CARGO_RUSTC_CURRENT_DIR is causing forced rebuilds

[ehuss]

Problem

In the cargo repo, there is an environment override setting the CARGO_RUSTC_CURRENT_DIR environment variable:

cargo/.cargo/config.toml

Lines 7 to 10 in 79866e1

	[env]
	# HACK: Until this is stabilized, `snapbox`s polyfill could get confused
	# inside of the rust-lang/rust repo because it looks for the furthest-away `Cargo.toml`
	CARGO_RUSTC_CURRENT_DIR = { value = "", relative = true }

This is causing testsuite to always be considered dirty on my system. I am getting:

FsStatusOutdated(StaleItem(ChangedEnv 
{ var: "CARGO_RUSTC_CURRENT_DIR", 
previous: Some("/Users/eric/Proj/rust/cargo"), 
current: Some("/Users/eric/Proj/rust/cargo/") 
}

Note the difference in trailing /

Steps

1. Check out rust-lang/cargo
2. cargo test --test testsuite --no-run
3. cargo test --test testsuite --no-run -- This should build testsuite again.

Possible Solution(s)

No response

Notes

No response

Version

cargo 1.84.0-nightly (031049782 2024-11-01)
release: 1.84.0-nightly
commit-hash: 0310497822a7a673a330a5dd068b7aaa579a265e
commit-date: 2024-11-01
host: aarch64-apple-darwin
libgit2: 1.8.1 (sys:0.19.0 vendored)
libcurl: 8.7.1 (sys:0.4.74+curl-8.9.0 system ssl:(SecureTransport) LibreSSL/3.3.6)
ssl: OpenSSL 1.1.1w  11 Sep 2023
os: Mac OS 14.6.1 [64-bit]

[epage]

I'm not able to reproduce this on my system on stable

❯ cargo test --test testsuite --no-run
warning: ignoring `resolver` config table without `-Zmsrv-policy`
   Compiling cargo v0.85.0 (/home/epage/src/personal/cargo)
   Compiling cargo-util v0.2.17 (/home/epage/src/personal/cargo/crates/cargo-util)
   Compiling cargo-credential v0.4.7 (/home/epage/src/personal/cargo/credential/cargo-credential)
   Compiling crates-io v0.40.7 (/home/epage/src/personal/cargo/crates/crates-io)
   Compiling cargo-util-schemas v0.7.1 (/home/epage/src/personal/cargo/crates/cargo-util-schemas)
   Compiling rustfix v0.9.0 (/home/epage/src/personal/cargo/crates/rustfix)
   Compiling cargo-platform v0.1.9 (/home/epage/src/personal/cargo/crates/cargo-platform)
   Compiling cargo-credential-libsecret v0.4.10 (/home/epage/src/personal/cargo/credential/cargo-credential-libsecret)
   Compiling cargo-test-support v0.6.0 (/home/epage/src/personal/cargo/crates/cargo-test-support)
    Finished `test` profile [unoptimized + debuginfo] target(s) in 37.46s
  Executable tests/testsuite/main.rs (target/debug/deps/testsuite-b494325e491a8e98)

cargo on  clippy is 📦 v0.85.0 took 37s
❯ cargo test --test testsuite --no-run
warning: ignoring `resolver` config table without `-Zmsrv-policy`
    Finished `test` profile [unoptimized + debuginfo] target(s) in 0.10s
  Executable tests/testsuite/main.rs (target/debug/deps/testsuite-b494325e491a8e98)

[epage]

Reproduces on nightly

cargo on  clippy is 📦 v0.85.0
❯ cargo +nightly test --test testsuite --no-run
   Compiling cargo-util v0.2.17 (/home/epage/src/personal/cargo/crates/cargo-util)
   Compiling cargo v0.85.0 (/home/epage/src/personal/cargo)
   Compiling cargo-credential v0.4.7 (/home/epage/src/personal/cargo/credential/cargo-credential)
   Compiling crates-io v0.40.7 (/home/epage/src/personal/cargo/crates/crates-io)
   Compiling cargo-util-schemas v0.7.1 (/home/epage/src/personal/cargo/crates/cargo-util-schemas)
   Compiling rustfix v0.9.0 (/home/epage/src/personal/cargo/crates/rustfix)
   Compiling cargo-platform v0.1.9 (/home/epage/src/personal/cargo/crates/cargo-platform)
   Compiling cargo-test-support v0.6.0 (/home/epage/src/personal/cargo/crates/cargo-test-support)
   Compiling cargo-test-macro v0.3.3 (/home/epage/src/personal/cargo/crates/cargo-test-macro)
   Compiling cargo-credential-libsecret v0.4.10 (/home/epage/src/personal/cargo/credential/cargo-credential-libsecret)
    Finished `test` profile [unoptimized + debuginfo] target(s) in 32.26s
  Executable tests/testsuite/main.rs (target/debug/deps/testsuite-ffba239b1f3ab958)

cargo on  clippy is 📦 v0.85.0 took 32s
❯ cargo +nightly test --test testsuite --no-run
   Compiling cargo v0.85.0 (/home/epage/src/personal/cargo)
    Finished `test` profile [unoptimized + debuginfo] target(s) in 4.08s
  Executable tests/testsuite/main.rs (target/debug/deps/testsuite-ffba239b1f3ab958)

[epage]

Wonder if this was #14701

[epage]

My nightly isn't too old yet if I run out of master, I don't see it

cargo-14701 on  main is 📦 v0.1.0
❯ nargo check
warning: ignoring `resolver` config table without `-Zmsrv-policy`
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.11s
     Running `/home/epage/src/personal/cargo/target/debug/cargo -Zscript -Zmsrv-policy check`
    Checking cargo-14701 v0.1.0 (/home/epage/src/personal/dump/cargo-14701)
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.09s

cargo-14701 on  main is 📦 v0.1.0
❯ nargo check
warning: ignoring `resolver` config table without `-Zmsrv-policy`
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.10s
     Running `/home/epage/src/personal/cargo/target/debug/cargo -Zscript -Zmsrv-policy check`
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.04s

I even switched to 8315873 and didn't see it

[ehuss]

A reproduction without the cargo repo:

// src/main.rs
fn main() {
    println!("{:?}", option_env!("CARGO_RUSTC_CURRENT_DIR"));
}

# .cargo/config.toml
[env]
CARGO_RUSTC_CURRENT_DIR = { value = "", relative = true }

cargo build

[epage]

When I run nargo, I'm using the default rustc.

I wonder if rustc changed something about how it records paths...

[epage]

I switched my default rustc to nightly and still not reproducing this out of cargo master.

[epage]

   0.006690626s  INFO main:exec:compile_ws:compile:compile{unit=Unit { pkg: Package { id: PackageId { name: "cargo-147
01", version: "0.1.0", source: "/home/epage/src/personal/dump/cargo-14701" }, ..: ".." }, target: TargetInner { name:
"cargo-14701", doc: true, ..: with_path("/home/epage/src/personal/dump/cargo-14701/src/main.rs", Edition2021) }, profi
le: Profile { debuginfo: Resolved(LineTablesOnly), split_debuginfo: Some("unpacked"), ..: default_dev() }, kind: Host,
 mode: Check { test: false }, features: [], rustflags: [], rustdocflags: [], links_overrides: {}, artifact: false, art
ifact_target_for_features: None, is_std: false, dep_hash: 2202906307356721367 } force_rebuild=false}:prepare_target{fo
rce=false package_id=cargo-14701 v0.1.0 (/home/epage/src/personal/dump/cargo-14701) target="cargo-14701"}: cargo::core
::compiler::fingerprint:     dirty: FsStatusOutdated(StaleItem(ChangedEnv { var: "CARGO_RUSTC_CURRENT_DIR", previous:
Some("/home/epage/src/personal/dump/cargo-14701"), current: Some("/home/epage/src/personal/dump/cargo-14701/") }))
       Dirty cargo-14701 v0.1.0 (/home/epage/src/personal/dump/cargo-14701): the environment variable CARGO_RUSTC_CURR
ENT_DIR changed
     Running `CARGO=/home/epage/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/cargo CARGO_BIN_NAME=cargo-147
01 CARGO_CRATE_NAME=cargo_14701 CARGO_MANIFEST_DIR=/home/epage/src/personal/dump/cargo-14701 CARGO_MANIFEST_PATH=/home
/epage/src/personal/dump/cargo-14701/Cargo.toml CARGO_PKG_AUTHORS='' CARGO_PKG_DESCRIPTION='' CARGO_PKG_HOMEPAGE='' CA
RGO_PKG_LICENSE='' CARGO_PKG_LICENSE_FILE='' CARGO_PKG_NAME=cargo-14701 CARGO_PKG_README='' CARGO_PKG_REPOSITORY='' CA
RGO_PKG_RUST_VERSION='' CARGO_PKG_VERSION=0.1.0 CARGO_PKG_VERSION_MAJOR=0 CARGO_PKG_VERSION_MINOR=1 CARGO_PKG_VERSION_
PATCH=0 CARGO_PKG_VERSION_PRE='' CARGO_PRIMARY_PACKAGE=1 CARGO_RUSTC_CURRENT_DIR=/home/epage/src/personal/dump/cargo-1
4701 LD_LIBRARY_PATH='/home/epage/src/personal/dump/cargo-14701/target/debug/deps:/home/epage/.rustup/toolchains/night
ly-x86_64-unknown-linux-gnu/lib' foo=bar /home/epage/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/rustc --c
rate-name cargo_14701 --edition=2021 src/main.rs --error-format=json --json=diagnostic-rendered-ansi,artifacts,future-
incompat --crate-type bin --emit=dep-info,metadata -C embed-bitcode=no -C debuginfo=line-tables-only -C split-debuginf
o=unpacked --check-cfg 'cfg(docsrs)' --check-cfg 'cfg(feature, values())' -C metadata=d0f79a6560e2ae7d -C extra-filena
me=-d0f79a6560e2ae7d --out-dir /home/epage/src/personal/dump/cargo-14701/target/debug/deps -C incremental=/home/epage/
src/personal/dump/cargo-14701/target/debug/incremental -L dependency=/home/epage/src/personal/dump/cargo-14701/target/
debug/deps`

Specifically

dirty: FsStatusOutdated(StaleItem(ChangedEnv { var: "CARGO_RUSTC_CURRENT_DIR", previous:
Some("/home/epage/src/personal/dump/cargo-14701"), current: Some("/home/epage/src/personal/dump/cargo-14701/") }))

yet the env variable we pass to rustc is different.

[epage]

Ah, this is specific to CARGO_RUSTC_CURRENT_DIR. We decided to not stabilized it in #13644 but I never removed the code. The [env] is setting it one way and then we are overriding it a different way.

I'll remove that code.

[weihanglo]

This is indeed related to #14701, and was pointed out as a caveat #14701 (comment).

[weihanglo]

If any "internal" environment Cargo sets for crates is set the [env] table, it would be captured in dep-info files. If values from [env] and from Cargo internal don't match, Cargo rebuilds.

I think it is generally a mistake to set Cargo internal envs, as they won't have any effect. We could do something to improve the situation,

• Warn if those are set.
• Filter out those when needed, like when fingerprint comparison.