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Bisecting

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created September 12, 2012 · complexity basic · author Ryanking · version 7.0

Debugging Vim problems is a classic example of working with a system that is often too complex to sit back, stroke your beard, and reason your way through. Perhaps it is the "Hello World" of this class of problems?

So learn about bisecting, aka Binary Chop, aka Delta Debugging, aka Divide and Conquer.

When you do bisect, you have to start with a ☺ version and a ☠ version. Then you pick a point in between the two, and test to see if it's ☺ or ☠. After you've done that, you've moved the two closer together, so your search space is smaller.

When you are debugging, you have your "☠" version automatically, because you've got something that's not working currently.

An important test in Vim is to use vim -u NONE (which skips almost all of the startup sequence) to see if the problem reproduces there or not.

Generally it will not.

  • If debugging a .gvimrc problem, you might want to trygvim -U NONE after you determine the status of the lower-cased version.
  • Try vim -u NORC to see if loading plugins but not rc-files works.
  • Try vim --noplugin to see if loading rc-files but not plugins works.

Then the next step is a bit of a mess.

  1. vim's bairui has a plan for a script, bisectly, that will help you with it, but at the moment his batsuit is at the batdrycleaners, so we're batwaiting with bated batbreath.

In the mean-time, what you can do is:

mv ~/.vimrc ~/.vim /tmp && mkdir ~/.vim

Then do:

mv /tmp/.vimrc ~ && vim

And test the behavior again. (Note that tools like Pathogen and the Vim-Addon-Manager will complicate this first step a bit). If the problem reappears descend into your ~/.vimrc and comment out half of it (with something like 50%:.,$s/^/" ) and find the section that is causing the problem.

If it doesn't reappear, then move one of the pieces of /tmp/.vim/* back into ~/.vim/ and try again.

Keep doing this until you find the source of your problem.

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