Comment by nicoburns
2 days ago
UPDATE: tried compiling stalwart on my machine, and it took 14 minutes, with a really weird timing profile:
- 99% of the ~700 crates were done compiling in about a minute or 2 - RocksDB (a C++ dependency) was 2 minutes by itself - And then it took 10 minutes (ten!) just for the final binary at the end.
That's not normal for Rust code at all. Even large ones like Servo or Rustc or Zed.
UPDATE2: turns out they have LTO enabled by default. Disabling that brings the compile time down to 7 minutes. But that's still really unexpectedly slow.
Disabling codegen units = 1 speeds up the compilation further. But it’s still too many dependencies and too slow. The binary is pretty huge too.
> But it’s still too many dependencies and too slow.
I definitely agree that it's too slow. I just don't think the cause is "too many dependencies" because I've compiled Rust codebases with twice as many dependencies in half the time!
It seems to produce a 94MB binary. So it may be partly that there are some very big dependencies. But the amount of compilation time that ends up in the top-level crate (even with LTO disabled) also makes me feel like this must be triggering a compiler bug. Either that or using far too many generics.
I agree it's probably monomorphization (speculation without looking at it). Generic function parameters might be the root cause, but number of dependencies is a combinatorial multiplier.
I've hit compiler bugs that behave this way. Here's one from an LLVM upgrade [1]. The test case I discovered apparently took over 20 minutes to compile, up from 26 seconds on stable! Their value tracking algorithm was accidentally quadratic.
[1]: https://github.com/rust-lang/rust/issues/137909
> But it’s still too many dependencies and too slow. The binary is pretty huge too.
Ah yes, my never-ending crusade to raise awareness that the cost of free (as in effort) dependencies is bloat.
You can make useful tools that are tiny and compile fast [1], but it takes a lot of effort; exactly what developers don't want to spend.
[1]: Like https://github.com/parasyte/hd -- And I wrote about one of the tricks that it uses: https://blog.kodewerx.org/2023/04/improving-build-times-for-...