rustdoc: Don't allow `#![feature(...)]` on stable or beta

diff --git a/src/librustdoc/core.rs b/src/librustdoc/core.rs
index 50d62027c8c6d9c774590728b6b478c62663c9f2..efac0d28d3b542dcf2c724b2304ba430a427e812 100644 (file)
--- a/src/librustdoc/core.rs
+++ b/src/librustdoc/core.rs
@@ -302,8 +302,7 @@ pub fn run_core(options: RustdocOptions) -> (clean::Crate, RenderInfo, RenderOpt
         cg: codegen_options,
         externs,
         target_triple: target,
-        // Ensure that rustdoc works even if rustc is feature-staged
-        unstable_features: UnstableFeatures::Allow,
+        unstable_features: UnstableFeatures::from_environment(),
         actually_rustdoc: true,
         debugging_opts: debugging_options,
         error_format,