From fc9da8f795b2670dd1f211d17c0896cc2ea85d45 Mon Sep 17 00:00:00 2001
From: Alex Crichton <alex@alexcrichton.com>
Date: Thu, 19 Apr 2018 17:50:31 -0700
Subject: [PATCH] rustc: Whitelist upstream target_features

When compiling crates we'll be calculating and parsing `#[target_feature]` for
upstream crates. We'll also be checking the stability of listed features, but we
only want to check the listed stability during the actual crate that wrote the
relevant code. This commit updates the `target_feature` process to ignore
foreign `DefId` instances and only check the feature whitelist for local
functions.

Closes #50094
---
 src/librustc_typeck/collect.rs                |  5 +++--
 .../using-target-feature-unstable.rs          | 15 ++++++++++++++
 .../run-pass/using-target-feature-unstable.rs | 20 +++++++++++++++++++
 3 files changed, 38 insertions(+), 2 deletions(-)
 create mode 100644 src/test/run-pass/auxiliary/using-target-feature-unstable.rs
 create mode 100644 src/test/run-pass/using-target-feature-unstable.rs

diff --git a/src/librustc_typeck/collect.rs b/src/librustc_typeck/collect.rs
index 6bd38244e8c..a1eb043995a 100644
--- a/src/librustc_typeck/collect.rs
+++ b/src/librustc_typeck/collect.rs
@@ -1682,6 +1682,7 @@ fn is_foreign_item<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 
 fn from_target_feature(
     tcx: TyCtxt,
+    id: DefId,
     attr: &ast::Attribute,
     whitelist: &FxHashMap<String, Option<String>>,
     target_features: &mut Vec<Symbol>,
@@ -1752,7 +1753,7 @@ fn from_target_feature(
                 Some(name) => bug!("unknown target feature gate {}", name),
                 None => true,
             };
-            if !allowed {
+            if !allowed && id.is_local() {
                 feature_gate::emit_feature_err(
                     &tcx.sess.parse_sess,
                     feature_gate.as_ref().unwrap(),
@@ -1877,7 +1878,7 @@ fn trans_fn_attrs<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, id: DefId) -> TransFnAt
                            `unsafe` function";
                 tcx.sess.span_err(attr.span, msg);
             }
-            from_target_feature(tcx, attr, &whitelist, &mut trans_fn_attrs.target_features);
+            from_target_feature(tcx, id, attr, &whitelist, &mut trans_fn_attrs.target_features);
         } else if attr.check_name("linkage") {
             if let Some(val) = attr.value_str() {
                 trans_fn_attrs.linkage = Some(linkage_by_name(tcx, id, &val.as_str()));
diff --git a/src/test/run-pass/auxiliary/using-target-feature-unstable.rs b/src/test/run-pass/auxiliary/using-target-feature-unstable.rs
new file mode 100644
index 00000000000..8b7d0332fe9
--- /dev/null
+++ b/src/test/run-pass/auxiliary/using-target-feature-unstable.rs
@@ -0,0 +1,15 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#![feature(mmx_target_feature)]
+
+#[inline]
+#[target_feature(enable = "mmx")]
+pub unsafe fn foo() {}
diff --git a/src/test/run-pass/using-target-feature-unstable.rs b/src/test/run-pass/using-target-feature-unstable.rs
new file mode 100644
index 00000000000..614c8d4e1d4
--- /dev/null
+++ b/src/test/run-pass/using-target-feature-unstable.rs
@@ -0,0 +1,20 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// only-x86_64
+// aux-build:using-target-feature-unstable.rs
+
+extern crate using_target_feature_unstable;
+
+fn main() {
+    unsafe {
+        using_target_feature_unstable::foo();
+    }
+}