Rollup of 8 pull requests

src/libcore/num/mod.rs

@@ -1499,8 +1499,8 @@ any high-order bits of `rhs` that would cause the shift to exceed the bitwidth o
 
 Note that this is *not* the same as a rotate-left; the RHS of a wrapping shift-left is restricted to
 the range of the type, rather than the bits shifted out of the LHS being returned to the other end.
-The primitive integer types all implement a `rotate_left` function, which may be what you want
-instead.
+The primitive integer types all implement a `[`rotate_left`](#method.rotate_left) function,
+which may be what you want instead.
 
 # Examples
 
@@ -1531,8 +1531,8 @@ removes any high-order bits of `rhs` that would cause the shift to exceed the bi
 
 Note that this is *not* the same as a rotate-right; the RHS of a wrapping shift-right is restricted
 to the range of the type, rather than the bits shifted out of the LHS being returned to the other
-end. The primitive integer types all implement a `rotate_right` function, which may be what you want
-instead.
+end. The primitive integer types all implement a [`rotate_right`](#method.rotate_right) function,
+which may be what you want instead.
 
 # Examples
 
@@ -3610,8 +3610,8 @@ Note that this is *not* the same as a rotate-left; the
 RHS of a wrapping shift-left is restricted to the range
 of the type, rather than the bits shifted out of the LHS
 being returned to the other end. The primitive integer
-types all implement a `rotate_left` function, which may
-be what you want instead.
+types all implement a [`rotate_left`](#method.rotate_left) function,
+which may be what you want instead.
 
 # Examples
 
@@ -3644,8 +3644,8 @@ Note that this is *not* the same as a rotate-right; the
 RHS of a wrapping shift-right is restricted to the range
 of the type, rather than the bits shifted out of the LHS
 being returned to the other end. The primitive integer
-types all implement a `rotate_right` function, which may
-be what you want instead.
+types all implement a [`rotate_right`](#method.rotate_right) function,
+which may be what you want instead.
 
 # Examples
 

src/librustc_middle/hir/map/mod.rs

@@ -390,11 +390,7 @@ impl<'hir> Map<'hir> {
     /// Given a `HirId`, returns the `BodyId` associated with it,
     /// if the node is a body owner, otherwise returns `None`.
     pub fn maybe_body_owned_by(&self, hir_id: HirId) -> Option<BodyId> {
-        if let Some(node) = self.find(hir_id) {
-            associated_body(node)
-        } else {
-            bug!("no entry for id `{}`", hir_id)
-        }
+        self.find(hir_id).map(associated_body).flatten()
     }
 
     /// Given a body owner's id, returns the `BodyId` associated with it.

src/librustc_middle/query/mod.rs

@@ -1164,6 +1164,12 @@ rustc_queries! {
             desc { "evaluating trait selection obligation `{}`", goal.value }
         }
 
+        query type_implements_trait(
+            key: (DefId, Ty<'tcx>, SubstsRef<'tcx>, ty::ParamEnv<'tcx>, )
+        ) -> bool {
+            desc { "evaluating `type_implements_trait` `{:?}`", key }
+        }
+
         /// Do not call this query directly: part of the `Eq` type-op
         query type_op_ascribe_user_type(
             goal: CanonicalTypeOpAscribeUserTypeGoal<'tcx>

src/librustc_middle/ty/query/keys.rs

@@ -295,3 +295,15 @@ impl Key for (Symbol, u32, u32) {
         DUMMY_SP
     }
 }
+
+impl<'tcx> Key for (DefId, Ty<'tcx>, SubstsRef<'tcx>, ty::ParamEnv<'tcx>) {
+    type CacheSelector = DefaultCacheSelector;
+
+    fn query_crate(&self) -> CrateNum {
+        LOCAL_CRATE
+    }
+
+    fn default_span(&self, _tcx: TyCtxt<'_>) -> Span {
+        DUMMY_SP
+    }
+}

src/librustc_mir/monomorphize/mod.rs

@@ -2,6 +2,8 @@ use rustc_middle::traits;
 use rustc_middle::ty::adjustment::CustomCoerceUnsized;
 use rustc_middle::ty::{self, Ty, TyCtxt};
 
+use rustc_hir::lang_items::CoerceUnsizedTraitLangItem;
+
 pub mod collector;
 pub mod partitioning;
 
@@ -10,7 +12,7 @@ pub fn custom_coerce_unsize_info<'tcx>(
     source_ty: Ty<'tcx>,
     target_ty: Ty<'tcx>,
 ) -> CustomCoerceUnsized {
-    let def_id = tcx.lang_items().coerce_unsized_trait().unwrap();
+    let def_id = tcx.require_lang_item(CoerceUnsizedTraitLangItem, None);
 
     let trait_ref = ty::Binder::bind(ty::TraitRef {
         def_id,

src/librustc_mir/transform/const_prop.rs

@@ -616,6 +616,13 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
         value: OpTy<'tcx>,
         source_info: SourceInfo,
     ) {
+        if let Rvalue::Use(Operand::Constant(c)) = rval {
+            if !matches!(c.literal.val, ConstKind::Unevaluated(..)) {
+                trace!("skipping replace of Rvalue::Use({:?} because it is already a const", c);
+                return;
+            }
+        }
+
         trace!("attepting to replace {:?} with {:?}", rval, value);
         if let Err(e) = self.ecx.const_validate_operand(
             value,

src/librustc_mir_build/hair/pattern/const_to_pat.rs

@@ -141,7 +141,8 @@ impl<'a, 'tcx> ConstToPat<'a, 'tcx> {
                 // code at the moment, because types like `for <'a> fn(&'a ())` do
                 // not *yet* implement `PartialEq`. So for now we leave this here.
                 let ty_is_partial_eq: bool = {
-                    let partial_eq_trait_id = self.tcx().require_lang_item(EqTraitLangItem, None);
+                    let partial_eq_trait_id =
+                        self.tcx().require_lang_item(EqTraitLangItem, Some(self.span));
                     let obligation: PredicateObligation<'_> = predicate_for_trait_def(
                         self.tcx(),
                         self.param_env,

src/librustc_trait_selection/traits/error_reporting/mod.rs

@@ -402,6 +402,7 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
                         self.suggest_remove_reference(&obligation, &mut err, &trait_ref);
                         self.suggest_semicolon_removal(&obligation, &mut err, span, &trait_ref);
                         self.note_version_mismatch(&mut err, &trait_ref);
+                        self.suggest_await_before_try(&mut err, &obligation, &trait_ref, span);
                         if self.suggest_impl_trait(&mut err, span, &obligation, &trait_ref) {
                             err.emit();
                             return;

src/librustc_trait_selection/traits/error_reporting/suggestions.rs

@@ -1,14 +1,17 @@
 use super::{
     EvaluationResult, Obligation, ObligationCause, ObligationCauseCode, PredicateObligation,
+    SelectionContext,
 };
 
 use crate::infer::InferCtxt;
+use crate::traits::normalize_projection_type;
 
 use rustc_errors::{error_code, struct_span_err, Applicability, DiagnosticBuilder, Style};
 use rustc_hir as hir;
 use rustc_hir::def::DefKind;
 use rustc_hir::def_id::DefId;
 use rustc_hir::intravisit::Visitor;
+use rustc_hir::lang_items;
 use rustc_hir::{AsyncGeneratorKind, GeneratorKind, Node};
 use rustc_middle::ty::TypeckTables;
 use rustc_middle::ty::{
@@ -150,6 +153,15 @@ pub trait InferCtxtExt<'tcx> {
         T: fmt::Display;
 
     fn suggest_new_overflow_limit(&self, err: &mut DiagnosticBuilder<'_>);
+
+    /// Suggest to await before try: future? => future.await?
+    fn suggest_await_before_try(
+        &self,
+        err: &mut DiagnosticBuilder<'_>,
+        obligation: &PredicateObligation<'tcx>,
+        trait_ref: &ty::Binder<ty::TraitRef<'tcx>>,
+        span: Span,
+    );
 }
 
 fn predicate_constraint(generics: &hir::Generics<'_>, pred: String) -> (Span, String) {
@@ -1822,6 +1834,95 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
             suggested_limit, self.tcx.crate_name,
         ));
     }
+
+    fn suggest_await_before_try(
+        &self,
+        err: &mut DiagnosticBuilder<'_>,
+        obligation: &PredicateObligation<'tcx>,
+        trait_ref: &ty::Binder<ty::TraitRef<'tcx>>,
+        span: Span,
+    ) {
+        debug!(
+            "suggest_await_befor_try: obligation={:?}, span={:?}, trait_ref={:?}, trait_ref_self_ty={:?}",
+            obligation,
+            span,
+            trait_ref,
+            trait_ref.self_ty()
+        );
+        let body_hir_id = obligation.cause.body_id;
+        let item_id = self.tcx.hir().get_parent_node(body_hir_id);
+
+        if let Some(body_id) = self.tcx.hir().maybe_body_owned_by(item_id) {
+            let body = self.tcx.hir().body(body_id);
+            if let Some(hir::GeneratorKind::Async(_)) = body.generator_kind {
+                let future_trait =
+                    self.tcx.require_lang_item(lang_items::FutureTraitLangItem, None);
+
+                let self_ty = self.resolve_vars_if_possible(&trait_ref.self_ty());
+
+                let impls_future = self.tcx.type_implements_trait((
+                    future_trait,
+                    self_ty,
+                    ty::List::empty(),
+                    obligation.param_env,
+                ));
+
+                let item_def_id = self
+                    .tcx
+                    .associated_items(future_trait)
+                    .in_definition_order()
+                    .next()
+                    .unwrap()
+                    .def_id;
+                // `<T as Future>::Output`
+                let projection_ty = ty::ProjectionTy {
+                    // `T`
+                    substs: self.tcx.mk_substs_trait(
+                        trait_ref.self_ty(),
+                        self.fresh_substs_for_item(span, item_def_id),
+                    ),
+                    // `Future::Output`
+                    item_def_id,
+                };
+
+                let mut selcx = SelectionContext::new(self);
+
+                let mut obligations = vec![];
+                let normalized_ty = normalize_projection_type(
+                    &mut selcx,
+                    obligation.param_env,
+                    projection_ty,
+                    obligation.cause.clone(),
+                    0,
+                    &mut obligations,
+                );
+
+                debug!(
+                    "suggest_await_befor_try: normalized_projection_type {:?}",
+                    self.resolve_vars_if_possible(&normalized_ty)
+                );
+                let try_obligation = self.mk_obligation_for_def_id(
+                    trait_ref.def_id(),
+                    normalized_ty,
+                    obligation.cause.clone(),
+                    obligation.param_env,
+                );
+                debug!("suggest_await_befor_try: try_trait_obligation {:?}", try_obligation);
+                if self.predicate_may_hold(&try_obligation) && impls_future {
+                    if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span) {
+                        if snippet.ends_with('?') {
+                            err.span_suggestion(
+                                span,
+                                "consider using `.await` here",
+                                format!("{}.await?", snippet.trim_end_matches('?')),
+                                Applicability::MaybeIncorrect,
+                            );
+                        }
+                    }
+                }
+            }
+        }
+    }
 }
 
 /// Collect all the returned expressions within the input expression.

src/librustc_trait_selection/traits/mod.rs

@@ -31,7 +31,9 @@ use rustc_hir::def_id::DefId;
 use rustc_middle::middle::region;
 use rustc_middle::ty::fold::TypeFoldable;
 use rustc_middle::ty::subst::{InternalSubsts, SubstsRef};
-use rustc_middle::ty::{self, GenericParamDefKind, ToPredicate, Ty, TyCtxt, WithConstness};
+use rustc_middle::ty::{
+    self, GenericParamDefKind, ParamEnv, ToPredicate, Ty, TyCtxt, WithConstness,
+};
 use rustc_span::Span;
 
 use std::fmt::Debug;
@@ -523,6 +525,43 @@ fn vtable_methods<'tcx>(
     }))
 }
 
+/// Check whether a `ty` implements given trait(trait_def_id).
+///
+/// NOTE: Always return `false` for a type which needs inference.
+fn type_implements_trait<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    key: (
+        DefId,    // trait_def_id,
+        Ty<'tcx>, // type
+        SubstsRef<'tcx>,
+        ParamEnv<'tcx>,
+    ),
+) -> bool {
+    let (trait_def_id, ty, params, param_env) = key;
+
+    debug!(
+        "type_implements_trait: trait_def_id={:?}, type={:?}, params={:?}, param_env={:?}",
+        trait_def_id, ty, params, param_env
+    );
+
+    // Do not check on infer_types to avoid panic in evaluate_obligation.
+    if ty.has_infer_types() {
+        return false;
+    }
+
+    let ty = tcx.erase_regions(&ty);
+
+    let trait_ref = ty::TraitRef { def_id: trait_def_id, substs: tcx.mk_substs_trait(ty, params) };
+
+    let obligation = Obligation {
+        cause: ObligationCause::dummy(),
+        param_env,
+        recursion_depth: 0,
+        predicate: trait_ref.without_const().to_predicate(),
+    };
+    tcx.infer_ctxt().enter(|infcx| infcx.predicate_must_hold_modulo_regions(&obligation))
+}
+
 pub fn provide(providers: &mut ty::query::Providers<'_>) {
     object_safety::provide(providers);
     *providers = ty::query::Providers {
@@ -531,6 +570,7 @@ pub fn provide(providers: &mut ty::query::Providers<'_>) {
         codegen_fulfill_obligation: codegen::codegen_fulfill_obligation,
         vtable_methods,
         substitute_normalize_and_test_predicates,
+        type_implements_trait,
         ..*providers
     };
 }

src/librustc_trait_selection/traits/structural_match.rs

@@ -4,6 +4,7 @@ use crate::traits::{self, ConstPatternStructural, TraitEngine};
 
 use rustc_data_structures::fx::FxHashSet;
 use rustc_hir as hir;
+use rustc_hir::lang_items::{StructuralPeqTraitLangItem, StructuralTeqTraitLangItem};
 use rustc_middle::ty::{self, AdtDef, Ty, TyCtxt, TypeFoldable, TypeVisitor};
 use rustc_span::Span;
 
@@ -69,7 +70,7 @@ pub fn type_marked_structural(
     let mut fulfillment_cx = traits::FulfillmentContext::new();
     let cause = ObligationCause::new(span, id, ConstPatternStructural);
     // require `#[derive(PartialEq)]`
-    let structural_peq_def_id = infcx.tcx.lang_items().structural_peq_trait().unwrap();
+    let structural_peq_def_id = infcx.tcx.require_lang_item(StructuralPeqTraitLangItem, Some(span));
     fulfillment_cx.register_bound(
         infcx,
         ty::ParamEnv::empty(),
@@ -80,7 +81,7 @@ pub fn type_marked_structural(
     // for now, require `#[derive(Eq)]`. (Doing so is a hack to work around
     // the type `for<'a> fn(&'a ())` failing to implement `Eq` itself.)
     let cause = ObligationCause::new(span, id, ConstPatternStructural);
-    let structural_teq_def_id = infcx.tcx.lang_items().structural_teq_trait().unwrap();
+    let structural_teq_def_id = infcx.tcx.require_lang_item(StructuralTeqTraitLangItem, Some(span));
     fulfillment_cx.register_bound(
         infcx,
         ty::ParamEnv::empty(),

src/librustc_typeck/check/closure.rs

@@ -6,7 +6,7 @@ use crate::astconv::AstConv;
 use crate::middle::region;
 use rustc_hir as hir;
 use rustc_hir::def_id::DefId;
-use rustc_hir::lang_items;
+use rustc_hir::lang_items::{FutureTraitLangItem, GeneratorTraitLangItem};
 use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
 use rustc_infer::infer::LateBoundRegionConversionTime;
 use rustc_infer::infer::{InferOk, InferResult};
@@ -245,7 +245,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         let trait_ref = projection.to_poly_trait_ref(tcx);
 
         let is_fn = tcx.fn_trait_kind_from_lang_item(trait_ref.def_id()).is_some();
-        let gen_trait = tcx.require_lang_item(lang_items::GeneratorTraitLangItem, cause_span);
+        let gen_trait = tcx.require_lang_item(GeneratorTraitLangItem, cause_span);
         let is_gen = gen_trait == trait_ref.def_id();
         if !is_fn && !is_gen {
             debug!("deduce_sig_from_projection: not fn or generator");
@@ -678,7 +678,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
         // Check that this is a projection from the `Future` trait.
         let trait_ref = predicate.projection_ty.trait_ref(self.tcx);
-        let future_trait = self.tcx.lang_items().future_trait().unwrap();
+        let future_trait = self.tcx.require_lang_item(FutureTraitLangItem, Some(cause_span));
         if trait_ref.def_id != future_trait {
             debug!("deduce_future_output_from_projection: not a future");
             return None;