claude
e94c46f2ec
CI / shellcheck + selftests (pull_request) Successful in 1m21s
Review finding on #13, and the last change to this function. A typo'd variable name on a line that HAS its `|| exit 2` guard — `$CONTNET_B` for `$CONTENT_B` — fails in EXPANSION, before the command runs, so neither the guard nor the ERR trap ever sees it. Under `set -u` that exits 1, which was the code meaning "measured, and the answer is mtime". Not a live defect: the probe references only set variables today, and the 1 gitdan-ci reports is a genuine measurement. The defect is that the answer codes and the error codes overlapped at all. Three rounds on this function each found a narrower way for a shell-generated 1 to be read as a measurement — an unguarded command, then a guarded line whose guard could not fire — and each was closed by narrowing the failure surface, which is a game with no last move. INACTIVE is now 3, and anything that is not 0 or 3 is NOT MEASURED. Bash generates 1, 2, 126, 127 and 128+n for its own errors and never 3, so "not an answer" is decided by a property of the shell rather than by an enumeration of the ways a step can go wrong. A step added later without a guard, or with a guard that cannot fire, lands on NOT MEASURED by construction. The guards and the trap stay, with their job restated: reporting rather than correctness. They put a failed step on 2 with both probe logs printed instead of on some incidental status — nicer to debug, and the same destination either way. The `set +e` bracket at the call site keeps its own note, since a `set -e` that cannot fire is the kind of thing a reader assumes works. The not-measured message now quotes the actual exit code, so the two ways to reach it are distinguishable in a log without reading this file. Red-proven with the reviewer's own mutation, A/B: with INACTIVE at 1 the typo reports `mode: off — resolves freshness by mtime`, a false measurement; at 3 it reports `mode: unmeasured — the probe exited 1`. All four paths re-verified — unmodified 4 assertions; env stripped inside the probe, measured INACTIVE with the mtime reason; a broken probe build, unmeasured via a guard; an unguarded `false`, unmeasured via the trap.
340 lines
17 KiB
Bash
Executable File
340 lines
17 KiB
Bash
Executable File
#!/usr/bin/env bash
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# Regression test for the single assumption this whole caching scheme rests
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# on: that a build running inside a hardlink clone cannot mutate the directory
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# it was cloned from.
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#
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# That assumption is FALSE for a plain `cp -al`. Measured, and asserted below
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# as an explicit control: build in a raw `cp -al` clone and the source's
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# `.fingerprint/<unit>/dep-*` (under CARGO_UNSTABLE_CHECKSUM_FRESHNESS),
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# `build/<pkg>/output`, `build/<pkg>/out/**` and `deps/*.d` all change,
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# because Cargo and build scripts write those with a plain truncating write
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# rather than the write-then-rename Cargo uses for real artifacts.
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#
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# The consequence is not a slow build, it is a wrong one: a PR clone rewrites
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# the base's dep-info to describe the PR's sources while the base's cache
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# still holds the artifact built from the base's sources; once the PR merges,
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# the base's next run finds the checksums match its (now merged) sources,
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# reports `Fresh`, and links a binary built from the pre-merge code.
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#
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# cache-lib.sh's unshare_mutable_paths() is what closes that, and this test is
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# what proves it stays closed. The control matters as much as the fix: a
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# scenario that passes for both would prove nothing.
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#
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# Needs a working cargo on PATH. Everything happens under a mktemp -d scratch
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# tree. Run by hand: bash scripts/hardlink-clone-selftest.sh
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set -euo pipefail
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script_dir=$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)
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. "$script_dir/cache-lib.sh"
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command -v cargo >/dev/null || { echo "SKIP: no cargo on PATH"; exit 0; }
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scratch=$(mktemp -d)
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trap 'rm -rf "$scratch"' EXIT
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pass_count=0
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fail() { echo "ASSERTION FAILED: $*" >&2; exit 1; }
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ok() { pass_count=$((pass_count + 1)); echo "PASS: $*"; }
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# Content hash of every file in a tree, keyed by relative path.
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snapshot_tree() { (cd "$1" && find . -type f -print0 | sort -z | xargs -0 -r sha1sum) 2>/dev/null; }
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# `diff` exits 1 when the trees differ, which is the expected case here and
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# must not trip `pipefail` — the difference IS the result.
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mutated_paths() {
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{ diff <(printf '%s' "$1") <(printf '%s' "$2") || true; } 2>/dev/null \
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| awk '/^[<>]/ { print $3 }' | sort -u
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}
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# A crate with a build script, because build-script OUT_DIR writes are one of
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# the two mutation families and are invisible without one.
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mkcrate() {
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local dir="$1"
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mkdir -p "$dir/src"
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cat > "$dir/Cargo.toml" <<'TOML'
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[package]
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name = "probe"
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version = "0.1.0"
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edition = "2021"
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[workspace]
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TOML
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cat > "$dir/build.rs" <<'RS'
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use std::{env, fs, path::PathBuf};
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fn main() {
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println!("cargo::rerun-if-changed=src/lib.rs");
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let out = PathBuf::from(env::var("OUT_DIR").unwrap());
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let src = fs::read_to_string("src/lib.rs").unwrap();
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fs::write(out.join("gen.txt"), format!("generated from {} bytes", src.len())).unwrap();
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}
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RS
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}
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crate_dir="$scratch/probe"
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mkcrate "$crate_dir"
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cd "$crate_dir"
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export CARGO_INCREMENTAL=0
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# Every assertion below reads cargo's own words out of a build log
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# (`Compiling libdep`, `Fresh probe`). A CI image that forces colour splices an
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# ANSI reset between the status word and the crate name, at which point every
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# one of those greps silently stops matching and the suite reports the
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# opposite of what happened — observed on gitdan-ci's runner image, where
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# scenario 2 failed while the log it printed plainly showed `Compiling libdep`.
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# Pin the format the assertions are written against.
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export CARGO_TERM_COLOR=never
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# Checksum freshness is where the worst failure lives (the dep-* file carries
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# per-source checksums and is rewritten in place). Only available on nightly;
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# without it the test still covers the build/ and *.d families.
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CONTENT_A='pub fn f() -> u32 { 1 }'
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CONTENT_B='pub fn f() -> u32 { 22222 } pub fn g() -> u32 { 7 }'
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# Probe the BEHAVIOUR, not the channel and not the flag. Two weaker probes
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# were tried against gitdan-ci's runner and each let the suite assert a
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# property the toolchain did not have:
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#
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# `cargo +nightly -V` — answers "did a proxy called with
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# +nightly exit 0". `-V`
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# short-circuits before `-Z` is
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# even parsed.
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# `cargo +nightly -Z checksum-freshness — answers "is this flag still
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# locate-project` accepted". 1.100.0-nightly
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# (2026-08-25) accepts it and does
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# not resolve freshness by content
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# anyway.
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#
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# The scenario at the end of this file depends on one thing and it is neither
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# of those: that changed content with an OLDER mtime rebuilds. Under mtime
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# freshness the correct answer is Fresh, so under mtime freshness that
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# scenario asserts a bug. So the probe simply performs that experiment, on its
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# own crate and its own target dir, with no clone anywhere near it — which is
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# also what makes it a control rather than a restatement of the scenario: the
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# probe establishes that the toolchain rebuilds on content, the scenario
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# establishes that a hardlink clone did not take that away.
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# THREE OUTCOMES, NOT TWO. An experiment that cannot tell a negative result
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# from a failed measurement is not settling the question, and the two are not
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# interchangeable here: "this toolchain resolves freshness by mtime" is a
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# statement about Cargo, while "a probe build failed" is a statement about this
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# machine. Collapsing them — which an earlier cut of this did, by returning
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# non-zero for both — makes a half-installed toolchain print a confident and
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# wrong explanation and quietly drop a scenario. The scenario still has to be
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# skipped in either case; what must not happen is the log claiming to know why.
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#
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# 0 content freshness measured ACTIVE — both builds ran, the backdated
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# rebuild recompiled
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# 3 measured INACTIVE — both builds ran, the backdated
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# rebuild reported Fresh
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# anything else NOT MEASURED — nothing was learned about the
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# toolchain
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#
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# THE ANSWER CODES ARE 0 AND 3, AND THE GAP IS THE MECHANISM. Bash produces 1
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# for an ordinary command failure, 2 for a usage error, 126/127 for a command
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# it could not run, 128+n for a signal, and — this is the one that matters —
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# 1 for an unbound-variable or other EXPANSION failure, which happens before
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# the command runs and is therefore invisible to a `||` guard and to an ERR
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# trap alike. It never produces 3. So "not an answer code" is decided by a
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# property of the shell rather than by an enumeration of the ways a step can
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# go wrong, and a step added later without a guard, or with a guard that
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# cannot fire, lands on NOT MEASURED by construction.
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#
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# That is the whole reason INACTIVE is not 1. It was, and three review rounds
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# on this function each found a narrower way for a shell-generated 1 to be read
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# as a measurement — an unguarded command, then a typo'd variable name on a
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# line that HAS its guard. Each was closed by narrowing the failure surface,
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# which is a game with no last move. Moving the answer off the codes bash can
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# generate ends it instead: there is no longer a mutation that turns an error
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# into an answer, only mutations that turn an error into a different error.
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#
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# The guards below stay, and so does the trap, but their job is now reporting
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# rather than correctness: they make a failed step land on 2 with its logs
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# printed instead of on some incidental status, which is nicer to debug and
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# lands in the same place either way.
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#
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# One piece of that reporting layer is load-bearing and not obvious. A command
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# on the left of `||` — or in an `if` condition — runs with errexit suppressed,
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# and that suppression propagates into a subshell and is NOT undone by a
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# `set -e` inside it (measured on bash 5.3: an unguarded `false` there falls
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# through to `exit 0`). Calling with errexit disarmed at the site is the only
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# form that lets the subshell re-arm it; hence the `set +e` bracket. The ERR
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# trap is then required on top, because a bare `set -e` abort exits with the
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# FAILING COMMAND's status, and `false` gives 1.
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#
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# WHY NOT-MEASURED SKIPS RATHER THAN FAILS. The scenario it gates is the only thing in
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# this suite that depends on freshness mode; everything else still runs and
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# still catches real regressions. Failing instead would turn a statement about
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# one machine's toolchain into a red gate reading "the hardlink scheme is
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# broken" across the three repos consuming this action — the same category
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# error the three-state split exists to prevent, one level up. What would
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# change the answer is not-measured becoming the everyday CI outcome; it is not
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# (gitdan-ci reports a measured INACTIVE, by measurement).
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CHECKSUM_MODE="off"
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CHECKSUM_REASON="no nightly on PATH accepting -Z checksum-freshness"
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CARGO_BIN=(cargo)
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checksum_freshness_probe() {
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local d="$scratch/freshness-probe" t="$scratch/freshness-probe-target"
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mkcrate "$d" || return 2 # 2 is simply "not 0 and not 3"; see the header
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(
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set -e
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trap 'exit 2' ERR
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cd "$d" || exit 2
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printf '%s\n' "$CONTENT_A" > src/lib.rs || exit 2
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CARGO_TARGET_DIR="$t" cargo +nightly build -q > "$scratch/freshness-probe-warm.log" 2>&1 || exit 2
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printf '%s\n' "$CONTENT_B" > src/lib.rs || exit 2
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touch -d '@1000000000' src/lib.rs || exit 2
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CARGO_TARGET_DIR="$t" cargo +nightly build -v > "$scratch/freshness-probe.log" 2>&1 || exit 2
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# 3, not 1: see the header. This is the only statement in the subshell that
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# may report a measurement, and it is the only one that may exit 3.
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if grep -qE '^\s+Fresh probe' "$scratch/freshness-probe.log"; then exit 3; fi
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exit 0
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)
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}
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if cargo +nightly -Z checksum-freshness locate-project > /dev/null 2>&1; then
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export CARGO_UNSTABLE_CHECKSUM_FRESHNESS=true
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# Errexit off across the call, so the subshell can arm its own — see the
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# header. `probe_rc` is read before it is restored.
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probe_rc=0
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set +e
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checksum_freshness_probe
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probe_rc=$?
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set -e
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case "$probe_rc" in
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0)
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CARGO_BIN=(cargo +nightly)
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CHECKSUM_MODE="on"
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CHECKSUM_REASON=""
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;;
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3)
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unset CARGO_UNSTABLE_CHECKSUM_FRESHNESS
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CHECKSUM_REASON="this nightly accepts -Z checksum-freshness but resolves freshness by mtime"
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;;
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*)
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unset CARGO_UNSTABLE_CHECKSUM_FRESHNESS
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CHECKSUM_MODE="unmeasured"
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CHECKSUM_REASON="the probe exited ${probe_rc}, which is not one of its answer codes, so this was NOT MEASURED — this toolchain may or may not resolve freshness by content"
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# Loud, because the cost is silently lost coverage on a machine that
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# might have had it. The suite continues: everything else it asserts is
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# independent of freshness mode.
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echo "::warning::hardlink-clone-selftest: could not measure whether this toolchain resolves freshness by content — the probe exited ${probe_rc}. This is a failure to measure, not a finding about Cargo."
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tail -n 15 "$scratch/freshness-probe-warm.log" "$scratch/freshness-probe.log" 2>/dev/null | sed 's/^/ /' >&2 || true
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;;
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esac
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fi
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cd "$crate_dir"
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echo "=== checksum-freshness mode: ${CHECKSUM_MODE}${CHECKSUM_REASON:+ — ${CHECKSUM_REASON}} ==="
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build_base() {
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local dir="$1"
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printf '%s\n' "$CONTENT_A" > src/lib.rs
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CARGO_TARGET_DIR="$dir" "${CARGO_BIN[@]}" build -q
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}
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echo
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echo "=== control: a raw \`cp -al\` clone DOES mutate its source ==="
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base_ctl="$scratch/base-ctl"; clone_ctl="$scratch/clone-ctl"
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build_base "$base_ctl"
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before=$(snapshot_tree "$base_ctl")
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cp -al "$base_ctl" "$clone_ctl"
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strip_cargo_locks "$clone_ctl" # locks alone are not the hazard under test
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printf '%s\n' "$CONTENT_B" > src/lib.rs
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CARGO_TARGET_DIR="$clone_ctl" "${CARGO_BIN[@]}" build -q
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after=$(snapshot_tree "$base_ctl")
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ctl_mutated=$(mutated_paths "$before" "$after")
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if [ -z "$ctl_mutated" ]; then
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fail "control produced no mutation — the test can no longer distinguish fixed from broken"
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fi
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ok "raw cp -al clone mutates the source ($(printf '%s\n' "$ctl_mutated" | wc -l) paths)"
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printf '%s\n' "$ctl_mutated" | sed 's/^/ /'
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# Reported, not asserted, and the distinction is the point. The control's job
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# is to prove the hazard exists at all, which the non-empty set above already
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# does; this line records WHICH families a given Cargo exhibits.
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#
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# `.fingerprint/*/dep-*` is the worst of them — it carries the per-source
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# checksums, so mutating it through a shared inode turns a hardlink clone into
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# silent stale-artifact reuse rather than a slow build. It was measured on
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# cargo 1.9x nightly (see unshare_mutable_paths in cache-lib.sh) and is NOT
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# reproduced on 1.100.0-nightly (2026-08-25), where the control mutates only
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# the build/ and *.d families. Failing on its absence would mean this suite
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# goes red whenever upstream stops doing something we never wanted it to do —
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# and it would go red in the CONTROL, where a failure reads as "the hazard is
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# gone" rather than "upstream changed". Nothing is lost by reporting it: the
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# fix scenario below asserts the source is byte-identical after a full rebuild
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# in the clone, which covers every family this Cargo has, named or not.
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if [ "$CHECKSUM_MODE" = "on" ]; then
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if printf '%s' "$ctl_mutated" | grep -q '\.fingerprint/.*/dep-'; then
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echo " note: this cargo DOES rewrite .fingerprint/*/dep-* in place under checksum freshness"
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else
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echo " note: this cargo does NOT rewrite .fingerprint/*/dep-* in place; only the build/ and *.d families appear above"
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fi
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fi
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echo
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echo "=== fix: hardlink_clone_into() leaves the source byte-identical ==="
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base_fix="$scratch/base-fix"; clone_fix="$scratch/clone-fix"
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build_base "$base_fix"
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before=$(snapshot_tree "$base_fix")
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hardlink_clone_into "$base_fix" "$clone_fix" "selftest" || fail "hardlink_clone_into reported the destination already existed"
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# The clone's contract, asserted before anything builds in it: artifacts
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# share inodes (that is what makes the clone near-free), and every file Cargo
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# rewrites in place does not (that is what makes it sound). Checking after a
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# rebuild would prove nothing — the rebuild replaces those files anyway.
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shared=0; unshared=0
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while IFS= read -r f; do
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rel="${f#"$base_fix"/}"
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[ -e "$clone_fix/$rel" ] || continue
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if [ "$(stat -c '%i' "$f")" = "$(stat -c '%i' "$clone_fix/$rel")" ]; then
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case "$rel" in
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*/.fingerprint/*|*/build/*|*.d|.rustc_info.json)
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fail "mutable path still shares an inode with the source: $rel" ;;
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esac
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shared=$((shared + 1))
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else
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unshared=$((unshared + 1))
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fi
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done < <(find "$base_fix" -type f)
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[ "$shared" -gt 0 ] || fail "nothing is shared — the clone degenerated into a full copy"
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[ "$unshared" -gt 0 ] || fail "nothing was unshared — unshare_mutable_paths did not run"
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ok "fresh clone shares ${shared} artifact files and privately owns ${unshared} mutable ones"
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printf '%s\n' "$CONTENT_B" > src/lib.rs
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CARGO_TARGET_DIR="$clone_fix" "${CARGO_BIN[@]}" build -q
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after=$(snapshot_tree "$base_fix")
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fix_mutated=$(mutated_paths "$before" "$after")
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if [ -n "$fix_mutated" ]; then
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echo " still mutated:" >&2
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printf '%s\n' "$fix_mutated" | sed 's/^/ /' >&2
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fail "a build in the clone mutated the source through a shared inode"
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fi
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ok "no file in the source changed after a full rebuild in the clone"
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echo
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if [ "$CHECKSUM_MODE" = "on" ]; then
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echo "=== the whole point: the source's next build is still correct ==="
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# The source's cache holds artifacts built from CONTENT_A. Advance the
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# source to CONTENT_B (as a merge would) and rebuild in it. If the clone had
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# corrupted its dep-info, Cargo would report Fresh and keep the stale rlib.
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#
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# CHECKSUM-FRESHNESS ONLY, and the backdated mtime is why. Under checksum
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# freshness the dep-info file's per-source checksums decide, so a 2001
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# timestamp on changed content must still rebuild — the assertion below.
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# Under Cargo's ordinary MTIME freshness the same timestamp means the source
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# is older than the artifact, and reporting Fresh is the correct answer;
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# asserting otherwise asserts a bug. This scenario was written against a
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# machine with a nightly installed and, run without one, failed on that
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# correct answer.
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printf '%s\n' "$CONTENT_B" > src/lib.rs
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touch -d '@1000000000' src/lib.rs
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log="$scratch/rebuild.log"
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CARGO_TARGET_DIR="$base_fix" "${CARGO_BIN[@]}" build -v > "$log" 2>&1 || { cat "$log"; fail "rebuild in the source failed"; }
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if grep -qE '^\s+Fresh probe' "$log"; then
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fail "source declared its own crate Fresh against sources it has never built — stale-artifact reuse"
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fi
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ok "source correctly rebuilt its crate after advancing to the clone's content"
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else
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echo "=== skipped: the source's-next-build scenario needs content-based freshness ==="
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echo " reason: ${CHECKSUM_REASON}"
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fi
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echo
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echo "hardlink-clone-selftest: ${pass_count} assertions passed"
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