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

3 files changed, 38 insertions, 2 deletions

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();
+    }
+}