At least for Servo, should we add a check to tidy (
https://github.com/servo/servo/blob/master/python/tidy/servo_tidy/tidy.py)
immediately to catch the use of that fairly-unique formatting string, as we
do for a bunch of other random stuff? We can always exempt particular
files/folder where we think it shouldn't matter, but if it's that easy to
footgun we might as well put some simple guards in place.
- Lars
PS - welcome back!
On Fri, Jan 12, 2018 at 11:07 PM, Bobby Holley <bobbyhol...@gmail.com>
wrote:
> 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/7fb999d1d39418fd331284fab909df
> 076b967ac6/servo/ports/geckolib/Cargo.toml#21
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