Massive slowdown with Rust implementation
After a lot of debugging I finally narrowed down the problem that is affecting my machine and it started to happen in librsvg 2.41.1.
I tried to bisect the issue, which was a complete NIGHTMARE, and I finally narrowed down one commit (RsvgLength::parse() - return a Result, not an RsvgLength): https://github.com/GNOME/librsvg/commit/e299ef0e285f7d1267528a38d8c41596b89da526.
But it seems that's not the only commit that is slowing down the whole library, merely the first that does so dramatically.
I wrote a small test to compare the previous implementation (strtod) with the new one (number_and_units), and it's twice as slow. Not to mention the fact that they are not functionally equivalent ("normal" is handled differently).
A simple way to experience this massive slowdown is using the FlatWoken icon theme: https://github.com/alecive/FlatWoken.
The way I experience the problem is running xfce4-appfinder, but you can easily reproduce the slowness in GNOME Shell too.