Check the invariant for `principal` inside the method

25 files changed, 112 insertions, 151 deletions

diff --git a/src/librustc/traits/coherence.rs b/src/librustc/traits/coherence.rs
index 7add8ef05ee..817e9ffcbb5 100644
--- a/src/librustc/traits/coherence.rs
+++ b/src/librustc/traits/coherence.rs
@@ -418,9 +418,7 @@ fn fundamental_ty(tcx: TyCtxt<'_, '_, '_>, ty: Ty<'_>) -> bool {
     match ty.sty {
         ty::Ref(..) => true,
         ty::Adt(def, _) => def.is_fundamental(),
-        ty::Dynamic(ref data, ..) => {
-            data.principal().map_or(false, |p| tcx.has_attr(p.def_id(), "fundamental"))
-        }
+        ty::Dynamic(ref data, ..) => tcx.has_attr(data.principal().def_id(), "fundamental"),
         _ => false
     }
 }
@@ -467,11 +465,7 @@ fn ty_is_local_constructor(ty: Ty<'_>, in_crate: InCrate) -> bool {
         ty::Adt(def, _) => def_id_is_local(def.did, in_crate),
         ty::Foreign(did) => def_id_is_local(did, in_crate),
 
-        ty::Dynamic(ref tt, ..) => {
-            tt.principal().map_or(false, |p|
-                def_id_is_local(p.def_id(), in_crate)
-            )
-        }
+        ty::Dynamic(ref tt, ..) => def_id_is_local(tt.principal().def_id(), in_crate),
 
         ty::Error => true,
 
diff --git a/src/librustc/traits/select.rs b/src/librustc/traits/select.rs
index 82d881e10b1..8e8024e51da 100644
--- a/src/librustc/traits/select.rs
+++ b/src/librustc/traits/select.rs
@@ -2088,10 +2088,7 @@ impl<'cx, 'gcx, 'tcx> SelectionContext<'cx, 'gcx, 'tcx> {
                         return;
                     }
 
-                    match data.principal() {
-                        Some(p) => p.with_self_ty(this.tcx(), self_ty),
-                        None => return,
-                    }
+                    data.principal().with_self_ty(this.tcx(), self_ty)
                 }
                 ty::Infer(ty::TyVar(_)) => {
                     debug!("assemble_candidates_from_object_ty: ambiguous");
@@ -2183,15 +2180,10 @@ impl<'cx, 'gcx, 'tcx> SelectionContext<'cx, 'gcx, 'tcx> {
                 //
                 // We always upcast when we can because of reason
                 // #2 (region bounds).
-                match (data_a.principal(), data_b.principal()) {
-                    (Some(a), Some(b)) => {
-                        a.def_id() == b.def_id()
-                            && data_b.auto_traits()
-                            // All of a's auto traits need to be in b's auto traits.
-                            .all(|b| data_a.auto_traits().any(|a| a == b))
-                    }
-                    _ => false,
-                }
+                data_a.principal().def_id() == data_b.principal().def_id()
+                    && data_b.auto_traits()
+                    // All of a's auto traits need to be in b's auto traits.
+                    .all(|b| data_a.auto_traits().any(|a| a == b))
             }
 
             // T -> Trait.
@@ -2981,7 +2973,7 @@ impl<'cx, 'gcx, 'tcx> SelectionContext<'cx, 'gcx, 'tcx> {
             .shallow_resolve(*obligation.self_ty().skip_binder());
         let poly_trait_ref = match self_ty.sty {
             ty::Dynamic(ref data, ..) => {
-                data.principal().unwrap().with_self_ty(self.tcx(), self_ty)
+                data.principal().with_self_ty(self.tcx(), self_ty)
             }
             _ => span_bug!(obligation.cause.span, "object candidate with non-object"),
         };
@@ -3244,10 +3236,7 @@ impl<'cx, 'gcx, 'tcx> SelectionContext<'cx, 'gcx, 'tcx> {
             (&ty::Dynamic(ref data_a, r_a), &ty::Dynamic(ref data_b, r_b)) => {
                 // See assemble_candidates_for_unsizing for more info.
                 let existential_predicates = data_a.map_bound(|data_a| {
-                    let principal = data_a.principal();
-                    let iter = principal
-                        .into_iter()
-                        .map(ty::ExistentialPredicate::Trait)
+                    let iter = iter::once(ty::ExistentialPredicate::Trait(data_a.principal()))
                         .chain(
                             data_a
                                 .projection_bounds()
@@ -3285,7 +3274,7 @@ impl<'cx, 'gcx, 'tcx> SelectionContext<'cx, 'gcx, 'tcx> {
             // T -> Trait.
             (_, &ty::Dynamic(ref data, r)) => {
                 let mut object_dids = data.auto_traits()
-                    .chain(data.principal().map(|p| p.def_id()));
+                    .chain(iter::once(data.principal().def_id()));
                 if let Some(did) = object_dids.find(|did| !tcx.is_object_safe(*did)) {
                     return Err(TraitNotObjectSafe(did));
                 }
diff --git a/src/librustc/ty/error.rs b/src/librustc/ty/error.rs
index 3123f0fbe31..d886d5ed204 100644
--- a/src/librustc/ty/error.rs
+++ b/src/librustc/ty/error.rs
@@ -208,8 +208,7 @@ impl<'a, 'gcx, 'lcx, 'tcx> ty::TyS<'tcx> {
             ty::FnDef(..) => "fn item".into(),
             ty::FnPtr(_) => "fn pointer".into(),
             ty::Dynamic(ref inner, ..) => {
-                inner.principal().map_or_else(|| "trait".into(),
-                    |p| format!("trait {}", tcx.item_path_str(p.def_id())).into())
+                format!("trait {}", tcx.item_path_str(inner.principal().def_id())).into()
             }
             ty::Closure(..) => "closure".into(),
             ty::Generator(..) => "generator".into(),
diff --git a/src/librustc/ty/fast_reject.rs b/src/librustc/ty/fast_reject.rs
index 0f68e7aba4d..e6aaf8b1bb2 100644
--- a/src/librustc/ty/fast_reject.rs
+++ b/src/librustc/ty/fast_reject.rs
@@ -78,7 +78,7 @@ pub fn simplify_type<'a, 'gcx, 'tcx>(tcx: TyCtxt<'a, 'gcx, 'tcx>,
         ty::Array(..) | ty::Slice(_) => Some(ArraySimplifiedType),
         ty::RawPtr(_) => Some(PtrSimplifiedType),
         ty::Dynamic(ref trait_info, ..) => {
-            trait_info.principal().map(|p| TraitSimplifiedType(p.def_id()))
+            Some(TraitSimplifiedType(trait_info.principal().def_id()))
         }
         ty::Ref(_, ty, _) => {
             // since we introduce auto-refs during method lookup, we
diff --git a/src/librustc/ty/item_path.rs b/src/librustc/ty/item_path.rs
index ab081324036..c4a25971da3 100644
--- a/src/librustc/ty/item_path.rs
+++ b/src/librustc/ty/item_path.rs
@@ -436,7 +436,7 @@ pub fn characteristic_def_id_of_type(ty: Ty<'_>) -> Option<DefId> {
     match ty.sty {
         ty::Adt(adt_def, _) => Some(adt_def.did),
 
-        ty::Dynamic(data, ..) => data.principal().map(|p| p.def_id()),
+        ty::Dynamic(data, ..) => Some(data.principal().def_id()),
 
         ty::Array(subty, _) |
         ty::Slice(subty) => characteristic_def_id_of_type(subty),
diff --git a/src/librustc/ty/sty.rs b/src/librustc/ty/sty.rs
index 145c122e75d..cc6e6b2861e 100644
--- a/src/librustc/ty/sty.rs
+++ b/src/librustc/ty/sty.rs
@@ -559,10 +559,10 @@ impl<'a, 'gcx, 'tcx> Binder<ExistentialPredicate<'tcx>> {
 impl<'tcx> serialize::UseSpecializedDecodable for &'tcx List<ExistentialPredicate<'tcx>> {}
 
 impl<'tcx> List<ExistentialPredicate<'tcx>> {
-    pub fn principal(&self) -> Option<ExistentialTraitRef<'tcx>> {
-        match self.get(0) {
-            Some(&ExistentialPredicate::Trait(tr)) => Some(tr),
-            _ => None,
+    pub fn principal(&self) -> ExistentialTraitRef<'tcx> {
+        match self[0] {
+            ExistentialPredicate::Trait(tr) => tr,
+            other => bug!("first predicate is {:?}", other),
         }
     }
 
@@ -589,8 +589,8 @@ impl<'tcx> List<ExistentialPredicate<'tcx>> {
 }
 
 impl<'tcx> Binder<&'tcx List<ExistentialPredicate<'tcx>>> {
-    pub fn principal(&self) -> Option<PolyExistentialTraitRef<'tcx>> {
-        self.skip_binder().principal().map(Binder::bind)
+    pub fn principal(&self) -> PolyExistentialTraitRef<'tcx> {
+        Binder::bind(self.skip_binder().principal())
     }
 
     #[inline]
@@ -1825,9 +1825,7 @@ impl<'a, 'gcx, 'tcx> TyS<'tcx> {
             }
             Dynamic(ref obj, region) => {
                 let mut v = vec![region];
-                if let Some(p) = obj.principal() {
-                    v.extend(p.skip_binder().substs.regions());
-                }
+                v.extend(obj.principal().skip_binder().substs.regions());
                 v
             }
             Adt(_, substs) | Opaque(_, substs) => {
diff --git a/src/librustc/ty/wf.rs b/src/librustc/ty/wf.rs
index 7af838845cd..27747970f76 100644
--- a/src/librustc/ty/wf.rs
+++ b/src/librustc/ty/wf.rs
@@ -387,7 +387,7 @@ impl<'a, 'gcx, 'tcx> WfPredicates<'a, 'gcx, 'tcx> {
 
                     let cause = self.cause(traits::MiscObligation);
                     let component_traits =
-                        data.auto_traits().chain(data.principal().map(|p| p.def_id()));
+                        data.auto_traits().chain(once(data.principal().def_id()));
                     self.out.extend(
                         component_traits.map(|did| traits::Obligation::new(
                             cause.clone(),
diff --git a/src/librustc/util/ppaux.rs b/src/librustc/util/ppaux.rs
index 33534ab27f1..f3b5503b8d0 100644
--- a/src/librustc/util/ppaux.rs
+++ b/src/librustc/util/ppaux.rs
@@ -621,16 +621,16 @@ define_print! {
                 // Use a type that can't appear in defaults of type parameters.
                 let dummy_self = tcx.mk_infer(ty::FreshTy(0));
 
-                if let Some(p) = self.principal() {
-                    let principal = tcx.lift(&p).expect("could not lift TraitRef for printing")
-                        .with_self_ty(tcx, dummy_self);
-                    let projections = self.projection_bounds().map(|p| {
-                        tcx.lift(&p)
-                            .expect("could not lift projection for printing")
-                            .with_self_ty(tcx, dummy_self)
-                    }).collect::<Vec<_>>();
-                    cx.parameterized(f, principal.substs, principal.def_id, &projections)?;
-                }
+                let principal = tcx
+                    .lift(&self.principal())
+                    .expect("could not lift TraitRef for printing")
+                    .with_self_ty(tcx, dummy_self);
+                let projections = self.projection_bounds().map(|p| {
+                    tcx.lift(&p)
+                        .expect("could not lift projection for printing")
+                        .with_self_ty(tcx, dummy_self)
+                }).collect::<Vec<_>>();
+                cx.parameterized(f, principal.substs, principal.def_id, &projections)?;
 
                 // Builtin bounds.
                 for did in self.auto_traits() {
diff --git a/src/librustc_codegen_llvm/context.rs b/src/librustc_codegen_llvm/context.rs
index 578018c7adc..e6197423738 100644
--- a/src/librustc_codegen_llvm/context.rs
+++ b/src/librustc_codegen_llvm/context.rs
@@ -59,7 +59,7 @@ pub struct CodegenCx<'a, 'tcx: 'a> {
     /// Cache instances of monomorphic and polymorphic items
     pub instances: RefCell<FxHashMap<Instance<'tcx>, &'a Value>>,
     /// Cache generated vtables
-    pub vtables: RefCell<FxHashMap<(Ty<'tcx>, Option<ty::PolyExistentialTraitRef<'tcx>>),
+    pub vtables: RefCell<FxHashMap<(Ty<'tcx>, ty::PolyExistentialTraitRef<'tcx>),
                                    &'a Value>>,
     /// Cache of constant strings,
     pub const_cstr_cache: RefCell<FxHashMap<LocalInternedString, &'a Value>>,
diff --git a/src/librustc_codegen_llvm/debuginfo/metadata.rs b/src/librustc_codegen_llvm/debuginfo/metadata.rs
index 706568b5446..6eff086a2ba 100644
--- a/src/librustc_codegen_llvm/debuginfo/metadata.rs
+++ b/src/librustc_codegen_llvm/debuginfo/metadata.rs
@@ -435,12 +435,7 @@ fn trait_pointer_metadata(
     // But it does not describe the trait's methods.
 
     let containing_scope = match trait_type.sty {
-        ty::Dynamic(ref data, ..) => if let Some(principal) = data.principal() {
-            let def_id = principal.def_id();
-            Some(get_namespace_for_item(cx, def_id))
-        } else {
-            NO_SCOPE_METADATA
-        },
+        ty::Dynamic(ref data, ..) => Some(get_namespace_for_item(cx, data.principal().def_id())),
         _ => {
             bug!("debuginfo: Unexpected trait-object type in \
                   trait_pointer_metadata(): {:?}",
diff --git a/src/librustc_codegen_llvm/debuginfo/type_names.rs b/src/librustc_codegen_llvm/debuginfo/type_names.rs
index 2f110fd552a..06b9318a5e8 100644
--- a/src/librustc_codegen_llvm/debuginfo/type_names.rs
+++ b/src/librustc_codegen_llvm/debuginfo/type_names.rs
@@ -116,14 +116,12 @@ pub fn push_debuginfo_type_name<'a, 'tcx>(cx: &CodegenCx<'a, 'tcx>,
             }
         },
         ty::Dynamic(ref trait_data, ..) => {
-            if let Some(principal) = trait_data.principal() {
-                let principal = cx.tcx.normalize_erasing_late_bound_regions(
-                    ty::ParamEnv::reveal_all(),
-                    &principal,
-                );
-                push_item_name(cx, principal.def_id, false, output);
-                push_type_params(cx, principal.substs, output);
-            }
+            let principal = cx.tcx.normalize_erasing_late_bound_regions(
+                ty::ParamEnv::reveal_all(),
+                &trait_data.principal(),
+            );
+            push_item_name(cx, principal.def_id, false, output);
+            push_type_params(cx, principal.substs, output);
         },
         ty::FnDef(..) | ty::FnPtr(_) => {
             let sig = t.fn_sig(cx.tcx);
diff --git a/src/librustc_codegen_llvm/meth.rs b/src/librustc_codegen_llvm/meth.rs
index 8a1159bc477..db06b87f44e 100644
--- a/src/librustc_codegen_llvm/meth.rs
+++ b/src/librustc_codegen_llvm/meth.rs
@@ -72,7 +72,7 @@ impl<'a, 'tcx> VirtualIndex {
 pub fn get_vtable(
     cx: &CodegenCx<'ll, 'tcx>,
     ty: Ty<'tcx>,
-    trait_ref: Option<ty::PolyExistentialTraitRef<'tcx>>,
+    trait_ref: ty::PolyExistentialTraitRef<'tcx>,
 ) -> &'ll Value {
     let tcx = cx.tcx;
 
@@ -86,23 +86,19 @@ pub fn get_vtable(
     // Not in the cache. Build it.
     let nullptr = C_null(Type::i8p(cx));
 
+    let methods = tcx.vtable_methods(trait_ref.with_self_ty(tcx, ty));
+    let methods = methods.iter().cloned().map(|opt_mth| {
+        opt_mth.map_or(nullptr, |(def_id, substs)| {
+            callee::resolve_and_get_fn(cx, def_id, substs)
+        })
+    });
+
     let (size, align) = cx.size_and_align_of(ty);
-    let mut components: Vec<_> = [
+    let components: Vec<_> = [
         callee::get_fn(cx, monomorphize::resolve_drop_in_place(cx.tcx, ty)),
         C_usize(cx, size.bytes()),
         C_usize(cx, align.abi())
-    ].iter().cloned().collect();
-
-    if let Some(trait_ref) = trait_ref {
-        let trait_ref = trait_ref.with_self_ty(tcx, ty);
-        let methods = tcx.vtable_methods(trait_ref);
-        let methods = methods.iter().cloned().map(|opt_mth| {
-            opt_mth.map_or(nullptr, |(def_id, substs)| {
-                callee::resolve_and_get_fn(cx, def_id, substs)
-            })
-        });
-        components.extend(methods);
-    }
+    ].iter().cloned().chain(methods).collect();
 
     let vtable_const = C_struct(cx, &components, false);
     let align = cx.data_layout().pointer_align;
diff --git a/src/librustc_mir/interpret/cast.rs b/src/librustc_mir/interpret/cast.rs
index bfc7e6801fc..32ce16212e4 100644
--- a/src/librustc_mir/interpret/cast.rs
+++ b/src/librustc_mir/interpret/cast.rs
@@ -326,7 +326,7 @@ impl<'a, 'mir, 'tcx, M: Machine<'a, 'mir, 'tcx>> EvalContext<'a, 'mir, 'tcx, M>
             }
             (_, &ty::Dynamic(ref data, _)) => {
                 // Initial cast from sized to dyn trait
-                let trait_ref = data.principal().unwrap().with_self_ty(
+                let trait_ref = data.principal().with_self_ty(
                     *self.tcx,
                     src_pointee_ty,
                 );
diff --git a/src/librustc_mir/monomorphize/collector.rs b/src/librustc_mir/monomorphize/collector.rs
index 29f16762944..dd83d3157ba 100644
--- a/src/librustc_mir/monomorphize/collector.rs
+++ b/src/librustc_mir/monomorphize/collector.rs
@@ -907,22 +907,20 @@ fn create_mono_items_for_vtable_methods<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
             !impl_ty.needs_subst() && !impl_ty.has_escaping_regions());
 
     if let ty::Dynamic(ref trait_ty, ..) = trait_ty.sty {
-        if let Some(principal) = trait_ty.principal() {
-            let poly_trait_ref = principal.with_self_ty(tcx, impl_ty);
-            assert!(!poly_trait_ref.has_escaping_regions());
-
-            // Walk all methods of the trait, including those of its supertraits
-            let methods = tcx.vtable_methods(poly_trait_ref);
-            let methods = methods.iter().cloned().filter_map(|method| method)
-                .map(|(def_id, substs)| ty::Instance::resolve(
-                        tcx,
-                        ty::ParamEnv::reveal_all(),
-                        def_id,
-                        substs).unwrap())
-                .filter(|&instance| should_monomorphize_locally(tcx, &instance))
-                .map(|instance| create_fn_mono_item(instance));
-            output.extend(methods);
-        }
+        let poly_trait_ref = trait_ty.principal().with_self_ty(tcx, impl_ty);
+        assert!(!poly_trait_ref.has_escaping_regions());
+
+        // Walk all methods of the trait, including those of its supertraits
+        let methods = tcx.vtable_methods(poly_trait_ref);
+        let methods = methods.iter().cloned().filter_map(|method| method)
+            .map(|(def_id, substs)| ty::Instance::resolve(
+                    tcx,
+                    ty::ParamEnv::reveal_all(),
+                    def_id,
+                    substs).unwrap())
+            .filter(|&instance| should_monomorphize_locally(tcx, &instance))
+            .map(|instance| create_fn_mono_item(instance));
+        output.extend(methods);
         // Also add the destructor
         visit_drop_use(tcx, impl_ty, false, output);
     }
diff --git a/src/librustc_mir/monomorphize/item.rs b/src/librustc_mir/monomorphize/item.rs
index f0ea93bfffd..4c4d56c8938 100644
--- a/src/librustc_mir/monomorphize/item.rs
+++ b/src/librustc_mir/monomorphize/item.rs
@@ -320,12 +320,13 @@ impl<'a, 'tcx> DefPathBasedNames<'a, 'tcx> {
                 output.push(']');
             },
             ty::Dynamic(ref trait_data, ..) => {
-                if let Some(principal) = trait_data.principal() {
-                    self.push_def_path(principal.def_id(), output);
-                    self.push_type_params(principal.skip_binder().substs,
-                        trait_data.projection_bounds(),
-                        output);
-                }
+                let principal = trait_data.principal();
+                self.push_def_path(principal.def_id(), output);
+                self.push_type_params(
+                    principal.skip_binder().substs,
+                    trait_data.projection_bounds(),
+                    output,
+                );
             },
             ty::Foreign(did) => self.push_def_path(did, output),
             ty::FnDef(..) |
diff --git a/src/librustc_privacy/lib.rs b/src/librustc_privacy/lib.rs
index 60679d6d430..989851bb1b9 100644
--- a/src/librustc_privacy/lib.rs
+++ b/src/librustc_privacy/lib.rs
@@ -93,8 +93,7 @@ impl<'a, 'tcx> EmbargoVisitor<'a, 'tcx> {
         let ty_def_id = match self.tcx.type_of(item_def_id).sty {
             ty::Adt(adt, _) => adt.did,
             ty::Foreign(did) => did,
-            ty::Dynamic(ref obj, ..) if obj.principal().is_some() =>
-                obj.principal().unwrap().def_id(),
+            ty::Dynamic(ref obj, ..) => obj.principal().def_id(),
             ty::Projection(ref proj) => proj.trait_ref(self.tcx).def_id,
             _ => return Some(AccessLevel::Public)
         };
@@ -484,7 +483,7 @@ impl<'b, 'a, 'tcx> TypeVisitor<'tcx> for ReachEverythingInTheInterfaceVisitor<'b
         let ty_def_id = match ty.sty {
             ty::Adt(adt, _) => Some(adt.did),
             ty::Foreign(did) => Some(did),
-            ty::Dynamic(ref obj, ..) => obj.principal().map(|p| p.def_id()),
+            ty::Dynamic(ref obj, ..) => Some(obj.principal().def_id()),
             ty::Projection(ref proj) => Some(proj.item_def_id),
             ty::FnDef(def_id, ..) |
             ty::Closure(def_id, ..) |
@@ -1456,7 +1455,7 @@ impl<'a, 'tcx: 'a> TypeVisitor<'tcx> for SearchInterfaceForPrivateItemsVisitor<'
         let ty_def_id = match ty.sty {
             ty::Adt(adt, _) => Some(adt.did),
             ty::Foreign(did) => Some(did),
-            ty::Dynamic(ref obj, ..) => obj.principal().map(|p| p.def_id()),
+            ty::Dynamic(ref obj, ..) => Some(obj.principal().def_id()),
             ty::Projection(ref proj) => {
                 if self.required_visibility == ty::Visibility::Invisible {
                     // Conservatively approximate the whole type alias as public without
diff --git a/src/librustc_typeck/check/cast.rs b/src/librustc_typeck/check/cast.rs
index 285fed9544d..e0ee26cba08 100644
--- a/src/librustc_typeck/check/cast.rs
+++ b/src/librustc_typeck/check/cast.rs
@@ -73,7 +73,7 @@ enum PointerKind<'tcx> {
     /// No metadata attached, ie pointer to sized type or foreign type
     Thin,
     /// A trait object
-    Vtable(Option<DefId>),
+    Vtable(DefId),
     /// Slice
     Length,
     /// The unsize info of this projection
@@ -105,7 +105,7 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
         Ok(match t.sty {
             ty::Slice(_) | ty::Str => Some(PointerKind::Length),
             ty::Dynamic(ref tty, ..) =>
-                Some(PointerKind::Vtable(tty.principal().map(|p| p.def_id()))),
+                Some(PointerKind::Vtable(tty.principal().def_id())),
             ty::Adt(def, substs) if def.is_struct() => {
                 match def.non_enum_variant().fields.last() {
                     None => Some(PointerKind::Thin),
diff --git a/src/librustc_typeck/check/closure.rs b/src/librustc_typeck/check/closure.rs
index 202789d1d8a..940fa4d3916 100644
--- a/src/librustc_typeck/check/closure.rs
+++ b/src/librustc_typeck/check/closure.rs
@@ -198,9 +198,7 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
                         self.deduce_sig_from_projection(None, &pb)
                     })
                     .next();
-                let kind = object_type
-                    .principal()
-                    .and_then(|p| self.tcx.lang_items().fn_trait_kind(p.def_id()));
+                let kind = self.tcx.lang_items().fn_trait_kind(object_type.principal().def_id());
                 (sig, kind)
             }
             ty::Infer(ty::TyVar(vid)) => self.deduce_expectations_from_obligations(vid),
diff --git a/src/librustc_typeck/check/method/confirm.rs b/src/librustc_typeck/check/method/confirm.rs
index 4e5488b432d..75f5bf74c6a 100644
--- a/src/librustc_typeck/check/method/confirm.rs
+++ b/src/librustc_typeck/check/method/confirm.rs
@@ -290,7 +290,7 @@ impl<'a, 'gcx, 'tcx> ConfirmContext<'a, 'gcx, 'tcx> {
             .include_raw_pointers()
             .filter_map(|(ty, _)|
                 match ty.sty {
-                    ty::Dynamic(ref data, ..) => data.principal().map(|p| closure(self, ty, p)),
+                    ty::Dynamic(ref data, ..) => Some(closure(self, ty, data.principal())),
                     _ => None,
                 }
             )
diff --git a/src/librustc_typeck/check/method/probe.rs b/src/librustc_typeck/check/method/probe.rs
index ec4483204f0..ae02cd64c38 100644
--- a/src/librustc_typeck/check/method/probe.rs
+++ b/src/librustc_typeck/check/method/probe.rs
@@ -452,10 +452,9 @@ impl<'a, 'gcx, 'tcx> ProbeContext<'a, 'gcx, 'tcx> {
 
         match self_ty.sty {
             ty::Dynamic(ref data, ..) => {
-                if let Some(p) = data.principal() {
-                    self.assemble_inherent_candidates_from_object(self_ty, p);
-                    self.assemble_inherent_impl_candidates_for_type(p.def_id());
-                }
+                let p = data.principal();
+                self.assemble_inherent_candidates_from_object(self_ty, p);
+                self.assemble_inherent_impl_candidates_for_type(p.def_id());
             }
             ty::Adt(def, _) => {
                 self.assemble_inherent_impl_candidates_for_type(def.did);
diff --git a/src/librustc_typeck/check/method/suggest.rs b/src/librustc_typeck/check/method/suggest.rs
index 28b9dcb9bfd..2006796a100 100644
--- a/src/librustc_typeck/check/method/suggest.rs
+++ b/src/librustc_typeck/check/method/suggest.rs
@@ -663,8 +663,7 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
                 ty::Adt(def, _) => def.did.is_local(),
                 ty::Foreign(did) => did.is_local(),
 
-                ty::Dynamic(ref tr, ..) => tr.principal()
-                    .map_or(false, |p| p.def_id().is_local()),
+                ty::Dynamic(ref tr, ..) => tr.principal().def_id().is_local(),
 
                 ty::Param(_) => true,
 
diff --git a/src/librustc_typeck/coherence/inherent_impls.rs b/src/librustc_typeck/coherence/inherent_impls.rs
index 1955a709dbf..ec979dea4fd 100644
--- a/src/librustc_typeck/coherence/inherent_impls.rs
+++ b/src/librustc_typeck/coherence/inherent_impls.rs
@@ -108,8 +108,8 @@ impl<'a, 'tcx, 'v> ItemLikeVisitor<'v> for InherentCollect<'a, 'tcx> {
             ty::Foreign(did) => {
                 self.check_def_id(item, did);
             }
-            ty::Dynamic(ref data, ..) if data.principal().is_some() => {
-                self.check_def_id(item, data.principal().unwrap().def_id());
+            ty::Dynamic(ref data, ..) => {
+                self.check_def_id(item, data.principal().def_id());
             }
             ty::Char => {
                 self.check_primitive_impl(def_id,
diff --git a/src/librustc_typeck/coherence/mod.rs b/src/librustc_typeck/coherence/mod.rs
index 616ca97a7a7..9b17654d469 100644
--- a/src/librustc_typeck/coherence/mod.rs
+++ b/src/librustc_typeck/coherence/mod.rs
@@ -181,13 +181,12 @@ fn check_impl_overlap<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, node_id: ast::NodeI
         // This is something like impl Trait1 for Trait2. Illegal
         // if Trait1 is a supertrait of Trait2 or Trait2 is not object safe.
 
-        if data.principal().map_or(true, |p| !tcx.is_object_safe(p.def_id())) {
+        if !tcx.is_object_safe(data.principal().def_id()) {
             // This is an error, but it will be reported by wfcheck.  Ignore it here.
             // This is tested by `coherence-impl-trait-for-trait-object-safe.rs`.
         } else {
             let mut supertrait_def_ids =
-                traits::supertrait_def_ids(tcx,
-                                           data.principal().unwrap().def_id());
+                traits::supertrait_def_ids(tcx, data.principal().def_id());
             if supertrait_def_ids.any(|d| d == trait_def_id) {
                 let sp = tcx.sess.source_map().def_span(tcx.span_of_impl(impl_def_id).unwrap());
                 struct_span_err!(tcx.sess,
diff --git a/src/librustc_typeck/outlives/implicit_infer.rs b/src/librustc_typeck/outlives/implicit_infer.rs
index 254146c0ef3..132da8f5cea 100644
--- a/src/librustc_typeck/outlives/implicit_infer.rs
+++ b/src/librustc_typeck/outlives/implicit_infer.rs
@@ -203,28 +203,27 @@ fn insert_required_predicates_to_be_wf<'tcx>(
                 debug!("Dynamic");
                 debug!("field_ty = {}", &field_ty);
                 debug!("ty in field = {}", &ty);
-                if let Some(ex_trait_ref) = obj.principal() {
-                    // Here, we are passing the type `usize` as a
-                    // placeholder value with the function
-                    // `with_self_ty`, since there is no concrete type
-                    // `Self` for a `dyn Trait` at this
-                    // stage. Therefore when checking explicit
-                    // predicates in `check_explicit_predicates` we
-                    // need to ignore checking the explicit_map for
-                    // Self type.
-                    let substs = ex_trait_ref
-                        .with_self_ty(tcx, tcx.types.usize)
-                        .skip_binder()
-                        .substs;
-                    check_explicit_predicates(
-                        tcx,
-                        &ex_trait_ref.skip_binder().def_id,
-                        substs,
-                        required_predicates,
-                        explicit_map,
-                        IgnoreSelfTy(true),
-                    );
-                }
+                let ex_trait_ref = obj.principal();
+                // Here, we are passing the type `usize` as a
+                // placeholder value with the function
+                // `with_self_ty`, since there is no concrete type
+                // `Self` for a `dyn Trait` at this
+                // stage. Therefore when checking explicit
+                // predicates in `check_explicit_predicates` we
+                // need to ignore checking the explicit_map for
+                // Self type.
+                let substs = ex_trait_ref
+                    .with_self_ty(tcx, tcx.types.usize)
+                    .skip_binder()
+                    .substs;
+                check_explicit_predicates(
+                    tcx,
+                    &ex_trait_ref.skip_binder().def_id,
+                    substs,
+                    required_predicates,
+                    explicit_map,
+                    IgnoreSelfTy(true),
+                );
             }
 
             ty::Projection(obj) => {
diff --git a/src/librustc_typeck/variance/constraints.rs b/src/librustc_typeck/variance/constraints.rs
index 32a591777db..3e523c0c7f5 100644
--- a/src/librustc_typeck/variance/constraints.rs
+++ b/src/librustc_typeck/variance/constraints.rs
@@ -311,11 +311,11 @@ impl<'a, 'tcx> ConstraintContext<'a, 'tcx> {
                 let contra = self.contravariant(variance);
                 self.add_constraints_from_region(current, r, contra);
 
-                if let Some(p) = data.principal() {
-                    let poly_trait_ref = p.with_self_ty(self.tcx(), self.tcx().types.err);
-                    self.add_constraints_from_trait_ref(
-                        current, *poly_trait_ref.skip_binder(), variance);
-                }
+                let poly_trait_ref = data
+                    .principal()
+                    .with_self_ty(self.tcx(), self.tcx().types.err);
+                self.add_constraints_from_trait_ref(
+                    current, *poly_trait_ref.skip_binder(), variance);
 
                 for projection in data.projection_bounds() {
                     self.add_constraints_from_ty(