Excess spaces wile rendering multiline string in Rails 5 - ruby-on-rails

Question

I end up with strange bug (feature?):
Here is how test.html.erb file looks like:
<textarea><%= "a\nb\nc" %></textarea>
and in rendered textarea I expect something like that:
a
b
c
But I got:
Where these excess spaces came from?
Rails 5.0.0.beta2
UDP: I should mention it before, but I have the same problem while using f.text_area inside of form_for block. It looks like:
.form
=form_for article do |f|
.form-group
=field_label f, :text, true
=f.text_area :text, class: %w(form-control), rows: 20, placeholder: t('placeholder.article_text')
(HAML)
I end up with it, and just simplified the exploit to simple erb file with one string
UDP2:
Here how it looks with simple_format: <textarea><%= simple_format("a\nb\nc") %></textarea>
I should clearify some thing: this textarea is used to edit article text. And then it (text) will be processed with markdown processor (RDiscount) before appears in html page. I have no any idea, why I should use simple_format to display raw text in textarea and why this
should became this
after save?

Answer 1

In HAML, use
~ f.text_area :text
instead of
= f.text_area :text
The ~ operator suppresses "pretty" newlines in HAML, which is useful with TEXTAREA and PRE tags. See Whitespace preservation in HAML for more information.

Answer 2

<textarea><%= "a\r\nb\r\nc" %></textarea>
\n is new line it will take to next line at same position where you was in previous line \r is carriage return mean move to start of line.
But I wont recommend this approach You should use <br/> tag instead
so use
<textarea><%= WhatEverTheTextIs.gsub(/\n/, '<br/>').html_safe %></textarea>
This will replace all new line characters to <br> tag
One more easy solution is to use simple_format i-e:
<textarea><%= simple_format(YOUR_TEXT_HERE) %></textarea>
UPDATE
Here is the code to use for form helper
.form
=form_for article do |f|
.form-group
=field_label f, :text, true
=f.text_area :text,:value=>simple_format(article.text), class: %w(form-control), rows: 20, placeholder: t('placeholder.article_text')

Answer 3

I just ran into the exact same problem. It all comes down to whitespace in your templates and layouts. In my case my main application is using HAML and has an application.html.haml with a section like so
#content.container{tabindex: "-1"}
.row
- if content_for?(:left_nav)
.col-md-3.sidebar
= yield(:left_nav)
.col-md-9
= flash_helper
= yield
%footer
= render :partial => 'shared/footer'
That's at least 10 spaces before the "yield" of the main content.
Then I was using a view from a gem that was in ERB, not HAML. But, since my main application layout is HAML, the view rendering/handling goes through the HAML renderers. HAML has dealt with whitespace and texareas already, but when the final and complete view is rendered, all of the extra whitespace from the main layout is included in the html and causes the content of the textarea to be indented.
Why is the first row not indented? Because the HAML "preserve" function cleans up the whitespace for the first row in the text area. See https://github.com/haml/haml/issues/516.
For me, the easy fix is to configure HAML to use "ugly" mode. This gets rid of all the leading whitespace when rendering the views. There is more about "ugly" mode and newlines in textareas in the HAML FAQ. To configure HAML to use ugly mode:
To improve performance, Haml defaults to {Haml::Options#ugly "ugly" mode} in Rails apps running in production. Ugly mode is when whitespace is stripped out, and this can cause issues occassionally.
If you are using Rails, you can change the default behaviour by creating a config/initializers/haml.rb file and adding in the following line.
Haml::Template.options[:ugly] = true
Links I found helpful while researching this:
https://github.com/haml/haml/issues/643
ERB view embedded in a Haml layout: what to do about whitespace now? (although the proposed solution didn't work for me b/c the ERB view would always be picked up before the HAML view)
https://github.com/haml/haml/blob/master/lib/haml/buffer.rb (fix_textareas)
https://github.com/haml/haml/blob/master/lib/haml/helpers.rb (specifically the preserve method)
My versions are Rails 4.2.6 and HAML 4.0.7