Merge conflicts why they happen in Git - Step-by-Step Execution

Process Flow - Merge conflicts why they happen

Start with Branch A and Branch B

↓

Both branches change same file

↓

Git tries to merge changes

↓

Check if changes overlap

↓

Merge conflict

↓

User resolves conflict

↓

Merge completes

This flow shows how merge conflicts happen when two branches change the same part of a file and Git cannot automatically combine them.

Execution Sample

Git

git checkout branchA
# edit file.txt: change line 3
git commit -am "Change line 3 in branchA"

git checkout branchB
# edit file.txt: change line 3 differently
git commit -am "Change line 3 in branchB"

git checkout branchA
git merge branchB

This sequence shows two branches changing the same line in a file, then trying to merge, causing a conflict.

Process Table

Step	Branch	File Change	Git Action	Result
1	branchA	Change line 3 in file.txt	Commit	Change saved in branchA
2	branchB	Change line 3 differently in file.txt	Commit	Change saved in branchB
3	branchA	No change	Checkout branchA	Switched to branchA
4	branchA + branchB	Conflicting changes on line 3	Merge branchB into branchA	Merge conflict detected
5	branchA	User edits file.txt to fix conflict	Resolve conflict manually	Conflict markers removed
6	branchA	No conflict	Commit merge	Merge completed successfully

💡 Merge stops at conflict because Git cannot auto-merge overlapping changes.

Status Tracker

Variable	Start	After Step 1	After Step 2	After Step 4	After Step 5	Final
file.txt line 3 content	Original line 3	Changed by branchA	Changed differently by branchB	Conflict markers added	Conflict resolved by user	Merged final content

Key Moments - 3 Insights

Why does Git stop the merge at step 4?

Git stops because both branches changed the same line differently, so it cannot decide which change to keep automatically (see execution_table step 4).

What does the user do to fix the conflict?

The user edits the file to choose or combine changes, removing conflict markers before committing (see execution_table step 5).

Why is it safe to commit after resolving conflicts?

Because the user manually fixed the overlapping changes, so the file is now consistent and ready to be merged (see execution_table step 6).

Visual Quiz - 3 Questions

Look at the execution table, what happens at step 4?

A User commits changes

B Git automatically merges changes

C Git detects a merge conflict

D Branch is deleted

💡 Hint

Check the 'Result' column at step 4 in the execution_table

At which step does the user fix the conflict?

A Step 2

B Step 5

C Step 4

D Step 6

💡 Hint

Look for 'User edits file.txt to fix conflict' in the Git Action column

If branchB changed a different line than branchA, what would happen at step 4?

A Merge completes automatically

B User must resolve conflict

C Merge conflict detected

D Merge is aborted

💡 Hint

Refer to the 'No' branch in the concept_flow after 'Check if changes overlap'

Concept Snapshot

Merge conflicts happen when two branches change the same part of a file.
Git tries to merge but stops if changes overlap.
User must manually fix conflicts by editing the file.
After resolving, commit to complete the merge.
Avoid conflicts by communicating and pulling often.

Full Transcript

Merge conflicts occur when two branches change the same line or part of a file differently. Git tries to merge changes automatically but stops if it cannot decide which change to keep. This is called a merge conflict. The user must open the file, see conflict markers, and edit the file to fix the conflict. After fixing, the user commits the changes to complete the merge. This process ensures the final file has consistent content from both branches.

Practice

1. Why do merge conflicts happen in Git?

easy

A. Because Git lost the commit history

B. Because the same part of a file was changed differently in two branches

C. Because the repository is too large

D. Because the branch names are the same

Solution

1. Step 1: Understand what causes merge conflicts

   Merge conflicts happen when Git tries to combine changes but finds different edits in the same part of a file from two branches.

2. Step 2: Identify the correct cause

   Only when the same lines are changed differently does Git stop and ask for help, causing a conflict.

3. Final Answer:

   Because the same part of a file was changed differently in two branches -> Option B

4. Quick Check:

   Same file part changed differently = merge conflict [OK]

Hint: Conflicts happen when edits overlap in the same file area [OK]

Common Mistakes:

• Thinking conflicts happen due to repo size
• Believing branch names cause conflicts
• Assuming commit history loss causes conflicts

2. Which Git command is used to start a merge that might cause conflicts?

easy

A. git push

B. git branch

C. git clone

D. git merge

Solution

1. Step 1: Identify the command that combines branches

   The git merge command is used to combine changes from one branch into another.

2. Step 2: Understand when conflicts occur

   Conflicts can happen during this merge if changes overlap, so git merge is the command that triggers this process.

3. Final Answer:

   git merge -> Option D

4. Quick Check:

   git merge starts merges that may conflict [OK]

Hint: Use git merge to combine branches and check for conflicts [OK]

Common Mistakes:

• Confusing git branch with git merge
• Using git clone to merge
• Thinking git push merges branches

3. Given two branches, master and feature, both changed the same line in app.txt. What will happen when you run git merge feature on master?

medium

A. Git will automatically merge without any issues

B. Git will delete app.txt

C. Git will create a merge conflict in app.txt

D. Git will ignore changes from feature branch

Solution

1. Step 1: Analyze the changes in both branches

   Both branches changed the same line in app.txt, so Git cannot decide which change to keep automatically.

2. Step 2: Understand Git's behavior on conflicting changes

   Git will stop the merge and mark app.txt as conflicted, requiring manual resolution.

3. Final Answer:

   Git will create a merge conflict in app.txt -> Option C

4. Quick Check:

   Same line changed differently = conflict created [OK]

Hint: Same line changed in both branches causes conflict [OK]

Common Mistakes:

• Assuming Git merges automatically always
• Thinking Git deletes files on conflict
• Believing Git ignores conflicting changes

4. You ran git merge feature and got a conflict. Which step should you take to fix it?

medium

A. Edit the file to choose which changes to keep, then commit

B. Rename the branch and try merging again

C. Run git push immediately

D. Delete the conflicting file and commit

Solution

1. Step 1: Understand how to resolve merge conflicts

   When a conflict occurs, you must open the conflicting file and decide which changes to keep or combine.

2. Step 2: Complete the merge after resolving conflicts

   After editing and saving the file, you add it and commit to finish the merge process.

3. Final Answer:

   Edit the file to choose which changes to keep, then commit -> Option A

4. Quick Check:

   Resolve conflicts by editing files, then commit [OK]

Hint: Fix conflicts by editing files before committing [OK]

Common Mistakes:

• Deleting files instead of resolving conflicts
• Pushing before resolving conflicts
• Renaming branches to fix conflicts

5. Two developers edited different parts of the same file in separate branches. When merging, why might Git NOT report a conflict?

hard

A. Because changes are in different lines and Git can merge automatically

B. Because Git ignores changes in one branch

C. Because the file was deleted in one branch

D. Because the branches have the same name

Solution

1. Step 1: Understand Git's merge behavior with non-overlapping changes

   If changes are made in different parts of a file, Git can combine them automatically without conflicts.

2. Step 2: Recognize why no conflict occurs

   Since the edits do not overlap, Git merges both changes smoothly.

3. Final Answer:

   Because changes are in different lines and Git can merge automatically -> Option A

4. Quick Check:

   Non-overlapping changes merge without conflict [OK]

Hint: Different lines changed merge automatically [OK]

Common Mistakes:

• Thinking Git ignores one branch's changes
• Assuming file deletion causes no conflict
• Believing branch names affect conflicts