use Cargo.lock file from rust-src if present

src/sysroot.rs

@@ -4,6 +4,7 @@ use std::hash::{Hash, Hasher};
 use std::path::PathBuf;
 use std::process::Command;
 use std::io::{self, Write};
+use std::fs;
 
 use rustc_version::VersionMeta;
 use tempdir::TempDir;
@@ -34,6 +35,7 @@ fn build(
     ctoml: &cargo::Toml,
     home: &Home,
     rustflags: &Rustflags,
+    src: &Src,
     hash: u64,
     verbose: bool,
 ) -> Result<()> {
@@ -66,6 +68,15 @@ version = "0.0.0"
             stoml.push_str(&profile.to_string())
         }
 
+        {
+            // Recent rust-src comes with a lockfile for libstd. Use it.
+            let lockfile = src.path().join("Cargo.lock");
+            if lockfile.exists() {
+                fs::copy(lockfile, &td.join("Cargo.lock")).chain_err(
+                    || "couldn't copy lock file",
+                )?;
+            }
+        }
         util::write(&td.join("Cargo.toml"), &stoml)?;
         util::mkdir(&td.join("src"))?;
         util::write(&td.join("src/lib.rs"), "")?;
@@ -187,7 +198,7 @@ pub fn update(
     let hash = hash(cmode, &blueprint, rustflags, &ctoml, meta)?;
 
     if old_hash(cmode, home)? != Some(hash) {
-        build(cmode, blueprint, &ctoml, home, rustflags, hash, verbose)?;
+        build(cmode, blueprint, &ctoml, home, rustflags, src, hash, verbose)?;
     }
 
     // copy host artifacts into the sysroot, if necessary