trait_sel: MetaSized always holds temporarily

davidtwco · davidtwco · commit 8d64937dc25e · 2025-07-16T12:35:44.000Z
As a temporary measure while a proper fix for
`tests/ui/sized-hierarchy/incomplete-inference-issue-143992.rs`
is implemented, make `MetaSized` obligations always hold. In effect,
temporarily reverting the `sized_hierarchy` feature. This is a small
change that can be backported.
diff --git a/compiler/rustc_trait_selection/src/traits/util.rs b/compiler/rustc_trait_selection/src/traits/util.rs
@@ -378,6 +378,13 @@ pub fn sizedness_fast_path<'tcx>(tcx: TyCtxt<'tcx>, predicate: ty::Predicate<'tc
             _ => return false,
         };
 
+        // FIXME(sized_hierarchy): this temporarily reverts the `sized_hierarchy` feature
+        // while a proper fix for `tests/ui/sized-hierarchy/incomplete-inference-issue-143992.rs`
+        // is pending a proper fix
+        if !tcx.features().sized_hierarchy() && matches!(sizedness, SizedTraitKind::MetaSized) {
+            return true;
+        }
+
         if trait_pred.self_ty().has_trivial_sizedness(tcx, sizedness) {
             debug!("fast path -- trivial sizedness");
             return true;
diff --git a/tests/ui/consts/const-size_of_val-align_of_val-extern-type.rs b/tests/ui/consts/const-size_of_val-align_of_val-extern-type.rs
@@ -8,8 +8,8 @@ extern "C" {
 }
 
 const _SIZE: usize = unsafe { size_of_val(&4 as *const i32 as *const Opaque) };
-//~^ ERROR the size for values of type `Opaque` cannot be known
+//~^ ERROR `extern type` does not have known layout
 const _ALIGN: usize = unsafe { align_of_val(&4 as *const i32 as *const Opaque) };
-//~^ ERROR the size for values of type `Opaque` cannot be known
+//~^ ERROR `extern type` does not have known layout
 
 fn main() {}
diff --git a/tests/ui/consts/const-size_of_val-align_of_val-extern-type.stderr b/tests/ui/consts/const-size_of_val-align_of_val-extern-type.stderr
@@ -1,39 +1,15 @@
-error[E0277]: the size for values of type `Opaque` cannot be known
-  --> $DIR/const-size_of_val-align_of_val-extern-type.rs:10:43
+error[E0080]: `extern type` does not have known layout
+  --> $DIR/const-size_of_val-align_of_val-extern-type.rs:10:31
    |
 LL | const _SIZE: usize = unsafe { size_of_val(&4 as *const i32 as *const Opaque) };
-   |                               ----------- ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `MetaSized` is not implemented for `Opaque`
-   |                               |
-   |                               required by a bound introduced by this call
-   |
-   = note: the trait bound `Opaque: MetaSized` is not satisfied
-note: required by a bound in `std::intrinsics::size_of_val`
-  --> $SRC_DIR/core/src/intrinsics/mod.rs:LL:COL
-help: consider borrowing here
-   |
-LL | const _SIZE: usize = unsafe { size_of_val(&(&4 as *const i32 as *const Opaque)) };
-   |                                           ++                                 +
-LL | const _SIZE: usize = unsafe { size_of_val(&mut (&4 as *const i32 as *const Opaque)) };
-   |                                           ++++++                                 +
+   |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ evaluation of `_SIZE` failed here
 
-error[E0277]: the size for values of type `Opaque` cannot be known
-  --> $DIR/const-size_of_val-align_of_val-extern-type.rs:12:45
+error[E0080]: `extern type` does not have known layout
+  --> $DIR/const-size_of_val-align_of_val-extern-type.rs:12:32
    |
 LL | const _ALIGN: usize = unsafe { align_of_val(&4 as *const i32 as *const Opaque) };
-   |                                ------------ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `MetaSized` is not implemented for `Opaque`
-   |                                |
-   |                                required by a bound introduced by this call
-   |
-   = note: the trait bound `Opaque: MetaSized` is not satisfied
-note: required by a bound in `std::intrinsics::align_of_val`
-  --> $SRC_DIR/core/src/intrinsics/mod.rs:LL:COL
-help: consider borrowing here
-   |
-LL | const _ALIGN: usize = unsafe { align_of_val(&(&4 as *const i32 as *const Opaque)) };
-   |                                             ++                                 +
-LL | const _ALIGN: usize = unsafe { align_of_val(&mut (&4 as *const i32 as *const Opaque)) };
-   |                                             ++++++                                 +
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ evaluation of `_ALIGN` failed here
 
 error: aborting due to 2 previous errors
 
-For more information about this error, try `rustc --explain E0277`.
+For more information about this error, try `rustc --explain E0080`.
diff --git a/tests/ui/extern/extern-types-size_of_val.rs b/tests/ui/extern/extern-types-size_of_val.rs
@@ -1,4 +1,4 @@
-//@ check-fail
+//@ check-pass
 #![feature(extern_types)]
 
 use std::mem::{align_of_val, size_of_val};
@@ -11,7 +11,5 @@ fn main() {
     let x: &A = unsafe { &*(1usize as *const A) };
 
     size_of_val(x);
-    //~^ ERROR the size for values of type `A` cannot be known
     align_of_val(x);
-    //~^ ERROR the size for values of type `A` cannot be known
 }
diff --git a/tests/ui/extern/extern-types-size_of_val.stderr b/tests/ui/extern/extern-types-size_of_val.stderr
diff --git a/tests/ui/extern/extern-types-unsized.rs b/tests/ui/extern/extern-types-unsized.rs
@@ -27,9 +27,7 @@ fn main() {
 
     assert_sized::<Bar<A>>();
     //~^ ERROR the size for values of type
-    //~| ERROR the size for values of type
 
     assert_sized::<Bar<Bar<A>>>();
     //~^ ERROR the size for values of type
-    //~| ERROR the size for values of type
 }
diff --git a/tests/ui/extern/extern-types-unsized.stderr b/tests/ui/extern/extern-types-unsized.stderr
@@ -59,21 +59,8 @@ help: consider relaxing the implicit `Sized` restriction
 LL | fn assert_sized<T: ?Sized>() {}
    |                  ++++++++
 
-error[E0277]: the size for values of type `A` cannot be known
-  --> $DIR/extern-types-unsized.rs:28:20
-   |
-LL |     assert_sized::<Bar<A>>();
-   |                    ^^^^^^ doesn't have a known size
-   |
-   = help: the trait `MetaSized` is not implemented for `A`
-note: required by a bound in `Bar`
-  --> $DIR/extern-types-unsized.rs:14:12
-   |
-LL | struct Bar<T: ?Sized> {
-   |            ^ required by this bound in `Bar`
-
 error[E0277]: the size for values of type `A` cannot be known at compilation time
-  --> $DIR/extern-types-unsized.rs:32:20
+  --> $DIR/extern-types-unsized.rs:31:20
    |
 LL |     assert_sized::<Bar<Bar<A>>>();
    |                    ^^^^^^^^^^^ doesn't have a size known at compile-time
@@ -94,19 +81,6 @@ help: consider relaxing the implicit `Sized` restriction
 LL | fn assert_sized<T: ?Sized>() {}
    |                  ++++++++
 
-error[E0277]: the size for values of type `A` cannot be known
-  --> $DIR/extern-types-unsized.rs:32:20
-   |
-LL |     assert_sized::<Bar<Bar<A>>>();
-   |                    ^^^^^^^^^^^ doesn't have a known size
-   |
-   = help: the trait `MetaSized` is not implemented for `A`
-note: required by a bound in `Bar`
-  --> $DIR/extern-types-unsized.rs:14:12
-   |
-LL | struct Bar<T: ?Sized> {
-   |            ^ required by this bound in `Bar`
-
-error: aborting due to 6 previous errors
+error: aborting due to 4 previous errors
 
 For more information about this error, try `rustc --explain E0277`.
diff --git a/tests/ui/extern/unsized-extern-derefmove.rs b/tests/ui/extern/unsized-extern-derefmove.rs
@@ -7,14 +7,10 @@ extern "C" {
 }
 
 unsafe fn make_device() -> Box<Device> {
-//~^ ERROR the size for values of type `Device` cannot be known
     Box::from_raw(0 as *mut _)
-//~^ ERROR the size for values of type `Device` cannot be known
-//~| ERROR the size for values of type `Device` cannot be known
 }
 
 fn main() {
     let d: Device = unsafe { *make_device() };
 //~^ ERROR the size for values of type `Device` cannot be known
-//~| ERROR the size for values of type `Device` cannot be known
 }
diff --git a/tests/ui/extern/unsized-extern-derefmove.stderr b/tests/ui/extern/unsized-extern-derefmove.stderr
@@ -1,43 +1,5 @@
-error[E0277]: the size for values of type `Device` cannot be known
-  --> $DIR/unsized-extern-derefmove.rs:9:28
-   |
-LL | unsafe fn make_device() -> Box<Device> {
-   |                            ^^^^^^^^^^^ doesn't have a known size
-   |
-   = help: the trait `MetaSized` is not implemented for `Device`
-note: required by a bound in `Box`
-  --> $SRC_DIR/alloc/src/boxed.rs:LL:COL
-
-error[E0277]: the size for values of type `Device` cannot be known
-  --> $DIR/unsized-extern-derefmove.rs:11:19
-   |
-LL |     Box::from_raw(0 as *mut _)
-   |     ------------- ^^^^^^^^^^^ the trait `MetaSized` is not implemented for `Device`
-   |     |
-   |     required by a bound introduced by this call
-   |
-   = note: the trait bound `Device: MetaSized` is not satisfied
-note: required by a bound in `Box::<T>::from_raw`
-  --> $SRC_DIR/alloc/src/boxed.rs:LL:COL
-help: consider borrowing here
-   |
-LL |     Box::from_raw(&(0 as *mut _))
-   |                   ++           +
-LL |     Box::from_raw(&mut (0 as *mut _))
-   |                   ++++++           +
-
-error[E0277]: the size for values of type `Device` cannot be known
-  --> $DIR/unsized-extern-derefmove.rs:11:5
-   |
-LL |     Box::from_raw(0 as *mut _)
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a known size
-   |
-   = help: the trait `MetaSized` is not implemented for `Device`
-note: required by a bound in `Box`
-  --> $SRC_DIR/alloc/src/boxed.rs:LL:COL
-
 error[E0277]: the size for values of type `Device` cannot be known at compilation time
-  --> $DIR/unsized-extern-derefmove.rs:17:9
+  --> $DIR/unsized-extern-derefmove.rs:14:9
    |
 LL |     let d: Device = unsafe { *make_device() };
    |         ^ doesn't have a size known at compile-time
@@ -49,16 +11,6 @@ help: consider borrowing here
 LL |     let d: &Device = unsafe { *make_device() };
    |            +
 
-error[E0277]: the size for values of type `Device` cannot be known
-  --> $DIR/unsized-extern-derefmove.rs:17:31
-   |
-LL |     let d: Device = unsafe { *make_device() };
-   |                               ^^^^^^^^^^^^^ doesn't have a known size
-   |
-   = help: the trait `MetaSized` is not implemented for `Device`
-note: required by a bound in `Box`
-  --> $SRC_DIR/alloc/src/boxed.rs:LL:COL
-
-error: aborting due to 5 previous errors
+error: aborting due to 1 previous error
 
 For more information about this error, try `rustc --explain E0277`.
diff --git a/tests/ui/layout/unconstrained-param-ice-137308.rs b/tests/ui/layout/unconstrained-param-ice-137308.rs
@@ -17,4 +17,3 @@ impl<C: ?Sized> A for u8 { //~ ERROR: the type parameter `C` is not constrained
 #[rustc_layout(debug)]
 struct S([u8; <u8 as A>::B]);
 //~^ ERROR: the type has an unknown layout
-//~| ERROR: type annotations needed
diff --git a/tests/ui/layout/unconstrained-param-ice-137308.stderr b/tests/ui/layout/unconstrained-param-ice-137308.stderr
@@ -4,19 +4,12 @@ error[E0207]: the type parameter `C` is not constrained by the impl trait, self
 LL | impl<C: ?Sized> A for u8 {
    |      ^ unconstrained type parameter
 
-error[E0282]: type annotations needed
-  --> $DIR/unconstrained-param-ice-137308.rs:18:16
-   |
-LL | struct S([u8; <u8 as A>::B]);
-   |                ^^ cannot infer type for type parameter `C`
-
 error: the type has an unknown layout
   --> $DIR/unconstrained-param-ice-137308.rs:18:1
    |
 LL | struct S([u8; <u8 as A>::B]);
    | ^^^^^^^^
 
-error: aborting due to 3 previous errors
+error: aborting due to 2 previous errors
 
-Some errors have detailed explanations: E0207, E0282.
-For more information about an error, try `rustc --explain E0207`.
+For more information about this error, try `rustc --explain E0207`.
diff --git a/tests/ui/nll/issue-50716.rs b/tests/ui/nll/issue-50716.rs
@@ -5,7 +5,7 @@ trait A {
     type X: ?Sized;
 }
 
-fn foo<'a, T: 'static>(s: Box<<&'a T as A>::X>) //~ ERROR
+fn foo<'a, T: 'static>(s: Box<<&'a T as A>::X>)
 where
     for<'b> &'b T: A,
     <&'static T as A>::X: Sized
diff --git a/tests/ui/nll/issue-50716.stderr b/tests/ui/nll/issue-50716.stderr
@@ -1,18 +1,3 @@
-error[E0308]: mismatched types
-  --> $DIR/issue-50716.rs:8:27
-   |
-LL | fn foo<'a, T: 'static>(s: Box<<&'a T as A>::X>)
-   |                           ^^^^^^^^^^^^^^^^^^^^ lifetime mismatch
-   |
-   = note: expected trait `<<&'a T as A>::X as MetaSized>`
-              found trait `<<&'static T as A>::X as MetaSized>`
-note: the lifetime `'a` as defined here...
-  --> $DIR/issue-50716.rs:8:8
-   |
-LL | fn foo<'a, T: 'static>(s: Box<<&'a T as A>::X>)
-   |        ^^
-   = note: ...does not necessarily outlive the static lifetime
-
 error: lifetime may not live long enough
   --> $DIR/issue-50716.rs:13:14
    |
@@ -22,6 +7,5 @@ LL | fn foo<'a, T: 'static>(s: Box<<&'a T as A>::X>)
 LL |     let _x = *s;
    |              ^^ proving this value is `Sized` requires that `'a` must outlive `'static`
 
-error: aborting due to 2 previous errors
+error: aborting due to 1 previous error
 
-For more information about this error, try `rustc --explain E0308`.
diff --git a/tests/ui/sized-hierarchy/incomplete-inference-issue-143992.next.stderr b/tests/ui/sized-hierarchy/incomplete-inference-issue-143992.next.stderr
@@ -0,0 +1,17 @@
+error[E0308]: mismatched types
+  --> $DIR/incomplete-inference-issue-143992.rs:27:28
+   |
+LL |     let _x = T::Assoc::new(());
+   |              ------------- ^^ expected `[u32; 1]`, found `()`
+   |              |
+   |              arguments to this function are incorrect
+   |
+note: associated function defined here
+  --> $DIR/incomplete-inference-issue-143992.rs:18:8
+   |
+LL |     fn new(r: R) -> R {
+   |        ^^^ ----
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0308`.
diff --git a/tests/ui/sized-hierarchy/incomplete-inference-issue-143992.rs b/tests/ui/sized-hierarchy/incomplete-inference-issue-143992.rs
@@ -0,0 +1,29 @@
+//@ compile-flags: --crate-type=lib
+//@ revisions: current next
+//@ ignore-compare-mode-next-solver (explicit revisions)
+//@[current] check-pass
+//@[next] compile-flags: -Znext-solver
+//@[next] check-fail
+
+// Test that we avoid incomplete inference when normalizing. Without this,
+// `Trait`'s implicit `MetaSized` supertrait requires proving `T::Assoc<_>: MetaSized`
+// before checking the `new` arguments, resulting in eagerly constraining the inference
+// var to `u32`. This is undesirable and would breaking code.
+
+pub trait Trait {
+    type Assoc<G>: OtherTrait<G>;
+}
+
+pub trait OtherTrait<R> {
+    fn new(r: R) -> R {
+        r
+    }
+}
+
+pub fn function<T: Trait>()
+where
+    T::Assoc<[u32; 1]>: Clone,
+{
+    let _x = T::Assoc::new(());
+//[next]~^ ERROR mismatched types
+}
diff --git a/tests/ui/sized-hierarchy/overflow.current.stderr b/tests/ui/sized-hierarchy/overflow.current.stderr
diff --git a/tests/ui/sized-hierarchy/overflow.rs b/tests/ui/sized-hierarchy/overflow.rs
diff --git a/tests/ui/traits/resolve-impl-before-constrain-check.rs b/tests/ui/traits/resolve-impl-before-constrain-check.rs
diff --git a/tests/ui/traits/resolve-impl-before-constrain-check.stderr b/tests/ui/traits/resolve-impl-before-constrain-check.stderr

Original file line number	Diff line number	Diff line change
`@@ -8,8 +8,8 @@ extern "C" {`
`8`	`8`	`}`
`9`	`9`
`10`	`10`	`const _SIZE: usize = unsafe { size_of_val(&4 as const i32 as const Opaque) };`
`11`		-//~^ ERROR the size for values of type `Opaque` cannot be known
	`11`	+//~^ ERROR `extern type` does not have known layout
`12`	`12`	`const _ALIGN: usize = unsafe { align_of_val(&4 as const i32 as const Opaque) };`
`13`		-//~^ ERROR the size for values of type `Opaque` cannot be known
	`13`	+//~^ ERROR `extern type` does not have known layout
`14`	`14`
`15`	`15`	`fn main() {}`
Original file line number	Diff line number	Diff line change
`@@ -27,9 +27,7 @@ fn main() {`
`27`	`27`
`28`	`28`	`assert_sized::<Bar<A>>();`
`29`	`29`	`//~^ ERROR the size for values of type`
`30`		`- //~\| ERROR the size for values of type`
`31`	`30`
`32`	`31`	`assert_sized::<Bar<Bar<A>>>();`
`33`	`32`	`//~^ ERROR the size for values of type`
`34`		`- //~\| ERROR the size for values of type`
`35`	`33`	`}`
Original file line number	Diff line number	Diff line change
`@@ -7,14 +7,10 @@ extern "C" {`
`7`	`7`	`}`
`8`	`8`
`9`	`9`	`unsafe fn make_device() -> Box<Device> {`
`10`		-//~^ ERROR the size for values of type `Device` cannot be known
`11`	`10`	`Box::from_raw(0 as *mut _)`
`12`		-//~^ ERROR the size for values of type `Device` cannot be known
`13`		-//~\| ERROR the size for values of type `Device` cannot be known
`14`	`11`	`}`
`15`	`12`
`16`	`13`	`fn main() {`
`17`	`14`	`let d: Device = unsafe { *make_device() };`
`18`	`15`	//~^ ERROR the size for values of type `Device` cannot be known
`19`		-//~\| ERROR the size for values of type `Device` cannot be known
`20`	`16`	`}`