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A mergetool rant

diffconflicts is not special or noteworthy. That is true for the original sed shell script and the Vim/vimscript plugin. The core idea from this plugin is extremely simple and can be expressed as a sed one-liner. What is special is that most people and most mergetools don't recognize the following points.

The goal of this rant is to get all mergetools to recognize these ideas and to adopt this technique. Editor holy wars are not important; making merge conflict resolution easier is important.

  • Git provides a great deal of value by automatically resolving many conflicts. The fruit of this effort is only expressed in the file containing conflict markers.
  • It is difficult for a human to look at a file containing conflict markers. It is impossible to reliably spot subtle differences.
  • A human should never manually edit a file containing conflict markers. It is too easy to make mistakes. Eyeballing two hunks of changes, positioned vertically, is a fool's errand without tooling support.
  • Often a conflict resolution requires a mix of both left and right and not just all of left or all of right. Because it is difficult to carefully read and mentally compare each change many people simply choose the left or the right change which can result in the loss of a wanted change.
  • A diff between LOCAL and REMOTE is a bad approach. It bypasses all the work Git already did to automatically resolve conflicts and and forces the user to resolve those yet again but manually. It presents unecessary visual noise to the user by showing things that were already resolved to the user.

Mergetool Benchmarks

There's a few noteworthy things in the conflicts that the make-conflicts.sh script produces. These points can be used to benchmark the effectiveness of a given mergetool. More should be added.

  1. The bri1lig -> brillig conflict was automatically resolved. It should not be shown to the user.

  2. The m0me -> mome conflict was automatically resolved. It should not be shown to the user.

  3. The did -> Did conflict was automatically resolved. It should not be shown to the user.

  4. All conflicts in the second stanza were automatically resolved. They should not be shown to the user.

  5. The conflict on the first line is an "ours vs. theirs" situation. We only want theirs.

  6. The conflict on the third line is not an "ours vs. theirs" situation. We want changes from both:

    • Want the capitalization change from theirs.
    • Want the extra 'r' removal from ours.
    • Want the hanging punctuation change from ours.

  7. The conflict on the fourth line should be easily noticeable. We want the 'r'.