Auto merge of rust-lang#130547 - workingjubilee:rollup-tw30khz, r=workingjubilee

Rollup of 3 pull requests

Successful merges:

 - rust-lang#130531 (Check params for unsafety in THIR)
 - rust-lang#130533 (Never patterns constitute a read for unsafety)
 - rust-lang#130542 (Stabilize const `MaybeUninit::as_mut_ptr`)

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

Author: bors

compiler/rustc_mir_build/src/check_unsafety.rs

@@ -218,6 +218,13 @@ impl<'tcx> UnsafetyVisitor<'_, 'tcx> {
                 warnings: self.warnings,
                 suggest_unsafe_block: self.suggest_unsafe_block,
             };
+            // params in THIR may be unsafe, e.g. a union pattern.
+            for param in &inner_thir.params {
+                if let Some(param_pat) = param.pat.as_deref() {
+                    inner_visitor.visit_pat(param_pat);
+                }
+            }
+            // Visit the body.
             inner_visitor.visit_expr(&inner_thir[expr]);
             // Unsafe blocks can be used in the inner body, make sure to take it into account
             self.safety_context = inner_visitor.safety_context;
@@ -315,14 +322,15 @@ impl<'a, 'tcx> Visitor<'a, 'tcx> for UnsafetyVisitor<'a, 'tcx> {
                 | PatKind::DerefPattern { .. }
                 | PatKind::Range { .. }
                 | PatKind::Slice { .. }
-                | PatKind::Array { .. } => {
+                | PatKind::Array { .. }
+                // Never constitutes a witness of uninhabitedness.
+                | PatKind::Never => {
                     self.requires_unsafe(pat.span, AccessToUnionField);
                     return; // we can return here since this already requires unsafe
                 }
-                // wildcard/never don't take anything
+                // wildcard doesn't read anything.
                 PatKind::Wild |
-                PatKind::Never |
-                // these just wrap other patterns
+                // these just wrap other patterns, which we recurse on below.
                 PatKind::Or { .. } |
                 PatKind::InlineConstant { .. } |
                 PatKind::AscribeUserType { .. } |
@@ -1032,6 +1040,13 @@ pub(crate) fn check_unsafety(tcx: TyCtxt<'_>, def: LocalDefId) {
         warnings: &mut warnings,
         suggest_unsafe_block: true,
     };
+    // params in THIR may be unsafe, e.g. a union pattern.
+    for param in &thir.params {
+        if let Some(param_pat) = param.pat.as_deref() {
+            visitor.visit_pat(param_pat);
+        }
+    }
+    // Visit the body.
     visitor.visit_expr(&thir[expr]);
 
     warnings.sort_by_key(|w| w.block_span);

library/alloc/src/lib.rs

@@ -110,7 +110,6 @@
 #![feature(const_cow_is_borrowed)]
 #![feature(const_eval_select)]
 #![feature(const_heap)]
-#![feature(const_maybe_uninit_as_mut_ptr)]
 #![feature(const_maybe_uninit_write)]
 #![feature(const_option)]
 #![feature(const_pin)]

library/core/src/lib.rs

@@ -132,7 +132,6 @@
 #![feature(const_ipv4)]
 #![feature(const_ipv6)]
 #![feature(const_likely)]
-#![feature(const_maybe_uninit_as_mut_ptr)]
 #![feature(const_maybe_uninit_assume_init)]
 #![feature(const_nonnull_new)]
 #![feature(const_num_midpoint)]

library/core/src/mem/maybe_uninit.rs

@@ -393,7 +393,6 @@ impl<T> MaybeUninit<T> {
     // These are OK to allow since we do not leak &mut to user-visible API
     #[rustc_allow_const_fn_unstable(const_mut_refs)]
     #[rustc_allow_const_fn_unstable(const_ptr_write)]
-    #[rustc_allow_const_fn_unstable(const_maybe_uninit_as_mut_ptr)]
     #[rustc_const_stable(feature = "const_maybe_uninit_zeroed", since = "1.75.0")]
     pub const fn zeroed() -> MaybeUninit<T> {
         let mut u = MaybeUninit::<T>::uninit();
@@ -570,7 +569,11 @@ 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_mut_ptr", issue = "75251")]
+    #[rustc_const_stable(
+        feature = "const_maybe_uninit_as_mut_ptr",
+        since = "CURRENT_RUSTC_VERSION"
+    )]
+    #[cfg_attr(bootstrap, rustc_allow_const_fn_unstable(const_mut_refs))]
     #[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.

library/core/tests/lib.rs

@@ -26,7 +26,6 @@
 #![feature(const_ipv4)]
 #![feature(const_ipv6)]
 #![feature(const_likely)]
-#![feature(const_maybe_uninit_as_mut_ptr)]
 #![feature(const_nonnull_new)]
 #![feature(const_option)]
 #![feature(const_option_ext)]

tests/ui/rfcs/rfc-0000-never_patterns/never-pattern-is-a-read.rs

@@ -0,0 +1,16 @@
+// Make sure we consider `!` to be a union read.
+
+#![feature(never_type, never_patterns)]
+//~^ WARN the feature `never_patterns` is incomplete
+
+union U {
+    a: !,
+    b: usize,
+}
+
+fn foo<T>(u: U) -> ! {
+    let U { a: ! } = u;
+    //~^ ERROR access to union field is unsafe
+}
+
+fn main() {}

tests/ui/rfcs/rfc-0000-never_patterns/never-pattern-is-a-read.stderr

@@ -0,0 +1,20 @@
+warning: the feature `never_patterns` is incomplete and may not be safe to use and/or cause compiler crashes
+  --> $DIR/never-pattern-is-a-read.rs:3:24
+   |
+LL | #![feature(never_type, never_patterns)]
+   |                        ^^^^^^^^^^^^^^
+   |
+   = note: see issue #118155 <https://github.com/rust-lang/rust/issues/118155> for more information
+   = note: `#[warn(incomplete_features)]` on by default
+
+error[E0133]: access to union field is unsafe and requires unsafe function or block
+  --> $DIR/never-pattern-is-a-read.rs:12:16
+   |
+LL |     let U { a: ! } = u;
+   |                ^ access to union field
+   |
+   = note: the field may not be properly initialized: using uninitialized data will cause undefined behavior
+
+error: aborting due to 1 previous error; 1 warning emitted
+
+For more information about this error, try `rustc --explain E0133`.

tests/ui/unsafe/union-pat-in-param.rs

@@ -0,0 +1,19 @@
+union U {
+    a: &'static i32,
+    b: usize,
+}
+
+fn fun(U { a }: U) {
+    //~^ ERROR access to union field is unsafe
+    dbg!(*a);
+}
+
+fn main() {
+    fun(U { b: 0 });
+
+    let closure = |U { a }| {
+        //~^ ERROR access to union field is unsafe
+        dbg!(*a);
+    };
+    closure(U { b: 0 });
+}

tests/ui/unsafe/union-pat-in-param.stderr

@@ -0,0 +1,19 @@
+error[E0133]: access to union field is unsafe and requires unsafe function or block
+  --> $DIR/union-pat-in-param.rs:6:12
+   |
+LL | fn fun(U { a }: U) {
+   |            ^ access to union field
+   |
+   = note: the field may not be properly initialized: using uninitialized data will cause undefined behavior
+
+error[E0133]: access to union field is unsafe and requires unsafe function or block
+  --> $DIR/union-pat-in-param.rs:14:24
+   |
+LL |     let closure = |U { a }| {
+   |                        ^ access to union field
+   |
+   = note: the field may not be properly initialized: using uninitialized data will cause undefined behavior
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0133`.