Add lint for unknown feature attributes

src/librustc/middle/lib_features.rs

@@ -0,0 +1,153 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// Detecting lib features (i.e. features that are not lang features).
+//
+// These are declared using stability attributes (e.g. `#[stable(..)]`
+// and `#[unstable(..)]`), but are not declared in one single location
+// (unlike lang features), which means we need to collect them instead.
+
+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 rustc_data_structures::fx::{FxHashSet, FxHashMap};
+use errors::DiagnosticId;
+
+pub struct LibFeatures {
+    // A map from feature to stabilisation version.
+    pub stable: FxHashMap<Symbol, Symbol>,
+    pub unstable: FxHashSet<Symbol>,
+}
+
+impl LibFeatures {
+    fn new() -> LibFeatures {
+        LibFeatures {
+            stable: FxHashMap(),
+            unstable: FxHashSet(),
+        }
+    }
+
+    pub fn iter(&self) -> Vec<(Symbol, Option<Symbol>)> {
+        self.stable.iter().map(|(f, s)| (*f, Some(*s)))
+            .chain(self.unstable.iter().map(|f| (*f, None)))
+            .collect()
+    }
+}
+
+pub struct LibFeatureCollector<'a, 'tcx: 'a> {
+    tcx: TyCtxt<'a, 'tcx, 'tcx>,
+    lib_features: LibFeatures,
+}
+
+impl<'a, 'tcx> LibFeatureCollector<'a, 'tcx> {
+    fn new(tcx: TyCtxt<'a, 'tcx, 'tcx>) -> LibFeatureCollector<'a, 'tcx> {
+        LibFeatureCollector {
+            tcx,
+            lib_features: LibFeatures::new(),
+        }
+    }
+
+    fn extract(&self, attrs: &[Attribute]) -> Vec<(Symbol, Option<Symbol>, Span)> {
+        let stab_attrs = vec!["stable", "unstable", "rustc_const_unstable"];
+        let mut features = vec![];
+
+        for attr in attrs {
+            // FIXME(varkor): the stability attribute might be behind a `#[cfg]` attribute.
+
+            // Find a stability attribute (i.e. `#[stable(..)]`, `#[unstable(..)]`,
+            // `#[rustc_const_unstable(..)]`).
+            if stab_attrs.iter().any(|stab_attr| attr.check_name(stab_attr)) {
+                let meta_item = attr.meta();
+                if let Some(MetaItem { node: MetaItemKind::List(ref metas), .. }) = meta_item {
+                    let mut feature = None;
+                    let mut since = None;
+                    for meta in metas {
+                        if let Some(mi) = meta.meta_item() {
+                            // Find the `feature = ".."` meta-item.
+                            match (&*mi.name().as_str(), mi.value_str()) {
+                                ("feature", val) => feature = val,
+                                ("since", val) => since = val,
+                                _ => {}
+                            }
+                        }
+                    }
+                    if let Some(feature) = feature {
+                        features.push((feature, since, attr.span));
+                    }
+                    // We need to iterate over the other attributes, because
+                    // `rustc_const_unstable` is not mutually exclusive with
+                    // the other stability attributes, so we can't just `break`
+                    // here.
+                }
+            }
+        }
+
+        features
+    }
+
+    fn collect_feature(&mut self, feature: Symbol, since: Option<Symbol>, span: Span) {
+        let already_in_stable = self.lib_features.stable.contains_key(&feature);
+        let already_in_unstable = self.lib_features.unstable.contains(&feature);
+
+        match (since, already_in_stable, already_in_unstable) {
+            (Some(since), _, false) => {
+                self.lib_features.stable.insert(feature, since);
+            }
+            (None, false, _) => {
+                self.lib_features.unstable.insert(feature);
+            }
+            (Some(_), _, true) | (None, true, _) => {
+                let msg = format!(
+                    "feature `{}` is declared {}, but was previously declared {}",
+                    feature,
+                    if since.is_some() { "stable"} else { "unstable" },
+                    if since.is_none() { "stable"} else { "unstable" },
+                );
+                self.tcx.sess.struct_span_err_with_code(span, &msg,
+                    DiagnosticId::Error("E0711".into())).emit();
+            }
+        }
+    }
+
+    fn collect_from_attrs(&mut self, attrs: &[Attribute]) {
+        for (feature, stable, span) in self.extract(attrs) {
+            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() {
+        for &(feature, since) in tcx.defined_lib_features(cnum).iter() {
+            collector.collect_feature(feature, since, DUMMY_SP);
+        }
+    }
+    collector.collect_from_attrs(&tcx.hir.krate().attrs);
+    tcx.hir.krate().visit_all_item_likes(&mut collector);
+    collector.lib_features
+}