From 50d2b85841a3d1804b6c9a0197e5c9e07c008ee7 Mon Sep 17 00:00:00 2001
From: Taiki Endo <te316e89@gmail.com>
Date: Tue, 23 Feb 2021 18:51:08 +0900
Subject: [PATCH] Make loom dependency optional

---
 ci/crossbeam-epoch-loom.sh    | 2 +-
 crossbeam-epoch/Cargo.toml    | 8 +++++++-
 crossbeam-epoch/src/lib.rs    | 3 +++
 crossbeam-epoch/tests/loom.rs | 1 +
 crossbeam-utils/Cargo.toml    | 2 +-
 5 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/ci/crossbeam-epoch-loom.sh b/ci/crossbeam-epoch-loom.sh
index 094993cea..125785548 100755
--- a/ci/crossbeam-epoch-loom.sh
+++ b/ci/crossbeam-epoch-loom.sh
@@ -8,4 +8,4 @@ export RUSTFLAGS="-D warnings --cfg crossbeam_loom --cfg crossbeam_sanitize"
 # With MAX_PREEMPTIONS=2 the loom tests (currently) take around 11m.
 # If we were to run with =3, they would take several times that,
 # which is probably too costly for CI.
-env LOOM_MAX_PREEMPTIONS=2 cargo test --test loom --release -- --nocapture
+env LOOM_MAX_PREEMPTIONS=2 cargo test --test loom --release --features loom -- --nocapture
diff --git a/crossbeam-epoch/Cargo.toml b/crossbeam-epoch/Cargo.toml
index 1d404a1ed..7c302991d 100644
--- a/crossbeam-epoch/Cargo.toml
+++ b/crossbeam-epoch/Cargo.toml
@@ -32,6 +32,12 @@ alloc = []
 # of crossbeam may make breaking changes to them at any time.
 nightly = ["crossbeam-utils/nightly", "const_fn"]
 
+# Enable the use of loom for concurrency testing.
+#
+# This configuration option is outside of the normal semver guarantees: minor
+# versions of crossbeam may make breaking changes to it at any time.
+loom = ["loom-crate", "crossbeam-utils/loom"]
+
 [dependencies]
 cfg-if = "1"
 const_fn = { version = "0.4.4", optional = true }
@@ -42,7 +48,7 @@ memoffset = "0.6"
 # This configuration option is outside of the normal semver guarantees: minor
 # versions of crossbeam may make breaking changes to it at any time.
 [target.'cfg(crossbeam_loom)'.dependencies]
-loom = "0.4"
+loom-crate = { package = "loom", version = "0.4", optional = true }
 
 [dependencies.crossbeam-utils]
 version = "0.8"
diff --git a/crossbeam-epoch/src/lib.rs b/crossbeam-epoch/src/lib.rs
index 72877d7fe..99da911ba 100644
--- a/crossbeam-epoch/src/lib.rs
+++ b/crossbeam-epoch/src/lib.rs
@@ -65,6 +65,9 @@
 #![cfg_attr(feature = "nightly", feature(cfg_target_has_atomic))]
 #![cfg_attr(feature = "nightly", feature(const_fn))]
 
+#[cfg(crossbeam_loom)]
+extern crate loom_crate as loom;
+
 use cfg_if::cfg_if;
 
 #[cfg(crossbeam_loom)]
diff --git a/crossbeam-epoch/tests/loom.rs b/crossbeam-epoch/tests/loom.rs
index c0025fa45..4e56acdbc 100644
--- a/crossbeam-epoch/tests/loom.rs
+++ b/crossbeam-epoch/tests/loom.rs
@@ -1,6 +1,7 @@
 #![cfg(crossbeam_loom)]
 
 use crossbeam_epoch as epoch;
+use loom_crate as loom;
 
 use epoch::*;
 use epoch::{Atomic, Owned};
diff --git a/crossbeam-utils/Cargo.toml b/crossbeam-utils/Cargo.toml
index c3682be1f..3db56fff9 100644
--- a/crossbeam-utils/Cargo.toml
+++ b/crossbeam-utils/Cargo.toml
@@ -37,7 +37,7 @@ lazy_static = { version = "1.4.0", optional = true }
 # This configuration option is outside of the normal semver guarantees: minor
 # versions of crossbeam may make breaking changes to it at any time.
 [target.'cfg(crossbeam_loom)'.dependencies]
-loom = "0.4"
+loom = { version = "0.4", optional = true }
 
 [build-dependencies]
 autocfg = "1.0.0"