Hi Derrick and Junio!
Thanks for confirming my suspicions, that there isn't existing apparatus for doing this, and a new bit can be added as a flag. Thanks for the *pointers, I'll try working it out! With Antonio, in fact, since they'd need the same thing for implementing the opposite feature.
As for the justification, to elaborate on what I said in the opening mail:
This option would be pretty useful when used with diff options, to see how much two forks have diverged. I recently wanted to compare two long-running forks of a project and see how far they have diverged. I used the options: --simplufy-by-decoration --decorate-refs="refs/remotes/*/main" -p
But currently with this history simplification, the diffs for both divergent histories will be created against the last "relevant" (decorated) commit instead of the last common ancestor, which creates pretty useless diffs with a lot of intersection between them.
You're right that the option doesn't sound very useful when thought of in regards to history limiting by path, but IMO it's pretty useful in cases like these, when you use simplify to get an 'overview' of the history.
Also sorry for the blank/duplicate emails everyone! My email client seems to be misbehaving, largely because I tried to tinker with it :P
- Aiyee Bee