X-Git-Url: https://git.lizzy.rs/?a=blobdiff_plain;f=compiler%2Frustc_middle%2Fsrc%2Fty%2Flayout.rs;h=dfd016569c27a51de3135d2dbcef1706291d9747;hb=548ae602fc92b35d7a28fa9d70a7be51bc3328f9;hp=9e0ca44d0981df0dbcf4afc9a3282310d37d1c1e;hpb=da07053ee1e80ef44707bd4dd25630d9dd8180dc;p=rust.git

diff --git a/compiler/rustc_middle/src/ty/layout.rs b/compiler/rustc_middle/src/ty/layout.rs
index 9e0ca44d098..dfd016569c2 100644
--- a/compiler/rustc_middle/src/ty/layout.rs
+++ b/compiler/rustc_middle/src/ty/layout.rs
@@ -670,29 +670,50 @@ fn field_ty_or_layout<'tcx>(
                         });
                     }
 
-                    match tcx.struct_tail_erasing_lifetimes(pointee, cx.param_env()).kind() {
-                        ty::Slice(_) | ty::Str => TyMaybeWithLayout::Ty(tcx.types.usize),
-                        ty::Dynamic(_, _, ty::Dyn) => {
-                            TyMaybeWithLayout::Ty(tcx.mk_imm_ref(
-                                tcx.lifetimes.re_static,
-                                tcx.mk_array(tcx.types.usize, 3),
-                            ))
-                            /* FIXME: use actual fn pointers
-                            Warning: naively computing the number of entries in the
-                            vtable by counting the methods on the trait + methods on
-                            all parent traits does not work, because some methods can
-                            be not object safe and thus excluded from the vtable.
-                            Increase this counter if you tried to implement this but
-                            failed to do it without duplicating a lot of code from
-                            other places in the compiler: 2
-                            tcx.mk_tup(&[
-                                tcx.mk_array(tcx.types.usize, 3),
-                                tcx.mk_array(Option<fn()>),
-                            ])
-                            */
+                    let mk_dyn_vtable = || {
+                        tcx.mk_imm_ref(tcx.lifetimes.re_static, tcx.mk_array(tcx.types.usize, 3))
+                        /* FIXME: use actual fn pointers
+                        Warning: naively computing the number of entries in the
+                        vtable by counting the methods on the trait + methods on
+                        all parent traits does not work, because some methods can
+                        be not object safe and thus excluded from the vtable.
+                        Increase this counter if you tried to implement this but
+                        failed to do it without duplicating a lot of code from
+                        other places in the compiler: 2
+                        tcx.mk_tup(&[
+                            tcx.mk_array(tcx.types.usize, 3),
+                            tcx.mk_array(Option<fn()>),
+                        ])
+                        */
+                    };
+
+                    let metadata = if let Some(metadata_def_id) = tcx.lang_items().metadata_type() {
+                        let metadata = tcx.normalize_erasing_regions(
+                            cx.param_env(),
+                            tcx.mk_projection(metadata_def_id, [pointee]),
+                        );
+
+                        // Map `Metadata = DynMetadata<dyn Trait>` back to a vtable, since it
+                        // offers better information than `std::ptr::metadata::VTable`,
+                        // and we rely on this layout information to trigger a panic in
+                        // `std::mem::uninitialized::<&dyn Trait>()`, for example.
+                        if let ty::Adt(def, substs) = metadata.kind()
+                            && Some(def.did()) == tcx.lang_items().dyn_metadata()
+                            && substs.type_at(0).is_trait()
+                        {
+                            mk_dyn_vtable()
+                        } else {
+                            metadata
                         }
-                        _ => bug!("TyAndLayout::field({:?}): not applicable", this),
-                    }
+                    } else {
+                        match tcx.struct_tail_erasing_lifetimes(pointee, cx.param_env()).kind() {
+                            ty::Slice(_) | ty::Str => tcx.types.usize,
+                            ty::Dynamic(_, _, ty::Dyn) => mk_dyn_vtable(),
+                            _ => bug!("TyAndLayout::field({:?}): not applicable", this),
+                        }
+                    };
+
+                    TyMaybeWithLayout::Ty(metadata)
                 }
 
                 // Arrays and slices.
@@ -858,7 +879,7 @@ fn ty_and_layout_pointee_info_at(
                     //
                     // If the niche is a pointer, it's either valid (according
                     // to its type), or null (which the niche field's scalar
-                    // validity range encodes).  This allows using
+                    // validity range encodes). This allows using
                     // `dereferenceable_or_null` for e.g., `Option<&T>`, and
                     // this will continue to work as long as we don't start
                     // using more niches than just null (e.g., the first page of