"./x.py test mir-opt --bless" no longer works

[RalfJung]

Trying to bless mir-opt tests used to work fine on my Linux box, but some recent-ish change broke that:

Testing stage1 compiletest suite=mir-opt mode=mir-opt (x86_64-unknown-linux-gnu)

running 75 tests
...........................................................................

test result: ok. 75 passed; 0 failed; 0 ignored; 0 measured; 219 filtered out; finished in 267.97ms

Building stage1 library artifacts (x86_64-unknown-linux-gnu -> aarch64-unknown-linux-gnu)
    Finished `release` profile [optimized + debuginfo] target(s) in 0.07s
Testing stage1 compiletest suite=mir-opt mode=mir-opt (x86_64-unknown-linux-gnu -> aarch64-unknown-linux-gnu)

running 75 tests
...........................................................................

test result: ok. 75 passed; 0 failed; 0 ignored; 0 measured; 219 filtered out; finished in 470.37ms

Building stage1 library artifacts (x86_64-unknown-linux-gnu -> i686-pc-windows-msvc)
    Finished `release` profile [optimized + debuginfo] target(s) in 0.07s
Testing stage1 compiletest suite=mir-opt mode=mir-opt (x86_64-unknown-linux-gnu -> i686-pc-windows-msvc)

running 75 tests
...........................................................................

test result: ok. 75 passed; 0 failed; 0 ignored; 0 measured; 219 filtered out; finished in 499.16ms



error occurred: Failed to find tool. Is `xcrun` installed?

[RalfJung]

xcrun seems to be some macOS/Apple SDK tool.

mir-opt --bless does build std for a bunch of foreign targets, but that used to work, so something must have changed, and now xcrun is required. I'm not even sure where that error comes from, Failed to find tool does not occur as a string in the Rust repository...

Cc @saethlin

[RalfJung]

Maybe #122504 is related? xcrun appears in the discussion there, and this line here looks like it may be the one printing the error. Cc @jfgoog @NobodyXu

But this can't be a build script, right? bootstrap must be calling cc directly but then printing its errors without giving any context. Cc @rust-lang/bootstrap

[saethlin]

In general, the mir-opt test setup is designed to dodge any use of the cc crate, because the whole strategy of the mir-opt tests is oriented around not needing a C toolchain.

[saethlin]

I've posted a fix in #125369. It seems to work locally.