How to fix error: Merging is not possible because you have unmerged files in Git

First, understand what state your repository is in:

git status

Example output when in merge conflict state:

On branch main
You have unmerged paths.
  (fix conflicts and run "git commit")
  (use "git merge --abort" to abort the merge)

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   src/app.js
	both modified:   src/config.json

no changes added to commit (use "git add" and/or "git commit -a")

This tells you which files have conflicts that need resolution.

Use git diff to see what changes are in conflict:

# See all conflicts
git diff

# See conflicts in a specific file
git diff src/app.js

You can also view which files are conflicted:

# List only unmerged files
git diff --name-only --diff-filter=U

This helps you understand what changes need to be reconciled before proceeding.

Open each conflicted file and look for conflict markers:

<<<<<<< HEAD
// Your current branch's version
const port = 3000;
=======
// The incoming branch's version
const port = 8080;
>>>>>>> feature-branch

To resolve:
1. Decide which version to keep (or combine both)
2. Remove all conflict markers (<<<<<<<, =======, >>>>>>>)
3. Save the file

Example resolution (keeping port 8080):

const port = 8080;

Using VS Code or your editor:
Most modern editors detect conflict markers and provide clickable options:
- "Accept Current Change" (keep HEAD version)
- "Accept Incoming Change" (keep the other branch)
- "Accept Both Changes" (combine both)
- "Compare Changes" (see side-by-side diff)

If you want to accept one side's changes completely:

Accept your current branch's version (discard incoming):

git checkout --ours path/to/file.js

Accept the incoming branch's version (discard yours):

git checkout --theirs path/to/file.js

For all conflicted files:

# Accept all of ours
git checkout --ours .

# Accept all of theirs
git checkout --theirs .

After using checkout, you still need to stage the files with git add.

After resolving conflicts, mark the files as resolved by staging them:

# Stage a specific resolved file
git add src/app.js

# Stage all resolved files
git add .

Verify all conflicts are resolved:

git status

You should now see:

On branch main
All conflicts fixed but you are still merging.
  (use "git commit" to conclude merge)

Changes to be committed:
	modified:   src/app.js
	modified:   src/config.json

Once all conflicts are resolved and staged, complete the merge:

git commit

Git will open your default editor with a pre-filled merge commit message:

Merge branch 'feature-branch' into main

# Conflicts:
#	src/app.js
#	src/config.json

Save and close the editor to complete the merge.

Or use a custom message:

git commit -m "Merge feature-branch: resolve config conflicts"

After this, you're out of the merge state and can proceed with new operations.

If you want to abandon the merge and go back to the state before it started:

git merge --abort

This will:
- Restore your working directory to the state before the merge
- Clear the merge state
- Discard any conflict resolutions you made

Verify the abort worked:

git status

You should see a clean working directory without merge conflicts.

Note: If you have uncommitted changes before the merge, --abort will try to restore them, but this may not always be possible. It's best to commit or stash changes before merging.

For complex conflicts, use a visual merge tool:

git mergetool

This launches your configured merge tool (vimdiff, meld, kdiff3, VS Code, etc.).

Configure a merge tool:

# Set VS Code as the merge tool
git config --global merge.tool vscode
git config --global mergetool.vscode.cmd 'code --wait $MERGED'

# Set meld as the merge tool
git config --global merge.tool meld

# List available tools
git mergetool --tool-help

After using mergetool:
Git automatically stages resolved files, but creates .orig backup files. Clean them up:

# Remove .orig files
find . -name "*.orig" -delete

# Or configure Git to not create them
git config --global mergetool.keepBackup false

If you made a mess of resolving conflicts and want to start fresh:

# Re-checkout the file with conflict markers
git checkout --conflict=merge path/to/file.js

This restores the original conflict markers so you can try resolving again.

Or use git restore (Git 2.23+):

# Restore to conflicted state
git restore --conflict=merge path/to/file.js

# Unstage a file without losing changes
git restore --staged path/to/file.js

This is useful when you accidentally removed the wrong code during conflict resolution.