add test for using target features in doctests

src/test/rustdoc/doc-cfg-target-feature.rs

@@ -0,0 +1,31 @@
+// Copyright 2017 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
+// compile-flags:--test
+// should-fail
+// no-system-llvm
+
+// #49723: rustdoc didn't add target features when extracting or running doctests
+
+#![feature(doc_cfg)]
+
+/// Foo
+///
+/// # Examples
+///
+/// ```
+/// #![feature(cfg_target_feature)]
+///
+/// #[cfg(target_feature = "sse")]
+/// assert!(false);
+/// ```
+#[doc(cfg(target_feature = "sse"))]
+pub unsafe fn foo() {}