Standard Rust setup causes full rebuild every time. Setting g:ycm_rust_toolchain_root solves the problem

[JasonXJ]

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Issue Details

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So a few days ago I updated my rust toolchain with rustup update, and my cargo repo starts to do a full rebuild (instead of incremental build) every time. Often time, cargo build will also print "blocking waiting for file lock" at the beginning for a while. I was able to eventually solve this by manually setting g:ycm_rust_toolchain_root to the one that my system is using.

I believe the reason is that the YCM's standard rust setup is to download it own rust toolchain with a pinned version, and when this version does not match the one that your system is using, the rust-analyzer run by YCM and cargo build just keep erasing the cache and rebuild everything. Since full rebuild is slow, cargo build often time print "blocking waiting for file lock" because rust-analyzer is rebuilding everything.

I think YCM standard setup is probably a recipe for trouble. Maybe it is better to change the document to recommend pointing g:ycm_rust_toolchain_root to your system toolchain instead? And we can prompt the user when the required toolchain components (e.g. rust-src, rust-analyzer) is missing?

[puremourning]

The reason we pin a version is that we know that version works and passes our regression tests. We have bitter and extremely frustrating experience of rust analyser making incompatible changes and breaking things repeatedly, and often being in rustup "nightly" or whatever it's called.

We have the g:ycm_rust_toolchain_root for exactly your use case and if you use a version we don't test, then YMMV.

I'm not sure what we can fix here, tbh. We don't have the capacity to support wild versions of rust analyser if the server is frequently either broken or changing its api, but if you're a rust expert and have the capacity and inclination to help support us by maintaining the YCM rust integration and supporting users, then contributions are always extremely welcome.

The first step might be just to add an FAQ entry: https://github.com/ycm-core/YouCompleteMe/wiki/FAQ

but as for this issue, I don't really know what we can change.

[puremourning]

https://github.com/ycm-core/YouCompleteMe/wiki/FAQ#im-using-rust-with-ycm-and-this-causes-breaks-incremental-builds-of-my-project