foo.diff

diff --git a/src/bootstrap/builder.rs b/src/bootstrap/builder.rs
index f93f3e72f8..10ad613329 100644
--- a/src/bootstrap/builder.rs
+++ b/src/bootstrap/builder.rs
@@ -831,14 +831,19 @@ impl<'a> Builder<'a> {
 
         // FIXME: Temporary fix for https://github.com/rust-lang/cargo/issues/3005
         // Force cargo to output binaries with disambiguating hashes in the name
-        let metadata = if compiler.stage == 0 {
+        let mut metadata = if compiler.stage == 0 {
             // Treat stage0 like special channel, whether it's a normal prior-
             // release rustc or a local rebuild with the same version, so we
             // never mix these libraries by accident.
-            "bootstrap"
+            "bootstrap".to_string()
         } else {
-            &self.config.channel
+            self.config.channel.to_string()
         };
+        match mode {
+            Mode::Std => metadata.push_str("std"),
+            Mode::Test => metadata.push_str("test"),
+            _ => {}
+        }
         cargo.env("__CARGO_DEFAULT_LIB_METADATA", &metadata);
 
         let stage;