From e8e5eb58c0d6890f73ea01354e18f51b1a6697f8 Mon Sep 17 00:00:00 2001
From: Josh Stone <jistone@redhat.com>
Date: Tue, 15 May 2018 17:48:02 -0700
Subject: [PATCH] Ensure libraries built in stage0 have unique metadata

Issue #50786 shows a case with local rebuild where the libraries built
by stage0 had the same suffix as stage0's own, and were accidentally
loaded by that stage0 rustc when compiling `librustc_trans`.

Now we set `__CARGO_DEFAULT_LIB_METADATA` to "bootstrap" during stage0,
rather than the release channel like usual, so the library suffix will
always be completely distinct from the stage0 compiler.
---
 src/bootstrap/builder.rs | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/src/bootstrap/builder.rs b/src/bootstrap/builder.rs
index 17f19222e6ea..e5824010ef2c 100644
--- a/src/bootstrap/builder.rs
+++ b/src/bootstrap/builder.rs
@@ -592,7 +592,15 @@ 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
-        cargo.env("__CARGO_DEFAULT_LIB_METADATA", &self.config.channel);
+        let 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"
+        } else {
+            &self.config.channel
+        };
+        cargo.env("__CARGO_DEFAULT_LIB_METADATA", &metadata);
 
         let stage;
         if compiler.stage == 0 && self.local_rebuild {
-- 
2.17.0