test(benches): support benches with optional dev dependency without MSRV

Cargo.toml

@@ -11,21 +11,31 @@ homepage = "https://github.com/statrs-dev/statrs"
 repository = "https://github.com/statrs-dev/statrs"
 edition = "2018"
 rust-version = "1.61"
-include = ["src/", "benches/", "README.md", "CHANGELOG.md", "LICENSE.md", ]
+include = ["src/", "README.md", "CHANGELOG.md", "LICENSE.md", ]
 
 [lib]
 name = "statrs"
 path = "src/lib.rs"
 
+[features]
+benches = [
+  "dep:criterion"
+  # this enables the `order_statistics` benchmark
+  # requiring `criterion` crate (higher rust-version as of commit c661687)
+  ]
+
 [dependencies]
 rand = "0.8"
 nalgebra = { version = "0.32", features = ["rand"] }
 approx = "0.5.0"
 num-traits = "0.2.14"
 
+# effectively an optional dev-dependency for benchmarking with criterion
+criterion = { version = "0.3.3", default-features = false, optional = true }
+
 [dev-dependencies]
-criterion = "0.3.3"
 
 [[bench]]
 name = "order_statistics"
 harness = false
+required-features = [ "benches" ]

README.md

@@ -36,6 +36,11 @@ statrs = "*" # replace * by the latest version of the crate.
 
 For examples, view [the docs](https://docs.rs/statrs/*/statrs/).
 
+## Features
+This crate has 1 feature. It is not for the lib provided by `statrs`.
+
+- `benches`: enables benchmarking; simulates optional dev-dependency on `criterion` (unsupported, see [`rust-lang/cargo#1596`](https://github.com/rust-lang/cargo/issues/1596)). As of commit c661687, requires higher MSRV than this package.
+
 ## Contributing
 
 Thanks for your help to improve the project!
@@ -102,4 +107,6 @@ Please allow at least one week before pinging issues/pr's.
 
 
 ## MSRV Policy
-Not all of our dependencies have an MSRV policy, but our CI will check that our MSRV !(https://img.shields.io/crates/msrv/statrs) is upheld.
+Not all of our dependencies have an MSRV policy, but our CI will check that our MSRV ![statrs MSRV badge](https://img.shields.io/crates/msrv/statrs) is upheld with depends via a `Cargo.lock.msrv` file (lockfile not distributed with `crates.io` package)
+The provided value for `rust-version` specifies what the `statrs` lib, libtests, and doctests require.
+

benches/order_statistics.rs

@@ -1,3 +1,4 @@
+#![cfg(feature = "benches")]
 extern crate rand;
 extern crate statrs;
 use criterion::{black_box, criterion_group, criterion_main, BatchSize, Criterion};