Create a potential conflict

[Mathias-Thomsen]

One of the most important reasons for using git is it's ability to merge files - it's the number one collaboration tool in our industry.

I makes sense to study and understand exactly what a git merge is.

Three-way-merge

Git uses (default) a standard three-way-merge when it merges files.

It's a simple algorithm.

• Two (2) files must be merged

• They have a (1) common ancestor - 2+1=3 - hence the name - three-way--merge

• Each contributing file is line-by-line compared against the common ancestor

• Change rules if one of the contributors has either deleted, added or altered a line in the file, then that change also goes into the result.

• If both contributors have different opinions about the same line - then it's a conflict

  Let's stir the pot and potentially create a conflict - which we can then solve.

• [ ] Copy this code into a terminal and run it - read the code first, can you predict what it does?

  git co master
  cd $(git root)
  mkdir merge-lab && cd "$_"
  
  cat <<EOF > poem.txt
  Eeny, meeny, miny, moe,
  Catch a tiger by the toe.
  If he hollers, let him go,
  Eeny, meeny, miny, moe.
  
  My mother told me to pick 
  the very best one and you - are - it!" 
  EOF
  
  git add poem.txt && git commit -m "I wrote a poem"
  git tag ancestor
  

  Open the file in an editor and see what it contains.

  Now we want to mimic a team of four developers hacking in the same file:

  @DenverCoder: First one branches out and changes tiger to lion @WWhite: Second one branches out and changes mother to father @JulesW: Third one branches out and changes tiger to turtle YOU: Change the exclamation mark in the end to a punctuation mark directly on the master.

  NOTE: The code snippet below makes use of the aliases you created earlier: co and root.

  # We'll be working in the same file - all the time
  POEM=$(git root)/merge-lab/poem.txt
  
  # Here comes dev1
  git co -b lion master
  sed -i 's/tiger/lion/g' $POEM
  git add $POEM && git commit --author="DenverCoder <denvercoder@dark.net>" -m "Tiger is lion"
  
  # Here comes dev2
  git co -b father master
  sed -i 's/mother/father/g' $POEM
  git add $POEM && git commit --author="WWhite <ww@bb.io>" -m "Mother is father"
  
  # Here comes dev3
  git co -b turtle master
  sed -i 's/tiger/turtle/g' $POEM
  git add $POEM && git commit --author="JulesW <jw@pulp.fiction>" -m "Tiger is turtle"
  
  # Here comes you
  git co master
  sed -i 's/\!/\./g' $POEM
  git add $POEM && git commit -m "! is ."
  

  What on earth is going on in that snippet?

  

  Usually when you've made changes to files and your workspace, the git icon will show a number of changes to be added og committed.

  

  But this time it's clean as a whistle - why is that?

  I'll give you a hint - Try to run this command - what are you looking at?

  git log --oneline --all --graph

[Mathias-Thomsen]

Done!