Auto merge of #53397 - varkor:feature-collector-expand-visitor, r=nikomatsakis

Visit all attributes for feature collection

Previously feature attributes were just collected on item-like "things" as well as exported macros and crate attributes. This ignored some places feature attributes could be specified, such as on enum variants.

Fixes https://github.com/rust-lang/rust/issues/53391.

src/librustc/middle/lib_features.rs

@@ -18,8 +18,7 @@ use ty::TyCtxt;
 use syntax::symbol::Symbol;
 use syntax::ast::{Attribute, MetaItem, MetaItemKind};
 use syntax_pos::{Span, DUMMY_SP};
-use hir;
-use hir::itemlikevisit::ItemLikeVisitor;
+use hir::intravisit::{self, NestedVisitorMap, Visitor};
 use rustc_data_structures::fx::{FxHashSet, FxHashMap};
 use errors::DiagnosticId;
 
@@ -59,11 +58,9 @@ impl<'a, 'tcx> LibFeatureCollector<'a, 'tcx> {
         }
     }
 
-    fn extract(&self, attrs: &[Attribute]) -> Vec<(Symbol, Option<Symbol>, Span)> {
+    fn extract(&self, attr: &Attribute) -> Option<(Symbol, Option<Symbol>, Span)> {
         let stab_attrs = vec!["stable", "unstable", "rustc_const_unstable"];
-        let mut features = vec![];
 
-        for attr in attrs {
         // Find a stability attribute (i.e. `#[stable (..)]`, `#[unstable (..)]`,
         // `#[rustc_const_unstable (..)]`).
         if let Some(stab_attr) = stab_attrs.iter().find(|stab_attr| {
@@ -88,7 +85,7 @@ impl<'a, 'tcx> LibFeatureCollector<'a, 'tcx> {
                     // don't emit additional, irrelevant errors for malformed
                     // attributes.
                     if *stab_attr != "stable" || since.is_some() {
-                            features.push((feature, since, attr.span));
+                        return Some((feature, since, attr.span));
                     }
                 }
                 // We need to iterate over the other attributes, because
@@ -97,9 +94,8 @@ impl<'a, 'tcx> LibFeatureCollector<'a, 'tcx> {
                 // here.
             }
         }
-        }
 
-        features
+        None
     }
 
     fn collect_feature(&mut self, feature: Symbol, since: Option<Symbol>, span: Span) {
@@ -140,28 +136,20 @@ impl<'a, 'tcx> LibFeatureCollector<'a, 'tcx> {
             }
         }
     }
+}
 
-    fn collect_from_attrs(&mut self, attrs: &[Attribute]) {
-        for (feature, stable, span) in self.extract(attrs) {
+impl<'a, 'tcx> Visitor<'tcx> for LibFeatureCollector<'a, 'tcx> {
+    fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
+        NestedVisitorMap::All(&self.tcx.hir)
+    }
+
+    fn visit_attribute(&mut self, attr: &'tcx Attribute) {
+        if let Some((feature, stable, span)) = self.extract(attr) {
             self.collect_feature(feature, stable, span);
         }
     }
 }
 
-impl<'a, 'v, 'tcx> ItemLikeVisitor<'v> for LibFeatureCollector<'a, 'tcx> {
-    fn visit_item(&mut self, item: &hir::Item) {
-        self.collect_from_attrs(&item.attrs);
-    }
-
-    fn visit_trait_item(&mut self, trait_item: &hir::TraitItem) {
-        self.collect_from_attrs(&trait_item.attrs);
-    }
-
-    fn visit_impl_item(&mut self, impl_item: &hir::ImplItem) {
-        self.collect_from_attrs(&impl_item.attrs);
-    }
-}
-
 pub fn collect<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>) -> LibFeatures {
     let mut collector = LibFeatureCollector::new(tcx);
     for &cnum in tcx.crates().iter() {
@@ -169,10 +157,6 @@ pub fn collect<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>) -> LibFeatures {
             collector.collect_feature(feature, since, DUMMY_SP);
         }
     }
-    collector.collect_from_attrs(&tcx.hir.krate().attrs);
-    tcx.hir.krate().visit_all_item_likes(&mut collector);
-    for exported_macro in &tcx.hir.krate().exported_macros {
-        collector.collect_from_attrs(&exported_macro.attrs);
-    }
+    intravisit::walk_crate(&mut collector, tcx.hir.krate());
     collector.lib_features
 }