document and enforce minimum rustc requirement of 1.49.0

CHANGELOG.md

@@ -6,6 +6,7 @@
  - update `nng` dependency for optional `gaggle` feature
  - simplify `examples/umami` regex when parsing form
  - allow configuration of algorithm for allocating `GooseTask`s the same as `GooseTaskSet`s; `GooseTaskSetScheduler` becomes more generically `GooseScheduler`
+ - specify (and detect) minimum `rustc` requirement of `1.49.0`, due to `flume` dependency which in turn depends on `spinning_top` which uses `hint::spin_loop` which stabilized in `rustc` version `1.49.0
 
 ## 0.11.0 April 9, 2021
  - capture errors and count frequency for each, including summary in metrics report; optionally disable with `--no-error-summary`

Cargo.toml

@@ -41,6 +41,9 @@ default = ["reqwest/default-tls"]
 gaggle = ["nng"]
 rustls = ["reqwest/rustls-tls"]
 
+[build-dependencies]
+rustc_version = "0.3"
+
 [dev-dependencies]
 httpmock = "0.5"
 serial_test = "0.5"

README.md

@@ -22,6 +22,10 @@ Goose is a Rust load testing tool inspired by [Locust](https://locust.io/). User
   - [Gaggle: a distributed load test](https://www.tag1consulting.com/blog/show-me-how-flock-flies-working-gaggle-goose)
   - [Optimizing Goose performance](https://www.tag1consulting.com/blog/golden-goose-egg-compile-time-adventure)
 
+### Requirements
+
+- Minimum required `rustc` version is `1.49.0`: `goose` depends on [`flume`](https://docs.rs/flume) for communication between threads, which in turn depends on [`spinning_top`](https://docs.rs/spinning_top) which uses `hint::spin_loop` which stabilized in `rustc` version `1.49.0`. More detail in https://github.com/rust-lang/rust/issues/55002.
+
 ## Getting Started
 
 The [in-line documentation](https://docs.rs/goose/*/goose/#creating-a-simple-goose-load-test) offers much more detail about Goose specifics. For a general background to help you get started with Rust and Goose, read on.

build.rs

@@ -0,0 +1,22 @@
+use rustc_version::{version, Version};
+use std::io::{self, Write};
+use std::process::exit;
+
+fn main() {
+    // Goose can only be compiled with rustc version 1.49.0 or greater.
+    if version().expect("failed to determine rustc version")
+        < Version::parse("1.49.0").expect("failed to parse minimum required version")
+    {
+        writeln!(&mut io::stderr(), "goose dependency `flume` depends on `spinning_top` crate which requires rustc >= 1.49.0.").expect("failed to write to stderr");
+        writeln!(
+            &mut io::stderr(),
+            "detected rustc version: {}",
+            version().expect("failed to determine rustc version")
+        )
+        .expect("failed to write to stderr");
+        writeln!(&mut io::stderr(), "note: see issue #55002 <https://github.com/rust-lang/rust/issues/55002> for more information").expect("failed to write to stderr");
+        // Exit to avoid a more confusing error message and simplify debugging if
+        // trying to build Goose with an unsupported version of rustc.
+        exit(1);
+    }
+}