Indentation in ERB templates - ruby-on-rails

Question

I have the following entry in an erb template:
# Lorem Ipsum...
<% unless #foo['bar'] == nil %>
<% #foo['bar'].each do |property, value| %>
<%= "zaz.#{property} #{value}" %>
<% end %>
<% end %>
That is parsed to:
# Lorem Ipsum...
zaz.property value
How can I remove the leading spaces so that lines are not indented in the resolved template?
I would like to avoid using something like:
# Lorem Ipsum...
<% unless #foo['bar'] == nil %>
<% #foo['bar'].each do |property, value| %>
<%= "zaz.#{property} #{value}" %>
<% end %>
<% end %>

Answer 1

The only solution I can offer is hackish adding <%- 'whatever here' %> before the <%= %> entry:
<% [1,2,3].each do |f| %>
<%- 1 %><%= f %>
<% end %>
it outputs in irb
irb(main):018:0> ERB.new(File.read('f.txt'), nil, '-').result
=> "\n1\n\n2\n\n3\n\n"
Rails doc claims, that default value for ERB trim_mode is -
http://edgeguides.rubyonrails.org/configuring.html#configuring-action-view
And according to https://www.systutorials.com/docs/linux/man/1-erb/ ERB should remove spaces before <%- when - mode is enabled.

Answer 2

You could indent the code instead of the ERB tags:
# Lorem Ipsum...
<% unless #foo['bar'] == nil %>
<% #foo['bar'].each do |property, value| %>
<%= "zaz.#{property} #{value}" %>
<% end %>
<% end %>

Answer 3

If you're controlling the string passed to ERB.new, then you can make yourself a new tag to use.
Given a template in a file:
<%~ 'hello' %>
<%~ 'world' %>
<%~ '!' %>
Do:
string = File.read(file_path).gsub('<%~', '<%-%><%=')
print ERB.new(string, trim_mode: '-').result
And get:
hello
world
!
I'd love it if ERB would include this tag itself, but until then I'm doing it myself.