Make serde_test build script buildable with older rustc

serde_test/build.rs

@@ -1,6 +1,6 @@
 use std::env;
 use std::process::Command;
-use std::str;
+use std::str::{self, FromStr};
 
 // The rustc-cfg strings below are *not* public API. Please let us know by
 // opening a GitHub issue if your build environment requires some way to enable
@@ -19,12 +19,30 @@ fn main() {
 }
 
 fn rustc_minor_version() -> Option<u32> {
- let rustc = env::var_os("RUSTC")?;
- let output = Command::new(rustc).arg("--version").output().ok()?;
- let version = str::from_utf8(&output.stdout).ok()?;
+ let rustc = match env::var_os("RUSTC") {
+ Some(rustc) => rustc,
+ None => return None,
+ };
+
+ let output = match Command::new(rustc).arg("--version").output() {
+ Ok(output) => output,
+ Err(_) => return None,
+ };
+
+ let version = match str::from_utf8(&output.stdout) {
+ Ok(version) => version,
+ Err(_) => return None,
+ };
+
  let mut pieces = version.split('.');
  if pieces.next() != Some("rustc 1") {
  return None;
  }
- pieces.next()?.parse().ok()
+
+ let next = match pieces.next() {
+ Some(next) => next,
+ None => return None,
+ };
+
+ u32::from_str(next).ok()
 }