Chris's Wiki :: blog/programming/Rust1BackwardIncompatibility

For a long time now, I've needed (or at least wanted) to simultaneously put a stress load on a test NFS fileserver and a stress CPU and memory load on another machine. Back in the old days on Linux, I would have done this by compiling the Linux kernel repeatedly, but in today's modern age the Linux kernel isn't big enough any more; it builds too fast and isn't big enough. I eventually settled on repeatedly building Firefox from source, partly because it's something I'm already familiar with. Specifically, on one of our Ubuntu 18.04 LTS machines I wound up building the then current release version of Firefox with a then current Rust version installed into a custom location with Rustup. Everything worked fine for a long time, and then one day I made the mistake of absently deciding to run 'rustup upgrade' on my custom Rust location. My Firefox builds immediately blew up with a series of Cargo errors and then later Rust errors.

I was unable to fix this and restore my Firefox build environment to a working state. In particular, it appears that older versions of Firefox (beyond some point I didn't try to determine precisely) can't be built with modern versions of Rust and Cargo (which is tightly coupled to Rust). You can to some extent patch Cargo.toml files so that Cargo will accept them, but the Rust errors were beyond my ability to deal with. My eventual solution was to obtain the current Firefox release, the current Rust release, and run Firefox's own 'build a custom virtual environment with all of your build dependencies' script. Someday this too will break, and in the mean time any performance measurements from before this transition aren't compatible with those after it, since I'm building different things with a different toolchain.

Leave a Comment