[minitech]

> Further, using Rust as an example, even a project which takes 5 minutes to build cold only takes a second or two on a hot build thanks to caching of already-built artifacts.

So optimizing compile times isn’t worthwhile because we already do things to optimize compile times? Interesting take.

What about projects for which hot builds take significantly longer than a few seconds? That’s what I assumed everyone was already talking about. It’s certainly the kind of case that I most care about when it comes to iteration speed.

[timschmidt]

> So optimizing compile times isn’t worthwhile because we already do things to optimize compile times?

That seems strange to you? If build times constituted a significant portion of my development time I might think differently. They don't. Seems the compiler developers have done an excellent job. No complaints. The pareto principle and law of diminishing returns apply.

> What about projects for which hot builds take significantly longer than a few seconds?

A hot build of Servo, one of the larger Rust projects I can think of off the top of my head, takes just a couple seconds, mostly linking. You're thinking of something larger? Which can't be broken up into smaller compilation units? That'd be an unusual project. I can think of lots of things which are probably more important than optimizing for rare projects. Can't you?

[minitech]

The part that seems strange to me is your evidence that multi-minute compile times are acceptable being couple-second compile times. It seems like everyone actually agrees that couple-second iteration is important.

[timschmidt]

It seems like you might have missed a few words in this comment, I'm honestly having trouble parsing it to figure out what you're trying to say.

Just for fun, I kicked off a cold build of Bevy, the largest Rust project in my working folder at the moment, which has 830 dependencies, and that took 1m 23s. A second hot build took 0.22s. Since I only have to do the cold build once, right after cloning the repository which takes just as long, that seems pretty great to me.

Are you telling me that you need faster build times than 0.22s on projects with more than 800 dependencies?

[minitech]

This is the context:

> > The reason to care about compile time is because it affects your iteration speed. You can iterate much faster on a program that takes 1 second to compile vs 1 minute.

> Color me skeptical. I've only got 30 years of development under the belt, but even a 1 minute compile time is dwarfed by the time it takes to write and reason about code, run tests, work with version control, etc.

If your counterexample to 1-minute builds being disruptive is a 1-second hot build, I think we’re just talking past each other. Iteration implies hot builds. A 1-minute hot build is disruptive. To answer your earlier question, I don’t experience those in my current Rust projects (where I’m usually iterating on `cargo check` anyway), but I did in C++ projects (even trivial ones that used certain pathological libraries) as well as some particularly badly-written Node ones, and build times are a serious consideration when I’m making tech decisions. (The original context seemed language-agnostic to me.)

[timschmidt]

I see. Perhaps I wasn't clear. I've never encountered a 1 minute hot build in Rust, and given my experience with large Rust codebases like Bevy I'm not even sure such a thing exists in a real Rust codebase. I was pointing out that no matter how slow a cold build is, hot builds are fast, and are what matters most for iteration. It seems we agree on that.

I too have encountered slow builds in C++. I can't think of a language with a worse tooling story. Certainly good C++ tooling exists, but is not the default, and the ecosystem suffers from decades of that situation. Thankfully modern langs do not.