Auto merge of #56837 - arielb1:nonprincipal-trait-objects, r=nikomatsakis

Add support for trait-objects without a principal

The hard-error version of #56481 - should be merged after we do something about the `traitobject` crate.

Fixes #33140.
Fixes #57057.

r? @nikomatsakis

2 files changed, 11 insertions, 4 deletions

diff --git a/src/librustc_codegen_ssa/meth.rs b/src/librustc_codegen_ssa/meth.rs
index 31640826262..98ad2616eea 100644
--- a/src/librustc_codegen_ssa/meth.rs
+++ b/src/librustc_codegen_ssa/meth.rs
@@ -69,7 +69,7 @@ impl<'a, 'tcx: 'a> VirtualIndex {
 pub fn get_vtable<'tcx, Cx: CodegenMethods<'tcx>>(
     cx: &Cx,
     ty: Ty<'tcx>,
-    trait_ref: ty::PolyExistentialTraitRef<'tcx>,
+    trait_ref: Option<ty::PolyExistentialTraitRef<'tcx>>,
 ) -> Cx::Value {
     let tcx = cx.tcx();
 
@@ -83,8 +83,15 @@ pub fn get_vtable<'tcx, Cx: CodegenMethods<'tcx>>(
     // Not in the cache. Build it.
     let nullptr = cx.const_null(cx.type_i8p());
 
-    let methods = tcx.vtable_methods(trait_ref.with_self_ty(tcx, ty));
-    let methods = methods.iter().cloned().map(|opt_mth| {
+    let methods_root;
+    let methods = if let Some(trait_ref) = trait_ref {
+        methods_root = tcx.vtable_methods(trait_ref.with_self_ty(tcx, ty));
+        methods_root.iter()
+    } else {
+        (&[]).iter()
+    };
+
+    let methods = methods.cloned().map(|opt_mth| {
         opt_mth.map_or(nullptr, |(def_id, substs)| {
             callee::resolve_and_get_fn_for_vtable(cx, def_id, substs)
         })
diff --git a/src/librustc_codegen_ssa/traits/misc.rs b/src/librustc_codegen_ssa/traits/misc.rs
index c297288b255..b2315556366 100644
--- a/src/librustc_codegen_ssa/traits/misc.rs
+++ b/src/librustc_codegen_ssa/traits/misc.rs
@@ -11,7 +11,7 @@ use std::sync::Arc;
 pub trait MiscMethods<'tcx>: BackendTypes {
     fn vtables(
         &self,
-    ) -> &RefCell<FxHashMap<(Ty<'tcx>, ty::PolyExistentialTraitRef<'tcx>), Self::Value>>;
+    ) -> &RefCell<FxHashMap<(Ty<'tcx>, Option<ty::PolyExistentialTraitRef<'tcx>>), Self::Value>>;
     fn check_overflow(&self) -> bool;
     fn instances(&self) -> &RefCell<FxHashMap<Instance<'tcx>, Self::Value>>;
     fn get_fn(&self, instance: Instance<'tcx>) -> Self::Value;