Display more useful error if Rust version too old

Closes #232

Cargo.lock

@@ -347,6 +347,7 @@ dependencies = [
  "miniz_oxide 0.3.6 (registry+https://github.com/rust-lang/crates.io-index)",
  "rayon 1.3.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "rgb 0.8.17 (registry+https://github.com/rust-lang/crates.io-index)",
+ "rustc_version 0.2.3 (registry+https://github.com/rust-lang/crates.io-index)",
  "stderrlog 0.4.3 (registry+https://github.com/rust-lang/crates.io-index)",
  "wild 2.0.3 (registry+https://github.com/rust-lang/crates.io-index)",
  "zopfli 0.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -403,11 +404,32 @@ name = "rgb"
 version = "0.8.17"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 
+[[package]]
+name = "rustc_version"
+version = "0.2.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "semver 0.9.0 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
 [[package]]
 name = "scopeguard"
 version = "1.1.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 
+[[package]]
+name = "semver"
+version = "0.9.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "semver-parser 0.7.0 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
+name = "semver-parser"
+version = "0.7.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
 [[package]]
 name = "stderrlog"
 version = "0.4.3"
@@ -594,7 +616,10 @@ dependencies = [
 "checksum redox_syscall 0.1.56 (registry+https://github.com/rust-lang/crates.io-index)" = "2439c63f3f6139d1b57529d16bc3b8bb855230c8efcc5d3a896c8bea7c3b1e84"
 "checksum redox_termios 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)" = "7e891cfe48e9100a70a3b6eb652fef28920c117d366339687bd5576160db0f76"
 "checksum rgb 0.8.17 (registry+https://github.com/rust-lang/crates.io-index)" = "a85b83fd629b0ce765f45316774fa6aaa95947fd74c8e4bbf3c6d1e349701d95"
+"checksum rustc_version 0.2.3 (registry+https://github.com/rust-lang/crates.io-index)" = "138e3e0acb6c9fb258b19b67cb8abd63c00679d2851805ea151465464fe9030a"
 "checksum scopeguard 1.1.0 (registry+https://github.com/rust-lang/crates.io-index)" = "d29ab0c6d3fc0ee92fe66e2d99f700eab17a8d57d1c1d3b748380fb20baa78cd"
+"checksum semver 0.9.0 (registry+https://github.com/rust-lang/crates.io-index)" = "1d7eb9ef2c18661902cc47e535f9bc51b78acd254da71d375c2f6720d9a40403"
+"checksum semver-parser 0.7.0 (registry+https://github.com/rust-lang/crates.io-index)" = "388a1df253eca08550bef6c72392cfe7c30914bf41df5269b68cbd6ff8f570a3"
 "checksum stderrlog 0.4.3 (registry+https://github.com/rust-lang/crates.io-index)" = "32e5ee9b90a5452c570a0b0ac1c99ae9498db7e56e33d74366de7f2a7add7f25"
 "checksum strsim 0.8.0 (registry+https://github.com/rust-lang/crates.io-index)" = "8ea5119cdb4c55b55d432abb513a0429384878c15dde60cc77b1c99de1a95a6a"
 "checksum termcolor 1.1.0 (registry+https://github.com/rust-lang/crates.io-index)" = "bb6bfa289a4d7c5766392812c0a1f4c1ba45afa1ad47803c11e1f407d846d75f"

Cargo.toml

@@ -15,6 +15,7 @@ homepage = "https://github.com/shssoichiro/oxipng"
 license = "MIT"
 name = "oxipng"
 repository = "https://github.com/shssoichiro/oxipng"
+build = "build.rs"
 version = "3.0.0"
 
 [badges]
@@ -60,6 +61,9 @@ version = "0.23"
 [target.'cfg(any(target_arch = "x86_64", target_arch = "aarch64"))'.dependencies]
 cloudflare-zlib = "^0.2.2"
 
+[build-dependencies]
+rustc_version = "0.2"
+
 [features]
 binary = [
     "clap",

build.rs

@@ -0,0 +1,11 @@
+use rustc_version::{version, Version};
+use std::process::exit;
+
+fn main() {
+    // This should match the version in Github Actions scripts and the Readme
+    const REQUIRED_VERSION: &str = "1.41.0";
+    if version().unwrap() < Version::parse(REQUIRED_VERSION).unwrap() {
+        eprintln!("oxipng requires rustc >= {}.", REQUIRED_VERSION);
+        exit(1);
+    }
+}