Change default ERB template engine to erubi

[tkmru]

Erubi is a simplified fork of Erubis, Erubi is faster than erubis and erb.

In rails, default ERB template engine is erubi from rails 5.1(Change ActionView ERB Handler from Erubis to Erubi by jeremyevans · Pull Request #27757 · rails/rails).

Erubi offers the following advantages for erubis:

• Handles postfix conditionals when using escaping (e.g. <%= foo if bar %>)
• Supports frozen_string_literal: true in templates via :freeze option
• Works with ruby's –enable-frozen-string-literal option
• Automatically freezes strings for template text when ruby optimizes it (on ruby 2.1+)
• Escapes ' (apostrophe) when escaping for better XSS protection
• Has 6x faster escaping on ruby 2.3+ by using cgi/escape
• Has 86% smaller memory footprint
• Does no monkey patching (Erubis adds a method to Kernel)
• Uses an immutable design (all options passed to the constructor, which returns a frozen object)
• Has simpler internals (1 file, <150 lines of code)
• Is not dead (Erubis hasn't been updated since 2011)

[tkmru]

I'm sorry to be leaving that it fell in a test.

I'm confused at a result of the test. falls back to engine layout test was failed with Errno::ENOENT: No such file or directory @ rb_sysopen - sinatra/test/views/layout.erubi.
Why is this extension(.erubi) attached? .erubi does not exist in the code.

[namusyaka]

First of all, we don't need to set erubi in the erb helper because we're using Tilt. It handles the template engines switching automatically and it supports for erubi of course.
For example, if you've installed erubis on your app, your app will use erubis as a ERB template engine.
I would say the same is true of erubi.
If you'd like to use erubi on your app, you should just install erubi on your app.

Thus, your changes is not necessary for enabling erubi.
If you would like to continue the contribution around erubi, you can commit to the docs, testing, and the sinatra-contrib library.
Otherwise, please close this PR.

[namusyaka]

Why do you add require 'erubi' in this? By reflecting this code, the method call for erb will largely be slowed down because the unnecessary method call is always happened.

[namusyaka]

In addition to my comment,
we don't have the erubis as a default template engine. It's only enabled when erubis is required.

[tkmru]

OK, Thank you for the comment.