Add BetterErrors gem.

Gemfile

@@ -65,6 +65,8 @@ group :development do
   gem 'stackprof'
   gem 'flamegraph'
   gem 'memory_profiler'
+  gem 'better_errors'
+  gem 'binding_of_caller'
 end
 
 group :development, :test do

Gemfile.lock

@@ -115,6 +115,12 @@ GEM
     aws-sigv4 (1.2.2)
       aws-eventstream (~> 1, >= 1.0.2)
     bcrypt (3.1.16)
+    better_errors (2.9.1)
+      coderay (>= 1.0.0)
+      erubi (>= 1.0.0)
+      rack (>= 0.9.0)
+    binding_of_caller (1.0.0)
+      debug_inspector (>= 0.0.1)
     bootsnap (1.5.1)
       msgpack (~> 1.0)
     builder (3.2.4)
@@ -153,6 +159,7 @@ GEM
     crass (1.0.6)
     daemons (1.3.1)
     dante (0.2.0)
+    debug_inspector (1.0.0)
     delayed_job (4.1.9)
       activesupport (>= 3.0, < 6.2)
     delayed_job_active_record (4.1.5)
@@ -415,6 +422,8 @@ DEPENDENCIES
   addressable
   aws-sdk-sqs (~> 1)
   bcrypt
+  better_errors
+  binding_of_caller
   bootsnap
   builder
   capistrano (~> 3.10)

app/controllers/application_controller.rb

@@ -120,7 +120,7 @@ class ApplicationController < ActionController::Base
     when PG::ConnectionBad
       render_error_page(503, exception, message: "The database is unavailable. Try again later.")
     else
-      raise exception if Danbooru.config.debug_mode
+      raise exception if !Rails.env.production? || Danbooru.config.debug_mode
       render_error_page(500, exception)
     end
   end

config/environments/development.rb

@@ -63,4 +63,7 @@ Rails.application.configure do
 
   # Uncomment if you wish to allow Action Cable access from any origin.
   # config.action_cable.disable_request_forgery_protection = true
+
+  BetterErrors::Middleware.allow_ip!(IPAddr.new("0.0.0.0/0"))
+  BetterErrors::Middleware.allow_ip!(IPAddr.new("::/0"))
 end