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

3 files changed, 15 insertions, 9 deletions

diff --git a/src/librustc_codegen_llvm/context.rs b/src/librustc_codegen_llvm/context.rs
index 3a5da29c681..2b03e99161d 100644
--- a/src/librustc_codegen_llvm/context.rs
+++ b/src/librustc_codegen_llvm/context.rs
@@ -50,7 +50,8 @@ pub struct CodegenCx<'ll, 'tcx: 'll> {
     /// Cache instances of monomorphic and polymorphic items
     pub instances: RefCell<FxHashMap<Instance<'tcx>, &'ll Value>>,
     /// Cache generated vtables
-    pub vtables: RefCell<FxHashMap<(Ty<'tcx>, ty::PolyExistentialTraitRef<'tcx>), &'ll Value>>,
+    pub vtables: RefCell<FxHashMap<
+            (Ty<'tcx>, Option<ty::PolyExistentialTraitRef<'tcx>>), &'ll Value>>,
     /// Cache of constant strings,
     pub const_cstr_cache: RefCell<FxHashMap<LocalInternedString, &'ll Value>>,
 
@@ -311,7 +312,7 @@ impl<'ll, 'tcx> CodegenCx<'ll, 'tcx> {
 
 impl MiscMethods<'tcx> for CodegenCx<'ll, 'tcx> {
     fn vtables(&self) -> &RefCell<FxHashMap<(Ty<'tcx>,
-                                ty::PolyExistentialTraitRef<'tcx>), &'ll Value>>
+                                Option<ty::PolyExistentialTraitRef<'tcx>>), &'ll Value>>
     {
         &self.vtables
     }
diff --git a/src/librustc_codegen_llvm/debuginfo/metadata.rs b/src/librustc_codegen_llvm/debuginfo/metadata.rs
index 0fd04e9d203..72ed55df946 100644
--- a/src/librustc_codegen_llvm/debuginfo/metadata.rs
+++ b/src/librustc_codegen_llvm/debuginfo/metadata.rs
@@ -429,7 +429,8 @@ fn trait_pointer_metadata(
     // But it does not describe the trait's methods.
 
     let containing_scope = match trait_type.sty {
-        ty::Dynamic(ref data, ..) => Some(get_namespace_for_item(cx, data.principal().def_id())),
+        ty::Dynamic(ref data, ..) =>
+            data.principal_def_id().map(|did| get_namespace_for_item(cx, did)),
         _ => {
             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 c8cbd735e85..32432f7e4ec 100644
--- a/src/librustc_codegen_llvm/debuginfo/type_names.rs
+++ b/src/librustc_codegen_llvm/debuginfo/type_names.rs
@@ -107,12 +107,16 @@ pub fn push_debuginfo_type_name<'a, 'tcx>(cx: &CodegenCx<'a, 'tcx>,
             }
         },
         ty::Dynamic(ref trait_data, ..) => {
-            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);
+            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);
+            } else {
+                output.push_str("dyn '_");
+            }
         },
         ty::FnDef(..) | ty::FnPtr(_) => {
             let sig = t.fn_sig(cx.tcx);