Kdiff3 as Git mergetool and –auto pitfall

In Git, when merging you can sometimes observe the behavior when a conflict has been somehow auto-magically solved without any user interaction at all and without displaying resolution tool window. I have experienced this with commonly used Kdiff3 tool set up as the default mergetool. It turns out that Git has hardcoded --auto option when invoking Kdiff3. This option instructs Kdiff3 to perform merge automatically and silently and display the window only if it is not able to figure out conflict resolutions itself. My understanding is, that it is intended solely for trivial cases and most of the time the window is displayed anyway. However, I am writing this post obviously because such “feature” once has got me into trouble — the tool fixed conflict, but should not have and, of course, did it wrong. In my opinion it is undoubtedly better to always make the decision on your own, instead of relying on some not well known logic of the tool.

The solution is to define custom tool in .gitconfig with Kdiff3 executable and custom command line parameters. Here is the configuration which I use on Windows:

    tool = kdiff3NoAuto
    conflictstyle = diff3

[mergetool "kdiff3NoAuto"]
    cmd = C:/Program\\ Files\\ \\(x86\\)/KDiff3/kdiff3.exe --L1 \"$MERGED (Base)\" --L2 \"$MERGED (Local)\" --L3 \"$MERGED (Remote)\" -o \"$MERGED\" \"$BASE\" \"$LOCAL\" \"$REMOTE\"

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