error: The following untracked working tree files would be overwritten by merge: - git-merge

Question

Thanks in advance for the help!
I was just finishing up chapter 6 of Rails Tutorial:
http://ruby.railstutorial.org/chapters/modeling-users#sec-6_4
I ran:
❤ git checkout master
Which went fine and then I ran:
❤ git merge modeling-users
And got the following error:
Updating fc9f72a..90d1ba6
error: The following untracked working tree files would be overwritten by merge:
app/models/user.rb
Please move or remove them before you can merge.
Aborting
This is my app/models/user.rb file:
# == Schema Information
#
# Table name: users
#
# id :integer not null, primary key
# name :string(255)
# email :string(255)
# created_at :datetime not null
# updated_at :datetime not null
#
class User < ActiveRecord::Base
attr_accessible :name, :email, :password, :password_confirmation
has_secure_password
before_save { |user| user.email = email.downcase }
validates :name, presence: true, length: { maximum: 50 }
VALID_EMAIL_REGEX = /\A[\w+\-.]+#[a-z\d\-.]+\.[a-z]+\z/i
validates :email, presence: true,
format: { with: VALID_EMAIL_REGEX },
uniqueness: { case_sensitive: false }
validates :password, presence: true, length: { minimum: 6 }
validates :password_confirmation, presence: true
end
And now my Sublime Text 2 user_spec.rb and application_helper_spec.rb files wont save and get the following errors:
Unable to save ~/code/rails_projects/sample_app/spec/models/user_spec.rb
user_spec.rb:
# == Schema Information
#
# Table name: users
#
# id :integer not null, primary key
# name :string(255)
# email :string(255)
# created_at :datetime not null
# updated_at :datetime not null
#
require 'spec_helper'
describe User do
before do
#user = User.new(name: "Example User", email: "user#example.com",
password: "foobar", password_confirmation: "foobar")
end
subject { #user }
it { should respond_to(:name) }
it { should respond_to(:email) }
it { should respond_to(:password_digest) }
it { should respond_to(:password) }
it { should respond_to(:password_confirmation) }
it { should respond_to(:authenticate) }
it { should be_valid }
describe "when name is not present" do
before { #user.name = " " * 51 }
it { should_not be_valid }
end
describe "when email format is valid" do
it "should be valid" do
addresses = %w[user#foo.COM A_US-ER#f.b.org frst.lst#foo.jp a+b#bax.cn]
addresses.each do |valid_address|
#user.email = valid_address
#user.should be_valid
end
end
end
describe "when email format is valid" do
it "should be valid" do
addresses = %w[user#foo.COM A_US-ER#f.b.org frst.lst#foo.jp a+b#baz.cn]
addresses.each do |valid_address|
#user.email = valid_address
#user.should be_valid
end
end
end
describe "when email address is already taken" do
before do
user_with_same_email = #user.dup
user_with_same_email.email = #user.email.upcase
user_with_same_email.save
end
it { should_not be_valid }
end
describe "when password is not present" do
before { #user.password = #user.password_confirmation = " " }
it { should_not be_valid }
end
describe "when password doesn't match confirmation" do
before { #user.password_confirmation = "mismatch" }
it { should_not be_valid }
end
describe "when password confirmation is nil" do
before { #user.password_confirmation = nil }
it { should_not be_valid }
end
describe "with a password that's too short" do
before { #user.password = #user.password_confirmation = "a" * 5 }
it { should be_invalid }
end
describe "return value of authenticate method" do
before { #user.save }
let(:found_user) { User.find_by_email(#user.email) }
describe "with valid password" do
it { should == found_user.authenticate(#user.password) }
end
describe "with invalid password" do
let(:user_for_invalid_password) { found_user.authenticate("invalid") }
it { should_not == user_for_invalid_password }
specify { user_for_invalid_password.should be_false }
end
end
end
and my application_helper_spec.rb file:
require 'spec_helper'
describe ApplicationHelper do
describe "full_title" do
it "should include the page title" do
full_title("foo").should =~ /foo/
end
it "should include the base title" do
full_title("foo").should =~ /^Ruby on Rails Tutorial Sample App/
end
it "should not include a bar for the home page" do
full_title("").should_not =~ /\|/
end
end
end

Answer 1

The error The following untracked working tree files would be overwritten by merge is happening because there is a app/models/user.rb file in the folder which is currently not added to any branch.
You can verify this by running the git status command; it should show an output similar to the following:
$ git status
# On branch master
#
# Untracked files:
# (use "git add <file>..." to include in what will be committed)
#
# app/models/user.rb
no changes added to commit (use "git add" and/or "git commit -a")
When you run git merge modeling-users, it is trying to merge the modeling-users branch to master branch. The modeling-users branch already has a copy of app/models/user.rb included in it. The merge command is making it overwrite the untracked version of the file with the one already within the modeling-users branch. Hence the error message to warn you about possibly losing something you want to keep.
As the git status message indicates, add the file to the master branch by running git add app/models/user.rb command.
The Unable to save ~/code/rails_projects/sample_app/spec/models/user_spec.rb message seems to be unrelated to this. Not much can be made out of the error message; perhaps there is more info somewhere else.
It might help to close the project and re-open it again. You may also want to try saving the files in a different editor (vim, perhaps?)