Add `-Z allow_features=...` flag

3 files changed, 28 insertions, 4 deletions

diff --git a/src/libsyntax/config.rs b/src/libsyntax/config.rs
index 4e4432a3f33..2abb7e407eb 100644
--- a/src/libsyntax/config.rs
+++ b/src/libsyntax/config.rs
@@ -24,8 +24,8 @@ pub struct StripUnconfigured<'a> {
 }
 
 // `cfg_attr`-process the crate's attributes and compute the crate's features.
-pub fn features(mut krate: ast::Crate, sess: &ParseSess, edition: Edition)
-                -> (ast::Crate, Features) {
+pub fn features(mut krate: ast::Crate, sess: &ParseSess, edition: Edition,
+                allow_features: &Option<Vec<String>>) -> (ast::Crate, Features) {
     let features;
     {
         let mut strip_unconfigured = StripUnconfigured {
@@ -43,7 +43,7 @@ pub fn features(mut krate: ast::Crate, sess: &ParseSess, edition: Edition)
             return (krate, Features::new());
         }
 
-        features = get_features(&sess.span_diagnostic, &krate.attrs, edition);
+        features = get_features(&sess.span_diagnostic, &krate.attrs, edition, allow_features);
 
         // Avoid reconfiguring malformed `cfg_attr`s
         if err_count == sess.span_diagnostic.err_count() {
diff --git a/src/libsyntax/diagnostic_list.rs b/src/libsyntax/diagnostic_list.rs
index 2c367f1f402..ac24475cab8 100644
--- a/src/libsyntax/diagnostic_list.rs
+++ b/src/libsyntax/diagnostic_list.rs
@@ -378,6 +378,21 @@ Erroneous code example:
 
 "##,
 
+E0725: r##"
+A feature attribute named a feature that was disallowed in the compiler
+command line flags.
+
+Erroneous code example:
+
+```ignore (can't specify compiler flags from doctests)
+#![feature(never_type)] // error: the feature `never_type` is not in
+                        // the list of allowed features
+```
+
+Delete the offending feature attribute, or add it to the list of allowed
+features in the `-Z allow_features` flag.
+"##,
+
 }
 
 register_diagnostics! {
diff --git a/src/libsyntax/feature_gate.rs b/src/libsyntax/feature_gate.rs
index 279e2089f5d..77e8e75d832 100644
--- a/src/libsyntax/feature_gate.rs
+++ b/src/libsyntax/feature_gate.rs
@@ -2008,7 +2008,7 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
 }
 
 pub fn get_features(span_handler: &Handler, krate_attrs: &[ast::Attribute],
-                    crate_edition: Edition) -> Features {
+                    crate_edition: Edition, allow_features: &Option<Vec<String>>) -> Features {
     fn feature_removed(span_handler: &Handler, span: Span, reason: Option<&str>) {
         let mut err = struct_span_err!(span_handler, span, E0557, "feature has been removed");
         if let Some(reason) = reason {
@@ -2127,6 +2127,15 @@ pub fn get_features(span_handler: &Handler, krate_attrs: &[ast::Attribute],
             }
 
             if let Some((.., set)) = ACTIVE_FEATURES.iter().find(|f| name == f.0) {
+                if let Some(allowed) = allow_features.as_ref() {
+                    if allowed.iter().find(|f| *f == name.as_str()).is_none() {
+                        span_err!(span_handler, mi.span, E0725,
+                                  "the feature `{}` is not in the list of allowed features",
+                                  name);
+                        continue;
+                    }
+                }
+
                 set(&mut features, mi.span);
                 features.declared_lang_features.push((name, mi.span, None));
                 continue