Improved diagnostic on failure to meet send bound on future in a foreign crate

compiler/rustc_metadata/src/rmeta/decoder.rs

@@ -28,6 +28,7 @@ use rustc_middle::mir::interpret::{AllocDecodingSession, AllocDecodingState};
 use rustc_middle::thir;
 use rustc_middle::ty::codec::TyDecoder;
 use rustc_middle::ty::fast_reject::SimplifiedType;
+use rustc_middle::ty::GeneratorDiagnosticData;
 use rustc_middle::ty::{self, Ty, TyCtxt, Visibility};
 use rustc_serialize::{opaque, Decodable, Decoder};
 use rustc_session::cstore::{
@@ -1732,6 +1733,24 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
                 .collect()
         })
     }
+
+    fn get_generator_diagnostic_data(
+        self,
+        tcx: TyCtxt<'tcx>,
+        id: DefIndex,
+    ) -> Option<GeneratorDiagnosticData<'tcx>> {
+        self.root
+            .tables
+            .generator_diagnostic_data
+            .get(self, id)
+            .map(|param| param.decode((self, tcx)))
+            .map(|generator_data| GeneratorDiagnosticData {
+                generator_interior_types: generator_data.generator_interior_types,
+                hir_owner: generator_data.hir_owner,
+                nodes_types: generator_data.nodes_types,
+                adjustments: generator_data.adjustments,
+            })
+    }
 }
 
 impl CrateMetadata {

compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs

@@ -246,6 +246,7 @@ provide! { <'tcx> tcx, def_id, other, cdata,
 
     crate_extern_paths => { cdata.source().paths().cloned().collect() }
     expn_that_defined => { cdata.get_expn_that_defined(def_id.index, tcx.sess) }
+    generator_diagnostic_data => { cdata.get_generator_diagnostic_data(tcx, def_id.index) }
 }
 
 pub(in crate::rmeta) fn provide(providers: &mut Providers) {

compiler/rustc_metadata/src/rmeta/encoder.rs

@@ -1550,16 +1550,17 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
     fn encode_info_for_closure(&mut self, hir_id: hir::HirId) {
         let def_id = self.tcx.hir().local_def_id(hir_id);
         debug!("EncodeContext::encode_info_for_closure({:?})", def_id);
-
         // NOTE(eddyb) `tcx.type_of(def_id)` isn't used because it's fully generic,
         // including on the signature, which is inferred in `typeck.
-        let ty = self.tcx.typeck(def_id).node_type(hir_id);
-
+        let typeck_result: &'tcx ty::TypeckResults<'tcx> = self.tcx.typeck(def_id);
+        let ty = typeck_result.node_type(hir_id);
         match ty.kind() {
             ty::Generator(..) => {
                 let data = self.tcx.generator_kind(def_id).unwrap();
+                let generator_diagnostic_data = typeck_result.get_generator_diagnostic_data();
                 record!(self.tables.kind[def_id.to_def_id()] <- EntryKind::Generator);
                 record!(self.tables.generator_kind[def_id.to_def_id()] <- data);
+                record!(self.tables.generator_diagnostic_data[def_id.to_def_id()]  <- generator_diagnostic_data);
             }
 
             ty::Closure(..) => {

compiler/rustc_metadata/src/rmeta/mod.rs

@@ -19,6 +19,7 @@ use rustc_middle::mir;
 use rustc_middle::thir;
 use rustc_middle::ty::fast_reject::SimplifiedType;
 use rustc_middle::ty::query::Providers;
+use rustc_middle::ty::GeneratorDiagnosticData;
 use rustc_middle::ty::{self, ReprOptions, Ty};
 use rustc_serialize::opaque::Encoder;
 use rustc_session::config::SymbolManglingVersion;
@@ -358,6 +359,7 @@ define_tables! {
     def_keys: Table<DefIndex, Lazy<DefKey>>,
     def_path_hashes: Table<DefIndex, DefPathHash>,
     proc_macro_quoted_spans: Table<usize, Lazy<Span>>,
+    generator_diagnostic_data: Table<DefIndex, Lazy<GeneratorDiagnosticData<'tcx>>>,
 }
 
 #[derive(Copy, Clone, MetadataEncodable, MetadataDecodable)]

compiler/rustc_middle/src/query/mod.rs

@@ -1962,4 +1962,10 @@ rustc_queries! {
         eval_always
         desc { "computing the backend features for CLI flags" }
     }
+
+    query generator_diagnostic_data(key: DefId) -> Option<GeneratorDiagnosticData<'tcx>> {
+        storage(ArenaCacheSelector<'tcx>)
+        desc { |tcx| "looking up generator diagnostic data of `{}`", tcx.def_path_str(key) }
+        separate_provide_extern
+    }
 }

compiler/rustc_middle/src/ty/context.rs

@@ -367,6 +367,16 @@ pub struct GeneratorInteriorTypeCause<'tcx> {
     pub expr: Option<hir::HirId>,
 }
 
+// This type holds diagnostic information on generators and async functions across crate boundaries
+// and is used to provide better error messages
+#[derive(TyEncodable, TyDecodable, Clone, Debug, HashStable)]
+pub struct GeneratorDiagnosticData<'tcx> {
+    pub generator_interior_types: ty::Binder<'tcx, Vec<GeneratorInteriorTypeCause<'tcx>>>,
+    pub hir_owner: DefId,
+    pub nodes_types: ItemLocalMap<Ty<'tcx>>,
+    pub adjustments: ItemLocalMap<Vec<ty::adjustment::Adjustment<'tcx>>>,
+}
+
 #[derive(TyEncodable, TyDecodable, Debug, HashStable)]
 pub struct TypeckResults<'tcx> {
     /// The `HirId::owner` all `ItemLocalId`s in this table are relative to.
@@ -623,6 +633,28 @@ impl<'tcx> TypeckResults<'tcx> {
         LocalTableInContextMut { hir_owner: self.hir_owner, data: &mut self.node_types }
     }
 
+    pub fn get_generator_diagnostic_data(&self) -> GeneratorDiagnosticData<'tcx> {
+        let generator_interior_type = self.generator_interior_types.map_bound_ref(|vec| {
+            vec.iter()
+                .map(|item| {
+                    GeneratorInteriorTypeCause {
+                        ty: item.ty,
+                        span: item.span,
+                        scope_span: item.scope_span,
+                        yield_span: item.yield_span,
+                        expr: None, //FIXME: Passing expression over crate boundaries is impossible at the moment
+                    }
+                })
+                .collect::<Vec<_>>()
+        });
+        GeneratorDiagnosticData {
+            generator_interior_types: generator_interior_type,
+            hir_owner: self.hir_owner.to_def_id(),
+            nodes_types: self.node_types.clone(),
+            adjustments: self.adjustments.clone(),
+        }
+    }
+
     pub fn node_type(&self, id: hir::HirId) -> Ty<'tcx> {
         self.node_type_opt(id).unwrap_or_else(|| {
             bug!("node_type: no type for node `{}`", tls::with(|tcx| tcx.hir().node_to_string(id)))

compiler/rustc_middle/src/ty/mod.rs

@@ -67,8 +67,9 @@ pub use self::consts::{
 };
 pub use self::context::{
     tls, CanonicalUserType, CanonicalUserTypeAnnotation, CanonicalUserTypeAnnotations,
-    CtxtInterners, DelaySpanBugEmitted, FreeRegionInfo, GeneratorInteriorTypeCause, GlobalCtxt,
-    Lift, OnDiskCache, TyCtxt, TypeckResults, UserType, UserTypeAnnotationIndex,
+    CtxtInterners, DelaySpanBugEmitted, FreeRegionInfo, GeneratorDiagnosticData,
+    GeneratorInteriorTypeCause, GlobalCtxt, Lift, OnDiskCache, TyCtxt, TypeckResults, UserType,
+    UserTypeAnnotationIndex,
 };
 pub use self::instance::{Instance, InstanceDef};
 pub use self::list::List;

compiler/rustc_middle/src/ty/query.rs

@@ -31,8 +31,11 @@ use crate::traits::{self, ImplSource};
 use crate::ty::fast_reject::SimplifiedType;
 use crate::ty::subst::{GenericArg, SubstsRef};
 use crate::ty::util::AlwaysRequiresDrop;
+use crate::ty::GeneratorDiagnosticData;
 use crate::ty::{self, AdtSizedConstraint, CrateInherentImpls, ParamEnvAnd, Ty, TyCtxt};
+use rustc_ast as ast;
 use rustc_ast::expand::allocator::AllocatorKind;
+use rustc_attr as attr;
 use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexMap};
 use rustc_data_structures::steal::Steal;
 use rustc_data_structures::svh::Svh;
@@ -49,13 +52,10 @@ use rustc_session::cstore::{CrateDepKind, CrateSource};
 use rustc_session::cstore::{ExternCrate, ForeignModule, LinkagePreference, NativeLib};
 use rustc_session::utils::NativeLibKind;
 use rustc_session::Limits;
-use rustc_target::abi;
-use rustc_target::spec::PanicStrategy;
-
-use rustc_ast as ast;
-use rustc_attr as attr;
 use rustc_span::symbol::Symbol;
 use rustc_span::{Span, DUMMY_SP};
+use rustc_target::abi;
+use rustc_target::spec::PanicStrategy;
 use std::ops::Deref;
 use std::path::PathBuf;
 use std::sync::Arc;