Rollup of 9 pull requests

compiler/rustc_codegen_llvm/src/coverageinfo/mapgen.rs

@@ -1,6 +1,5 @@
 use crate::common::CodegenCx;
 use crate::coverageinfo;
-use crate::errors::InstrumentCoverageRequiresLLVM12;
 use crate::llvm;
 
 use llvm::coverageinfo::CounterMappingRegion;
@@ -19,8 +18,8 @@ use std::ffi::CString;
 
 /// Generates and exports the Coverage Map.
 ///
-/// Rust Coverage Map generation supports LLVM Coverage Mapping Format versions
-/// 5 (LLVM 12, only) and 6 (zero-based encoded as 4 and 5, respectively), as defined at
+/// Rust Coverage Map generation supports LLVM Coverage Mapping Format version
+/// 6 (zero-based encoded as 5), as defined at
 /// [LLVM Code Coverage Mapping Format](https://github.com/rust-lang/llvm-project/blob/rustc/13.0-2021-09-30/llvm/docs/CoverageMappingFormat.rst#llvm-code-coverage-mapping-format).
 /// These versions are supported by the LLVM coverage tools (`llvm-profdata` and `llvm-cov`)
 /// bundled with Rust's fork of LLVM.
@@ -33,13 +32,10 @@ use std::ffi::CString;
 pub fn finalize(cx: &CodegenCx<'_, '_>) {
     let tcx = cx.tcx;
 
-    // Ensure the installed version of LLVM supports at least Coverage Map
-    // Version 5 (encoded as a zero-based value: 4), which was introduced with
-    // LLVM 12.
+    // Ensure the installed version of LLVM supports Coverage Map Version 6
+    // (encoded as a zero-based value: 5), which was introduced with LLVM 13.
     let version = coverageinfo::mapping_version();
-    if version < 4 {
-        tcx.sess.emit_fatal(InstrumentCoverageRequiresLLVM12);
-    }
+    assert_eq!(version, 5, "The `CoverageMappingVersion` exposed by `llvm-wrapper` is out of sync");
 
     debug!("Generating coverage map for CodegenUnit: `{}`", cx.codegen_unit.name());
 
@@ -61,7 +57,7 @@ pub fn finalize(cx: &CodegenCx<'_, '_>) {
         return;
     }
 
-    let mut mapgen = CoverageMapGenerator::new(tcx, version);
+    let mut mapgen = CoverageMapGenerator::new(tcx);
 
     // Encode coverage mappings and generate function records
     let mut function_data = Vec::new();
@@ -124,25 +120,18 @@ struct CoverageMapGenerator {
 }
 
 impl CoverageMapGenerator {
-    fn new(tcx: TyCtxt<'_>, version: u32) -> Self {
+    fn new(tcx: TyCtxt<'_>) -> Self {
         let mut filenames = FxIndexSet::default();
-        if version >= 5 {
-            // LLVM Coverage Mapping Format version 6 (zero-based encoded as 5)
-            // requires setting the first filename to the compilation directory.
-            // Since rustc generates coverage maps with relative paths, the
-            // compilation directory can be combined with the relative paths
-            // to get absolute paths, if needed.
-            let working_dir = tcx
-                .sess
-                .opts
-                .working_dir
-                .remapped_path_if_available()
-                .to_string_lossy()
-                .to_string();
-            let c_filename =
-                CString::new(working_dir).expect("null error converting filename to C string");
-            filenames.insert(c_filename);
-        }
+        // LLVM Coverage Mapping Format version 6 (zero-based encoded as 5)
+        // requires setting the first filename to the compilation directory.
+        // Since rustc generates coverage maps with relative paths, the
+        // compilation directory can be combined with the relative paths
+        // to get absolute paths, if needed.
+        let working_dir =
+            tcx.sess.opts.working_dir.remapped_path_if_available().to_string_lossy().to_string();
+        let c_filename =
+            CString::new(working_dir).expect("null error converting filename to C string");
+        filenames.insert(c_filename);
         Self { filenames }
     }
 

compiler/rustc_codegen_llvm/src/errors.rs

@@ -39,10 +39,6 @@ pub(crate) struct ErrorCreatingImportLibrary<'a> {
     pub error: String,
 }
 
-#[derive(Diagnostic)]
-#[diag(codegen_llvm_instrument_coverage_requires_llvm_12)]
-pub(crate) struct InstrumentCoverageRequiresLLVM12;
-
 #[derive(Diagnostic)]
 #[diag(codegen_llvm_symbol_already_defined)]
 pub(crate) struct SymbolAlreadyDefined<'a> {

compiler/rustc_codegen_ssa/src/back/link.rs

@@ -599,7 +599,8 @@ fn link_dwarf_object<'a>(
     cg_results: &CodegenResults,
     executable_out_filename: &Path,
 ) {
-    let dwp_out_filename = executable_out_filename.with_extension("dwp");
+    let mut dwp_out_filename = executable_out_filename.to_path_buf().into_os_string();
+    dwp_out_filename.push(".dwp");
     debug!(?dwp_out_filename, ?executable_out_filename);
 
     #[derive(Default)]

compiler/rustc_const_eval/src/transform/validate.rs

@@ -13,7 +13,7 @@ use rustc_middle::mir::{
     ProjectionElem, RetagKind, RuntimePhase, Rvalue, SourceScope, Statement, StatementKind,
     Terminator, TerminatorKind, UnOp, START_BLOCK,
 };
-use rustc_middle::ty::{self, InstanceDef, ParamEnv, Ty, TyCtxt, TypeVisitable};
+use rustc_middle::ty::{self, InstanceDef, ParamEnv, Ty, TyCtxt};
 use rustc_mir_dataflow::impls::MaybeStorageLive;
 use rustc_mir_dataflow::storage::always_storage_live_locals;
 use rustc_mir_dataflow::{Analysis, ResultsCursor};
@@ -230,11 +230,6 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
             // Equal types, all is good.
             return true;
         }
-        // Normalization reveals opaque types, but we may be validating MIR while computing
-        // said opaque types, causing cycles.
-        if (src, dest).has_opaque_types() {
-            return true;
-        }
 
         crate::util::is_subtype(self.tcx, self.param_env, src, dest)
     }

compiler/rustc_error_messages/locales/en-US/codegen_llvm.ftl

@@ -11,9 +11,6 @@ codegen_llvm_unknown_ctarget_feature_prefix =
 codegen_llvm_error_creating_import_library =
     Error creating import library for {$lib_name}: {$error}
 
-codegen_llvm_instrument_coverage_requires_llvm_12 =
-    rustc option `-C instrument-coverage` requires LLVM 12 or higher.
-
 codegen_llvm_symbol_already_defined =
     symbol `{$symbol_name}` is already defined
 

compiler/rustc_infer/src/infer/error_reporting/mod.rs

@@ -79,6 +79,7 @@ use std::path::PathBuf;
 use std::{cmp, fmt, iter};
 
 mod note;
+mod note_and_explain;
 mod suggest;
 
 pub(crate) mod need_type_info;
@@ -1846,7 +1847,8 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
         }
 
         self.check_and_note_conflicting_crates(diag, terr);
-        self.tcx.note_and_explain_type_err(diag, terr, cause, span, cause.body_id.to_def_id());
+
+        self.note_and_explain_type_err(diag, terr, cause, span, cause.body_id.to_def_id());
 
         if let Some(ValuePairs::PolyTraitRefs(exp_found)) = values
             && let ty::Closure(def_id, _) = exp_found.expected.skip_binder().self_ty().kind()

compiler/rustc_infer/src/infer/error_reporting/suggest.rs

@@ -380,7 +380,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                     return;
                 }
 
-                let (msg, sugg) = match (expected.is_ref(), found.is_ref()) {
+                let (msg, sug) = match (expected.is_ref(), found.is_ref()) {
                     (true, false) => {
                         let msg = "consider using a reference";
                         let sug = format!("&{fn_name}");
@@ -404,22 +404,58 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                         (msg, sug)
                     }
                 };
-                diag.span_suggestion(span, msg, &sugg, Applicability::MaybeIncorrect);
+                diag.span_suggestion(span, msg, sug, Applicability::MaybeIncorrect);
             }
             (ty::FnDef(did1, substs1), ty::FnDef(did2, substs2)) => {
                 let expected_sig =
                     &(self.normalize_fn_sig)(self.tcx.bound_fn_sig(*did1).subst(self.tcx, substs1));
                 let found_sig =
                     &(self.normalize_fn_sig)(self.tcx.bound_fn_sig(*did2).subst(self.tcx, substs2));
 
-                if self.same_type_modulo_infer(*found_sig, *expected_sig) {
-                    diag.note(
-                    "different fn items have unique types, even if their signatures are the same",
-                    );
+                if self.same_type_modulo_infer(*expected_sig, *found_sig) {
+                    diag.note("different fn items have unique types, even if their signatures are the same");
+                }
+
+                if !self.same_type_modulo_infer(*found_sig, *expected_sig)
+                    || !found_sig.is_suggestable(self.tcx, true)
+                    || !expected_sig.is_suggestable(self.tcx, true)
+                    || ty::util::is_intrinsic(self.tcx, *did1)
+                    || ty::util::is_intrinsic(self.tcx, *did2)
+                {
+                    return;
                 }
+
+                let fn_name = self.tcx.def_path_str_with_substs(*did2, substs2);
+                let sug = if found.is_ref() {
+                    format!("&({fn_name} as {found_sig})")
+                } else {
+                    format!("{fn_name} as {found_sig}")
+                };
+
+                let msg = format!(
+                    "consider casting both fn items to fn pointers using `as {expected_sig}`"
+                );
+
+                diag.span_suggestion_hidden(span, msg, sug, Applicability::MaybeIncorrect);
             }
-            (ty::FnDef(_, _), ty::FnPtr(_)) => {
-                diag.note("fn items are distinct from fn pointers");
+            (ty::FnDef(did, substs), ty::FnPtr(sig)) => {
+                let expected_sig =
+                    &(self.normalize_fn_sig)(self.tcx.bound_fn_sig(*did).subst(self.tcx, substs));
+                let found_sig = &(self.normalize_fn_sig)(*sig);
+
+                if !self.same_type_modulo_infer(*found_sig, *expected_sig) {
+                    return;
+                }
+
+                let fn_name = self.tcx.def_path_str_with_substs(*did, substs);
+
+                let casting = if expected.is_ref() {
+                    format!("&({fn_name} as {found_sig})")
+                } else {
+                    format!("{fn_name} as {found_sig}")
+                };
+
+                diag.help(&format!("consider casting the fn item to a fn pointer: `{}`", casting));
             }
             _ => {
                 return;

compiler/rustc_middle/src/ty/assoc.rs

@@ -130,7 +130,7 @@ impl std::fmt::Display for AssocKind {
 /// done only on items with the same name.
 #[derive(Debug, Clone, PartialEq, HashStable)]
 pub struct AssocItems<'tcx> {
-    pub(super) items: SortedIndexMultiMap<u32, Symbol, &'tcx ty::AssocItem>,
+    items: SortedIndexMultiMap<u32, Symbol, &'tcx ty::AssocItem>,
 }
 
 impl<'tcx> AssocItems<'tcx> {

compiler/rustc_middle/src/ty/query.rs

@@ -441,6 +441,10 @@ impl<'tcx> TyCtxt<'tcx> {
         self.opt_def_kind(def_id)
             .unwrap_or_else(|| bug!("def_kind: unsupported node: {:?}", def_id))
     }
+
+    pub fn bound_type_of(self, def_id: impl IntoQueryParam<DefId>) -> ty::EarlyBinder<Ty<'tcx>> {
+        ty::EarlyBinder(self.type_of(def_id))
+    }
 }
 
 impl<'tcx> TyCtxtAt<'tcx> {
@@ -449,4 +453,8 @@ impl<'tcx> TyCtxtAt<'tcx> {
         self.opt_def_kind(def_id)
             .unwrap_or_else(|| bug!("def_kind: unsupported node: {:?}", def_id))
     }
+
+    pub fn bound_type_of(self, def_id: impl IntoQueryParam<DefId>) -> ty::EarlyBinder<Ty<'tcx>> {
+        ty::EarlyBinder(self.type_of(def_id))
+    }
 }

compiler/rustc_middle/src/ty/util.rs

@@ -3,7 +3,6 @@
 use crate::middle::codegen_fn_attrs::CodegenFnAttrFlags;
 use crate::mir;
 use crate::ty::layout::IntegerExt;
-use crate::ty::query::TyCtxtAt;
 use crate::ty::{
     self, DefIdTree, FallibleTypeFolder, Ty, TyCtxt, TypeFoldable, TypeFolder, TypeSuperFoldable,
     TypeVisitable,
@@ -637,10 +636,6 @@ impl<'tcx> TyCtxt<'tcx> {
         if visitor.found_recursion { Err(expanded_type) } else { Ok(expanded_type) }
     }
 
-    pub fn bound_type_of(self, def_id: DefId) -> ty::EarlyBinder<Ty<'tcx>> {
-        ty::EarlyBinder(self.type_of(def_id))
-    }
-
     pub fn bound_return_position_impl_trait_in_trait_tys(
         self,
         def_id: DefId,
@@ -738,12 +733,6 @@ impl<'tcx> TyCtxt<'tcx> {
     }
 }
 
-impl<'tcx> TyCtxtAt<'tcx> {
-    pub fn bound_type_of(self, def_id: DefId) -> ty::EarlyBinder<Ty<'tcx>> {
-        ty::EarlyBinder(self.type_of(def_id))
-    }
-}
-
 struct OpaqueTypeExpander<'tcx> {
     // Contains the DefIds of the opaque types that are currently being
     // expanded. When we expand an opaque type we insert the DefId of

library/core/src/cell.rs

@@ -196,7 +196,7 @@ use crate::cmp::Ordering;
 use crate::fmt::{self, Debug, Display};
 use crate::marker::{PhantomData, Unsize};
 use crate::mem;
-use crate::ops::{CoerceUnsized, Deref, DerefMut};
+use crate::ops::{CoerceUnsized, Deref, DerefMut, DispatchFromDyn};
 use crate::ptr::{self, NonNull};
 
 mod lazy;
@@ -571,6 +571,16 @@ impl<T: Default> Cell<T> {
 #[unstable(feature = "coerce_unsized", issue = "18598")]
 impl<T: CoerceUnsized<U>, U> CoerceUnsized<Cell<U>> for Cell<T> {}
 
+// Allow types that wrap `Cell` to also implement `DispatchFromDyn`
+// and become object safe method receivers.
+// Note that currently `Cell` itself cannot be a method receiver
+// because it does not implement Deref.
+// In other words:
+// `self: Cell<&Self>` won't work
+// `self: CellWrapper<Self>` becomes possible
+#[unstable(feature = "dispatch_from_dyn", issue = "none")]
+impl<T: DispatchFromDyn<U>, U> DispatchFromDyn<Cell<U>> for Cell<T> {}
+
 impl<T> Cell<[T]> {
     /// Returns a `&[Cell<T>]` from a `&Cell<[T]>`
     ///
@@ -2078,6 +2088,16 @@ impl<T> const From<T> for UnsafeCell<T> {
 #[unstable(feature = "coerce_unsized", issue = "18598")]
 impl<T: CoerceUnsized<U>, U> CoerceUnsized<UnsafeCell<U>> for UnsafeCell<T> {}
 
+// Allow types that wrap `UnsafeCell` to also implement `DispatchFromDyn`
+// and become object safe method receivers.
+// Note that currently `UnsafeCell` itself cannot be a method receiver
+// because it does not implement Deref.
+// In other words:
+// `self: UnsafeCell<&Self>` won't work
+// `self: UnsafeCellWrapper<Self>` becomes possible
+#[unstable(feature = "dispatch_from_dyn", issue = "none")]
+impl<T: DispatchFromDyn<U>, U> DispatchFromDyn<UnsafeCell<U>> for UnsafeCell<T> {}
+
 /// [`UnsafeCell`], but [`Sync`].
 ///
 /// This is just an `UnsafeCell`, except it implements `Sync`
@@ -2169,6 +2189,17 @@ impl<T> const From<T> for SyncUnsafeCell<T> {
 //#[unstable(feature = "sync_unsafe_cell", issue = "95439")]
 impl<T: CoerceUnsized<U>, U> CoerceUnsized<SyncUnsafeCell<U>> for SyncUnsafeCell<T> {}
 
+// Allow types that wrap `SyncUnsafeCell` to also implement `DispatchFromDyn`
+// and become object safe method receivers.
+// Note that currently `SyncUnsafeCell` itself cannot be a method receiver
+// because it does not implement Deref.
+// In other words:
+// `self: SyncUnsafeCell<&Self>` won't work
+// `self: SyncUnsafeCellWrapper<Self>` becomes possible
+#[unstable(feature = "dispatch_from_dyn", issue = "none")]
+//#[unstable(feature = "sync_unsafe_cell", issue = "95439")]
+impl<T: DispatchFromDyn<U>, U> DispatchFromDyn<SyncUnsafeCell<U>> for SyncUnsafeCell<T> {}
+
 #[allow(unused)]
 fn assert_coerce_unsized(
     a: UnsafeCell<&i32>,

library/proc_macro/src/lib.rs

@@ -581,7 +581,7 @@ impl fmt::Debug for Span {
 
 /// A line-column pair representing the start or end of a `Span`.
 #[unstable(feature = "proc_macro_span", issue = "54725")]
-#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
 pub struct LineColumn {
     /// The 1-indexed line in the source file on which the span starts or ends (inclusive).
     #[unstable(feature = "proc_macro_span", issue = "54725")]

library/std/src/sync/mpmc/array.rs

@@ -319,19 +319,10 @@ impl<T> Channel<T> {
     ) -> Result<(), SendTimeoutError<T>> {
         let token = &mut Token::default();
         loop {
-            // Try sending a message several times.
-            let backoff = Backoff::new();
-            loop {
-                if self.start_send(token) {
-                    let res = unsafe { self.write(token, msg) };
-                    return res.map_err(SendTimeoutError::Disconnected);
-                }
-
-                if backoff.is_completed() {
-                    break;
-                } else {
-                    backoff.spin_light();
-                }
+            // Try sending a message.
+            if self.start_send(token) {
+                let res = unsafe { self.write(token, msg) };
+                return res.map_err(SendTimeoutError::Disconnected);
             }
 
             if let Some(d) = deadline {
@@ -379,6 +370,7 @@ impl<T> Channel<T> {
     pub(crate) fn recv(&self, deadline: Option<Instant>) -> Result<T, RecvTimeoutError> {
         let token = &mut Token::default();
         loop {
+            // Try receiving a message.
             if self.start_recv(token) {
                 let res = unsafe { self.read(token) };
                 return res.map_err(|_| RecvTimeoutError::Disconnected);

library/std/src/sync/mpmc/utils.rs

@@ -105,10 +105,8 @@ impl Backoff {
 
     /// Backs off using lightweight spinning.
     ///
-    /// This method should be used for:
-    ///     - Retrying an operation because another thread made progress. i.e. on CAS failure.
-    ///     - Waiting for an operation to complete by spinning optimistically for a few iterations
-    ///     before falling back to parking the thread (see `Backoff::is_completed`).
+    /// This method should be used for retrying an operation because another thread made
+    /// progress. i.e. on CAS failure.
     #[inline]
     pub fn spin_light(&self) {
         let step = self.step.get().min(SPIN_LIMIT);
@@ -134,10 +132,4 @@ impl Backoff {
 
         self.step.set(self.step.get() + 1);
     }
-
-    /// Returns `true` if quadratic backoff has completed and parking the thread is advised.
-    #[inline]
-    pub fn is_completed(&self) -> bool {
-        self.step.get() > SPIN_LIMIT
-    }
 }

library/std/src/sys/unix/thread_local_dtor.rs

@@ -11,13 +11,7 @@
 // Note, however, that we run on lots older linuxes, as well as cross
 // compiling from a newer linux to an older linux, so we also have a
 // fallback implementation to use as well.
-#[cfg(any(
-    target_os = "linux",
-    target_os = "fuchsia",
-    target_os = "redox",
-    target_os = "emscripten"
-))]
-#[cfg_attr(target_family = "wasm", allow(unused))] // might remain unused depending on target details (e.g. wasm32-unknown-emscripten)
+#[cfg(any(target_os = "linux", target_os = "fuchsia", target_os = "redox"))]
 pub unsafe fn register_dtor(t: *mut u8, dtor: unsafe extern "C" fn(*mut u8)) {
     use crate::mem;
     use crate::sys_common::thread_local_dtor::register_dtor_fallback;
@@ -89,7 +83,8 @@ pub unsafe fn register_dtor(t: *mut u8, dtor: unsafe extern "C" fn(*mut u8)) {
     }
 }
 
-#[cfg(any(target_os = "vxworks", target_os = "horizon"))]
+#[cfg(any(target_os = "vxworks", target_os = "horizon", target_os = "emscripten"))]
+#[cfg_attr(target_family = "wasm", allow(unused))] // might remain unused depending on target details (e.g. wasm32-unknown-emscripten)
 pub unsafe fn register_dtor(t: *mut u8, dtor: unsafe extern "C" fn(*mut u8)) {
     use crate::sys_common::thread_local_dtor::register_dtor_fallback;
     register_dtor_fallback(t, dtor);

tests/ui/associated-types/defaults-in-other-trait-items.rs

@@ -44,4 +44,18 @@ impl AssocConst for () {
     const C: Self::Ty = 0u8;
 }
 
+pub trait Trait {
+    type Res = isize; //~ NOTE associated type defaults can't be assumed inside the trait defining them
+
+    fn infer_me_correctly() -> Self::Res {
+        //~^ NOTE expected `<Self as Trait>::Res` because of return type
+
+        // {integer} == isize
+        2
+        //~^ ERROR mismatched types
+        //~| NOTE expected associated type, found integer
+        //~| NOTE expected associated type `<Self as Trait>::Res`
+    }
+}
+
 fn main() {}

tests/ui/associated-types/defaults-in-other-trait-items.stderr

@@ -24,6 +24,21 @@ LL |     const C: Self::Ty = 0u8;
    = note: expected associated type `<Self as AssocConst>::Ty`
                          found type `u8`
 
-error: aborting due to 2 previous errors
+error[E0308]: mismatched types
+  --> $DIR/defaults-in-other-trait-items.rs:54:9
+   |
+LL |     type Res = isize;
+   |     ----------------- associated type defaults can't be assumed inside the trait defining them
+LL |
+LL |     fn infer_me_correctly() -> Self::Res {
+   |                                --------- expected `<Self as Trait>::Res` because of return type
+...
+LL |         2
+   |         ^ expected associated type, found integer
+   |
+   = note: expected associated type `<Self as Trait>::Res`
+                         found type `{integer}`
+
+error: aborting due to 3 previous errors
 
 For more information about this error, try `rustc --explain E0308`.

tests/ui/associated-types/issue-26681.stderr

@@ -1,13 +1,13 @@
 error[E0308]: mismatched types
   --> $DIR/issue-26681.rs:17:39
    |
+LL |     type Fv: Foo = u8;
+   |     ------------------ associated type defaults can't be assumed inside the trait defining them
 LL |     const C: <Self::Fv as Foo>::Bar = 6665;
    |                                       ^^^^ expected associated type, found integer
    |
    = note: expected associated type `<<Self as Baz>::Fv as Foo>::Bar`
                          found type `{integer}`
-   = help: consider constraining the associated type `<<Self as Baz>::Fv as Foo>::Bar` to `{integer}`
-   = note: for more information, visit https://doc.rust-lang.org/book/ch19-03-advanced-traits.html
 
 error: aborting due to previous error
 

tests/ui/feature-gates/feature-gate-dispatch-from-dyn-cell.rs

@@ -0,0 +1,9 @@
+// Check that even though Cell: DispatchFromDyn it remains an invalid self parameter type
+
+use std::cell::Cell;
+
+trait Trait{
+    fn cell(self: Cell<&Self>); //~ ERROR invalid `self` parameter type: Cell<&Self>
+}
+
+fn main() {}

tests/ui/feature-gates/feature-gate-dispatch-from-dyn-cell.stderr

@@ -0,0 +1,12 @@
+error[E0307]: invalid `self` parameter type: Cell<&Self>
+  --> $DIR/feature-gate-dispatch-from-dyn-cell.rs:6:19
+   |
+LL |     fn cell(self: Cell<&Self>);
+   |                   ^^^^^^^^^^^
+   |
+   = note: type of `self` must be `Self` or a type that dereferences to it
+   = help: consider changing to `self`, `&self`, `&mut self`, `self: Box<Self>`, `self: Rc<Self>`, `self: Arc<Self>`, or `self: Pin<P>` (where P is one of the previous types except `Self`)
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0307`.

tests/ui/feature-gates/feature-gate-dispatch-from-dyn-missing-impl.rs

@@ -0,0 +1,35 @@
+// Check that a self parameter type requires a DispatchFromDyn impl to be object safe
+
+#![feature(arbitrary_self_types, unsize, coerce_unsized)]
+
+use std::{
+    marker::Unsize,
+    ops::{CoerceUnsized, Deref},
+};
+
+struct Ptr<T: ?Sized>(Box<T>);
+
+impl<T: ?Sized> Deref for Ptr<T> {
+    type Target = T;
+
+    fn deref(&self) -> &T {
+        &*self.0
+    }
+}
+
+impl<T: Unsize<U> + ?Sized, U: ?Sized> CoerceUnsized<Ptr<U>> for Ptr<T> {}
+// Because this impl is missing the coercion below fails.
+// impl<T: Unsize<U> + ?Sized, U: ?Sized> DispatchFromDyn<Ptr<U>> for Ptr<T> {}
+
+trait Trait {
+    fn ptr(self: Ptr<Self>);
+}
+impl Trait for i32 {
+    fn ptr(self: Ptr<Self>) {}
+}
+
+fn main() {
+    Ptr(Box::new(4)) as Ptr<dyn Trait>;
+    //~^ ERROR the trait `Trait` cannot be made into an object
+    //~^^ ERROR the trait `Trait` cannot be made into an object
+}

tests/ui/feature-gates/feature-gate-dispatch-from-dyn-missing-impl.stderr

@@ -0,0 +1,45 @@
+error[E0038]: the trait `Trait` cannot be made into an object
+  --> $DIR/feature-gate-dispatch-from-dyn-missing-impl.rs:32:25
+   |
+LL |     fn ptr(self: Ptr<Self>);
+   |                  --------- help: consider changing method `ptr`'s `self` parameter to be `&self`: `&Self`
+...
+LL |     Ptr(Box::new(4)) as Ptr<dyn Trait>;
+   |                         ^^^^^^^^^^^^^^ `Trait` cannot be made into an object
+   |
+note: for a trait to be "object safe" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety>
+  --> $DIR/feature-gate-dispatch-from-dyn-missing-impl.rs:25:18
+   |
+LL | trait Trait {
+   |       ----- this trait cannot be made into an object...
+LL |     fn ptr(self: Ptr<Self>);
+   |                  ^^^^^^^^^ ...because method `ptr`'s `self` parameter cannot be dispatched on
+
+error[E0038]: the trait `Trait` cannot be made into an object
+  --> $DIR/feature-gate-dispatch-from-dyn-missing-impl.rs:32:5
+   |
+LL |     fn ptr(self: Ptr<Self>);
+   |                  --------- help: consider changing method `ptr`'s `self` parameter to be `&self`: `&Self`
+...
+LL |     Ptr(Box::new(4)) as Ptr<dyn Trait>;
+   |     ^^^^^^^^^^^^^^^^ `Trait` cannot be made into an object
+   |
+note: for a trait to be "object safe" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety>
+  --> $DIR/feature-gate-dispatch-from-dyn-missing-impl.rs:25:18
+   |
+LL | trait Trait {
+   |       ----- this trait cannot be made into an object...
+LL |     fn ptr(self: Ptr<Self>);
+   |                  ^^^^^^^^^ ...because method `ptr`'s `self` parameter cannot be dispatched on
+note: required for `Ptr<{integer}>` to implement `CoerceUnsized<Ptr<dyn Trait>>`
+  --> $DIR/feature-gate-dispatch-from-dyn-missing-impl.rs:20:40
+   |
+LL | impl<T: Unsize<U> + ?Sized, U: ?Sized> CoerceUnsized<Ptr<U>> for Ptr<T> {}
+   |         ---------                      ^^^^^^^^^^^^^^^^^^^^^     ^^^^^^
+   |         |
+   |         unsatisfied trait bound introduced here
+   = note: required by cast to type `Ptr<dyn Trait>`
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0038`.

tests/ui/fn/fn-compare-mismatch.stderr

@@ -20,6 +20,7 @@ LL |     let x = f == g;
    = note: expected fn item `fn() {f}`
               found fn item `fn() {g}`
    = note: different fn items have unique types, even if their signatures are the same
+   = help: consider casting both fn items to fn pointers using `as fn()`
 
 error: aborting due to 2 previous errors
 

tests/ui/fn/fn-item-type.stderr

@@ -14,6 +14,7 @@ note: function defined here
    |
 LL | fn eq<T>(x: T, y: T) {}
    |    ^^          ----
+   = help: consider casting both fn items to fn pointers using `as fn(isize) -> isize`
 
 error[E0308]: mismatched types
   --> $DIR/fn-item-type.rs:29:19
@@ -31,6 +32,7 @@ note: function defined here
    |
 LL | fn eq<T>(x: T, y: T) {}
    |    ^^          ----
+   = help: consider casting both fn items to fn pointers using `as fn(isize) -> isize`
 
 error[E0308]: mismatched types
   --> $DIR/fn-item-type.rs:34:23
@@ -48,6 +50,7 @@ note: function defined here
    |
 LL | fn eq<T>(x: T, y: T) {}
    |    ^^          ----
+   = help: consider casting both fn items to fn pointers using `as fn(isize) -> isize`
 
 error[E0308]: mismatched types
   --> $DIR/fn-item-type.rs:41:26
@@ -65,6 +68,7 @@ note: function defined here
    |
 LL | fn eq<T>(x: T, y: T) {}
    |    ^^          ----
+   = help: consider casting both fn items to fn pointers using `as fn()`
 
 error[E0308]: mismatched types
   --> $DIR/fn-item-type.rs:46:19
@@ -76,7 +80,7 @@ LL |     eq(foo::<u8>, bar::<u8> as fn(isize) -> isize);
    |
    = note: expected fn item `fn(_) -> _ {foo::<u8>}`
            found fn pointer `fn(_) -> _`
-   = note: fn items are distinct from fn pointers
+   = help: consider casting the fn item to a fn pointer: `foo::<u8> as fn(isize) -> isize`
 note: function defined here
   --> $DIR/fn-item-type.rs:11:4
    |

tests/ui/fn/fn-pointer-mismatch.stderr

@@ -9,6 +9,7 @@ LL |     let g = if n % 2 == 0 { &foo } else { &bar };
    = note: expected reference `&fn(u32) -> u32 {foo}`
               found reference `&fn(u32) -> u32 {bar}`
    = note: different fn items have unique types, even if their signatures are the same
+   = help: consider casting both fn items to fn pointers using `as fn(u32) -> u32`
 
 error[E0308]: mismatched types
   --> $DIR/fn-pointer-mismatch.rs:23:9
@@ -21,6 +22,7 @@ LL |     a = bar;
    = note: expected fn item `fn(_) -> _ {foo}`
               found fn item `fn(_) -> _ {bar}`
    = note: different fn items have unique types, even if their signatures are the same
+   = help: consider casting both fn items to fn pointers using `as fn(u32) -> u32`
 
 error[E0308]: mismatched types
   --> $DIR/fn-pointer-mismatch.rs:31:18
@@ -35,6 +37,7 @@ LL |     b = Box::new(bar);
    = note: different fn items have unique types, even if their signatures are the same
 note: associated function defined here
   --> $SRC_DIR/alloc/src/boxed.rs:LL:COL
+   = help: consider casting both fn items to fn pointers using `as fn(u32) -> u32`
 
 error[E0308]: mismatched types
   --> $DIR/fn-pointer-mismatch.rs:36:29

tests/ui/self/arbitrary_self_types_pointers_and_wrappers.rs

@@ -3,6 +3,7 @@
 #![feature(rustc_attrs)]
 
 use std::{
+    cell::Cell,
     ops::{Deref, CoerceUnsized, DispatchFromDyn},
     marker::Unsize,
 };
@@ -20,6 +21,20 @@ impl<T: ?Sized> Deref for Ptr<T> {
 impl<T: Unsize<U> + ?Sized, U: ?Sized> CoerceUnsized<Ptr<U>> for Ptr<T> {}
 impl<T: Unsize<U> + ?Sized, U: ?Sized> DispatchFromDyn<Ptr<U>> for Ptr<T> {}
 
+
+struct CellPtr<'a, T: ?Sized>(Cell<&'a T>);
+
+impl<'a, T: ?Sized> Deref for CellPtr<'a, T> {
+    type Target = T;
+
+    fn deref(&self) -> &T {
+        self.0.get()
+    }
+}
+
+impl<'a, T: Unsize<U> + ?Sized, U: ?Sized> CoerceUnsized<CellPtr<'a, U>> for CellPtr<'a, T> {}
+impl<'a, T: Unsize<U> + ?Sized, U: ?Sized> DispatchFromDyn<CellPtr<'a, U>> for CellPtr<'a, T> {}
+
 struct Wrapper<T: ?Sized>(T);
 
 impl<T: ?Sized> Deref for Wrapper<T> {
@@ -42,6 +57,7 @@ trait Trait {
     fn ptr_wrapper(self: Ptr<Wrapper<Self>>) -> i32;
     fn wrapper_ptr(self: Wrapper<Ptr<Self>>) -> i32;
     fn wrapper_ptr_wrapper(self: Wrapper<Ptr<Wrapper<Self>>>) -> i32;
+    fn cell(self: CellPtr<Self>) -> i32;
 }
 
 impl Trait for i32 {
@@ -54,6 +70,9 @@ impl Trait for i32 {
     fn wrapper_ptr_wrapper(self: Wrapper<Ptr<Wrapper<Self>>>) -> i32 {
         ***self
     }
+    fn cell(self: CellPtr<Self>) -> i32 {
+        *self
+    }
 }
 
 fn main() {
@@ -65,4 +84,7 @@ fn main() {
 
     let wpw = Wrapper(Ptr(Box::new(Wrapper(7)))) as Wrapper<Ptr<Wrapper<dyn Trait>>>;
     assert_eq!(wpw.wrapper_ptr_wrapper(), 7);
+
+    let c = CellPtr(Cell::new(&8)) as CellPtr<dyn Trait>;
+    assert_eq!(c.cell(), 8);
 }