Dry run generate config with diff against current config

[RX14]

Currently there is a "dry run" option for pathvector, but it would be lovely to dry-run pathvector generate and have pathvector show the diff between the files which would have been generated and the current config. This would help to see the details of how the bird config changes when a new config or even a new pathvector version is used.

[natesales]

Pathvector stores the output of a dry run in cache-directory (defaults to /var/run/pathvector/cache/), so you can already diff the output:

$ pathvector gen --dry-run
INFO[0000] Starting Pathvector 6.3.2                    
INFO[0005] BIRD config validation passed                
INFO[0005] Processed 8 peers in 5s                      
$ diff /var/run/pathvector/cache/ /etc/bird/
Only in /etc/bird/: AS34553_LGAS34553NET.conf
diff /var/run/pathvector/cache/bird.conf /etc/bird/bird.conf
1c1
< # Update time: 1689659925
---
> # Update time: 1689659872
Only in /etc/bird/: envvars
Only in /etc/bird/: protocols.json

If there were to be config changes other than removing a peer, you'd see the individual line diffs too.

[RX14]

I didn't realise this, thanks!

Should this perhaps be documented somewhere?