Error on User Authentication not working - ruby-on-rails

Question

I have a sessions_helper file that finds a user and if the user is found logins to the application. However, if the user is not found, it should give an error.
module SessionsHelper
# Log a user in after authenticating, store in session
def log_in(user)
if user.id.nil?
format.html { redirect_to signin_path, notice: 'Invalid Email or password' }
format.json { head :no_content }
else
session[:user_id] = user.id
end
end
end
I have a sessions/unauth view.
<div class="col-md-4">
<div class="panel panel-default">
<div class="panel-heading">Log In!</div>
<div class="panel-body">
<%= form_for(:credentials, url: signin_path) do |f| %>
<div class="form-group">
<%= f.label :email%>
<%= f.email_field :email, class: 'form-control'%>
</div>
<div class="form-group">
<%= f.label :password%>
<%= f.password_field :password, class: 'form-control'%>
</div>
<%= submit_tag %>
<% end %>
</div>
</div>
</div>
This code allows user to login to app successfully, but if user is not found does not display an error on the application.

Answer 1

you need to include this into your view
<% if flash[:notice] %>
<div class="notice"><%= flash[:notice] %></div>
<% end %>
this code will display your error message.
read here

Answer 2

You've not published the flash message in the view.
--
Flash
The Rails Flash is a type of session variable used to store data generated in actions. It's means to give you the ability to call alerts / notices in either the view or layout.
There are 3 types of flash, although I think you can use as many as you wish:
notice
alert
error
When you call ... notice: 'Invalid Email or password' }, you're telling rails to populate the flash[:notice] object.
If you want to show this in your view, you need to invoke it, as following:
<div class="col-md-4">
<div class="panel panel-default">
<!-- Error -->
<%= flash[:notice] if flash[:notice] %>
<!-- Login -->
<div class="panel-heading">Log In!</div>
<div class="panel-body">
<%= form_for(:credentials, url: signin_path) do |f| %>
<div class="form-group">
<%= f.label :email%>
<%= f.email_field :email, class: 'form-control'%>
</div>
<div class="form-group">
<%= f.label :password%>
<%= f.password_field :password, class: 'form-control'%>
</div>
<%= submit_tag %>
<% end %>
</div>
</div>
</div>