Rollup merge of #127684 - RalfJung:unleashed-mutable-refs, r=oli-obk

consolidate miri-unleashed tests for mutable refs into one file

r? ```@oli-obk```

Author: matthiaskrgr

tests/ui/consts/miri_unleashed/mutable_references.rs

@@ -2,13 +2,20 @@
 //@ normalize-stderr-test: "(the raw bytes of the constant) \(size: [0-9]*, align: [0-9]*\)" -> "$1 (size: $$SIZE, align: $$ALIGN)"
 //@ normalize-stderr-test: "([0-9a-f][0-9a-f] |╾─*ALLOC[0-9]+(\+[a-z0-9]+)?(<imm>)?─*╼ )+ *│.*" -> "HEX_DUMP"
 
+#![allow(static_mut_refs)]
 #![deny(const_eval_mutable_ptr_in_final_value)]
 use std::cell::UnsafeCell;
+use std::sync::atomic::*;
+
+// # Plain `&mut` in the final value
 
 // This requires walking nested statics.
 static FOO: &&mut u32 = &&mut 42;
 //~^ ERROR it is undefined behavior to use this value
-
+//~| pointing to read-only memory
+static OH_YES: &mut i32 = &mut 42;
+//~^ ERROR it is undefined behavior to use this value
+//~| pointing to read-only memory
 static BAR: &mut () = &mut ();
 //~^ ERROR encountered mutable pointer in final value of static
 //~| WARNING this was previously accepted by the compiler
@@ -19,15 +26,92 @@ static BOO: &mut Foo<()> = &mut Foo(());
 //~^ ERROR encountered mutable pointer in final value of static
 //~| WARNING this was previously accepted by the compiler
 
+const BLUNT: &mut i32 = &mut 42;
+//~^ ERROR: it is undefined behavior to use this value
+//~| pointing to read-only memory
+
+const SUBTLE: &mut i32 = unsafe { static mut STATIC: i32 = 0; &mut STATIC };
+//~^ ERROR: it is undefined behavior to use this value
+//~| static
+
+// # Interior mutability
+
 struct Meh {
     x: &'static UnsafeCell<i32>,
 }
 unsafe impl Sync for Meh {}
 static MEH: Meh = Meh { x: &UnsafeCell::new(42) };
 //~^ ERROR it is undefined behavior to use this value
+//~| `UnsafeCell` in read-only memory
+// Same with a const:
+// the following will never be ok! no interior mut behind consts, because
+// all allocs interned here will be marked immutable.
+const MUH: Meh = Meh {
+    //~^ ERROR it is undefined behavior to use this value
+    //~| `UnsafeCell` in read-only memory
+    x: &UnsafeCell::new(42),
+};
+
+struct Synced {
+    x: UnsafeCell<i32>,
+}
+unsafe impl Sync for Synced {}
+
+// Make sure we also catch this behind a type-erased `dyn Trait` reference.
+const SNEAKY: &dyn Sync = &Synced { x: UnsafeCell::new(42) };
+//~^ ERROR: it is undefined behavior to use this value
+//~| `UnsafeCell` in read-only memory
+
+// # Check for mutable references to read-only memory
+
+static READONLY: i32 = 0;
+static mut MUT_TO_READONLY: &mut i32 = unsafe { &mut *(&READONLY as *const _ as *mut _) };
+//~^ ERROR: it is undefined behavior to use this value
+//~| pointing to read-only memory
+
+// # Check for consts pointing to mutable memory
+
+static mut MUTABLE: i32 = 42;
+const POINTS_TO_MUTABLE: &i32 = unsafe { &MUTABLE }; //~ERROR: undefined behavior
+//~| encountered reference to mutable memory
+static mut MUTABLE_REF: &mut i32 = &mut 42;
+const POINTS_TO_MUTABLE2: &i32 = unsafe { &*MUTABLE_REF };
+//~^ ERROR: evaluation of constant value failed
+//~| accesses mutable global memory
+
+const POINTS_TO_MUTABLE_INNER: *const i32 = &mut 42 as *mut _ as *const _;
+//~^ ERROR: mutable pointer in final value
+//~| WARNING this was previously accepted by the compiler
+
+const POINTS_TO_MUTABLE_INNER2: *const i32 = &mut 42 as *const _;
+//~^ ERROR: mutable pointer in final value
+//~| WARNING this was previously accepted by the compiler
+
+const INTERIOR_MUTABLE_BEHIND_RAW: *mut i32 = &UnsafeCell::new(42) as *const _ as *mut _;
+//~^ ERROR: mutable pointer in final value
+//~| WARNING this was previously accepted by the compiler
+
+struct SyncPtr<T> {
+    x: *const T,
+}
+unsafe impl<T> Sync for SyncPtr<T> {}
+
+// These pass the lifetime checks because of the "tail expression" / "outer scope" rule.
+// (This relies on `SyncPtr` being a curly brace struct.)
+// However, we intern the inner memory as read-only, so this must be rejected.
+// (Also see `static-no-inner-mut` for similar tests on `static`.)
+const RAW_SYNC: SyncPtr<AtomicI32> = SyncPtr { x: &AtomicI32::new(42) };
+//~^ ERROR mutable pointer in final value
+//~| WARNING this was previously accepted by the compiler
+
+const RAW_MUT_CAST: SyncPtr<i32> = SyncPtr { x: &mut 42 as *mut _ as *const _ };
+//~^ ERROR mutable pointer in final value
+//~| WARNING this was previously accepted by the compiler
+
+const RAW_MUT_COERCE: SyncPtr<i32> = SyncPtr { x: &mut 0 };
+//~^ ERROR mutable pointer in final value
+//~| WARNING this was previously accepted by the compiler
 
-static OH_YES: &mut i32 = &mut 42;
-//~^ ERROR it is undefined behavior to use this value
 
 fn main() {
     unsafe {