Turn INCOMPLETE_FEATURES into a lint.

src/librustc_lint/builtin.rs

@@ -33,13 +33,12 @@ use lint::{LintPass, LateLintPass, EarlyLintPass, EarlyContext};
 use rustc::util::nodemap::FxHashSet;
 
 use syntax::tokenstream::{TokenTree, TokenStream};
-use syntax::ast;
+use syntax::ast::{self, Expr};
 use syntax::ptr::P;
-use syntax::ast::Expr;
 use syntax::attr::{self, HasAttrs, AttributeTemplate};
 use syntax::source_map::Spanned;
 use syntax::edition::Edition;
-use syntax::feature_gate::{AttributeGate, AttributeType};
+use syntax::feature_gate::{self, AttributeGate, AttributeType};
 use syntax::feature_gate::{Stability, deprecated_attributes};
 use syntax_pos::{BytePos, Span, SyntaxContext};
 use syntax::symbol::{Symbol, kw, sym};
@@ -1831,3 +1830,35 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for ExplicitOutlivesRequirements {
         }
     }
 }
+
+declare_lint! {
+    pub INCOMPLETE_FEATURES,
+    Warn,
+    "incomplete features that may function improperly in some or all cases"
+}
+
+declare_lint_pass!(
+    /// Check for used feature gates in `INCOMPLETE_FEATURES` in `feature_gate.rs`.
+    IncompleteFeatures => [INCOMPLETE_FEATURES]
+);
+
+impl EarlyLintPass for IncompleteFeatures {
+    fn check_crate(&mut self, cx: &EarlyContext<'_>, _: &ast::Crate) {
+        let features = cx.sess.features_untracked();
+        features.declared_lang_features
+            .iter().map(|(name, span, _)| (name, span))
+            .chain(features.declared_lib_features.iter().map(|(name, span)| (name, span)))
+            .filter(|(name, _)| feature_gate::INCOMPLETE_FEATURES.iter().any(|f| name == &f))
+            .for_each(|(name, &span)| {
+                cx.struct_span_lint(
+                    INCOMPLETE_FEATURES,
+                    span,
+                    &format!(
+                        "the feature `{}` is incomplete and may cause the compiler to crash",
+                        name,
+                    )
+                )
+                .emit();
+            });
+    }
+}

src/librustc_lint/lib.rs

@@ -97,6 +97,7 @@ macro_rules! early_lint_passes {
             DeprecatedAttr: DeprecatedAttr::new(),
             WhileTrue: WhileTrue,
             NonAsciiIdents: NonAsciiIdents,
+            IncompleteFeatures: IncompleteFeatures,
         ]);
     )
 }

src/libsyntax/feature_gate.rs

@@ -569,10 +569,10 @@ declare_features! (
     // -------------------------------------------------------------------------
 );
 
-// Some features are known to be incomplete and using them is likely to have
+/// Some features are known to be incomplete and using them is likely to have
-// unanticipated results, such as compiler crashes. We warn the user about these
+/// unanticipated results, such as compiler crashes. We warn the user about these
-// to alert them.
+/// to alert them.
-const INCOMPLETE_FEATURES: &[Symbol] = &[
+pub const INCOMPLETE_FEATURES: &[Symbol] = &[
     sym::impl_trait_in_bindings,
     sym::generic_associated_types,
     sym::const_generics,
@@ -2338,15 +2338,6 @@ pub fn get_features(span_handler: &Handler, krate_attrs: &[ast::Attribute],
             }
 
             let name = mi.name_or_empty();
-            if INCOMPLETE_FEATURES.iter().any(|f| name == *f) {
-                span_handler.struct_span_warn(
-                    mi.span(),
-                    &format!(
-                        "the feature `{}` is incomplete and may cause the compiler to crash",
-                        name
-                    )
-                ).emit();
-            }
 
             if let Some(edition) = ALL_EDITIONS.iter().find(|e| name == e.feature_name()) {
                 if *edition <= crate_edition {