Show Rails error page for a morph reload

app/assets/javascripts/hotwire_spark.js

@@ -1578,13 +1578,34 @@ var HotwireSpark = (function () {
       });
     }
     #visitCurrentPage() {
+      this.#hideProgressbar();
       return new Promise(resolve => {
-        document.addEventListener("turbo:load", () => resolve(document), {
+        document.addEventListener("turbo:load", () => {
+          resolve(document);
+        }, {
           once: true
         });
+        this.#stopVisitOnError();
         window.Turbo.visit(window.location);
       });
     }
+    #hideProgressbar() {
+      const style = document.createElement('style');
+      style.type = 'text/css';
+      style.textContent = '.turbo-progress-bar { display: none; }';
+      document.head.appendChild(style);
+      return style;
+    }
+    #stopVisitOnError() {
+      document.addEventListener("turbo:before-fetch-response", event => {
+        const responseStatus = event.detail.fetchResponse.response.status;
+        if (responseStatus >= 400) {
+          event.preventDefault();
+        }
+      }, {
+        once: true
+      });
+    }
   }
 
   consumer.subscriptions.create({

app/javascript/hotwire/spark/reloaders/replace_html_reloader.js

@@ -23,9 +23,30 @@ export class ReplaceHtmlReloader {
   }
 
   #visitCurrentPage() {
+    this.#hideProgressbar()
     return new Promise(resolve => {
-      document.addEventListener("turbo:load", () => resolve(document), { once: true })
+      document.addEventListener("turbo:load", () => {
+        resolve(document)
+      }, { once: true })
+      this.#stopVisitOnError()
       window.Turbo.visit(window.location)
     })
   }
+
+  #hideProgressbar() {
+    const style = document.createElement('style');
+    style.type = 'text/css';
+    style.textContent = '.turbo-progress-bar { display: none; }';
+    document.head.appendChild(style);
+    return style
+  }
+
+  #stopVisitOnError() {
+    document.addEventListener("turbo:before-fetch-response", (event) => {
+      const responseStatus = event.detail.fetchResponse.response.status
+      if(responseStatus >= 400) {
+        event.preventDefault()
+      }
+    }, { once: true })
+  }
 }

lib/hotwire/spark/change.rb

@@ -23,7 +23,7 @@ def reload_message
 
     def canonical_changed_path
       changed_path.to_s.tap do |changed_path|
-        monitored_paths.each { |path| changed_path.gsub!(/^#{path}/, "")}
+        monitored_paths.each { |path| changed_path.gsub!(/^#{path}/, "") }
       end
     end
 

test/dummy/config/environments/test.rb

@@ -25,7 +25,7 @@
   config.cache_store = :null_store
 
   # Render exception templates for rescuable exceptions and raise for other exceptions.
-  config.action_dispatch.show_exceptions = :rescuable
+  config.action_dispatch.show_exceptions = true
 
   # Disable request forgery protection in test environment.
   config.action_controller.allow_forgery_protection = false

test/replace_html_reload_test.rb

@@ -14,4 +14,14 @@ class ReplaceHtmlReloadTest < ApplicationSystemTestCase
     assert_text "This is pretty amazing"
     assert_css "[data-turbo-navigated]"
   end
+
+  test "errors don't show the error page" do
+    visit root_path
+    assert_no_text "ZeroDivisionError"
+
+    edit_file "app/views/home/show.html.erb", replace: "_REPLACE_HTML_", with: "<%= 1 / 0 %>"
+
+    assert_css "[data-turbo-navigated]"
+    assert_no_text "ZeroDivisionError"
+  end
 end