`rust-analyzer +nightly` (and similar) should not set LD_LIBRARY_PATH

[jyn514]

Problem you are trying to solve

I am trying to reduce the number of spurious rebuilds that occur in rust-lang/rust itself. One such spurious rebuild happens when using rustup-managed rust-analyzer, in which case rustup sets LD_LIBRARY_PATH. See rust-lang/rust#138333 for more details about why that causes issues.

Solution you'd like

Rust-analyzer does not use rustc_private libraries, and my understanding is that their architecture is very specifically designed so that they will never need to (@rust-lang/rust-analyzer, can you confirm?). That means that rustup does not need to set LD_LIBRARY_PATH for that proxy.

In particular, the following should leave LD_LIBRARY_PATH unmodified:

• rust-analyzer (when rust-analyzer is a rustup-managed toolchain proxy)
• rust-analyzer +toolchain

these should still add rustc --print target-libdir to LD_LIBRARY_PATH:

• rustup run toolchain rust-analyzer
• cargo +nightly (and all other proxies)

Notes

(-zsh@pop-os) ~/src/rust3 spurious-llvm-rebuilds
; git log --oneline -n1 HEAD~
385970f0c1f (upstream/master, upstream/HEAD) Auto merge of #137655 - nnethercote:split-edges-iterator, r=nnethercote
; rustup --version
rustup 1.27.1 (54dd3d00f 2024-04-24)
info: This is the version for the rustup toolchain manager, not the rustc compiler.
info: The currently active `rustc` version is `rustc 1.87.0-nightly (00f245915 2025-02-26)`

[ChrisDenton]

Could you expand on the difference between rust-analyzer +toolchain and rustup run toolchain rust-analyzer? Why does one need LD_LIBRARY_PATH and the other one doesn't?

[jyn514]

rustup run toolchain is the general form, which can run any program, including non-proxied commands. for instance, rustup run nightly whoami just works: #3387 (and sometimes that's useful for "i have a cargo-foo extension in path that's not managed by rustup, but does depend on rustc_private": https://jyn.dev/rustc-driver/#a-digression-more-about-rustup-proxies). in every case where rustup run runs a command, it sets LD_LIBRARY_PATH, even for non-proxied commands. so i don't think rust-analyzer should be special there, especially since bootstrap doesn't ever use rustup run.

[Veykril]

We do depend on rustc crates when built in tree, and we also link against the rustc driver dylib iirc

[jyn514]

oh. well, never mind, then.