Provide a better diagnostic on failure to meet send bound on futures in a foreign crate

Adding diagnostic data on generators to the crate metadata and using it to provide
a better diagnostic on failure to meet send bound on futures originated from a foreign crate

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;