i128: enable support for 128-bit integers automatically

This adds a build.rs to byteorder that will set a conditional compilation
flag automatically if the current Rust compiler supports 128-bit integers.

This makes the i128 feature itself a no-op. We continue to allow the
feature to be supplied for backwards compatibility.

Addresses https://github.com/TyOverby/bincode/issues/250

1 files changed, 82 insertions, 0 deletions

diff --git a/build.rs b/build.rs
new file mode 100644
index 0000000..a2c8d18
--- /dev/null
+++ b/build.rs
@@ -0,0 +1,82 @@
+use std::env;
+use std::ffi::OsString;
+use std::process::Command;
+
+fn main() {
+    let version = match Version::read() {
+        Ok(version) => version,
+        Err(err) => {
+            eprintln!("failed to parse `rustc --version`: {}", err);
+            return;
+        }
+    };
+    enable_i128(version);
+}
+
+fn enable_i128(version: Version) {
+    if version < (Version { major: 1, minor: 26, patch: 0 }) {
+        return;
+    }
+
+    println!("cargo:rustc-cfg=byteorder_i128");
+}
+
+#[derive(Clone, Copy, Debug, Eq, PartialEq, PartialOrd, Ord)]
+struct Version {
+    major: u32,
+    minor: u32,
+    patch: u32,
+}
+
+impl Version {
+    fn read() -> Result<Version, String> {
+        let rustc = env::var_os("RUSTC").unwrap_or(OsString::from("rustc"));
+        let output = Command::new(&rustc)
+            .arg("--version")
+            .output()
+            .unwrap()
+            .stdout;
+        Version::parse(&String::from_utf8(output).unwrap())
+    }
+
+    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 })
+    }
+}