Miri fails to prepare a sysroot (did not expect repo at $HOME to be bare)

[V0ldek]

I tried to run miri on an Ubuntu machine I haven't used miri on before. Installed the nightly toolchain, ran cargo +nightly miri run and received this:

I will run `"rustup" "component" "add" "rust-src"` to install the `rust-src` component for the selected toolchain. Proceed? [Y/n] Y
info: downloading component 'rust-src'
info: installing component 'rust-src'
Preparing a sysroot for Miri (target: x86_64-unknown-linux-gnu)... fatal error: failed to build sysroot: sysroot build failed; stderr:
error: failed to determine package fingerprint for build script for compiler_builtins v0.1.160 (/home/mat/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/compiler-builtins/compiler-builtins)

Caused by:
  failed to determine the most recently modified file in /home/mat/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/compiler-builtins/compiler-builtins

Caused by:
  failed to determine list of files in /home/mat/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/compiler-builtins/compiler-builtins

Caused by:
  did not expect repo at /home/mat to be bare

/home/mat is my $HOME directory. The /home/mat/.../compiler-builtins/compiler-builtins directory exists, I can ls it:

drwxrwxr-x  3 mat mat  4096 Apr 21 17:38 ./
drwxrwxr-x 12 mat mat  4096 Apr 21 17:38 ../
-rw-r--r--  1 mat mat 28266 Apr 21 17:38 build.rs
-rw-r--r--  1 mat mat  1912 Apr 21 17:38 Cargo.toml
-rw-r--r--  1 mat mat  6636 Apr 21 17:38 CHANGELOG.md
-rw-r--r--  1 mat mat  4206 Apr 21 17:38 configure.rs
-rw-r--r--  1 mat mat 10453 Apr 21 17:38 README.md
drwxrwxr-x  8 mat mat  4096 Apr 21 17:38 src/

My rustup and nightly are:

rustup +nightly -V
rustup 1.26.0 (2024-04-01)
info: This is the version for the rustup toolchain manager, not the rustc compiler.
info: The currently active `rustc` version is `rustc 1.97.0-nightly (66da6cae1 2026-04-20)`

Not sure what other information would help in diagnosing this.

EDIT:
Not sure if this is relevant but my $HOME is not, in fact, a git repository at all 😅

[RalfJung]

Uh, no idea, sorry.^^ Any idea what might be special about your machine, given that this works fine on many people's "normal" Linux and CI machines? Does regular Rust development with the same nightly toolchain work inside your home directory?

The actual "failed to determine package fingerprint" error is a cargo error. Cc @epage @weihanglo

[RalfJung]

Also, what project did you run cargo +nightly miri run in? As in, what's your working dir when you run that command, and what are the contents of that working dir?

[V0ldek]

I've been developing Rust on this machine for years now, both on stable and nightly toolchains, but I usually didn't use too much unsafe. Now I have a crate with some unsafe and wanted to run it under miri and this popped up.

The workdir is a "normal" Rust project with a single bin and lib target:

drwxrwxr-x 4 mat mat 4096 Apr 21 17:52 ./
drwxrwxr-x 6 mat mat 4096 Apr 21 17:21 ../
-rw-rw-r-- 1 mat mat 5773 Apr 20 20:57 Cargo.lock
-rw-rw-r-- 1 mat mat  285 Apr 21 17:30 Cargo.toml
-rw-rw-r-- 1 mat mat   16 Apr 20 21:17 .gitignore
-rw-rw-r-- 1 mat mat 1445 Apr 21 17:31 README.md
drwxrwxr-x 5 mat mat 4096 Apr 21 14:46 src/
drwxrwxr-x 3 mat mat 4096 Apr 21 17:41 target/

In general I'd believe the machine isn't special in any way, it's Ubuntu 24.04 LTS, no bells or whistles

[RalfJung]

If you do something like cargo new miritest && cd miritest && cargo +nightly miri run, does that produce the same error?

[bjorn3]

And if that works fine, you could try with --vcs none passed to the cargo new command.

[weihanglo]

your entire home directory is a git repo?

[RalfJung]

No:

Not sure if this is relevant but my $HOME is not, in fact, a git repository at all 😅

[V0ldek]

If you do something like cargo new miritest && cd miritest && cargo +nightly miri run, does that produce the same error?

It is the same result

mat@mat-TUM:~/src$ cargo new miritest && cd miritest && cargo +nightly miri run
    Creating binary (application) `miritest` package
note: see more `Cargo.toml` keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
Preparing a sysroot for Miri (target: x86_64-unknown-linux-gnu)... fatal error: failed to build sysroot: sysroot build failed; stderr:
error: failed to determine package fingerprint for build script for compiler_builtins v0.1.160 (/home/mat/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/compiler-builtins/compiler-builtins)

Caused by:
  failed to determine the most recently modified file in /home/mat/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/compiler-builtins/compiler-builtins

Caused by:
  failed to determine list of files in /home/mat/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/compiler-builtins/compiler-builtins

Caused by:
  did not expect repo at /home/mat to be bare

--vcs none does the same.

[V0ldek]

your entire home directory is a git repo?

No, although if it were then would this error be expected? Sounds like a crazy edge-case

[V0ldek]

I am able to MRE this now. Apparently all you need is three specific files/dirs in your $HOME: a file named HEAD, a directory named objects, and directory named refs. It seems something in the pipeline then thinks $HOME is a git repository?

Run a clean ubuntu, e.g. with docker run -it ubuntu:24.04 /bin/bash. Setup rust:

apt update && apt install rustup git g++
rustup default nightly && rustup component add miri

Reproduce the problematic $HOME:

cd $HOME
touch HEAD
mkdir refs
mkdir objects

Now this fails with the same "bare repo" error as I reported:

cargo new miritest && cd miritest && cargo miri run

If you remove any of the files then miri works as expected.

[weihanglo]

Reproduce the problematic $HOME:

cd $HOME
touch HEAD
mkdir refs
mkdir objects

This does looks like a vestigial Git bare repo to me.

Anyway, bare repos don't have git workdir and cannot be used in Cargo file listing and tracking. This logic in Cargo is overly aggressive and should be changed to a tracing::debug!.

@rustbot transfer cargo

@rustbot label +A-git +S-accepted +E-easy +C-bug

[weihanglo]

@rustbot label +A-git +S-accepted +E-easy +C-bug