Survey pinpoints Rust compiler pain points

Overall, developers using Rust are satisfied with Rust compilation performance, but slow builds and rebuilds in several common workflows limit the productivity for a significant fraction of Rust users, according to the Rust Compiler Performance Survey, which was conducted the past two months by the Rust compiler performance working group.

Results of the survey, which received more than 3,700 responses, were reported in a September 10 blog post. To gauge overall sentiment, participants were asked to rate their satisfaction with build performance on a scale of zero (worst) to 10 (best). The average rating was six, with most respondents rating their experience with seven out of 10. “While it is great to see some developers being happy with the state we have today, it is clear that many people are not so lucky, and Rust’s build performance limits their productivity,” said Jakub Beranek on behalf of the working group. “Around 45% of respondents who answered that they are no longer using Rust said that at least one of the reasons why they stopped were long compile times.”

The survey found that the Rust build experience “differs wildly across users and workflows” and is not as clear-cut as “Rust builds are slow,” Beranek said. “We actually received many positive comments about users being happy with Rust build performance, and appreciation for it being improved vastly over the past several years to the point where it stopped being a problem.” But some survey respondents said the build performance of Rust was inferior to languages such as Go or Zig.

Challenges developers face with Rust build performance were not always as simple as slow compiler performance, said Beranek. “There are many diverse workflows with competing trade-offs, and optimizing build performance for them might require completely different solutions,” he said. “Some approaches for improving build performance can also be quite unintuitive. For example, stabilizing certain language features could help remove the need for certain build scripts or proc macros, and thus speed up compilation across the Rust ecosystem.”

Other findings of the Rust Compiler Performance Survey:

Waiting too long for an incremental rebuild after making a small source code change was by far the most common complaint in open answers received.

The incremental build of a single Rust compilation crate was too slow.

Several users mentioned that they would like to see Rust perform hot patching.

When Rust developers experience slow builds, it can be challenging to identify where exactly the compilation process is spending time, and what the bottleneck could be.

Beranek said that, while the Rust compiler is getting faster every year, the Rust compiler working group understands that many Rust developers need truly significant improvements to improve their productivity, rather than “just” incremental performance wins. The goal for the future is to stabilize long-standing initiatives that could improve build performance a lot, he said.