Auto merge of rust-lang#109413 - compiler-errors:pointer-like-abi, r=cjgillot

Enforce that `PointerLike` requires a pointer-like ABI

At least temporarily, let's ban coercing things that are pointer-sized and pointer-aligned but *not* `Abi::Scalar(..)` into `dyn*`. See: rust-lang#104694 (comment)

This can be lifted in the future if we decie that we *want* to be able to coerce something `repr(C)` into a `dyn*`, but we'll have to figure out what to do with Miri and codegen...

r? compiler

Author: bors

compiler/rustc_abi/src/lib.rs

@@ -1522,6 +1522,16 @@ impl<'a> Layout<'a> {
     pub fn size(self) -> Size {
         self.0.0.size
     }
+
+    /// Whether the layout is from a type that implements [`std::marker::PointerLike`].
+    ///
+    /// Currently, that means that the type is pointer-sized, pointer-aligned,
+    /// and has a scalar ABI.
+    pub fn is_pointer_like(self, data_layout: &TargetDataLayout) -> bool {
+        self.size() == data_layout.pointer_size
+            && self.align().abi == data_layout.pointer_align.abi
+            && matches!(self.abi(), Abi::Scalar(..))
+    }
 }
 
 #[derive(Copy, Clone, PartialEq, Eq, Debug)]

compiler/rustc_trait_selection/src/solve/trait_goals.rs

@@ -221,8 +221,7 @@ impl<'tcx> assembly::GoalKind<'tcx> for TraitPredicate<'tcx> {
         let self_ty = tcx.erase_regions(goal.predicate.self_ty());
 
         if let Ok(layout) = tcx.layout_of(goal.param_env.and(self_ty))
-            && layout.layout.size() == tcx.data_layout.pointer_size
-            && layout.layout.align().abi == tcx.data_layout.pointer_align.abi
+            && layout.layout.is_pointer_like(&tcx.data_layout)
         {
             // FIXME: We could make this faster by making a no-constraints response
             ecx.evaluate_added_goals_and_make_canonical_response(Certainty::Yes)

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

@@ -97,7 +97,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             } else if lang_items.tuple_trait() == Some(def_id) {
                 self.assemble_candidate_for_tuple(obligation, &mut candidates);
             } else if lang_items.pointer_like() == Some(def_id) {
-                self.assemble_candidate_for_ptr_sized(obligation, &mut candidates);
+                self.assemble_candidate_for_pointer_like(obligation, &mut candidates);
             } else if lang_items.fn_ptr_trait() == Some(def_id) {
                 self.assemble_candidates_for_fn_ptr_trait(obligation, &mut candidates);
             } else {
@@ -942,25 +942,24 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         }
     }
 
-    fn assemble_candidate_for_ptr_sized(
+    fn assemble_candidate_for_pointer_like(
         &mut self,
         obligation: &TraitObligation<'tcx>,
         candidates: &mut SelectionCandidateSet<'tcx>,
     ) {
         // The regions of a type don't affect the size of the type
-        let self_ty = self
-            .tcx()
-            .erase_regions(self.tcx().erase_late_bound_regions(obligation.predicate.self_ty()));
+        let tcx = self.tcx();
+        let self_ty =
+            tcx.erase_regions(tcx.erase_late_bound_regions(obligation.predicate.self_ty()));
 
         // But if there are inference variables, we have to wait until it's resolved.
         if self_ty.has_non_region_infer() {
             candidates.ambiguous = true;
             return;
         }
 
-        if let Ok(layout) = self.tcx().layout_of(obligation.param_env.and(self_ty))
-            && layout.layout.size() == self.tcx().data_layout.pointer_size
-            && layout.layout.align().abi == self.tcx().data_layout.pointer_align.abi
+        if let Ok(layout) = tcx.layout_of(obligation.param_env.and(self_ty))
+            && layout.layout.is_pointer_like(&tcx.data_layout)
         {
             candidates.vec.push(BuiltinCandidate { has_nested: false });
         }

library/core/src/marker.rs

@@ -879,7 +879,7 @@ pub trait Tuple {}
 #[unstable(feature = "pointer_like_trait", issue = "none")]
 #[lang = "pointer_like"]
 #[rustc_on_unimplemented(
-    message = "`{Self}` needs to have the same alignment and size as a pointer",
+    message = "`{Self}` needs to have the same ABI as a pointer",
     label = "`{Self}` needs to be a pointer-like type"
 )]
 pub trait PointerLike {}

tests/ui/dyn-star/align.normal.stderr

@@ -1,11 +1,20 @@
 warning: the feature `dyn_star` is incomplete and may not be safe to use and/or cause compiler crashes
-  --> $DIR/align.rs:4:12
+  --> $DIR/align.rs:3:12
    |
 LL | #![feature(dyn_star)]
    |            ^^^^^^^^
    |
    = note: see issue #102425 <https://github.com/rust-lang/rust/issues/102425> for more information
    = note: `#[warn(incomplete_features)]` on by default
 
-warning: 1 warning emitted
+error[E0277]: `AlignedUsize` needs to have the same ABI as a pointer
+  --> $DIR/align.rs:14:13
+   |
+LL |     let x = AlignedUsize(12) as dyn* Debug;
+   |             ^^^^^^^^^^^^^^^^ `AlignedUsize` needs to be a pointer-like type
+   |
+   = help: the trait `PointerLike` is not implemented for `AlignedUsize`
+
+error: aborting due to previous error; 1 warning emitted
 
+For more information about this error, try `rustc --explain E0277`.

tests/ui/dyn-star/align.over_aligned.stderr

@@ -1,14 +1,14 @@
 warning: the feature `dyn_star` is incomplete and may not be safe to use and/or cause compiler crashes
-  --> $DIR/align.rs:4:12
+  --> $DIR/align.rs:3:12
    |
 LL | #![feature(dyn_star)]
    |            ^^^^^^^^
    |
    = note: see issue #102425 <https://github.com/rust-lang/rust/issues/102425> for more information
    = note: `#[warn(incomplete_features)]` on by default
 
-error[E0277]: `AlignedUsize` needs to have the same alignment and size as a pointer
-  --> $DIR/align.rs:15:13
+error[E0277]: `AlignedUsize` needs to have the same ABI as a pointer
+  --> $DIR/align.rs:14:13
    |
 LL |     let x = AlignedUsize(12) as dyn* Debug;
    |             ^^^^^^^^^^^^^^^^ `AlignedUsize` needs to be a pointer-like type

tests/ui/dyn-star/align.rs

@@ -1,5 +1,4 @@
 // revisions: normal over_aligned
-//[normal] check-pass
 
 #![feature(dyn_star)]
 //~^ WARN the feature `dyn_star` is incomplete and may not be safe to use and/or cause compiler crashes
@@ -13,5 +12,5 @@ struct AlignedUsize(usize);
 
 fn main() {
     let x = AlignedUsize(12) as dyn* Debug;
-    //[over_aligned]~^ ERROR `AlignedUsize` needs to have the same alignment and size as a pointer
+    //~^ ERROR `AlignedUsize` needs to have the same ABI as a pointer
 }

tests/ui/dyn-star/check-size-at-cast-polymorphic-bad.rs

@@ -9,7 +9,7 @@ fn dyn_debug(_: (dyn* Debug + '_)) {
 
 fn polymorphic<T: Debug + ?Sized>(t: &T) {
     dyn_debug(t);
-    //~^ ERROR `&T` needs to have the same alignment and size as a pointer
+    //~^ ERROR `&T` needs to have the same ABI as a pointer
 }
 
 fn main() {}

tests/ui/dyn-star/check-size-at-cast-polymorphic-bad.stderr

@@ -1,4 +1,4 @@
-error[E0277]: `&T` needs to have the same alignment and size as a pointer
+error[E0277]: `&T` needs to have the same ABI as a pointer
   --> $DIR/check-size-at-cast-polymorphic-bad.rs:11:15
    |
 LL |     dyn_debug(t);

tests/ui/dyn-star/check-size-at-cast.rs

@@ -5,6 +5,6 @@ use std::fmt::Debug;
 
 fn main() {
     let i = [1, 2, 3, 4] as dyn* Debug;
-    //~^ ERROR `[i32; 4]` needs to have the same alignment and size as a pointer
+    //~^ ERROR `[i32; 4]` needs to have the same ABI as a pointer
     dbg!(i);
 }