Auto merge of rust-lang#91311 - matthiaskrgr:rollup-ju9xizl, r=matthiaskrgr

Rollup of 3 pull requests

Successful merges:

 - rust-lang#90896 (Stabilize some `MaybeUninit` behavior as const)
 - rust-lang#91254 (Only check for errors in predicate when skipping impl assembly)
 - rust-lang#91303 (Miri: fix alignment check in array initialization)

Failed merges:

r? `@ghost`
`@rustbot` modify labels: rollup

Author: bors

compiler/rustc_const_eval/src/interpret/step.rs

@@ -242,11 +242,15 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                     let elem_size = first.layout.size;
                     let first_ptr = first.ptr;
                     let rest_ptr = first_ptr.offset(elem_size, self)?;
+                    // For the alignment of `rest_ptr`, we crucially do *not* use `first.align` as
+                    // that place might be more aligned than its type mandates (a `u8` array could
+                    // be 4-aligned if it sits at the right spot in a struct). Instead we use
+                    // `first.layout.align`, i.e., the alignment given by the type.
                     self.memory.copy_repeatedly(
                         first_ptr,
                         first.align,
                         rest_ptr,
-                        first.align,
+                        first.layout.align.abi,
                         elem_size,
                         length - 1,
                         /*nonoverlapping:*/ true,

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

@@ -536,7 +536,10 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         // This helps us avoid overflow: see issue #72839
         // Since compilation is already guaranteed to fail, this is just
         // to try to show the 'nicest' possible errors to the user.
-        if obligation.references_error() {
+        // We don't check for errors in the `ParamEnv` - in practice,
+        // it seems to cause us to be overly aggressive in deciding
+        // to give up searching for candidates, leading to spurious errors.
+        if obligation.predicate.references_error() {
             return;
         }
 

library/core/src/intrinsics.rs

@@ -853,7 +853,7 @@ extern "rust-intrinsic" {
     /// This will statically either panic, or do nothing.
     ///
     /// This intrinsic does not have a stable counterpart.
-    #[rustc_const_unstable(feature = "const_assert_type", issue = "none")]
+    #[rustc_const_stable(feature = "const_assert_type", since = "1.59.0")]
     pub fn assert_inhabited<T>();
 
     /// A guard for unsafe functions that cannot ever be executed if `T` does not permit

library/core/src/lib.rs

@@ -101,7 +101,6 @@
 #![feature(const_align_of_val)]
 #![feature(const_alloc_layout)]
 #![feature(const_arguments_as_str)]
-#![feature(const_assert_type)]
 #![feature(const_bigint_helper_methods)]
 #![feature(const_caller_location)]
 #![feature(const_cell_into_inner)]
@@ -117,7 +116,7 @@
 #![feature(const_intrinsic_copy)]
 #![feature(const_intrinsic_forget)]
 #![feature(const_likely)]
-#![feature(const_maybe_uninit_as_ptr)]
+#![feature(const_maybe_uninit_as_mut_ptr)]
 #![feature(const_maybe_uninit_assume_init)]
 #![feature(const_num_from_num)]
 #![feature(const_ops)]

library/core/src/mem/maybe_uninit.rs

@@ -528,7 +528,7 @@ impl<T> MaybeUninit<T> {
     /// (Notice that the rules around references to uninitialized data are not finalized yet, but
     /// until they are, it is advisable to avoid them.)
     #[stable(feature = "maybe_uninit", since = "1.36.0")]
-    #[rustc_const_unstable(feature = "const_maybe_uninit_as_ptr", issue = "75251")]
+    #[rustc_const_stable(feature = "const_maybe_uninit_as_ptr", since = "1.59.0")]
     #[inline(always)]
     pub const fn as_ptr(&self) -> *const T {
         // `MaybeUninit` and `ManuallyDrop` are both `repr(transparent)` so we can cast the pointer.
@@ -567,7 +567,7 @@ impl<T> MaybeUninit<T> {
     /// (Notice that the rules around references to uninitialized data are not finalized yet, but
     /// until they are, it is advisable to avoid them.)
     #[stable(feature = "maybe_uninit", since = "1.36.0")]
-    #[rustc_const_unstable(feature = "const_maybe_uninit_as_ptr", issue = "75251")]
+    #[rustc_const_unstable(feature = "const_maybe_uninit_as_mut_ptr", issue = "75251")]
     #[inline(always)]
     pub const fn as_mut_ptr(&mut self) -> *mut T {
         // `MaybeUninit` and `ManuallyDrop` are both `repr(transparent)` so we can cast the pointer.
@@ -620,7 +620,7 @@ impl<T> MaybeUninit<T> {
     /// // `x` had not been initialized yet, so this last line caused undefined behavior. ⚠️
     /// ```
     #[stable(feature = "maybe_uninit", since = "1.36.0")]
-    #[rustc_const_unstable(feature = "const_maybe_uninit_assume_init", issue = "none")]
+    #[rustc_const_stable(feature = "const_maybe_uninit_assume_init", since = "1.59.0")]
     #[inline(always)]
     #[rustc_diagnostic_item = "assume_init"]
     #[track_caller]
@@ -788,7 +788,8 @@ impl<T> MaybeUninit<T> {
     /// }
     /// ```
     #[stable(feature = "maybe_uninit_ref", since = "1.55.0")]
-    #[rustc_const_unstable(feature = "const_maybe_uninit_assume_init", issue = "none")]
+    #[rustc_const_stable(feature = "const_maybe_uninit_assume_init", since = "1.59.0")]
+    #[cfg_attr(bootstrap, rustc_allow_const_fn_unstable(const_raw_ptr_deref))]
     #[inline(always)]
     pub const unsafe fn assume_init_ref(&self) -> &T {
         // SAFETY: the caller must guarantee that `self` is initialized.
@@ -968,7 +969,7 @@ impl<T> MaybeUninit<T> {
     ///
     /// [`assume_init_ref`]: MaybeUninit::assume_init_ref
     #[unstable(feature = "maybe_uninit_slice", issue = "63569")]
-    #[rustc_const_unstable(feature = "const_maybe_uninit_assume_init", issue = "none")]
+    #[rustc_const_unstable(feature = "maybe_uninit_slice", issue = "63569")]
     #[inline(always)]
     pub const unsafe fn slice_assume_init_ref(slice: &[Self]) -> &[T] {
         // SAFETY: casting slice to a `*const [T]` is safe since the caller guarantees that

library/core/tests/lib.rs

@@ -10,6 +10,7 @@
 #![feature(const_assume)]
 #![feature(const_cell_into_inner)]
 #![feature(const_convert)]
+#![feature(const_maybe_uninit_as_mut_ptr)]
 #![feature(const_maybe_uninit_assume_init)]
 #![feature(const_ptr_read)]
 #![feature(const_ptr_write)]

library/core/tests/mem.rs

@@ -269,3 +269,35 @@ fn uninit_const_assume_init_read() {
     const FOO: u32 = unsafe { MaybeUninit::new(42).assume_init_read() };
     assert_eq!(FOO, 42);
 }
+
+#[test]
+fn const_maybe_uninit() {
+    use std::ptr;
+
+    #[derive(Debug, PartialEq)]
+    struct Foo {
+        x: u8,
+        y: u8,
+    }
+
+    const FIELD_BY_FIELD: Foo = unsafe {
+        let mut val = MaybeUninit::uninit();
+        init_y(&mut val); // order shouldn't matter
+        init_x(&mut val);
+        val.assume_init()
+    };
+
+    const fn init_x(foo: &mut MaybeUninit<Foo>) {
+        unsafe {
+            *ptr::addr_of_mut!((*foo.as_mut_ptr()).x) = 1;
+        }
+    }
+
+    const fn init_y(foo: &mut MaybeUninit<Foo>) {
+        unsafe {
+            *ptr::addr_of_mut!((*foo.as_mut_ptr()).y) = 2;
+        }
+    }
+
+    assert_eq!(FIELD_BY_FIELD, Foo { x: 1, y: 2 });
+}

src/test/ui/const-generics/generic_const_exprs/issue-72787.min.stderr

@@ -1,5 +1,5 @@
 error: generic parameters may not be used in const operations
-  --> $DIR/issue-72787.rs:12:17
+  --> $DIR/issue-72787.rs:11:17
    |
 LL |     Condition<{ LHS <= RHS }>: True
    |                 ^^^ cannot perform const operation using `LHS`
@@ -8,7 +8,7 @@ LL |     Condition<{ LHS <= RHS }>: True
    = help: use `#![feature(generic_const_exprs)]` to allow generic const expressions
 
 error: generic parameters may not be used in const operations
-  --> $DIR/issue-72787.rs:12:24
+  --> $DIR/issue-72787.rs:11:24
    |
 LL |     Condition<{ LHS <= RHS }>: True
    |                        ^^^ cannot perform const operation using `RHS`
@@ -17,7 +17,7 @@ LL |     Condition<{ LHS <= RHS }>: True
    = help: use `#![feature(generic_const_exprs)]` to allow generic const expressions
 
 error: generic parameters may not be used in const operations
-  --> $DIR/issue-72787.rs:26:25
+  --> $DIR/issue-72787.rs:25:25
    |
 LL |     IsLessOrEqual<{ 8 - I }, { 8 - J }>: True,
    |                         ^ cannot perform const operation using `I`
@@ -26,7 +26,7 @@ LL |     IsLessOrEqual<{ 8 - I }, { 8 - J }>: True,
    = help: use `#![feature(generic_const_exprs)]` to allow generic const expressions
 
 error: generic parameters may not be used in const operations
-  --> $DIR/issue-72787.rs:26:36
+  --> $DIR/issue-72787.rs:25:36
    |
 LL |     IsLessOrEqual<{ 8 - I }, { 8 - J }>: True,
    |                                    ^ cannot perform const operation using `J`
@@ -35,29 +35,21 @@ LL |     IsLessOrEqual<{ 8 - I }, { 8 - J }>: True,
    = help: use `#![feature(generic_const_exprs)]` to allow generic const expressions
 
 error[E0283]: type annotations needed
-  --> $DIR/issue-72787.rs:10:38
-   |
-LL | impl<const LHS: u32, const RHS: u32> True for IsLessOrEqual<LHS, RHS> where
-   |                                      ^^^^ cannot infer type for struct `IsLessOrEqual<LHS, RHS>`
-   |
-   = note: cannot satisfy `IsLessOrEqual<LHS, RHS>: True`
-
-error[E0283]: type annotations needed
-  --> $DIR/issue-72787.rs:22:26
+  --> $DIR/issue-72787.rs:21:26
    |
 LL |     IsLessOrEqual<I, 8>: True,
    |                          ^^^^ cannot infer type for struct `IsLessOrEqual<I, 8_u32>`
    |
    = note: cannot satisfy `IsLessOrEqual<I, 8_u32>: True`
 
 error[E0283]: type annotations needed
-  --> $DIR/issue-72787.rs:22:26
+  --> $DIR/issue-72787.rs:21:26
    |
 LL |     IsLessOrEqual<I, 8>: True,
    |                          ^^^^ cannot infer type for struct `IsLessOrEqual<I, 8_u32>`
    |
    = note: cannot satisfy `IsLessOrEqual<I, 8_u32>: True`
 
-error: aborting due to 7 previous errors
+error: aborting due to 6 previous errors
 
 For more information about this error, try `rustc --explain E0283`.

src/test/ui/const-generics/generic_const_exprs/issue-72787.rs

@@ -8,7 +8,6 @@ pub struct Condition<const CONDITION: bool>;
 pub trait True {}
 
 impl<const LHS: u32, const RHS: u32> True for IsLessOrEqual<LHS, RHS> where
-//[min]~^ ERROR type annotations needed
     Condition<{ LHS <= RHS }>: True
 //[min]~^ Error generic parameters may not be used in const operations
 //[min]~| Error generic parameters may not be used in const operations

src/test/ui/issues/issue-77919.rs

@@ -10,4 +10,4 @@ struct Multiply<N, M> {
 }
 impl<N, M> TypeVal<usize> for Multiply<N, M> where N: TypeVal<VAL> {}
 //~^ ERROR cannot find type `VAL` in this scope
-//~| ERROR type annotations needed
+//~| ERROR not all trait items implemented, missing: `VAL`