Rails: link_to with do block doesn't work

Question

When 'link_to' is used without block it works perfectly:

<%= link_to "Ololo", {controller: "posts", action: "upvote", id: post.id}, method: :put, remote: true, class:"nav-link" %>

But when I try to use block it ends up with error:

        <%= link_to {controller: "posts", action: "upvote", id: post.id}, method: :put, remote: true, class:"nav-link" do %>
            <%= image_tag('icons/candy.svg', alt: "Candies", class:"rounded-circle icon-nav") %> 
            <%= post.get_upvotes.size %> 
        <% end %>

And here is the error message:

SyntaxError (/home/alex/test/app/views/application/_votes_exp.html.erb:5: syntax error, unexpected ':', expecting '}'
...r.append=  link_to {controller: controller_name, action: "up...
...                               ^
/home/alex/test/app/views/application/_votes_exp.html.erb:5: syntax error, unexpected ',', expecting '}'
...troller_name, action: "upvote", id: entity.id}, method: :put...
...                               ^
/home/alex/test/app/views/application/_votes_exp.html.erb:5: syntax error, unexpected tLABEL
...pvote", id: entity.id}, method: :put, class:"nav-link", remo...
...                               ^
/home/alex/test/app/views/application/_votes_exp.html.erb:5: syntax error, unexpected ',', expecting keyword_end
...method: :put, class:"nav-link", remote: true do @output_buff...
...                               ^
/home/alex/test/app/views/application/_votes_exp.html.erb:49: syntax error, unexpected keyword_ensure, expecting end-of-input):

So it seems like it doesn't understand literal hash, however, I'm too newbie to figure out what's wrong... Any help is appreciated!

PS: I can't remove literal hash, because link_to is messing up with css class (adds class as a part of address). Also I have to use older argument style instead of something like 'upvote_post_path' because controller name is represented by variable (in my example it is reduced for readability of the code)

UPDATE:

routes.rb

Rails.application.routes.draw do
  root to: "home#index"

  resources :posts do 
    member do
      put "upvote", to: "posts#upvote"
    end
  end
end

Answer 1

The opening brace in things like:

some_method { a: 'b' }

is ambiguous. The { could be opening a block as in a.each { ... } or it could be opening a hash literal. You think it is the latter but Ruby thinks it is the former and that's where the error comes from.

The easiest solution is to use method-calling-parentheses:

<%= link_to({controller: "posts", action: "upvote", id: post.id}, method: :put, remote: true, class:"nav-link") do %>
           ^--------------------------------------------------------------------------------------------------^

You could also use a variable to move the opening brace elsewhere:

<% upvote_post = { controller: 'posts', action: 'upvote', id: post.id } %>
<%= link_to upvote_post, method: :put, remote: true, class:"nav-link" do %>

This one:

link_to "Ololo", {controller: "posts", ... 

works fine because the first argument ( "Ololo", ) removes any ambiguity by telling Ruby that it is parsing an argument list.