Auto merge of #39518 - alexcrichton:update-cargo, r=arielb1

rustbuild: Use copies instead of hard links

The original motivation for hard links was to speed up the various stages of
rustbuild, but in the end this is causing problems on Windows (#39504).

This commit tweaks the build system to use copies instead of hard links
unconditionally to ensure that the files accessed by Windows are always
disjoint.

Locally this added .3s to a noop build, so it shouldn't be too much of a
regression hopefully!

Closes #39504

src/bootstrap/util.rs

@@ -20,6 +20,8 @@ use std::path::{Path, PathBuf};
 use std::process::Command;
 use std::time::Instant;
 
+use filetime::{self, FileTime};
+
 /// Returns the `name` as the filename of a static library for `target`.
 pub fn staticlib(name: &str, target: &str) -> String {
     if target.contains("windows") {
@@ -38,12 +40,18 @@ pub fn copy(src: &Path, dst: &Path) {
 
     // Attempt to "easy copy" by creating a hard link (symlinks don't work on
     // windows), but if that fails just fall back to a slow `copy` operation.
-    let res = fs::hard_link(src, dst);
-    let res = res.or_else(|_| fs::copy(src, dst).map(|_| ()));
+    // let res = fs::hard_link(src, dst);
+    let res = fs::copy(src, dst);
     if let Err(e) = res {
         panic!("failed to copy `{}` to `{}`: {}", src.display(),
                dst.display(), e)
     }
+    let metadata = t!(src.metadata());
+    t!(fs::set_permissions(dst, metadata.permissions()));
+    let atime = FileTime::from_last_access_time(&metadata);
+    let mtime = FileTime::from_last_modification_time(&metadata);
+    t!(filetime::set_file_times(dst, atime, mtime));
+
 }
 
 /// Copies the `src` directory recursively to `dst`. Both are assumed to exist

src/librustc_metadata/locator.rs

@@ -639,6 +639,34 @@ impl<'a> Context<'a> {
                                                          lib.display()));
                 continue;
             }
+
+            // Ok so at this point we've determined that `(lib, kind)` above is
+            // a candidate crate to load, and that `slot` is either none (this
+            // is the first crate of its kind) or if some the previous path has
+            // the exact same hash (e.g. it's the exact same crate).
+            //
+            // In principle these two candidate crates are exactly the same so
+            // we can choose either of them to link. As a stupidly gross hack,
+            // however, we favor crate in the sysroot.
+            //
+            // You can find more info in rust-lang/rust#39518 and various linked
+            // issues, but the general gist is that during testing libstd the
+            // compilers has two candidates to choose from: one in the sysroot
+            // and one in the deps folder. These two crates are the exact same
+            // crate but if the compiler chooses the one in the deps folder
+            // it'll cause spurious errors on Windows.
+            //
+            // As a result, we favor the sysroot crate here. Note that the
+            // candidates are all canonicalized, so we canonicalize the sysroot
+            // as well.
+            if let Some((ref prev, _)) = ret {
+                let sysroot = self.sess.sysroot();
+                let sysroot = sysroot.canonicalize()
+                                     .unwrap_or(sysroot.to_path_buf());
+                if prev.starts_with(&sysroot) {
+                    continue
+                }
+            }
             *slot = Some((hash, metadata));
             ret = Some((lib, kind));
         }

src/stage0.txt

@@ -13,4 +13,4 @@
 # released on `$date`
 
 rustc: beta-2017-02-01
-cargo: bfee18f73287687c543bda8c35e4e33808792715
+cargo: 407edef22e894266eb562618cba5ca9757051946