Add query for loading crates.

This commit adds a query that can be used to load crates in later
phases of the compiler for the purpose of diagnostics.

Author: davidtwco

src/librustc/dep_graph/dep_node.rs

@@ -58,7 +58,7 @@ use crate::ich::{Fingerprint, StableHashingContext};
 use rustc_data_structures::stable_hasher::{StableHasher, HashStable};
 use std::fmt;
 use std::hash::Hash;
-use syntax_pos::symbol::InternedString;
+use syntax_pos::symbol::{InternedString, Symbol};
 use crate::traits;
 use crate::traits::query::{
     CanonicalProjectionGoal, CanonicalTyGoal, CanonicalTypeOpAscribeUserTypeGoal,
@@ -593,6 +593,7 @@ define_dep_nodes!( <'tcx>
     [input] CrateDisambiguator(CrateNum),
     [input] CrateHash(CrateNum),
     [input] OriginalCrateName(CrateNum),
+    [input] MaybeLoadExternCrate(Symbol),
     [input] ExtraFileName(CrateNum),
 
     [] ImplementationsOfTrait { krate: CrateNum, trait_id: DefId },

src/librustc/middle/cstore.rs

@@ -201,6 +201,9 @@ pub trait CrateStore {
     fn extern_mod_stmt_cnum_untracked(&self, emod_id: ast::NodeId) -> Option<CrateNum>;
     fn item_generics_cloned_untracked(&self, def: DefId, sess: &Session) -> ty::Generics;
     fn postorder_cnums_untracked(&self) -> Vec<CrateNum>;
+    fn maybe_load_extern_crate_untracked(
+        &self, sess: &Session, name: Symbol
+    ) -> Option<CrateNum>;
 
     // This is basically a 1-based range of ints, which is a little
     // silly - I may fix that.

src/librustc/ty/context.rs

@@ -2989,6 +2989,9 @@ pub fn provide(providers: &mut ty::query::Providers<'_>) {
         assert_eq!(id, LOCAL_CRATE);
         tcx.crate_name
     };
+    providers.maybe_load_extern_crate = |tcx, name| {
+        tcx.cstore.maybe_load_extern_crate_untracked(tcx.sess, name)
+    };
     providers.get_lib_features = |tcx, id| {
         assert_eq!(id, LOCAL_CRATE);
         Lrc::new(middle::lib_features::collect(tcx))

src/librustc/ty/query/config.rs

@@ -18,7 +18,7 @@ use crate::util::profiling::ProfileCategory;
 use std::borrow::Cow;
 use std::hash::Hash;
 use std::fmt::Debug;
-use syntax_pos::symbol::InternedString;
+use syntax_pos::symbol::{Symbol, InternedString};
 use rustc_data_structures::sync::Lock;
 use rustc_data_structures::fingerprint::Fingerprint;
 use crate::ich::StableHashingContext;
@@ -706,6 +706,12 @@ impl<'tcx> QueryDescription<'tcx> for queries::original_crate_name<'tcx> {
     }
 }
 
+impl<'tcx> QueryDescription<'tcx> for queries::maybe_load_extern_crate<'tcx> {
+    fn describe(_tcx: TyCtxt<'_, '_, '_>, name: Symbol) -> Cow<'static, str> {
+        format!("loading crate with name {}", name).into()
+    }
+}
+
 impl<'tcx> QueryDescription<'tcx> for queries::extra_filename<'tcx> {
     fn describe(_tcx: TyCtxt<'_, '_, '_>, _: CrateNum) -> Cow<'static, str> {
         "looking up the extra filename for a crate".into()

src/librustc/ty/query/keys.rs

@@ -11,7 +11,7 @@ use crate::mir;
 use std::fmt::Debug;
 use std::hash::Hash;
 use syntax_pos::{Span, DUMMY_SP};
-use syntax_pos::symbol::InternedString;
+use syntax_pos::symbol::{Symbol, InternedString};
 
 /// The `Key` trait controls what types can legally be used as the key
 /// for a query.
@@ -190,6 +190,15 @@ impl Key for InternedString {
     }
 }
 
+impl Key for Symbol {
+    fn query_crate(&self) -> CrateNum {
+        LOCAL_CRATE
+    }
+    fn default_span(&self, _tcx: TyCtxt<'_, '_, '_>) -> Span {
+        DUMMY_SP
+    }
+}
+
 /// Canonical query goals correspond to abstract trait operations that
 /// are not tied to any crate in particular.
 impl<'tcx, T> Key for Canonical<'tcx, T>

src/librustc/ty/query/mod.rs

@@ -493,6 +493,7 @@ define_queries! { <'tcx>
         [] fn crate_disambiguator: CrateDisambiguator(CrateNum) -> CrateDisambiguator,
         [] fn crate_hash: CrateHash(CrateNum) -> Svh,
         [] fn original_crate_name: OriginalCrateName(CrateNum) -> Symbol,
+        [] fn maybe_load_extern_crate: MaybeLoadExternCrate(Symbol) -> Option<CrateNum>,
         [] fn extra_filename: ExtraFileName(CrateNum) -> String,
     },
 

src/librustc/ty/query/plumbing.rs

@@ -1242,6 +1242,7 @@ pub fn force_from_dep_node<'a, 'gcx, 'lcx>(tcx: TyCtxt<'a, 'gcx, 'lcx>,
         DepKind::MethodAutoderefSteps |
         DepKind::InstanceDefSizeEstimate |
         DepKind::ProgramClausesForEnv |
+        DepKind::MaybeLoadExternCrate |
 
         // This one should never occur in this context
         DepKind::Null => {

src/librustc_metadata/cstore_impl.rs

@@ -1,4 +1,5 @@
 use crate::cstore::{self, LoadedMacro};
+use crate::creader::CrateLoader;
 use crate::encoder;
 use crate::link_args;
 use crate::native_libs;
@@ -31,7 +32,7 @@ use syntax::edition::Edition;
 use syntax::parse::source_file_to_stream;
 use syntax::parse::parser::emit_unclosed_delims;
 use syntax::symbol::Symbol;
-use syntax_pos::{Span, NO_EXPANSION, FileName};
+use syntax_pos::{Span, DUMMY_SP, NO_EXPANSION, FileName};
 use rustc_data_structures::bit_set::BitSet;
 
 macro_rules! provide {
@@ -541,6 +542,15 @@ impl CrateStore for cstore::CStore {
         self.do_postorder_cnums_untracked()
     }
 
+    fn maybe_load_extern_crate_untracked(
+        &self,
+        sess: &Session,
+        name: Symbol
+    ) -> Option<CrateNum> {
+        let mut crate_loader = CrateLoader::new(sess, self, "");
+        crate_loader.maybe_process_path_extern(name, DUMMY_SP)
+    }
+
     fn encode_metadata<'a, 'tcx>(&self,
                                  tcx: TyCtxt<'a, 'tcx, 'tcx>)
                                  -> EncodedMetadata