

Fix debugger html

Author: alexcjohnson

CHANGELOG.md

@@ -26,6 +26,8 @@ This project adheres to [Semantic Versioning](https://semver.org/).
 
 - [#1976](https://github.com/plotly/dash/pull/1976) Fix [#1962](https://github.com/plotly/dash/issues/1962) in which DatePickerSingle and DatePickerRange are extremely slow when provided a long list of disabled_days.
 
+- [#2035](https://github.com/plotly/dash/pull/2035) Fix [#2033](https://github.com/plotly/dash/issues/2033) In-App error reporting does not render HTML.
+
 ### Changed
 
 - [#2016](https://github.com/plotly/dash/pull/2016) Drop the 375px width from default percy_snapshot calls, keep only 1280px

dash/dash-renderer/src/components/error/FrontEnd/FrontEndError.react.js

@@ -109,9 +109,10 @@ function UnconnectedErrorContent({error, base}) {
                 </div>
             )}
             {/* Backend Error */}
-            {typeof error.html !== 'string' ? null : error.html.indexOf(
-                  '<!DOCTYPE'
-              ) === 0 ? (
+            {typeof error.html !== 'string' ? null : error.html
+                  .split()[0]
+                  .toLowerCase()
+                  .startsWith('<!doctype') ? (
                 <div className='dash-be-error__st'>
                     <div className='dash-backend-error'>
                         {/* Embed werkzeug debugger in an iframe to prevent

dash/testing/browser.py

@@ -5,6 +5,7 @@
 import logging
 import warnings
 import percy
+import requests
 
 from selenium import webdriver
 from selenium.webdriver.support import expected_conditions as EC
@@ -188,8 +189,14 @@ def percy_snapshot(
             """
             )
 
+        try:
             self.percy_runner.snapshot(name=snapshot_name, widths=widths)
+        except requests.HTTPError as err:
+            # Ignore retries.
+            if err.request.status_code != 400:
+                raise err
 
+        if convert_canvases:
             self.driver.execute_script(
                 """
                 const stash = window._canvasStash;
@@ -204,9 +211,6 @@ def percy_snapshot(
             """
             )
 
-        else:
-            self.percy_runner.snapshot(name=snapshot_name, widths=widths)
-
     def take_snapshot(self, name):
         """Hook method to take snapshot when a selenium test fails. The
         snapshot is placed under.