Add special feature for inter-crate safe dev-related code reuse

ci/buildkite-pipeline.sh

@@ -140,7 +140,9 @@ wait_step() {
 }
 
 all_test_steps() {
-  command_step checks ". ci/rust-version.sh; ci/docker-run.sh \$\$rust_nightly_docker_image ci/test-checks.sh" 20 check
+  command_step checks1 ". ci/rust-version.sh; ci/docker-run.sh \$\$rust_nightly_docker_image ci/test-checks.sh" 20 check
+  command_step checks2 ". ci/rust-version.sh; ci/docker-run.sh \$\$rust_nightly_docker_image ci/test-dev-utils.sh check-bins" 15 check
+  command_step checks3 ". ci/rust-version.sh; ci/docker-run.sh \$\$rust_nightly_docker_image ci/test-dev-utils.sh check-all-targets" 15 check
   wait_step
 
   # Full test suite

ci/test-checks.sh

@@ -42,6 +42,8 @@ echo --- build environment
   cargo clippy --version --verbose
   $cargoNightly clippy --version --verbose
 
+  $cargoNightly hack --version --verbose
+
   # audit is done only with "$cargo stable"
   cargo audit --version
 
@@ -110,6 +112,8 @@ else
   _ scripts/cargo-for-all-lock-files.sh -- "+${rust_nightly}" sort --workspace --check
 fi
 
+_ scripts/check-dev-utils.sh tree
+
 _ scripts/cargo-for-all-lock-files.sh -- "+${rust_nightly}" fmt --all -- --check
 
 _ ci/do-audit.sh

ci/test-dev-utils.sh

@@ -0,0 +1,5 @@
+#!/usr/bin/env bash
+
+set -eo pipefail
+
+scripts/check-dev-utils.sh "$@"

scripts/check-dev-utils.sh

@@ -0,0 +1,84 @@
+#!/usr/bin/env bash
+
+set -eo pipefail
+cd "$(dirname "$0")/.."
+source ci/_
+# only nightly is used uniformly as we contain good amount of nightly-only code
+# (benches, frozen abi...)
+source ci/rust-version.sh nightly
+
+# There's a special common feature called `dev-utils` to
+# overcome cargo's issue: https://github.com/rust-lang/cargo/issues/8379
+# This feature is like `cfg(test)`, which works between crates.
+#
+# Unfortunately, this in turn needs some special checks to avoid common
+# pitfalls of `dev-utils` itself.
+#
+# Firstly, detect any misuse of dev-utils as normal/build dependencies.
+# Also, allow some exceptions for special purpose crates. This white-listing
+# mechanism can be used for core-development-oriented crates like bench bins.
+#
+# Put differently, use of dev-utils is forbidden for non-dev dependencies in
+# general. However, allow its use for non-dev dependencies only if its use
+# is confined under a dep. subgraph with all nodes being marked as dev-utils.
+
+# Add your troubled package which seems to want to use `dev-utils` as normal (not
+# dev) dependencies, only if you're sure that there's good reason to bend
+# dev-util's original intention and that listed package isn't part of released
+# binaries.
+# Note also that dev-utils-ci-marker feature must be added and all of its
+# dependencies should be edited likewise if any.
+declare dev_util_tainted_packages=(
+)
+
+mode=${1:-full}
+
+if [[ $mode = "tree" || $mode = "full" ]]; then
+  # Run against the entire workspace dep graph (sans $dev_util_tainted_packages)
+  dev_utils_excludes=$(for tainted in "${dev_util_tainted_packages[@]}"; do
+    echo "--exclude $tainted"
+  done)
+  # shellcheck disable=SC2086 # Don't want to double quote $dev_utils_excludes
+  _ cargo "+${rust_nightly}" tree --workspace -f "{p} {f}" --edges normal,build \
+    $dev_utils_excludes | (
+    if grep -E -C 3 -m 10 "[, ]dev-utils([, ]|$)"; then
+      echo "dev-utils must not be used as normal dependencies" > /dev/stderr
+      exit 1
+    fi
+  )
+
+  # Sanity-check that tainted packages has undergone the proper tedious rituals
+  # to be justified as such.
+  for tainted in "${dev_util_tainted_packages[@]}"; do
+    # dev-utils-ci-marker is special proxy feature needed only when using
+    # dev-utils code as part of normal dependency. dev-utils will be enabled
+    # indirectly via this feature only if prepared correctly
+    _ cargo "+${rust_nightly}" tree --workspace -f "{p} {f}" --edges normal,build \
+      --invert "$tainted" --features dev-utils-ci-marker | (
+      if grep -E -C 3 -m 10 -v "[, ]dev-utils([, ]|$)"; then
+        echo "$tainted: All inverted dependencies must be with dev-utils" \
+          > /dev/stderr
+        exit 1
+      fi
+    )
+  done
+fi
+
+# Detect possible compilation errors of problematic usage of `dev-utils`-gated code
+# without being explicitly declared as such in respective workspace member
+# `Cargo.toml`s. This cannot be detected with `--workspace --all-targets`, due
+# to unintentional `dev-utils` feature activation by cargo's feature
+# unification mechanism.
+# So, we use `cargo hack` to exhaustively build each individual workspace
+# members in isolation to work around.
+#
+# 1. Check implicit usage of `dev-utils`-gated code in non-dev (= production) code by
+# building without dev dependencies (= tests/benches) for each crate
+# 2. Check implicit usage of `dev-utils`-gated code in dev (= test/benches) code by
+# building in isolation from other crates, which might happen to enable `dev-utils`
+if [[ $mode = "check-bins" || $mode = "full" ]]; then
+  _ cargo "+${rust_nightly}" hack check --bins
+fi
+if [[ $mode = "check-all-targets" || $mode = "full" ]]; then
+  _ cargo "+${rust_nightly}" hack check --all-targets
+fi