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I did something similar a couple years ago. I needed to rewrite an entire repo's history so that I could reformat all the code _and_ modernize all the JS synta

I did something similar a couple years ago. I needed to rewrite an entire repo's history so that I could reformat all the code _and_ modernize all the JS syntax throughout every commit in the repo's history (dating back to 2013). I started with `filter-branch`, but found it way too slow (especially on a corporate-controlled Windows machine, where starting up additional processes seems to have a lot of overhead). I concluded that I needed to run the entire filtering logic in a single process to avoid that overhead. Started writing my own with `pygit2`, but then found a repo called `pylter-branch` which did most of that same "loop through commits and reprocess" work for me - I just had to add a lot of additional logic on top for the specific reprocessing I wanted to do. Ended up being able to reprocess about 15K commits in around 4.5 hours. Given the amount of processing I was doing, that was pretty good. I did an extensive writeup [1] on the problem statement, investigation, and techniques I used if anyone's interested. [0] https://github.com/sergelevin/pylter-branch https://github.com/sergelevin/pylter-branch [1] https://blog.isquaredsoftware.com/2018/11/git-js-history-rewriting/ https://blog.isquaredsoftware.com/2018/11/git-js-history-rew...

gumby 6y ago
Why did your group want to do a refacctor like that retrospectively rather than just checking in those changes on a forward going basis?
- acemarke 6y ago
  Heh. It wasn't even the rest of my team - I'm the only one who cared enough to do anything about it :) Per the post, I wanted to auto-reformat the entire codebase, as well as codemod the JS source to update it to more modern syntax (ES modules instead of AMD, `const/let` instead of `var`, shorthand object literals, etc). But, that would have left most of the codebase history showing that the last commit touching a line was "MARK REFORMATTED ALL THE THINGS". Since I was rewriting the entire repo history to strip out all the junk files that were consuming space, which was going to create an entirely new alternate history anyway, I figured I might as well take advantage of the opportunity to redo all the source as well: https://blog.isquaredsoftware.com/2018/11/git-js-history-rewriting/#the-plan-grows https://blog.isquaredsoftware.com/2018/11/git-js-history-rew...
  - gumby 6y ago
    > But, that would have left most of the codebase history showing that the last commit touching a line was "MARK REFORMATTED ALL THE THINGS". Indeed, this is a good reason to do as you chose. I hadn't thought of it (even though I have done the same to a code base).

gumby 6y ago

Why did your group want to do a refacctor like that retrospectively rather than just checking in those changes on a forward going basis?

acemarke 6y ago
Heh. It wasn't even the rest of my team - I'm the only one who cared enough to do anything about it :) Per the post, I wanted to auto-reformat the entire codebase, as well as codemod the JS source to update it to more modern syntax (ES modules instead of AMD, `const/let` instead of `var`, shorthand object literals, etc). But, that would have left most of the codebase history showing that the last commit touching a line was "MARK REFORMATTED ALL THE THINGS". Since I was rewriting the entire repo history to strip out all the junk files that were consuming space, which was going to create an entirely new alternate history anyway, I figured I might as well take advantage of the opportunity to redo all the source as well: https://blog.isquaredsoftware.com/2018/11/git-js-history-rewriting/#the-plan-grows https://blog.isquaredsoftware.com/2018/11/git-js-history-rew...
- gumby 6y ago
  > But, that would have left most of the codebase history showing that the last commit touching a line was "MARK REFORMATTED ALL THE THINGS". Indeed, this is a good reason to do as you chose. I hadn't thought of it (even though I have done the same to a code base).