Add extern crate items to extern prelude

src/librustc/ty/context.rs

@@ -931,7 +931,9 @@ pub struct GlobalCtxt<'tcx> {
 
     maybe_unused_trait_imports: FxHashSet<DefId>,
     maybe_unused_extern_crates: Vec<(DefId, Span)>,
-    pub extern_prelude: FxHashSet<ast::Name>,
+    /// Extern prelude entries. The value is `true` if the entry was introduced
+    /// via `extern crate` item and not `--extern` option or compiler built-in.
+    pub extern_prelude: FxHashMap<ast::Name, bool>,
 
     // Internal cache for metadata decoding. No need to track deps on this.
     pub rcache: Lock<FxHashMap<ty::CReaderCacheKey, Ty<'tcx>>>,

src/librustc/ty/item_path.rs

@@ -343,7 +343,7 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
                 // printing the `CrateRoot` so we don't prepend a `crate::` to paths.
                 let mut is_prelude_crate = false;
                 if let DefPathData::CrateRoot = self.def_key(parent_did).disambiguated_data.data {
-                    if self.extern_prelude.contains(&data.as_interned_str().as_symbol()) {
+                    if self.extern_prelude.contains_key(&data.as_interned_str().as_symbol()) {
                         is_prelude_crate = true;
                     }
                 }

src/librustc/ty/mod.rs

@@ -36,7 +36,7 @@ use ty::subst::{Subst, Substs};
 use ty::util::{IntTypeExt, Discr};
 use ty::walk::TypeWalker;
 use util::captures::Captures;
-use util::nodemap::{NodeSet, DefIdMap, FxHashMap, FxHashSet};
+use util::nodemap::{NodeSet, DefIdMap, FxHashMap};
 use arena::SyncDroplessArena;
 use session::DataTypeKind;
 
@@ -141,7 +141,9 @@ pub struct Resolutions {
     pub maybe_unused_trait_imports: NodeSet,
     pub maybe_unused_extern_crates: Vec<(NodeId, Span)>,
     pub export_map: ExportMap,
-    pub extern_prelude: FxHashSet<Name>,
+    /// Extern prelude entries. The value is `true` if the entry was introduced
+    /// via `extern crate` item and not `--extern` option or compiler built-in.
+    pub extern_prelude: FxHashMap<Name, bool>,
 }
 
 #[derive(Clone, Copy, PartialEq, Eq, Debug)]

src/librustc_driver/driver.rs

@@ -790,7 +790,9 @@ where
                 trait_map: resolver.trait_map,
                 maybe_unused_trait_imports: resolver.maybe_unused_trait_imports,
                 maybe_unused_extern_crates: resolver.maybe_unused_extern_crates,
-                extern_prelude: resolver.extern_prelude,
+                extern_prelude: resolver.extern_prelude.iter().map(|(ident, entry)| {
+                    (ident.name, entry.introduced_by_item)
+                }).collect(),
             },
 
             analysis: ty::CrateAnalysis {

src/librustc_resolve/build_reduced_graph.rs

@@ -17,7 +17,7 @@ use macros::{InvocationData, ParentScope, LegacyScope};
 use resolve_imports::ImportDirective;
 use resolve_imports::ImportDirectiveSubclass::{self, GlobImport, SingleImport};
 use {Module, ModuleData, ModuleKind, NameBinding, NameBindingKind, ToNameBinding};
-use {ModuleOrUniformRoot, PerNS, Resolver, ResolverArenas};
+use {ModuleOrUniformRoot, PerNS, Resolver, ResolverArenas, ExternPreludeEntry};
 use Namespace::{self, TypeNS, ValueNS, MacroNS};
 use {resolve_error, resolve_struct_error, ResolutionError};
 
@@ -28,6 +28,7 @@ use rustc::middle::cstore::CrateStore;
 use rustc_metadata::cstore::LoadedMacro;
 
 use std::cell::Cell;
+use std::ptr;
 use rustc_data_structures::sync::Lrc;
 
 use syntax::ast::{Name, Ident};
@@ -437,13 +438,32 @@ impl<'a, 'cl> Resolver<'a, 'cl> {
                 let module =
                     self.get_module(DefId { krate: crate_id, index: CRATE_DEF_INDEX });
                 self.populate_module_if_necessary(module);
-                if injected_crate_name().map_or(false, |name| item.ident.name == name) {
+                if injected_crate_name().map_or(false, |name| ident.name == name) {
                     self.injected_crate = Some(module);
                 }
 
                 let used = self.process_legacy_macro_imports(item, module, expansion);
                 let binding =
                     (module, ty::Visibility::Public, sp, expansion).to_name_binding(self.arenas);
+                if ptr::eq(self.current_module, self.graph_root) {
+                    if let Some(entry) = self.extern_prelude.get(&ident.modern()) {
+                        if expansion != Mark::root() && orig_name.is_some() &&
+                           entry.extern_crate_item.is_none() {
+                            self.session.span_err(item.span, "macro-expanded `extern crate` items \
+                                                              cannot shadow names passed with \
+                                                              `--extern`");
+                        }
+                    }
+                    let entry = self.extern_prelude.entry(ident.modern())
+                                                   .or_insert(ExternPreludeEntry {
+                        extern_crate_item: None,
+                        introduced_by_item: true,
+                    });
+                    entry.extern_crate_item = Some(binding);
+                    if orig_name.is_some() {
+                        entry.introduced_by_item = true;
+                    }
+                }
                 let directive = self.arenas.alloc_import_directive(ImportDirective {
                     root_id: item.id,
                     id: item.id,
@@ -468,7 +488,7 @@ impl<'a, 'cl> Resolver<'a, 'cl> {
 
             ItemKind::GlobalAsm(..) => {}
 
-            ItemKind::Mod(..) if item.ident == keywords::Invalid.ident() => {} // Crate root
+            ItemKind::Mod(..) if ident == keywords::Invalid.ident() => {} // Crate root
 
             ItemKind::Mod(..) => {
                 let def_id = self.definitions.local_def_id(item.id);

src/librustc_resolve/error_reporting.rs

@@ -137,7 +137,7 @@ impl<'a, 'b:'a, 'c: 'b> ImportResolver<'a, 'b, 'c> {
         // into a `BTreeMap` so we can get consistent ordering (and therefore the same diagnostic)
         // each time.
         let external_crate_names: BTreeSet<Symbol> = self.resolver.extern_prelude
-            .clone().drain().collect();
+            .iter().map(|(ident, _)| ident.name).collect();
 
         // Insert a new path segment that we can replace.
         let new_path_segment = path[0].clone();
@@ -146,19 +146,14 @@ impl<'a, 'b:'a, 'c: 'b> ImportResolver<'a, 'b, 'c> {
         // Iterate in reverse so that we start with crates at the end of the alphabet. This means
         // that we'll always get `std` before `core`.
         for name in external_crate_names.iter().rev() {
-            let ident = Ident::with_empty_ctxt(*name);
-            // Calling `maybe_process_path_extern` ensures that we're only running `resolve_path`
-            // on a crate name that won't ICE.
-            if let Some(_) = self.crate_loader.maybe_process_path_extern(*name, ident.span) {
-                // Replace the first after root (a placeholder we inserted) with a crate name
-                // and check if that is valid.
-                path[1].name = *name;
-                let result = self.resolve_path(None, &path, None, false, span, CrateLint::No);
-                debug!("make_external_crate_suggestion: name={:?} path={:?} result={:?}",
-                       name, path, result);
-                if let PathResult::Module(..) = result {
-                    return Some(path)
-                }
+            // Replace the first after root (a placeholder we inserted) with a crate name
+            // and check if that is valid.
+            path[1].name = *name;
+            let result = self.resolve_path(None, &path, None, false, span, CrateLint::No);
+            debug!("make_external_crate_suggestion: name={:?} path={:?} result={:?}",
+                    name, path, result);
+            if let PathResult::Module(..) = result {
+                return Some(path)
             }
         }
 

src/librustc_resolve/lib.rs

@@ -58,6 +58,7 @@ use syntax::ast::{self, Name, NodeId, Ident, FloatTy, IntTy, UintTy};
 use syntax::ext::base::SyntaxExtension;
 use syntax::ext::base::Determinacy::{self, Determined, Undetermined};
 use syntax::ext::base::MacroKind;
+use syntax::feature_gate::{emit_feature_err, GateIssue};
 use syntax::symbol::{Symbol, keywords};
 use syntax::util::lev_distance::find_best_match_for_name;
 
@@ -1340,6 +1341,12 @@ impl PrimitiveTypeTable {
     }
 }
 
+#[derive(Default, Clone)]
+pub struct ExternPreludeEntry<'a> {
+    extern_crate_item: Option<&'a NameBinding<'a>>,
+    pub introduced_by_item: bool,
+}
+
 /// The main resolver class.
 ///
 /// This is the visitor that walks the whole crate.
@@ -1352,7 +1359,7 @@ pub struct Resolver<'a, 'b: 'a> {
     graph_root: Module<'a>,
 
     prelude: Option<Module<'a>>,
-    pub extern_prelude: FxHashSet<Name>,
+    pub extern_prelude: FxHashMap<Ident, ExternPreludeEntry<'a>>,
 
     /// n.b. This is used only for better diagnostics, not name resolution itself.
     has_self: FxHashSet<DefId>,
@@ -1668,15 +1675,16 @@ impl<'a, 'crateloader: 'a> Resolver<'a, 'crateloader> {
         DefCollector::new(&mut definitions, Mark::root())
             .collect_root(crate_name, session.local_crate_disambiguator());
 
-        let mut extern_prelude: FxHashSet<Name> =
-            session.opts.externs.iter().map(|kv| Symbol::intern(kv.0)).collect();
+        let mut extern_prelude: FxHashMap<Ident, ExternPreludeEntry> =
+            session.opts.externs.iter().map(|kv| (Ident::from_str(kv.0), Default::default()))
+                                       .collect();
 
         if !attr::contains_name(&krate.attrs, "no_core") {
-            extern_prelude.insert(Symbol::intern("core"));
+            extern_prelude.insert(Ident::from_str("core"), Default::default());
             if !attr::contains_name(&krate.attrs, "no_std") {
-                extern_prelude.insert(Symbol::intern("std"));
+                extern_prelude.insert(Ident::from_str("std"), Default::default());
                 if session.rust_2018() {
-                    extern_prelude.insert(Symbol::intern("meta"));
+                    extern_prelude.insert(Ident::from_str("meta"), Default::default());
                 }
             }
         }
@@ -1963,21 +1971,10 @@ impl<'a, 'crateloader: 'a> Resolver<'a, 'crateloader> {
         }
 
         if !module.no_implicit_prelude {
-            if ns == TypeNS && self.extern_prelude.contains(&ident.name) {
-                let crate_id = if record_used {
-                    self.crate_loader.process_path_extern(ident.name, ident.span)
-                } else if let Some(crate_id) =
-                        self.crate_loader.maybe_process_path_extern(ident.name, ident.span) {
-                    crate_id
-                } else {
-                    return None;
-                };
-                let crate_root = self.get_module(DefId { krate: crate_id, index: CRATE_DEF_INDEX });
-                self.populate_module_if_necessary(&crate_root);
-
-                let binding = (crate_root, ty::Visibility::Public,
-                               ident.span, Mark::root()).to_name_binding(self.arenas);
-                return Some(LexicalScopeBinding::Item(binding));
+            if ns == TypeNS {
+                if let Some(binding) = self.extern_prelude_get(ident, !record_used, false) {
+                    return Some(LexicalScopeBinding::Item(binding));
+                }
             }
             if ns == TypeNS && is_known_tool(ident.name) {
                 let binding = (Def::ToolMod, ty::Visibility::Public,
@@ -4018,7 +4015,7 @@ impl<'a, 'crateloader: 'a> Resolver<'a, 'crateloader> {
                     } else {
                         // Items from the prelude
                         if !module.no_implicit_prelude {
-                            names.extend(self.extern_prelude.iter().cloned());
+                            names.extend(self.extern_prelude.iter().map(|(ident, _)| ident.name));
                             if let Some(prelude) = self.prelude {
                                 add_module_candidates(prelude, &mut names);
                             }
@@ -4459,11 +4456,9 @@ impl<'a, 'crateloader: 'a> Resolver<'a, 'crateloader> {
 
         if self.session.rust_2018() {
             let extern_prelude_names = self.extern_prelude.clone();
-            for &name in extern_prelude_names.iter() {
-                let ident = Ident::with_empty_ctxt(name);
-                if let Some(crate_id) = self.crate_loader.maybe_process_path_extern(name,
-                                                                                    ident.span)
-                {
+            for (ident, _) in extern_prelude_names.into_iter() {
+                if let Some(crate_id) = self.crate_loader.maybe_process_path_extern(ident.name,
+                                                                                    ident.span) {
                     let crate_root = self.get_module(DefId {
                         krate: crate_id,
                         index: CRATE_DEF_INDEX,
@@ -4825,6 +4820,35 @@ impl<'a, 'crateloader: 'a> Resolver<'a, 'crateloader> {
         err.emit();
         self.name_already_seen.insert(name, span);
     }
+
+    fn extern_prelude_get(&mut self, ident: Ident, speculative: bool, skip_feature_gate: bool)
+                          -> Option<&'a NameBinding<'a>> {
+        self.extern_prelude.get(&ident.modern()).cloned().and_then(|entry| {
+            if let Some(binding) = entry.extern_crate_item {
+                if !speculative && !skip_feature_gate && entry.introduced_by_item &&
+                   !self.session.features_untracked().extern_crate_item_prelude {
+                    emit_feature_err(&self.session.parse_sess, "extern_crate_item_prelude",
+                                     ident.span, GateIssue::Language,
+                                     "use of extern prelude names introduced \
+                                      with `extern crate` items is unstable");
+                }
+                Some(binding)
+            } else {
+                let crate_id = if !speculative {
+                    self.crate_loader.process_path_extern(ident.name, ident.span)
+                } else if let Some(crate_id) =
+                        self.crate_loader.maybe_process_path_extern(ident.name, ident.span) {
+                    crate_id
+                } else {
+                    return None;
+                };
+                let crate_root = self.get_module(DefId { krate: crate_id, index: CRATE_DEF_INDEX });
+                self.populate_module_if_necessary(&crate_root);
+                Some((crate_root, ty::Visibility::Public, ident.span, Mark::root())
+                    .to_name_binding(self.arenas))
+            }
+        })
+    }
 }
 
 fn is_self_type(path: &[Ident], namespace: Namespace) -> bool {

src/librustc_resolve/macros.rs

@@ -691,19 +691,14 @@ impl<'a, 'cl> Resolver<'a, 'cl> {
                     }
                 }
                 WhereToResolve::ExternPrelude => {
-                    if use_prelude && self.extern_prelude.contains(&ident.name) {
-                        let crate_id =
-                            self.crate_loader.process_path_extern(ident.name, ident.span);
-                        let crate_root =
-                            self.get_module(DefId { krate: crate_id, index: CRATE_DEF_INDEX });
-                        self.populate_module_if_necessary(crate_root);
-
-                        let binding = (crate_root, ty::Visibility::Public,
-                                       ident.span, Mark::root()).to_name_binding(self.arenas);
-                        Ok((binding, Flags::PRELUDE, Flags::empty()))
-                    } else {
-                        Err(Determinacy::Determined)
+                    let mut result = Err(Determinacy::Determined);
+                    if use_prelude {
+                        if let Some(binding) = self.extern_prelude_get(ident, !record_used,
+                                                                       innermost_result.is_some()) {
+                            result = Ok((binding, Flags::PRELUDE, Flags::empty()));
+                        }
                     }
+                    result
                 }
                 WhereToResolve::ToolPrelude => {
                     if use_prelude && is_known_tool(ident.name) {

src/librustc_resolve/resolve_imports.rs

@@ -21,7 +21,7 @@ use rustc_data_structures::ptr_key::PtrKey;
 use rustc::ty;
 use rustc::lint::builtin::BuiltinLintDiagnostics;
 use rustc::lint::builtin::{DUPLICATE_MACRO_EXPORTS, PUB_USE_OF_PRIVATE_EXTERN_CRATE};
-use rustc::hir::def_id::{CRATE_DEF_INDEX, DefId};
+use rustc::hir::def_id::DefId;
 use rustc::hir::def::*;
 use rustc::session::DiagnosticMessageId;
 use rustc::util::nodemap::FxHashSet;
@@ -202,7 +202,7 @@ impl<'a, 'crateloader> Resolver<'a, 'crateloader> {
                     if !(
                         ns == TypeNS &&
                         !ident.is_path_segment_keyword() &&
-                        self.extern_prelude.contains(&ident.name)
+                        self.extern_prelude.contains_key(&ident.modern())
                     ) {
                         // ... unless the crate name is not in the `extern_prelude`.
                         return binding;
@@ -220,12 +220,15 @@ impl<'a, 'crateloader> Resolver<'a, 'crateloader> {
                     self.resolve_crate_root(ident)
                 } else if
                     ns == TypeNS &&
-                    !ident.is_path_segment_keyword() &&
-                    self.extern_prelude.contains(&ident.name)
+                    !ident.is_path_segment_keyword()
                 {
-                    let crate_id =
-                        self.crate_loader.process_path_extern(ident.name, ident.span);
-                    self.get_module(DefId { krate: crate_id, index: CRATE_DEF_INDEX })
+                    if let Some(binding) = self.extern_prelude_get(ident, !record_used, false) {
+                        let module = self.get_module(binding.def().def_id());
+                        self.populate_module_if_necessary(module);
+                        return Ok(binding);
+                    } else {
+                        return Err(Determined);
+                    }
                 } else {
                     return Err(Determined);
                 };
@@ -738,10 +741,9 @@ impl<'a, 'b:'a, 'c: 'b> ImportResolver<'a, 'b, 'c> {
         let uniform_paths_feature = self.session.features_untracked().uniform_paths;
         for ((span, _, ns), results) in uniform_paths_canaries {
             let name = results.name;
-            let external_crate = if ns == TypeNS && self.extern_prelude.contains(&name) {
-                let crate_id =
-                    self.crate_loader.process_path_extern(name, span);
-                Some(Def::Mod(DefId { krate: crate_id, index: CRATE_DEF_INDEX }))
+            let external_crate = if ns == TypeNS {
+                self.extern_prelude_get(Ident::with_empty_ctxt(name), true, false)
+                    .map(|binding| binding.def())
             } else {
                 None
             };
@@ -1021,6 +1023,13 @@ impl<'a, 'b:'a, 'c: 'b> ImportResolver<'a, 'b, 'c> {
                             Some(this.dummy_binding);
                     }
                 }
+                if record_used && ns == TypeNS {
+                    if let ModuleOrUniformRoot::UniformRoot(..) = module {
+                        // Make sure single-segment import is resolved non-speculatively
+                        // at least once to report the feature error.
+                        this.extern_prelude_get(ident, false, false);
+                    }
+                }
             }
         });
 

src/librustc_typeck/check_unused.rs

@@ -164,7 +164,7 @@ fn unused_crates_lint<'tcx>(tcx: TyCtxt<'_, 'tcx, 'tcx>) {
         // If the extern crate isn't in the extern prelude,
         // there is no way it can be written as an `use`.
         let orig_name = extern_crate.orig_name.unwrap_or(item.name);
-        if !tcx.extern_prelude.contains(&orig_name) {
+        if !tcx.extern_prelude.get(&orig_name).map_or(false, |from_item| !from_item) {
             continue;
         }