EEx compiler should provide a warning if a block is used without <%=

[halostatue]

As I described on elixir-lang-core, I had a bug that happened because my eyes slipped over the following bug:

<% if @password do %>
  Temporary password: <%= @password %>
<% else %>
  You will need to log in with your password.
<% end %>

The error is easily corrected:

<%= if @password do %>
  Temporary password: <%= @password %>
<% else %>
  You will need to log in with your password.
<% end %>

It seems to me that the EEx compiler should be able to provide a compile warning if a block is used when <% … %> is used instead of <%= … %>.

This would introduce one possible incompatibility with the current compiler:

<% somevar = for item <- list do %>
  <% if(item % 2 == 0, do: item * 2, else: item * 3) %>
<% end %>

This can be resolved by combining these into a single tag:

<% somevar = form item <- list do
  if(item % 2 == 0, do: item * 2, else: item * 3)
end %>

As requested, I’ve opened an issue.

[v0idpwn]

I also experienced some bugs thanks to this behaviour and it became an attention point for me, while I believe it shouldn't.
It is also not really clear in the docs whether you should use <% or <%=` and then this problem gets even more tricky for newcomers.