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0 pointsnicoburns19h ago0 comments

Incremental Rust builds are almost never minutes (on recentish hardware)

A quick measurement on my web browser project with almost 600 dependencies:

- A clean "cargo check" was 31s

- An incremental "cargo check" with a meaningful change was 1.5s

Building is a little slower:

- A clean "cargo build" was 56.01s

- An incremental "cargo build" was 4s

But I find that LLMs are mostly calling "check" on Rust code.

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That's on an Apple M1 Pro. The latest M4/M5 machines as ~twice as fast.

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amazingamazing19h ago

I mean i wouldnt call a 100% a little slower wrt check vs build. In any case, the more you change the longer the incremental check or build will take.

J_Shelby_J18h ago

1.5s for a massive project, on a laptop,like the OP said is still barely anything in the context of agentic coding. It’s less than a single percentage point of the total time in the loop, even if the agent has to compile multiple times.

This is cope.

I do give you that rust is more verbose and thus more token heavy. However that verbosity is meaningful and the LLM would have to spend tokens thinking about the code to understand less verbose languages. So I’d consider that a wash - in some cases it hurts and in some it helps.

amazingamazing18h ago

We don’t know how massive the project is, but in any case building and immediately building again of course will be fast. How fast is it if all files have a single line changed, for example refactoring a log message?

Not to mention we haven't even gotten to discussing tests.

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nicoburnsOP18h ago

Sure, but when we're talking single-digit seconds it feels not that significant regardless?

amazingamazing18h ago

My point is that it isn't necessarily that fast. It is relative to the amount of changes and where they were made. For a fair comparison you would also have to present the worst case incremental build time which approaches the full build time (this goes for Go too), which per your own example is nearly a minute for rust.

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amazingamazing19h ago

I mean i wouldnt call a 100% a little slower wrt check vs build. In any case, the more you change the longer the incremental check or build will take.

J_Shelby_J18h ago

This is cope.

amazingamazing18h ago

Not to mention we haven't even gotten to discussing tests.

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nicoburnsOP18h ago

Sure, but when we're talking single-digit seconds it feels not that significant regardless?

amazingamazing18h ago

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