ripgrep: move minimum version to Rust stable

This also updates some code to make use of our more liberal versioning
requirement, including the use of crossbeam-channel instead of the MsQueue
from the older an unmaintained crossbeam 0.3. This does regrettably add
a sizable number of dependencies, however, compile times seem mostly
unaffected.

Closes #1019

build.rs

@@ -4,7 +4,6 @@ extern crate clap;
 extern crate lazy_static;
 
 use std::env;
-use std::ffi::OsString;
 use std::fs::{self, File};
 use std::io::{self, Read, Write};
 use std::path::Path;
@@ -19,22 +18,6 @@ use app::{RGArg, RGArgKind};
 mod app;
 
 fn main() {
-    // If our version of Rust has runtime SIMD detection, then set a cfg so
-    // we know we can test for it. We use this when generating ripgrep's
-    // --version output.
-    let version = rustc_version();
-    let parsed = match Version::parse(&version) {
-        Ok(parsed) => parsed,
-        Err(err) => {
-            eprintln!("failed to parse `rustc --version`: {}", err);
-            return;
-        }
-    };
-    let minimum = Version { major: 1, minor: 27, patch: 0 };
-    if version.contains("nightly") || parsed >= minimum {
-        println!("cargo:rustc-cfg=ripgrep_runtime_cpu");
-    }
-
     // OUT_DIR is set by Cargo and it's where any additional build artifacts
     // are written.
     let outdir = match env::var_os("OUT_DIR") {
@@ -199,63 +182,3 @@ fn formatted_doc_txt(arg: &RGArg) -> io::Result<String> {
 fn ioerr(msg: String) -> io::Error {
     io::Error::new(io::ErrorKind::Other, msg)
 }
-
-fn rustc_version() -> String {
-    let rustc = env::var_os("RUSTC").unwrap_or(OsString::from("rustc"));
-    let output = process::Command::new(&rustc)
-        .arg("--version")
-        .output()
-        .unwrap()
-        .stdout;
-    String::from_utf8(output).unwrap()
-}
-
-#[derive(Clone, Copy, Debug, Eq, PartialEq, PartialOrd, Ord)]
-struct Version {
-    major: u32,
-    minor: u32,
-    patch: u32,
-}
-
-impl Version {
-    fn parse(mut s: &str) -> Result<Version, String> {
-        if !s.starts_with("rustc ") {
-            return Err(format!("unrecognized version string: {}", s));
-        }
-        s = &s["rustc ".len()..];
-
-        let parts: Vec<&str> = s.split(".").collect();
-        if parts.len() < 3 {
-            return Err(format!("not enough version parts: {:?}", parts));
-        }
-
-        let mut num = String::new();
-        for c in parts[0].chars() {
-            if !c.is_digit(10) {
-                break;
-            }
-            num.push(c);
-        }
-        let major = num.parse::<u32>().map_err(|e| e.to_string())?;
-
-        num.clear();
-        for c in parts[1].chars() {
-            if !c.is_digit(10) {
-                break;
-            }
-            num.push(c);
-        }
-        let minor = num.parse::<u32>().map_err(|e| e.to_string())?;
-
-        num.clear();
-        for c in parts[2].chars() {
-            if !c.is_digit(10) {
-                break;
-            }
-            num.push(c);
-        }
-        let patch = num.parse::<u32>().map_err(|e| e.to_string())?;
-
-        Ok(Version { major, minor, patch })
-    }
-}