Make PointerLike opt-in as a trait

Author: compiler-errors

compiler/rustc_hir_analysis/src/coherence/builtin.rs

@@ -37,22 +37,23 @@ pub(super) fn check_trait<'tcx>(
 ) -> Result<(), ErrorGuaranteed> {
     let lang_items = tcx.lang_items();
     let checker = Checker { tcx, trait_def_id, impl_def_id, impl_header };
-    let mut res = checker.check(lang_items.drop_trait(), visit_implementation_of_drop);
-    res = res.and(checker.check(lang_items.copy_trait(), visit_implementation_of_copy));
-    res = res.and(checker.check(lang_items.const_param_ty_trait(), |checker| {
-        visit_implementation_of_const_param_ty(checker, LangItem::ConstParamTy)
-    }));
-    res = res.and(checker.check(lang_items.unsized_const_param_ty_trait(), |checker| {
-        visit_implementation_of_const_param_ty(checker, LangItem::UnsizedConstParamTy)
-    }));
-
-    res = res.and(
-        checker.check(lang_items.coerce_unsized_trait(), visit_implementation_of_coerce_unsized),
-    );
-    res.and(
-        checker
-            .check(lang_items.dispatch_from_dyn_trait(), visit_implementation_of_dispatch_from_dyn),
-    )
+    (|| {
+        checker.check(lang_items.drop_trait(), visit_implementation_of_drop)?;
+        checker.check(lang_items.copy_trait(), visit_implementation_of_copy)?;
+        checker.check(lang_items.const_param_ty_trait(), |checker| {
+            visit_implementation_of_const_param_ty(checker, LangItem::ConstParamTy)
+        })?;
+        checker.check(lang_items.unsized_const_param_ty_trait(), |checker| {
+            visit_implementation_of_const_param_ty(checker, LangItem::UnsizedConstParamTy)
+        })?;
+        checker.check(lang_items.coerce_unsized_trait(), visit_implementation_of_coerce_unsized)?;
+        checker.check(
+            lang_items.dispatch_from_dyn_trait(),
+            visit_implementation_of_dispatch_from_dyn,
+        )?;
+        checker.check(lang_items.pointer_like(), visit_implementation_of_pointer_like)?;
+        Ok(())
+    })()
 }
 
 struct Checker<'tcx> {
@@ -663,3 +664,63 @@ fn infringing_fields_error<'tcx>(
 
     err.emit()
 }
+
+fn visit_implementation_of_pointer_like(checker: &Checker<'_>) -> Result<(), ErrorGuaranteed> {
+    let tcx = checker.tcx;
+    let typing_env = ty::TypingEnv::non_body_analysis(tcx, checker.impl_def_id);
+    let impl_span = tcx.def_span(checker.impl_def_id);
+    let self_ty = tcx.impl_trait_ref(checker.impl_def_id).unwrap().instantiate_identity().self_ty();
+
+    // If an ADT is repr(transparent)...
+    if let ty::Adt(def, args) = *self_ty.kind()
+        && def.repr().transparent()
+    {
+        // FIXME(compiler-errors): This should and could be deduplicated into a query.
+        // Find the nontrivial field.
+        let adt_typing_env = ty::TypingEnv::non_body_analysis(tcx, def.did());
+        let nontrivial_field = def.all_fields().find(|field_def| {
+            let field_ty = tcx.type_of(field_def.did).instantiate_identity();
+            !tcx.layout_of(adt_typing_env.as_query_input(field_ty))
+                .is_ok_and(|layout| layout.layout.is_1zst())
+        });
+
+        if let Some(nontrivial_field) = nontrivial_field {
+            // Check that the nontrivial field implements `PointerLike`.
+            let nontrivial_field = nontrivial_field.ty(tcx, args);
+            let (infcx, param_env) = tcx.infer_ctxt().build_with_typing_env(typing_env);
+            let ocx = ObligationCtxt::new(&infcx);
+            ocx.register_bound(
+                ObligationCause::misc(impl_span, checker.impl_def_id),
+                param_env,
+                nontrivial_field,
+                tcx.lang_items().pointer_like().unwrap(),
+            );
+            // FIXME(dyn-star): We should regionck this implementation.
+            if ocx.select_all_or_error().is_empty() {
+                return Ok(());
+            }
+        }
+    }
+
+    let is_permitted_primitive = match *self_ty.kind() {
+        ty::Adt(def, _) => def.is_box(),
+        ty::Uint(..) | ty::Int(..) | ty::RawPtr(..) | ty::Ref(..) | ty::FnPtr(..) => true,
+        _ => false,
+    };
+
+    if is_permitted_primitive
+        && let Ok(layout) = tcx.layout_of(typing_env.as_query_input(self_ty))
+        && layout.layout.is_pointer_like(&tcx.data_layout)
+    {
+        return Ok(());
+    }
+
+    Err(tcx
+        .dcx()
+        .struct_span_err(
+            impl_span,
+            "implementation must be applied to type that has the same ABI as a pointer, \
+            or is `repr(transparent)` and whose field is `PointerLike`",
+        )
+        .emit())
+}

library/alloc/src/boxed.rs

@@ -191,6 +191,8 @@ use core::error::{self, Error};
 use core::fmt;
 use core::future::Future;
 use core::hash::{Hash, Hasher};
+#[cfg(not(bootstrap))]
+use core::marker::PointerLike;
 use core::marker::{Tuple, Unsize};
 use core::mem::{self, SizedTypeProperties};
 use core::ops::{
@@ -2131,3 +2133,7 @@ impl<E: Error> Error for Box<E> {
         Error::provide(&**self, request);
     }
 }
+
+#[cfg(not(bootstrap))]
+#[unstable(feature = "pointer_like_trait", issue = "none")]
+impl<T> PointerLike for Box<T> {}

library/alloc/src/lib.rs

@@ -136,6 +136,7 @@
 #![feature(panic_internals)]
 #![feature(pattern)]
 #![feature(pin_coerce_unsized_trait)]
+#![feature(pointer_like_trait)]
 #![feature(ptr_internals)]
 #![feature(ptr_metadata)]
 #![feature(ptr_sub_ptr)]

library/core/src/marker.rs

@@ -981,6 +981,18 @@ pub trait Tuple {}
 )]
 pub trait PointerLike {}
 
+#[cfg(not(bootstrap))]
+marker_impls! {
+    #[unstable(feature = "pointer_like_trait", issue = "none")]
+    PointerLike for
+        usize,
+        {T} &T,
+        {T} &mut T,
+        {T} *const T,
+        {T} *mut T,
+        {T: PointerLike} crate::pin::Pin<T>,
+}
+
 /// A marker for types which can be used as types of `const` generic parameters.
 ///
 /// These types must have a proper equivalence relation (`Eq`) and it must be automatically

tests/crashes/113280.rs

@@ -0,0 +1,9 @@
+//@ edition:2018
+
+#![feature(dyn_star, const_async_blocks)]
+//~^ WARN the feature `dyn_star` is incomplete
+
+static S: dyn* Send + Sync = async { 42 };
+//~^ needs to have the same ABI as a pointer
+
+pub fn main() {}

tests/crashes/127676.rs

@@ -0,0 +1,20 @@
+warning: the feature `dyn_star` is incomplete and may not be safe to use and/or cause compiler crashes
+  --> $DIR/async-block-dyn-star.rs:3:12
+   |
+LL | #![feature(dyn_star, const_async_blocks)]
+   |            ^^^^^^^^
+   |
+   = note: see issue #102425 <https://github.com/rust-lang/rust/issues/102425> for more information
+   = note: `#[warn(incomplete_features)]` on by default
+
+error[E0277]: `{async block@$DIR/async-block-dyn-star.rs:6:30: 6:35}` needs to have the same ABI as a pointer
+  --> $DIR/async-block-dyn-star.rs:6:30
+   |
+LL | static S: dyn* Send + Sync = async { 42 };
+   |                              ^^^^^^^^^^^^ `{async block@$DIR/async-block-dyn-star.rs:6:30: 6:35}` needs to be a pointer-like type
+   |
+   = help: the trait `PointerLike` is not implemented for `{async block@$DIR/async-block-dyn-star.rs:6:30: 6:35}`
+
+error: aborting due to 1 previous error; 1 warning emitted
+
+For more information about this error, try `rustc --explain E0277`.

tests/ui/dyn-star/async-block-dyn-star.rs

@@ -1,14 +1,17 @@
 error[E0277]: `&T` needs to have the same ABI as a pointer
   --> $DIR/check-size-at-cast-polymorphic-bad.rs:15:15
    |
+LL | fn polymorphic<T: Debug + ?Sized>(t: &T) {
+   |                - this type parameter needs to be `Sized`
 LL |     dyn_debug(t);
    |               ^ `&T` needs to be a pointer-like type
    |
-   = help: the trait `PointerLike` is not implemented for `&T`
-help: consider introducing a `where` clause, but there might be an alternative better way to express this requirement
+   = note: required for `&T` to implement `PointerLike`
+help: consider removing the `?Sized` bound to make the type parameter `Sized`
+   |
+LL - fn polymorphic<T: Debug + ?Sized>(t: &T) {
+LL + fn polymorphic<T: Debug>(t: &T) {
    |
-LL | fn polymorphic<T: Debug + ?Sized>(t: &T) where &T: PointerLike {
-   |                                          +++++++++++++++++++++
 
 error: aborting due to 1 previous error
 

tests/ui/dyn-star/async-block-dyn-star.stderr

@@ -1,14 +1,17 @@
 error[E0277]: `&T` needs to have the same ABI as a pointer
   --> $DIR/check-size-at-cast-polymorphic-bad.rs:15:15
    |
+LL | fn polymorphic<T: Debug + ?Sized>(t: &T) {
+   |                - this type parameter needs to be `Sized`
 LL |     dyn_debug(t);
    |               ^ `&T` needs to be a pointer-like type
    |
-   = help: the trait `PointerLike` is not implemented for `&T`
-help: consider introducing a `where` clause, but there might be an alternative better way to express this requirement
+   = note: required for `&T` to implement `PointerLike`
+help: consider removing the `?Sized` bound to make the type parameter `Sized`
+   |
+LL - fn polymorphic<T: Debug + ?Sized>(t: &T) {
+LL + fn polymorphic<T: Debug>(t: &T) {
    |
-LL | fn polymorphic<T: Debug + ?Sized>(t: &T) where &T: PointerLike {
-   |                                          +++++++++++++++++++++
 
 error: aborting due to 1 previous error