better flash + error messages

We had a confused meta thread today when a screenshot of a user deleting their
account was thought to be a ban.

app/controllers/login_controller.rb

@@ -108,7 +108,7 @@ class LoginController < ApplicationController
     @found_user = User.where("email = ? OR username = ?", params[:email], params[:email]).first
 
     if !@found_user
-      flash.now[:error] = "Invalid e-mail address or username."
+      flash.now[:error] = "Unknown e-mail address or username."
       return forgot_password
     end
 

app/controllers/settings_controller.rb

@@ -15,16 +15,18 @@ class SettingsController < ApplicationController
       return redirect_to settings_path
     end
     unless @user.try(:authenticate, params[:user][:password].to_s)
-      flash[:error] = "Your password could not be verified."
+      flash[:error] = "Given password doesn't match account."
       return redirect_to settings_path
     end
 
     @user.delete!
+    disown_text = ""
     if params[:user][:disown].present?
+      disown_text = " and disowned your stories and comments."
       InactiveUser.disown_all_by_author! @user
     end
     reset_session
-    flash[:success] = "Your account has been deleted."
+    flash[:success] = "You have deleted your account your account#{disown_text}. Bye."
     return redirect_to "/"
   end
 

app/controllers/users_controller.rb

@@ -6,7 +6,12 @@ class UsersController < ApplicationController
   before_action :only_user_or_moderator, only: [:standing]
 
   def show
-    @showing_user = User.where(:username => params[:username]).first!
+    @showing_user = User.where(:username => params[:username]).first
+
+    if @showing_user.nil?
+      return render action: :not_found, status: 404
+    end
+
     @title = "User #{@showing_user.username}"
 
     if @user.try(:is_moderator?)

app/views/users/not_found.html.erb

@@ -0,0 +1,8 @@
+<div class="box wide">
+  <div class="legend">User not found</div>
+
+  <p>
+    If this user used to exist, they changed their username.
+    Check the <a href="/moderations?moderator=%28Users%29&what%5Busers%5D=users">moderation log</a>.
+  </p>
+</div>