rustc_private linker error when llvm-tools is not installed

[Noratrieb]

#![feature(rustc_private)]
extern crate rustc_driver;

fn main() {}

With the rustc-dev component but without the llvm-tools component:

error: linking with `cc` failed: exit status: 1
  |
  = note:  "cc" "-m64" "/tmp/nix-shell-24333-0/rustchPbv3V/symbols.o" "<1 object files omitted>" "-Wl,--as-needed" "-Wl,-Bdynamic" "<sysroot>/lib/rustlib/x86_64-unknown-linux-gnu/lib/librustc_driver-0f916e861b45e5f3.so" "-Wl,-Bstatic" "<sysroot>/lib/rustlib/x86_64-unknown-linux-gnu/lib/{libcompiler_builtins-*}.rlib" "-Wl,-Bdynamic" "-lLLVM-20-rust-1.87.0-nightly" "-ldl" "-lgcc_s" "-lutil" "-lrt" "-lpthread" "-lm" "-ldl" "-lc" "-B<sysroot>/lib/rustlib/x86_64-unknown-linux-gnu/bin/gcc-ld" "-fuse-ld=lld" "-Wl,--eh-frame-hdr" "-Wl,-z,noexecstack" "-L" "<sysroot>/lib/rustlib/x86_64-unknown-linux-gnu/lib" "-o" "a" "-Wl,--gc-sections" "-pie" "-Wl,-z,relro,-z,now" "-nodefaultlibs"
  = note: some arguments are omitted. use `--verbose` to show all linker arguments
  = note: rust-lld: error: unable to find library -lLLVM-20-rust-1.87.0-nightly
          collect2: error: ld returned 1 exit status
          

error: aborting due to 1 previous error

libLLVM is part of the llvm-tools component, so that is needed for linkage. It would be nice if rustc had a more specialized error message for this, as it's very confusing if you're not aware of this.

[xizheyin]

Hi, how difficult is this task and could I try it?

[lolbinarycat]

@xizheyin it's a simple diagnostic issue, so all that needs to be done is to detect this error, and print a hint message alongside it like "consider using rustup to add the llvm-tools component".

[Noratrieb]

I expect that detecting this error will be quite nontrivial to do nicely, and honestly I have no idea how to best do it. I only have a bunch of bad ideas on how to do it

[xizheyin]

@Noratrieb This makes a lot of sense, I've encountered this error a few times recently and it took a while of troubleshooting to realize that I didn't have llvm-tools installed. I need to know how to go about fixing the diagnosis first.

@lolbinarycat Thanks for your help. I'm going to read up on this first, as I have no experience related to fixing diagnostics.

[xizheyin]

@rustbot claim