Gitにおける「エラー：チェックアウトによって追跡されていないワーキングツリーファイルが上書きされます」の対処法

Introduction

Git is a powerful version control system widely used by developers to track changes in their code. However, you might occasionally encounter the error message "error: untracked working tree files would be overwritten by checkout" when trying to switch branches. This error occurs when Git cannot safely perform a checkout operation because untracked files in your working directory would be overwritten.

In this lab, you will learn what causes this error, how to identify untracked files causing the conflict, and several methods to resolve the issue. By the end of this tutorial, you will understand how to handle this common Git error and maintain a clean Git workflow.

Skills Graph

Understanding the Git Checkout Conflict Scenario

Let's start by understanding what causes the "error: untracked working tree files would be overwritten by checkout" message in Git. This error typically occurs when you try to switch branches, but there are files in your current working directory that would be overwritten by the checkout operation.

Exploring Our Git Repository

First, let's navigate to our project directory and examine our Git repository:

cd ~/project/git-checkout-demo

Let's check the current status of our repository:

git status

You should see output similar to:

On branch main
nothing to commit, working tree clean

This means we're currently on the main branch and there are no uncommitted changes.

Listing Available Branches

Let's see what branches are available in our repository:

git branch

You should see output like:

  feature-branch
* main

The asterisk (*) indicates that we're currently on the main branch. The feature-branch is another branch in our repository.

Creating the Checkout Conflict

Now, let's create a situation that will cause the checkout conflict:

1. First, let's create a new file that has the same name as a file that exists in the feature-branch but not in our current branch:

echo "## My local changes to feature documentation" > feature.md

2. Check the status of our repository again:

git status

You should now see:

On branch main
Untracked files:
  (use "git add <file>..." to include in what will be committed)
        feature.md

nothing added to commit but untracked files present (use "git add" to track)

This output shows that feature.md is an untracked file in our working directory.

3. Now, let's try to switch to the feature-branch:

git checkout feature-branch

You should see the error message:

error: The following untracked working tree files would be overwritten by checkout:
        feature.md
Please move or remove them before you switch branches.
Aborting

This is the error we're learning to resolve! Git is telling us that switching to feature-branch would overwrite our untracked feature.md file, and it refuses to do so to prevent losing our changes.

In the next step, we'll learn how to identify all untracked files causing conflicts and understand different ways to resolve this issue.

Identifying Untracked Files and Understanding the Conflict

In the previous step, we created a scenario that triggered the "error: untracked working tree files would be overwritten by checkout" message. Now, let's understand how to properly identify all untracked files causing conflicts and why this error occurs.

Understanding Untracked Files in Git

An untracked file in Git is a file that exists in your working directory but isn't yet tracked by Git - meaning Git doesn't know about this file or its history. This typically happens when:

1. You create a new file but haven't added it to Git yet
2. You've explicitly told Git to ignore the file (via .gitignore)
3. You've cloned a repository that doesn't include the file

Why the Checkout Conflict Occurs

The checkout conflict occurs because:

1. You have an untracked file in your current branch (in our case, feature.md on the main branch)
2. The branch you're trying to switch to (in our case, feature-branch) already has a tracked version of that same file
3. Git refuses to overwrite your untracked file because you might lose changes that you intended to keep

Identifying All Untracked Files

Let's identify all untracked files in our working directory:

git status --untracked-files=all

The output should show:

On branch main
Untracked files:
  (use "git add <file>..." to include in what will be committed)
        feature.md

nothing added to commit but untracked files present (use "git add" to track)

For more detailed information about what's in the other branch, we can use:

git ls-tree -r feature-branch

This command lists all files tracked in the feature-branch. You should see feature.md and README.md in the output.

We can also compare what's different between the branches:

git diff --name-status main..feature-branch

The output should show:

A       feature.md

This indicates that feature.md was added in the feature-branch but doesn't exist in the main branch (at least not as a tracked file).

Understanding What Would Happen During Checkout

To better understand what would happen if we were to force the checkout, we can use:

git checkout --dry-run feature-branch

This command simulates a checkout without actually performing it. You'll see an error similar to:

error: The following untracked working tree files would be overwritten by checkout:
        feature.md
Please move or remove them before you switch branches.
Aborting

Now that we fully understand the conflict, in the next step, we'll explore multiple ways to resolve it.

Resolving the Checkout Conflict

Now that we understand the cause of the "error: untracked working tree files would be overwritten by checkout" message, let's explore multiple ways to resolve this issue. We'll try different approaches and see which one works best for our scenario.

Method 1: Stashing Untracked Files

One of the most convenient ways to resolve this issue is to use git stash to temporarily save your untracked files:

git stash push --include-untracked

You should see output similar to:

Saved working directory and index state WIP on main: [commit hash] Initial commit with README

Now, let's try checking out the feature branch:

git checkout feature-branch

This time, the checkout should succeed, and you should see:

Switched to branch 'feature-branch'

To verify we're on the feature branch and see its contents:

git branch
cat feature.md

You should see that the feature-branch has its own version of feature.md, which is different from the one we created.

If you want to get back your stashed changes, you can switch back to the main branch and apply the stash:

git checkout main
git stash apply

This would restore your untracked version of feature.md, potentially creating a conflict again.

Let's continue with the next method, so let's go back to our conflict state:

git checkout main
git stash drop ## This removes the stash we just created
echo "## My local changes to feature documentation" > feature.md

Method 2: Tracking the File Before Checkout

Another approach is to add the untracked file to Git and commit it before switching branches:

git add feature.md
git commit -m "Add my version of feature.md"

After committing, you can now check out the other branch:

git checkout feature-branch

You'll notice that Git seamlessly integrates the changes between branches. If there are conflicts, Git will prompt you to resolve them.

Let's go back to our main branch to try another method:

git checkout main

Let's reset our changes to get back to the conflict state:

git reset --hard HEAD~1 ## This removes the last commit
echo "## My local changes to feature documentation" > feature.md

Method 3: Using Git Clean to Remove Untracked Files

If your untracked files aren't important and can be deleted, you can use git clean to remove them:

## First, do a dry run to see what will be removed
git clean -n

You should see output indicating which files would be removed:

Would remove feature.md

If you're sure you want to delete these files, run:

git clean -f

This will remove the untracked files, and you should see:

Removing feature.md

Now you can check out the other branch without conflicts:

git checkout feature-branch

This approach is useful when you're sure you don't need the untracked files. If you're unsure, it's safer to use the stashing method.

Method 4: Temporarily Renaming the File

If you want to keep both versions of the file, you can rename your local version:

## First, go back to main and recreate our scenario
git checkout main
echo "## My local changes to feature documentation" > feature.md

## Rename the file
mv feature.md feature.md.local

Now, checking out the feature branch should work:

git checkout feature-branch

After checkout, you'll have both files:

• feature.md (from the feature branch)
• feature.md.local (your local version)

You can then compare them and merge the changes manually.

Congratulations! You've learned multiple methods to resolve the "error: untracked working tree files would be overwritten by checkout" in Git.

Best Practices to Avoid Checkout Conflicts

Now that you know how to resolve the "error: untracked working tree files would be overwritten by checkout" conflict, let's discuss some best practices to avoid encountering this error in the first place.

Understanding Git's Workflow

For effective Git usage, it's important to understand the basic workflow:

1. Working Directory: Where you modify files
2. Staging Area: Where you prepare changes for committing
3. Repository: Where committed changes are stored

Untracked files exist only in your working directory and are not yet part of Git's history.

Best Practices to Follow

1. Commit Your Changes Regularly

One of the simplest ways to avoid checkout conflicts is to regularly commit your changes:

## Add all changes to staging
git add .

## Commit changes with a meaningful message
git commit -m "Descriptive message about your changes"

Let's practice this with a new file:

## Go back to main branch
git checkout main

## Create a new file
echo "## New feature ideas" > ideas.md

## Add and commit the file
git add ideas.md
git commit -m "Add ideas for new features"

2. Use .gitignore for Files You Don't Want to Track

If there are files you never want to track (like build artifacts, temporary files, or environment-specific files), add them to a .gitignore file:

## Create a .gitignore file
echo "*.log" > .gitignore
echo "*.tmp" >> .gitignore
echo "node_modules/" >> .gitignore

## Add and commit the .gitignore file
git add .gitignore
git commit -m "Add .gitignore file"

3. Use Git Stash for Temporary Changes

If you're in the middle of changes but need to switch branches:

## Stash changes (including untracked files)
git stash push --include-untracked

## Switch branch
git checkout other-branch

## Later, when switching back
git checkout original-branch
git stash pop ## Apply and remove the most recent stash

4. Check What Will Change Before Checkout

Before switching branches, you can see what will change:

git checkout --dry-run another-branch

Or check files that differ between branches:

git diff --name-status main..feature-branch

Let's try a practice scenario:

## Create an untracked file
echo "## Temporary notes" > notes.txt

## See if it would cause a conflict with feature-branch
git checkout --dry-run feature-branch

Since notes.txt doesn't exist in feature-branch, you shouldn't see a conflict.

5. Use Worktrees for Working on Multiple Branches

For advanced users, Git worktrees allow you to check out multiple branches simultaneously in different directories:

## See current worktrees
git worktree list

## Add a new worktree
git worktree add ../feature-work feature-branch

This would create a new directory ../feature-work with the feature-branch checked out, allowing you to work on multiple branches without switching.

Handling Merge Conflicts

When you switch branches after committing changes, you might still encounter merge conflicts. These are different from checkout conflicts but are also important to handle:

## Resolve merge conflicts
git mergetool

## After resolving, complete the merge
git commit

By following these best practices, you'll minimize checkout conflicts and create a smoother Git workflow for yourself and your team.

Summary

In this lab, you learned how to handle the common Git error "error: untracked working tree files would be overwritten by checkout" through practical, hands-on exercises.

Here's what you accomplished:

1. Understanding the Problem: You created a conflict scenario and understood why Git prevents checkout operations when untracked files would be overwritten.

2. Identifying Untracked Files: You learned how to identify which files are causing checkout conflicts using commands like git status and git diff.

3. Resolving Checkout Conflicts: You explored multiple methods to resolve checkout conflicts:

   • Stashing untracked files with git stash push --include-untracked
   • Tracking and committing files before checkout
   • Removing untracked files with git clean
   • Temporarily renaming conflict files

4. Best Practices: You learned strategies to avoid checkout conflicts in the future:

   • Committing changes regularly
   • Using .gitignore for files you don't want to track
   • Utilizing git stash for temporary changes
   • Checking what will change before checkout
   • Using Git worktrees for advanced workflows

These skills will help you maintain a clean and efficient Git workflow, minimize disruptions, and collaborate more effectively with other developers. Remember that proper version control practices are fundamental to successful software development, and understanding how to handle common Git errors is an essential skill for any developer.