rails rescue_from ScriptError

Question

According to the family tree of Exception. SyntaxError is child to ScriptError

I wish to handle Syntax and/or ScriptError in my rails application.

Exception
    NoMemoryError
    ScriptError
        LoadError
        NotImplementedError
        SyntaxError
    SignalException
        Interrupt
    StandardError
        ArgumentError
        IOError
            EOFError
        IndexError
            StopIteration
        LocalJumpError
        NameError
            NoMethodError
        RangeError
            FloatDomainError
        RegexpError
        RuntimeError
        SecurityError
        SystemCallError
        SystemStackError
        ThreadError
        TypeError
        ZeroDivisionError
    SystemExit
    fatal

---

I did:

rescue_from ScriptError, :with => :notify_on_landing_page

but didn't worked.

Error raised on screen : SyntaxError in Bc::Muse::User::ProfileController#show

I have created an explicit syntax error, it should gracefully rescue it and do the things I want to.

Answer 1

Unfortunately, I don't think it works that way.

Rescuing from exceptions with rescue_from works only after creating a controller instance during request processing (see source code here and here ). Your SyntaxError is probably raised much earlier - during autoloading of the given controller and dependent classes / modules. So unless you were trying to rescue from a syntax error of code being loaded during a controller action execution, you are out of luck, I'm afraid.

Test: when you explicitly load a file with a syntax error in a controller action and the rescue_from will work as expected:

class MyController < ApplicationController
  rescue_from(::SyntaxError) { Rails.logger.error "SYNTAX ERROR!" }

  def index
    load "#{Rails.root}/test.rb"
  end
end

If you save a test.rb file in the rails root and add a deliberate syntax error in it, you will see the exception is handled correctly by rescue_from and the error message will be present in the log file.

On the other hand, if you look at the full stack trace of your SyntaxError , you will probably see that it does not even reach the ActionController methods for request processing.

Answer 2

Thanks!

I added a middleware to achieve this.

class RescueSyntaxError
  def initialize(app)
    @app = app
  end

  def call(env)
    @app.call(env)
  rescue SyntaxError => error

    request = Rack::Request.new(env)
    session = request.env['rack.session']
    params = request.params

    if session.try(:[], :user_object)
      ##Do validation stuff
      ...
      [302, {'Location' => '/'}, []]
    end
  end
end