Rollup merge of rust-lang#104594 - compiler-errors:dyn-star-rcvr, r=eholk,estebank

Properly handle `Pin<&mut dyn* Trait>` receiver in codegen

This ensures we can actually await a `dyn* Future`, which seems important for async fn in dyn trait.

Also, disable `dyn*` trait upcasting. It's not exactly complete right now, and can cause strange ICEs for no reason -- nobody's using it either. I thought it was cute to implement when I did it, but I didn't think about how it interacts structurally with `CoerceUnsized` correctly.

Fixes rust-lang#104794, presumably removing `dyn*` upcasting and its `CoerceUnsized` issues does the trick.

Author: matthiaskrgr

compiler/rustc_codegen_ssa/src/mir/block.rs

@@ -938,7 +938,9 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                         // that is understood elsewhere in the compiler as a method on
                         // `dyn Trait`.
                         // To get a `*mut RcBox<Self>`, we just keep unwrapping newtypes until
-                        // we get a value of a built-in pointer type
+                        // we get a value of a built-in pointer type.
+                        //
+                        // This is also relevant for `Pin<&mut Self>`, where we need to peel the `Pin`.
                         'descend_newtypes: while !op.layout.ty.is_unsafe_ptr()
                             && !op.layout.ty.is_region_ptr()
                         {
@@ -980,13 +982,29 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                         continue;
                     }
                     Immediate(_) => {
-                        let ty::Ref(_, ty, _) = op.layout.ty.kind() else {
-                            span_bug!(span, "can't codegen a virtual call on {:#?}", op);
-                        };
-                        if !ty.is_dyn_star() {
+                        // See comment above explaining why we peel these newtypes
+                        'descend_newtypes: while !op.layout.ty.is_unsafe_ptr()
+                            && !op.layout.ty.is_region_ptr()
+                        {
+                            for i in 0..op.layout.fields.count() {
+                                let field = op.extract_field(bx, i);
+                                if !field.layout.is_zst() {
+                                    // we found the one non-zero-sized field that is allowed
+                                    // now find *its* non-zero-sized field, or stop if it's a
+                                    // pointer
+                                    op = field;
+                                    continue 'descend_newtypes;
+                                }
+                            }
+
+                            span_bug!(span, "receiver has no non-zero-sized fields {:?}", op);
+                        }
+
+                        // Make sure that we've actually unwrapped the rcvr down
+                        // to a pointer or ref to `dyn* Trait`.
+                        if !op.layout.ty.builtin_deref(true).unwrap().ty.is_dyn_star() {
                             span_bug!(span, "can't codegen a virtual call on {:#?}", op);
                         }
-                        // FIXME(dyn-star): Make sure this is done on a &dyn* receiver
                         let place = op.deref(bx.cx());
                         let data_ptr = place.project_field(bx, 0);
                         let meta_ptr = place.project_field(bx, 1);

compiler/rustc_hir_typeck/src/coercion.rs

@@ -755,20 +755,9 @@ impl<'f, 'tcx> Coerce<'f, 'tcx> {
 
         if let ty::Dynamic(a_data, _, _) = a.kind()
             && let ty::Dynamic(b_data, _, _) = b.kind()
+            && a_data.principal_def_id() == b_data.principal_def_id()
         {
-            if a_data.principal_def_id() == b_data.principal_def_id() {
-                return self.unify_and(a, b, |_| vec![]);
-            } else if !self.tcx().features().trait_upcasting {
-                let mut err = feature_err(
-                    &self.tcx.sess.parse_sess,
-                    sym::trait_upcasting,
-                    self.cause.span,
-                    &format!(
-                        "cannot cast `{a}` to `{b}`, trait upcasting coercion is experimental"
-                    ),
-                );
-                err.emit();
-            }
+            return self.unify_and(a, b, |_| vec![]);
         }
 
         // Check the obligations of the cast -- for example, when casting
@@ -796,19 +785,16 @@ impl<'f, 'tcx> Coerce<'f, 'tcx> {
             ])
             .collect();
 
-        // Enforce that the type is `usize`/pointer-sized. For now, only those
-        // can be coerced to `dyn*`, except for `dyn* -> dyn*` upcasts.
-        if !a.is_dyn_star() {
-            obligations.push(Obligation::new(
-                self.tcx,
-                self.cause.clone(),
-                self.param_env,
-                ty::Binder::dummy(
-                    self.tcx.at(self.cause.span).mk_trait_ref(hir::LangItem::PointerSized, [a]),
-                )
-                .to_poly_trait_predicate(),
-            ));
-        }
+        // Enforce that the type is `usize`/pointer-sized.
+        obligations.push(Obligation::new(
+            self.tcx,
+            self.cause.clone(),
+            self.param_env,
+            ty::Binder::dummy(
+                self.tcx.at(self.cause.span).mk_trait_ref(hir::LangItem::PointerSized, [a]),
+            )
+            .to_poly_trait_predicate(),
+        ));
 
         Ok(InferOk {
             value: (vec![Adjustment { kind: Adjust::DynStar, target: b }], b),

compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs

@@ -776,9 +776,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
 
         match (source.kind(), target.kind()) {
             // Trait+Kx+'a -> Trait+Ky+'b (upcasts).
-            (&ty::Dynamic(ref data_a, _, dyn_a), &ty::Dynamic(ref data_b, _, dyn_b))
-                if dyn_a == dyn_b =>
-            {
+            (&ty::Dynamic(ref data_a, _, ty::Dyn), &ty::Dynamic(ref data_b, _, ty::Dyn)) => {
                 // Upcast coercions permit several things:
                 //
                 // 1. Dropping auto traits, e.g., `Foo + Send` to `Foo`

compiler/rustc_trait_selection/src/traits/select/confirmation.rs

@@ -803,9 +803,10 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         let upcast_trait_ref;
         match (source.kind(), target.kind()) {
             // TraitA+Kx+'a -> TraitB+Ky+'b (trait upcasting coercion).
-            (&ty::Dynamic(ref data_a, r_a, repr_a), &ty::Dynamic(ref data_b, r_b, repr_b))
-                if repr_a == repr_b =>
-            {
+            (
+                &ty::Dynamic(ref data_a, r_a, repr_a @ ty::Dyn),
+                &ty::Dynamic(ref data_b, r_b, ty::Dyn),
+            ) => {
                 // See `assemble_candidates_for_unsizing` for more info.
                 // We already checked the compatibility of auto traits within `assemble_candidates_for_unsizing`.
                 let principal_a = data_a.principal().unwrap();
@@ -831,7 +832,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                             .map(ty::Binder::dummy),
                     );
                 let existential_predicates = tcx.mk_poly_existential_predicates(iter);
-                let source_trait = tcx.mk_dynamic(existential_predicates, r_b, repr_b);
+                let source_trait = tcx.mk_dynamic(existential_predicates, r_b, repr_a);
 
                 // Require that the traits involved in this upcast are **equal**;
                 // only the **lifetime bound** is changed.

src/test/ui/dyn-star/dispatch-on-pin-mut.rs

@@ -0,0 +1,52 @@
+// run-pass
+// edition:2021
+// check-run-results
+
+#![feature(dyn_star)]
+//~^ WARN the feature `dyn_star` is incomplete and may not be safe to use and/or cause compiler crashes
+
+use std::future::Future;
+
+async fn foo(f: dyn* Future<Output = i32>) {
+    println!("value: {}", f.await);
+}
+
+async fn async_main() {
+    foo(Box::pin(async { 1 })).await
+}
+
+// ------------------------------------------------------------------------- //
+// Implementation Details Below...
+
+use std::pin::Pin;
+use std::task::*;
+
+pub fn noop_waker() -> Waker {
+    let raw = RawWaker::new(std::ptr::null(), &NOOP_WAKER_VTABLE);
+
+    // SAFETY: the contracts for RawWaker and RawWakerVTable are upheld
+    unsafe { Waker::from_raw(raw) }
+}
+
+const NOOP_WAKER_VTABLE: RawWakerVTable = RawWakerVTable::new(noop_clone, noop, noop, noop);
+
+unsafe fn noop_clone(_p: *const ()) -> RawWaker {
+    RawWaker::new(std::ptr::null(), &NOOP_WAKER_VTABLE)
+}
+
+unsafe fn noop(_p: *const ()) {}
+
+fn main() {
+    let mut fut = async_main();
+
+    // Poll loop, just to test the future...
+    let waker = noop_waker();
+    let ctx = &mut Context::from_waker(&waker);
+
+    loop {
+        match unsafe { Pin::new_unchecked(&mut fut).poll(ctx) } {
+            Poll::Pending => {}
+            Poll::Ready(()) => break,
+        }
+    }
+}

src/test/ui/dyn-star/dispatch-on-pin-mut.run.stdout

@@ -0,0 +1 @@
+value: 1

src/test/ui/dyn-star/dispatch-on-pin-mut.stderr

@@ -0,0 +1,11 @@
+warning: the feature `dyn_star` is incomplete and may not be safe to use and/or cause compiler crashes
+  --> $DIR/dispatch-on-pin-mut.rs:5:12
+   |
+LL | #![feature(dyn_star)]
+   |            ^^^^^^^^
+   |
+   = note: see issue #91611 <https://github.com/rust-lang/rust/issues/91611> for more information
+   = note: `#[warn(incomplete_features)]` on by default
+
+warning: 1 warning emitted
+

src/test/ui/dyn-star/dont-unsize-coerce-dyn-star.rs

@@ -1,7 +1,8 @@
-// check-pass
+// run-pass
+// check-run-results
 
 #![feature(dyn_star)]
-#![allow(incomplete_features)]
+//~^ WARN the feature `dyn_star` is incomplete and may not be safe to use and/or cause compiler crashes
 
 trait AddOne {
     fn add1(&mut self) -> usize;

src/test/ui/dyn-star/dont-unsize-coerce-dyn-star.run.stdout

@@ -0,0 +1,2 @@
+43
+44

src/test/ui/dyn-star/dont-unsize-coerce-dyn-star.stderr

@@ -0,0 +1,11 @@
+warning: the feature `dyn_star` is incomplete and may not be safe to use and/or cause compiler crashes
+  --> $DIR/dont-unsize-coerce-dyn-star.rs:4:12
+   |
+LL | #![feature(dyn_star)]
+   |            ^^^^^^^^
+   |
+   = note: see issue #91611 <https://github.com/rust-lang/rust/issues/91611> for more information
+   = note: `#[warn(incomplete_features)]` on by default
+
+warning: 1 warning emitted
+