TL;DR: To prevent code bloat, avoid {:?} in format strings for panic!(),
unreachable!(), error!(), warn!(), and info!() for Rust code that ships in
Gecko.Longer version: One nice thing about Rust is that you can #[derive(Debug)] for a type, and the compiler will generate a stringification method, which may in turn be inductively defined in terms of the Debug implementations of member types. This is great for logging and debugging, but the implementations can be quite large depending on the types involved. The linker will generally eliminate unused Debug implementations as dead code, but can't do so if they might be invoked in release builds. The most common way this seems to happen is in panic!() messages, where it can be tempting to include a stringified value to make the message more informative. It can also happen for the logging macros that don't get compiled out of release builds, which (at least for stylo) are info!(), warn!(), and error!() [1]. To demonstrate what's at stake here, this trivial patch eliminates more than 80K from libxul: https://github.com/servo/servo/pull/19756 Given how easy it is to mess this up and pull tons of unnecessary code into Firefox, and given that it's rather time-consuming to notice the problem and track down the culprit, I think we're best off categorically avoiding this pattern. Comments and alternative proposals welcome. bholley [1] https://searchfox.org/mozilla-central/rev/7fb999d1d39418fd331284fab909df076b967ac6/servo/ports/geckolib/Cargo.toml#21 _______________________________________________ dev-platform mailing list dev-platform@lists.mozilla.org https://lists.mozilla.org/listinfo/dev-platform
