From 6d78620bd77f1760e3730ef44aba7e53e3b38a23 Mon Sep 17 00:00:00 2001
From: Alex Crichton <alex@alexcrichton.com>
Date: Mon, 12 Sep 2016 22:43:48 -0700
Subject: [PATCH] rustbuild: Nicer error for host builds of targets

If a triple is configured only as a target, not a host, then trying to build
that triple with host artifacts would cause a panic. Fail a little nicer
instead.

Closes #36268
---
 src/bootstrap/lib.rs | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/src/bootstrap/lib.rs b/src/bootstrap/lib.rs
index 94c14f7ea25..efeda1d6b54 100644
--- a/src/bootstrap/lib.rs
+++ b/src/bootstrap/lib.rs
@@ -959,7 +959,11 @@ fn ar(&self, target: &str) -> Option<&Path> {
     /// Returns the path to the C++ compiler for the target specified, may panic
     /// if no C++ compiler was configured for the target.
     fn cxx(&self, target: &str) -> &Path {
-        self.cxx[target].path()
+        match self.cxx.get(target) {
+            Some(p) => p.path(),
+            None => panic!("\n\ntarget `{}` is not configured as a host,
+                            only as a target\n\n", target),
+        }
     }
 
     /// Returns flags to pass to the compiler to generate code for `target`.