Revert "rustc_resolve: move extern_prelude from Resolver to Session."

This reverts commit e90985ac.

src/librustc/session/mod.rs

@@ -35,7 +35,6 @@
 use syntax::feature_gate::{self, AttributeType};
 use syntax::json::JsonEmitter;
 use syntax::source_map;
-use syntax::symbol::Symbol;
 use syntax::parse::{self, ParseSess};
 use syntax_pos::{MultiSpan, Span};
 use util::profiling::SelfProfiler;
@@ -166,10 +165,6 @@ pub struct Session {
 
     /// Cap lint level specified by a driver specifically.
     pub driver_lint_caps: FxHashMap<lint::LintId, lint::Level>,
-
-    /// All the crate names specified with `--extern`, and the builtin ones.
-    /// Starting with the Rust 2018 edition, absolute paths resolve in this set.
-    pub extern_prelude: FxHashSet<Symbol>,
 }
 
 pub struct PerfStats {
@@ -1149,18 +1144,6 @@ pub fn build_session_(
         CguReuseTracker::new_disabled()
     };
 
-
-    let mut extern_prelude: FxHashSet<Symbol> =
-        sopts.externs.iter().map(|kv| Symbol::intern(kv.0)).collect();
-
-    // HACK(eddyb) this ignores the `no_{core,std}` attributes.
-    // FIXME(eddyb) warn (somewhere) if core/std is used with `no_{core,std}`.
-    // if !attr::contains_name(&krate.attrs, "no_core") {
-    // if !attr::contains_name(&krate.attrs, "no_std") {
-    extern_prelude.insert(Symbol::intern("core"));
-    extern_prelude.insert(Symbol::intern("std"));
-    extern_prelude.insert(Symbol::intern("meta"));
-
     let sess = Session {
         target: target_cfg,
         host,
@@ -1236,7 +1219,6 @@ pub fn build_session_(
         has_global_allocator: Once::new(),
         has_panic_handler: Once::new(),
         driver_lint_caps: FxHashMap(),
-        extern_prelude,
     };
 
     validate_commandline_args_with_session_available(&sess);

src/librustc_resolve/error_reporting.rs

@@ -136,7 +136,7 @@ fn make_external_crate_suggestion(
         // Need to clone else we can't call `resolve_path` without a borrow error. We also store
         // into a `BTreeMap` so we can get consistent ordering (and therefore the same diagnostic)
         // each time.
-        let external_crate_names: BTreeSet<Symbol> = self.resolver.session.extern_prelude
+        let external_crate_names: BTreeSet<Symbol> = self.resolver.extern_prelude
             .clone().drain().collect();
 
         // Insert a new path segment that we can replace.

src/librustc_resolve/lib.rs

@@ -1360,6 +1360,7 @@ pub struct Resolver<'a, 'b: 'a> {
     graph_root: Module<'a>,
 
     prelude: Option<Module<'a>>,
+    extern_prelude: FxHashSet<Name>,
 
     /// n.b. This is used only for better diagnostics, not name resolution itself.
     has_self: FxHashSet<DefId>,
@@ -1676,6 +1677,17 @@ pub fn new(session: &'a Session,
         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();
+
+        // HACK(eddyb) this ignore the `no_{core,std}` attributes.
+        // FIXME(eddyb) warn (elsewhere) if core/std is used with `no_{core,std}`.
+        // if !attr::contains_name(&krate.attrs, "no_core") {
+        // if !attr::contains_name(&krate.attrs, "no_std") {
+        extern_prelude.insert(Symbol::intern("core"));
+        extern_prelude.insert(Symbol::intern("std"));
+        extern_prelude.insert(Symbol::intern("meta"));
+
         let mut invocations = FxHashMap();
         invocations.insert(Mark::root(),
                            arenas.alloc_invocation_data(InvocationData::root(graph_root)));
@@ -1694,6 +1706,7 @@ pub fn new(session: &'a Session,
             // AST.
             graph_root,
             prelude: None,
+            extern_prelude,
 
             has_self: FxHashSet(),
             field_names: FxHashMap(),
@@ -1966,7 +1979,7 @@ fn resolve_ident_in_lexical_scope(&mut self,
 
         if !module.no_implicit_prelude {
             // `record_used` means that we don't try to load crates during speculative resolution
-            if record_used && ns == TypeNS && self.session.extern_prelude.contains(&ident.name) {
+            if record_used && ns == TypeNS && 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);
@@ -4018,7 +4031,7 @@ fn lookup_typo_candidate<FilterFn>(&mut self,
                     } else {
                         // Items from the prelude
                         if !module.no_implicit_prelude {
-                            names.extend(self.session.extern_prelude.iter().cloned());
+                            names.extend(self.extern_prelude.iter().cloned());
                             if let Some(prelude) = self.prelude {
                                 add_module_candidates(prelude, &mut names);
                             }
@@ -4464,7 +4477,8 @@ fn lookup_import_candidates<FilterFn>(&mut self,
         );
 
         if self.session.rust_2018() {
-            for &name in &self.session.extern_prelude {
+            let extern_prelude_names = self.extern_prelude.clone();
+            for &name in extern_prelude_names.iter() {
                 let ident = Ident::with_empty_ctxt(name);
                 match self.crate_loader.maybe_process_path_extern(name, ident.span) {
                     Some(crate_id) => {

src/librustc_resolve/macros.rs

@@ -692,7 +692,7 @@ struct Flags: u8 {
                     }
                 }
                 WhereToResolve::ExternPrelude => {
-                    if use_prelude && self.session.extern_prelude.contains(&ident.name) {
+                    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 =

src/librustc_resolve/resolve_imports.rs

@@ -199,7 +199,7 @@ pub fn resolve_ident_in_module_unadjusted(&mut self,
                     if !(
                         ns == TypeNS &&
                         !ident.is_path_segment_keyword() &&
-                        self.session.extern_prelude.contains(&ident.name)
+                        self.extern_prelude.contains(&ident.name)
                     ) {
                         // ... unless the crate name is not in the `extern_prelude`.
                         return binding;
@@ -218,7 +218,7 @@ pub fn resolve_ident_in_module_unadjusted(&mut self,
                 } else if
                     ns == TypeNS &&
                     !ident.is_path_segment_keyword() &&
-                    self.session.extern_prelude.contains(&ident.name)
+                    self.extern_prelude.contains(&ident.name)
                 {
                     let crate_id =
                         self.crate_loader.process_path_extern(ident.name, ident.span);
@@ -736,7 +736,7 @@ struct UniformPathsCanaryResults<'a> {
         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.session.extern_prelude.contains(&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 }))