---

yaml
---
r: 110541
b: refs/heads/master
c: cced02f
h: refs/heads/master
i:
  110539: eb79d44
v: v3

Author: alexcrichton

[refs]

@@ -1,5 +1,5 @@
 ---
-refs/heads/master: 5367c32c7ddb873babec89f739a936409d45476a
+refs/heads/master: cced02fcacfe4a6d1598e987003e00aa65713efb
 refs/heads/snap-stage1: e33de59e47c5076a89eadeb38f4934f58a3618a6
 refs/heads/snap-stage3: e263ef1df7b892ed29e53313565eb05ab75e52f4
 refs/heads/try: 597a645456b55e1c886ce15d23a192abdf4d55cf

trunk/src/librustc/metadata/loader.rs

@@ -317,15 +317,23 @@ impl<'a> Context<'a> {
     // read the metadata from it if `*slot` is `None`. If the metadata couldn't
     // be read, it is assumed that the file isn't a valid rust library (no
     // errors are emitted).
-    //
-    // FIXME(#10786): for an optimization, we only read one of the library's
-    //                metadata sections. In theory we should read both, but
-    //                reading dylib metadata is quite slow.
     fn extract_one(&mut self, m: HashSet<Path>, flavor: &str,
                    slot: &mut Option<MetadataBlob>) -> Option<Path> {
         let mut ret = None::<Path>;
         let mut error = 0;
 
+        if slot.is_some() {
+            // FIXME(#10786): for an optimization, we only read one of the
+            //                library's metadata sections. In theory we should
+            //                read both, but reading dylib metadata is quite
+            //                slow.
+            if m.len() == 0 {
+                return None
+            } else if m.len() == 1 {
+                return Some(m.move_iter().next().unwrap())
+            }
+        }
+
         for lib in m.move_iter() {
             info!("{} reading metadata from: {}", flavor, lib.display());
             let metadata = match get_metadata_section(self.os, &lib) {