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Why is the Rust compiler so slow?

(sharnoff.io)
302 points Bogdanp | 1 comments | 26 Jun 25 19:29 UTC | HN request time: 0.203s | source
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taylorallred ◴[26 Jun 25 20:29 UTC] No.44390996[source]▶
So there's this guy you may have heard of called Ryan Fleury who makes the RAD debugger for Epic. The whole thing is made with 278k lines of C and is built as a unity build (all the code is included into one file that is compiled as a single translation unit). On a decent windows machine it takes 1.5 seconds to do a clean compile. This seems like a clear case-study that compilation can be incredibly fast and makes me wonder why other languages like Rust and Swift can't just do something similar to achieve similar speeds.
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1. weinzierl ◴[27 Jun 25 09:04 UTC] No.44395135[source]▶
This is sometimes called amalgamation and you can do it Rust as well. Either manually or with tools. The point is that apart from very specific niches it is just not a practical approach.

It's not that it can't be done but that it usually is not worth the hassle and our goal should be for compilation to be fast despite not everything being in one file.

Turbo Pascal is a prime example for a compiler that won the market not least because of its - for the time - outstanding compilation speed.

In the same vein, a language can be designed for fast compilation. Pascal in general was designed for single-pass compilation which made it naturally fast. All the necessary forward declarations were a pain though and the victory of languages that are not designed for single-pass compilation proofs that while doable it was not worth it in the end.