Simplify pre-expansion gating in general.

Author: Centril

src/libsyntax/feature_gate.rs

@@ -30,7 +30,6 @@ use crate::tokenstream::TokenTree;
 
 use errors::{Applicability, DiagnosticBuilder, Handler};
 use rustc_data_structures::fx::FxHashMap;
-use rustc_data_structures::sync::Lock;
 use rustc_target::spec::abi::Abi;
 use syntax_pos::{Span, DUMMY_SP, MultiSpan};
 use log::debug;
@@ -2422,10 +2421,6 @@ pub fn get_features(span_handler: &Handler, krate_attrs: &[ast::Attribute],
     features
 }
 
-fn for_each_in_lock<T>(vec: &Lock<Vec<T>>, f: impl Fn(&T)) {
-    vec.borrow().iter().for_each(f);
-}
-
 pub fn check_crate(krate: &ast::Crate,
                    sess: &ParseSess,
                    features: &Features,
@@ -2438,33 +2433,16 @@ pub fn check_crate(krate: &ast::Crate,
         plugin_attributes,
     };
 
-    for_each_in_lock(&sess.param_attr_spans, |span| gate_feature!(
-        &ctx,
-        param_attrs,
-        *span,
-        "attributes on function parameters are unstable"
-    ));
-
-    for_each_in_lock(&sess.let_chains_spans, |span| gate_feature!(
-        &ctx,
-        let_chains,
-        *span,
-        "`let` expressions in this position are experimental"
-    ));
-
-    for_each_in_lock(&sess.async_closure_spans, |span| gate_feature!(
-        &ctx,
-        async_closure,
-        *span,
-        "async closures are unstable"
-    ));
-
-    for_each_in_lock(&sess.yield_spans, |span| gate_feature!(
-        &ctx,
-        generators,
-        *span,
-        "yield syntax is experimental"
-    ));
+    macro_rules! gate_all {
+        ($spans:ident, $gate:ident, $msg:literal) => {
+            for span in &*sess.$spans.borrow() { gate_feature!(&ctx, $gate, *span, $msg); }
+        }
+    }
+
+    gate_all!(param_attr_spans, param_attrs, "attributes on function parameters are unstable");
+    gate_all!(let_chains_spans, let_chains, "`let` expressions in this position are experimental");
+    gate_all!(async_closure_spans, async_closure, "async closures are unstable");
+    gate_all!(yield_spans, generators, "yield syntax is experimental");
 
     let visitor = &mut PostExpansionVisitor {
         context: &ctx,