Auto merge of #101212 - eholk:dyn-star, r=compiler-errors

Initial implementation of dyn*

This PR adds extremely basic and incomplete support for [dyn*](https://smallcultfollowing.com/babysteps//blog/2022/03/29/dyn-can-we-make-dyn-sized/). The goal is to get something in tree behind a flag to make collaboration easier, and also to make sure the implementation so far is not unreasonable. This PR does quite a few things:

* Introduce `dyn_star` feature flag
* Adds parsing for `dyn* Trait` types
* Defines `dyn* Trait` as a sized type
* Adds support for explicit casts, like `42usize as dyn* Debug`
  * Including const evaluation of such casts
* Adds codegen for drop glue so things are cleaned up properly when a `dyn* Trait` object goes out of scope
* Adds codegen for method calls, at least for methods that take `&self`

Quite a bit is still missing, but this gives us a starting point. Note that this is never intended to become stable surface syntax for Rust, but rather `dyn*` is planned to be used as an implementation detail for async functions in dyn traits.

Joint work with `@nikomatsakis` and `@compiler-errors.`

r? `@bjorn3`

14 files changed, 88 insertions, 20 deletions

diff --git a/compiler/rustc_middle/src/mir/mod.rs b/compiler/rustc_middle/src/mir/mod.rs
index 9a6d34c8ddd..526bb5d7285 100644
--- a/compiler/rustc_middle/src/mir/mod.rs
+++ b/compiler/rustc_middle/src/mir/mod.rs
@@ -1818,6 +1818,7 @@ impl<'tcx> Rvalue<'tcx> {
             // While the model is undecided, we should be conservative. See
             // <https://www.ralfj.de/blog/2022/04/11/provenance-exposed.html>
             Rvalue::Cast(CastKind::PointerExposeAddress, _, _) => false,
+            Rvalue::Cast(CastKind::DynStar, _, _) => false,
 
             Rvalue::Use(_)
             | Rvalue::CopyForDeref(_)
diff --git a/compiler/rustc_middle/src/mir/syntax.rs b/compiler/rustc_middle/src/mir/syntax.rs
index 1f7643a76af..d2bb897b5b6 100644
--- a/compiler/rustc_middle/src/mir/syntax.rs
+++ b/compiler/rustc_middle/src/mir/syntax.rs
@@ -1139,6 +1139,8 @@ pub enum CastKind {
     /// All sorts of pointer-to-pointer casts. Note that reference-to-raw-ptr casts are
     /// translated into `&raw mut/const *r`, i.e., they are not actually casts.
     Pointer(PointerCast),
+    /// Cast into a dyn* object.
+    DynStar,
     /// Remaining unclassified casts.
     Misc,
 }
diff --git a/compiler/rustc_middle/src/ty/cast.rs b/compiler/rustc_middle/src/ty/cast.rs
index c4b743dd467..981e2d3b6d2 100644
--- a/compiler/rustc_middle/src/ty/cast.rs
+++ b/compiler/rustc_middle/src/ty/cast.rs
@@ -33,6 +33,8 @@ pub enum CastTy<'tcx> {
     FnPtr,
     /// Raw pointers.
     Ptr(ty::TypeAndMut<'tcx>),
+    /// Casting into a `dyn*` value.
+    DynStar,
 }
 
 /// Cast Kind. See [RFC 401](https://rust-lang.github.io/rfcs/0401-coercions.html)
@@ -50,6 +52,7 @@ pub enum CastKind {
     ArrayPtrCast,
     FnPtrPtrCast,
     FnPtrAddrCast,
+    DynStarCast,
 }
 
 impl<'tcx> CastTy<'tcx> {
@@ -67,6 +70,7 @@ impl<'tcx> CastTy<'tcx> {
             ty::Adt(d, _) if d.is_enum() && d.is_payloadfree() => Some(CastTy::Int(IntTy::CEnum)),
             ty::RawPtr(mt) => Some(CastTy::Ptr(mt)),
             ty::FnPtr(..) => Some(CastTy::FnPtr),
+            ty::Dynamic(_, _, ty::DynStar) => Some(CastTy::DynStar),
             _ => None,
         }
     }
diff --git a/compiler/rustc_middle/src/ty/context.rs b/compiler/rustc_middle/src/ty/context.rs
index 94eddef944a..d0b49c4ee9e 100644
--- a/compiler/rustc_middle/src/ty/context.rs
+++ b/compiler/rustc_middle/src/ty/context.rs
@@ -63,7 +63,7 @@ use rustc_span::{Span, DUMMY_SP};
 use rustc_target::abi::{Layout, LayoutS, TargetDataLayout, VariantIdx};
 use rustc_target::spec::abi;
 use rustc_type_ir::sty::TyKind::*;
-use rustc_type_ir::{InternAs, InternIteratorElement, Interner, TypeFlags};
+use rustc_type_ir::{DynKind, InternAs, InternIteratorElement, Interner, TypeFlags};
 
 use std::any::Any;
 use std::borrow::Borrow;
@@ -2545,8 +2545,9 @@ impl<'tcx> TyCtxt<'tcx> {
         self,
         obj: &'tcx List<ty::Binder<'tcx, ExistentialPredicate<'tcx>>>,
         reg: ty::Region<'tcx>,
+        repr: DynKind,
     ) -> Ty<'tcx> {
-        self.mk_ty(Dynamic(obj, reg))
+        self.mk_ty(Dynamic(obj, reg, repr))
     }
 
     #[inline]
diff --git a/compiler/rustc_middle/src/ty/diagnostics.rs b/compiler/rustc_middle/src/ty/diagnostics.rs
index 648f5f7161f..855917fb828 100644
--- a/compiler/rustc_middle/src/ty/diagnostics.rs
+++ b/compiler/rustc_middle/src/ty/diagnostics.rs
@@ -467,7 +467,7 @@ impl<'tcx> TypeVisitor<'tcx> for IsSuggestableVisitor<'tcx> {
                 }
             }
 
-            Dynamic(dty, _) => {
+            Dynamic(dty, _, _) => {
                 for pred in *dty {
                     match pred.skip_binder() {
                         ExistentialPredicate::Trait(_) | ExistentialPredicate::Projection(_) => {
diff --git a/compiler/rustc_middle/src/ty/flags.rs b/compiler/rustc_middle/src/ty/flags.rs
index c22c899c5cc..98b8a7386fe 100644
--- a/compiler/rustc_middle/src/ty/flags.rs
+++ b/compiler/rustc_middle/src/ty/flags.rs
@@ -171,7 +171,7 @@ impl FlagComputation {
                 self.add_substs(substs);
             }
 
-            &ty::Dynamic(obj, r) => {
+            &ty::Dynamic(obj, r, _) => {
                 for predicate in obj.iter() {
                     self.bound_computation(predicate, |computation, predicate| match predicate {
                         ty::ExistentialPredicate::Trait(tr) => computation.add_substs(tr.substs),
diff --git a/compiler/rustc_middle/src/ty/layout.rs b/compiler/rustc_middle/src/ty/layout.rs
index abb7ddd88b1..042eeec3f46 100644
--- a/compiler/rustc_middle/src/ty/layout.rs
+++ b/compiler/rustc_middle/src/ty/layout.rs
@@ -625,6 +625,14 @@ impl<'tcx> LayoutCx<'tcx, TyCtxt<'tcx>> {
                 tcx.intern_layout(self.scalar_pair(data_ptr, metadata))
             }
 
+            ty::Dynamic(_, _, ty::DynStar) => {
+                let mut data = scalar_unit(Int(dl.ptr_sized_integer(), false));
+                data.valid_range_mut().start = 0;
+                let mut vtable = scalar_unit(Pointer);
+                vtable.valid_range_mut().start = 1;
+                tcx.intern_layout(self.scalar_pair(data, vtable))
+            }
+
             // Arrays and slices.
             ty::Array(element, mut count) => {
                 if count.has_projections() {
@@ -679,7 +687,7 @@ impl<'tcx> LayoutCx<'tcx, TyCtxt<'tcx>> {
 
             // Odd unit types.
             ty::FnDef(..) => univariant(&[], &ReprOptions::default(), StructKind::AlwaysSized)?,
-            ty::Dynamic(..) | ty::Foreign(..) => {
+            ty::Dynamic(_, _, ty::Dyn) | ty::Foreign(..) => {
                 let mut unit = self.univariant_uninterned(
                     ty,
                     &[],
@@ -2435,7 +2443,9 @@ where
                 | ty::FnDef(..)
                 | ty::GeneratorWitness(..)
                 | ty::Foreign(..)
-                | ty::Dynamic(..) => bug!("TyAndLayout::field({:?}): not applicable", this),
+                | ty::Dynamic(_, _, ty::Dyn) => {
+                    bug!("TyAndLayout::field({:?}): not applicable", this)
+                }
 
                 // Potentially-fat pointers.
                 ty::Ref(_, pointee, _) | ty::RawPtr(ty::TypeAndMut { ty: pointee, .. }) => {
@@ -2464,7 +2474,7 @@ where
 
                     match tcx.struct_tail_erasing_lifetimes(pointee, cx.param_env()).kind() {
                         ty::Slice(_) | ty::Str => TyMaybeWithLayout::Ty(tcx.types.usize),
-                        ty::Dynamic(_, _) => {
+                        ty::Dynamic(_, _, ty::Dyn) => {
                             TyMaybeWithLayout::Ty(tcx.mk_imm_ref(
                                 tcx.lifetimes.re_static,
                                 tcx.mk_array(tcx.types.usize, 3),
@@ -2533,6 +2543,22 @@ where
                     }
                 }
 
+                ty::Dynamic(_, _, ty::DynStar) => {
+                    if i == 0 {
+                        TyMaybeWithLayout::Ty(tcx.types.usize)
+                    } else if i == 1 {
+                        // FIXME(dyn-star) same FIXME as above applies here too
+                        TyMaybeWithLayout::Ty(
+                            tcx.mk_imm_ref(
+                                tcx.lifetimes.re_static,
+                                tcx.mk_array(tcx.types.usize, 3),
+                            ),
+                        )
+                    } else {
+                        bug!("no field {i} on dyn*")
+                    }
+                }
+
                 ty::Projection(_)
                 | ty::Bound(..)
                 | ty::Placeholder(..)
@@ -2728,6 +2754,7 @@ impl<'tcx> ty::Instance<'tcx> {
     // for `Instance` (e.g. typeck would use `Ty::fn_sig` instead),
     // or should go through `FnAbi` instead, to avoid losing any
     // adjustments `fn_abi_of_instance` might be performing.
+    #[tracing::instrument(level = "debug", skip(tcx, param_env))]
     fn fn_sig_for_fn_abi(
         &self,
         tcx: TyCtxt<'tcx>,
@@ -2874,6 +2901,7 @@ impl<'tcx> ty::Instance<'tcx> {
 /// with `-Cpanic=abort` will look like they can't unwind when in fact they
 /// might (from a foreign exception or similar).
 #[inline]
+#[tracing::instrument(level = "debug", skip(tcx))]
 pub fn fn_can_unwind<'tcx>(tcx: TyCtxt<'tcx>, fn_def_id: Option<DefId>, abi: SpecAbi) -> bool {
     if let Some(did) = fn_def_id {
         // Special attribute for functions which can't unwind.
@@ -3090,6 +3118,7 @@ pub trait FnAbiOf<'tcx>: FnAbiOfHelpers<'tcx> {
     /// NB: that includes virtual calls, which are represented by "direct calls"
     /// to an `InstanceDef::Virtual` instance (of `<dyn Trait as Trait>::fn`).
     #[inline]
+    #[tracing::instrument(level = "debug", skip(self))]
     fn fn_abi_of_instance(
         &self,
         instance: ty::Instance<'tcx>,
@@ -3236,6 +3265,10 @@ pub fn adjust_for_rust_scalar<'tcx>(
 impl<'tcx> LayoutCx<'tcx, TyCtxt<'tcx>> {
     // FIXME(eddyb) perhaps group the signature/type-containing (or all of them?)
     // arguments of this method, into a separate `struct`.
+    #[tracing::instrument(
+        level = "debug",
+        skip(self, caller_location, fn_def_id, force_thin_self_ptr)
+    )]
     fn fn_abi_new_uncached(
         &self,
         sig: ty::PolyFnSig<'tcx>,
@@ -3245,8 +3278,6 @@ impl<'tcx> LayoutCx<'tcx, TyCtxt<'tcx>> {
         // FIXME(eddyb) replace this with something typed, like an `enum`.
         force_thin_self_ptr: bool,
     ) -> Result<&'tcx FnAbi<'tcx, Ty<'tcx>>, FnAbiError<'tcx>> {
-        debug!("fn_abi_new_uncached({:?}, {:?})", sig, extra_args);
-
         let sig = self.tcx.normalize_erasing_late_bound_regions(self.param_env, sig);
 
         let conv = conv_from_spec_abi(self.tcx(), sig.abi);
@@ -3289,6 +3320,8 @@ impl<'tcx> LayoutCx<'tcx, TyCtxt<'tcx>> {
         let rust_abi = matches!(sig.abi, RustIntrinsic | PlatformIntrinsic | Rust | RustCall);
 
         let arg_of = |ty: Ty<'tcx>, arg_idx: Option<usize>| -> Result<_, FnAbiError<'tcx>> {
+            let span = tracing::debug_span!("arg_of");
+            let _entered = span.enter();
             let is_return = arg_idx.is_none();
 
             let layout = self.layout_of(ty)?;
@@ -3345,6 +3378,7 @@ impl<'tcx> LayoutCx<'tcx, TyCtxt<'tcx>> {
         Ok(self.tcx.arena.alloc(fn_abi))
     }
 
+    #[tracing::instrument(level = "trace", skip(self))]
     fn fn_abi_adjust_for_abi(
         &self,
         fn_abi: &mut FnAbi<'tcx, Ty<'tcx>>,
@@ -3419,6 +3453,7 @@ impl<'tcx> LayoutCx<'tcx, TyCtxt<'tcx>> {
     }
 }
 
+#[tracing::instrument(level = "debug", skip(cx))]
 fn make_thin_self_ptr<'tcx>(
     cx: &(impl HasTyCtxt<'tcx> + HasParamEnv<'tcx>),
     layout: TyAndLayout<'tcx>,
@@ -3430,7 +3465,7 @@ fn make_thin_self_ptr<'tcx>(
         tcx.mk_mut_ptr(layout.ty)
     } else {
         match layout.abi {
-            Abi::ScalarPair(..) => (),
+            Abi::ScalarPair(..) | Abi::Scalar(..) => (),
             _ => bug!("receiver type has unsupported layout: {:?}", layout),
         }
 
diff --git a/compiler/rustc_middle/src/ty/mod.rs b/compiler/rustc_middle/src/ty/mod.rs
index 3ff62647105..6641ab9b756 100644
--- a/compiler/rustc_middle/src/ty/mod.rs
+++ b/compiler/rustc_middle/src/ty/mod.rs
@@ -58,6 +58,7 @@ use std::ops::ControlFlow;
 use std::{fmt, str};
 
 pub use crate::ty::diagnostics::*;
+pub use rustc_type_ir::DynKind::*;
 pub use rustc_type_ir::InferTy::*;
 pub use rustc_type_ir::RegionKind::*;
 pub use rustc_type_ir::TyKind::*;
@@ -1113,6 +1114,12 @@ pub trait ToPredicate<'tcx> {
     fn to_predicate(self, tcx: TyCtxt<'tcx>) -> Predicate<'tcx>;
 }
 
+impl<'tcx> ToPredicate<'tcx> for Predicate<'tcx> {
+    fn to_predicate(self, _tcx: TyCtxt<'tcx>) -> Predicate<'tcx> {
+        self
+    }
+}
+
 impl<'tcx> ToPredicate<'tcx> for Binder<'tcx, PredicateKind<'tcx>> {
     #[inline(always)]
     fn to_predicate(self, tcx: TyCtxt<'tcx>) -> Predicate<'tcx> {
diff --git a/compiler/rustc_middle/src/ty/normalize_erasing_regions.rs b/compiler/rustc_middle/src/ty/normalize_erasing_regions.rs
index cac8560ce1c..9db5a289484 100644
--- a/compiler/rustc_middle/src/ty/normalize_erasing_regions.rs
+++ b/compiler/rustc_middle/src/ty/normalize_erasing_regions.rs
@@ -36,6 +36,7 @@ impl<'tcx> TyCtxt<'tcx> {
     ///
     /// This should only be used outside of type inference. For example,
     /// it assumes that normalization will succeed.
+    #[tracing::instrument(level = "debug", skip(self, param_env))]
     pub fn normalize_erasing_regions<T>(self, param_env: ty::ParamEnv<'tcx>, value: T) -> T
     where
         T: TypeFoldable<'tcx>,
@@ -100,6 +101,7 @@ impl<'tcx> TyCtxt<'tcx> {
     /// N.B., currently, higher-ranked type bounds inhibit
     /// normalization. Therefore, each time we erase them in
     /// codegen, we need to normalize the contents.
+    #[tracing::instrument(level = "debug", skip(self, param_env))]
     pub fn normalize_erasing_late_bound_regions<T>(
         self,
         param_env: ty::ParamEnv<'tcx>,
diff --git a/compiler/rustc_middle/src/ty/print/pretty.rs b/compiler/rustc_middle/src/ty/print/pretty.rs
index e9eecfe78d3..f7d5d3116af 100644
--- a/compiler/rustc_middle/src/ty/print/pretty.rs
+++ b/compiler/rustc_middle/src/ty/print/pretty.rs
@@ -619,12 +619,16 @@ pub trait PrettyPrinter<'tcx>:
             ty::Adt(def, substs) => {
                 p!(print_def_path(def.did(), substs));
             }
-            ty::Dynamic(data, r) => {
+            ty::Dynamic(data, r, repr) => {
                 let print_r = self.should_print_region(r);
                 if print_r {
                     p!("(");
                 }
-                p!("dyn ", print(data));
+                match repr {
+                    ty::Dyn => p!("dyn "),
+                    ty::DynStar => p!("dyn* "),
+                }
+                p!(print(data));
                 if print_r {
                     p!(" + ", print(r), ")");
                 }
diff --git a/compiler/rustc_middle/src/ty/relate.rs b/compiler/rustc_middle/src/ty/relate.rs
index 81476195d29..5b3750b8b4d 100644
--- a/compiler/rustc_middle/src/ty/relate.rs
+++ b/compiler/rustc_middle/src/ty/relate.rs
@@ -441,7 +441,9 @@ pub fn super_relate_tys<'tcx, R: TypeRelation<'tcx>>(
 
         (&ty::Foreign(a_id), &ty::Foreign(b_id)) if a_id == b_id => Ok(tcx.mk_foreign(a_id)),
 
-        (&ty::Dynamic(a_obj, a_region), &ty::Dynamic(b_obj, b_region)) => {
+        (&ty::Dynamic(a_obj, a_region, a_repr), &ty::Dynamic(b_obj, b_region, b_repr))
+            if a_repr == b_repr =>
+        {
             let region_bound = relation.with_cause(Cause::ExistentialRegionBound, |relation| {
                 relation.relate_with_variance(
                     ty::Contravariant,
@@ -450,7 +452,7 @@ pub fn super_relate_tys<'tcx, R: TypeRelation<'tcx>>(
                     b_region,
                 )
             })?;
-            Ok(tcx.mk_dynamic(relation.relate(a_obj, b_obj)?, region_bound))
+            Ok(tcx.mk_dynamic(relation.relate(a_obj, b_obj)?, region_bound, a_repr))
         }
 
         (&ty::Generator(a_id, a_substs, movability), &ty::Generator(b_id, b_substs, _))
diff --git a/compiler/rustc_middle/src/ty/structural_impls.rs b/compiler/rustc_middle/src/ty/structural_impls.rs
index 37f88016f60..d7e74d675de 100644
--- a/compiler/rustc_middle/src/ty/structural_impls.rs
+++ b/compiler/rustc_middle/src/ty/structural_impls.rs
@@ -1028,9 +1028,11 @@ impl<'tcx> TypeSuperFoldable<'tcx> for Ty<'tcx> {
             ty::Array(typ, sz) => ty::Array(typ.try_fold_with(folder)?, sz.try_fold_with(folder)?),
             ty::Slice(typ) => ty::Slice(typ.try_fold_with(folder)?),
             ty::Adt(tid, substs) => ty::Adt(tid, substs.try_fold_with(folder)?),
-            ty::Dynamic(trait_ty, region) => {
-                ty::Dynamic(trait_ty.try_fold_with(folder)?, region.try_fold_with(folder)?)
-            }
+            ty::Dynamic(trait_ty, region, representation) => ty::Dynamic(
+                trait_ty.try_fold_with(folder)?,
+                region.try_fold_with(folder)?,
+                representation,
+            ),
             ty::Tuple(ts) => ty::Tuple(ts.try_fold_with(folder)?),
             ty::FnDef(def_id, substs) => ty::FnDef(def_id, substs.try_fold_with(folder)?),
             ty::FnPtr(f) => ty::FnPtr(f.try_fold_with(folder)?),
@@ -1074,7 +1076,7 @@ impl<'tcx> TypeSuperVisitable<'tcx> for Ty<'tcx> {
             }
             ty::Slice(typ) => typ.visit_with(visitor),
             ty::Adt(_, substs) => substs.visit_with(visitor),
-            ty::Dynamic(ref trait_ty, ref reg) => {
+            ty::Dynamic(ref trait_ty, ref reg, _) => {
                 trait_ty.visit_with(visitor)?;
                 reg.visit_with(visitor)
             }
diff --git a/compiler/rustc_middle/src/ty/sty.rs b/compiler/rustc_middle/src/ty/sty.rs
index 702c2d27187..18169045c90 100644
--- a/compiler/rustc_middle/src/ty/sty.rs
+++ b/compiler/rustc_middle/src/ty/sty.rs
@@ -692,6 +692,9 @@ impl<'tcx> ExistentialPredicate<'tcx> {
 }
 
 impl<'tcx> Binder<'tcx, ExistentialPredicate<'tcx>> {
+    /// Given an existential predicate like `?Self: PartialEq<u32>` (e.g., derived from `dyn PartialEq<u32>`),
+    /// and a concrete type `self_ty`, returns a full predicate where the existentially quantified variable `?Self`
+    /// has been replaced with `self_ty` (e.g., `self_ty: PartialEq<u32>`, in our example).
     pub fn with_self_ty(&self, tcx: TyCtxt<'tcx>, self_ty: Ty<'tcx>) -> ty::Predicate<'tcx> {
         use crate::ty::ToPredicate;
         match self.skip_binder() {
@@ -1849,7 +1852,12 @@ impl<'tcx> Ty<'tcx> {
 
     #[inline]
     pub fn is_trait(self) -> bool {
-        matches!(self.kind(), Dynamic(..))
+        matches!(self.kind(), Dynamic(_, _, ty::Dyn))
+    }
+
+    #[inline]
+    pub fn is_dyn_star(self) -> bool {
+        matches!(self.kind(), Dynamic(_, _, ty::DynStar))
     }
 
     #[inline]
diff --git a/compiler/rustc_middle/src/ty/walk.rs b/compiler/rustc_middle/src/ty/walk.rs
index 831724bc4b0..a3e11bbf056 100644
--- a/compiler/rustc_middle/src/ty/walk.rs
+++ b/compiler/rustc_middle/src/ty/walk.rs
@@ -152,7 +152,7 @@ fn push_inner<'tcx>(stack: &mut TypeWalkerStack<'tcx>, parent: GenericArg<'tcx>)
             ty::Projection(data) => {
                 stack.extend(data.substs.iter().rev());
             }
-            ty::Dynamic(obj, lt) => {
+            ty::Dynamic(obj, lt, _) => {
                 stack.push(lt.into());
                 stack.extend(obj.iter().rev().flat_map(|predicate| {
                     let (substs, opt_ty) = match predicate.skip_binder() {