basic dyn* support for Miri

Author: RalfJung

tests/fail/branchless-select-i128-pointer.stderr

@@ -1,12 +1,12 @@
-error: Undefined Behavior: constructing invalid value: encountered a dangling reference (address $HEX is unallocated)
+error: Undefined Behavior: constructing invalid value: encountered a dangling reference ($HEX[noalloc] has no provenance)
   --> $DIR/branchless-select-i128-pointer.rs:LL:CC
    |
 LL | /             transmute::<_, &str>(
 LL | |
 LL | |                 !mask & transmute::<_, TwoPtrs>("false !")
 LL | |                     | mask & transmute::<_, TwoPtrs>("true !"),
 LL | |             )
-   | |_____________^ constructing invalid value: encountered a dangling reference (address $HEX is unallocated)
+   | |_____________^ constructing invalid value: encountered a dangling reference ($HEX[noalloc] has no provenance)
    |
    = help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior
    = help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information

tests/fail/validity/dangling_ref1.rs

@@ -3,5 +3,5 @@
 use std::mem;
 
 fn main() {
-    let _x: &i32 = unsafe { mem::transmute(16usize) }; //~ ERROR: encountered a dangling reference (address 0x10 is unallocated)
+    let _x: &i32 = unsafe { mem::transmute(16usize) }; //~ ERROR: encountered a dangling reference
 }

tests/fail/validity/dangling_ref1.stderr

@@ -1,8 +1,8 @@
-error: Undefined Behavior: constructing invalid value: encountered a dangling reference (address 0x10 is unallocated)
+error: Undefined Behavior: constructing invalid value: encountered a dangling reference (0x10[noalloc] has no provenance)
   --> $DIR/dangling_ref1.rs:LL:CC
    |
 LL |     let _x: &i32 = unsafe { mem::transmute(16usize) };
-   |                             ^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value: encountered a dangling reference (address 0x10 is unallocated)
+   |                             ^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value: encountered a dangling reference (0x10[noalloc] has no provenance)
    |
    = help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior
    = help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information

tests/pass/dyn-star.rs

@@ -0,0 +1,118 @@
+// Dyn* handling leads to some funky reentrancy in Stacked Borrows, for some reason
+//@compile-flags: -Zmiri-disable-stacked-borrows
+#![feature(dyn_star)]
+#![allow(incomplete_features)]
+
+use std::fmt::{Debug, Display};
+
+fn main() {
+    make_dyn_star();
+    method();
+    box_();
+    dispatch_on_pin_mut();
+    dyn_star_to_dyn();
+    dyn_to_dyn_star();
+}
+
+fn dyn_star_to_dyn() {
+    let x: dyn* Debug = &42;
+    let x = Box::new(x) as Box<dyn Debug>;
+    assert_eq!("42", format!("{x:?}"));
+}
+
+fn dyn_to_dyn_star() {
+    let x: Box<dyn Debug> = Box::new(42);
+    let x = &x as dyn* Debug;
+    assert_eq!("42", format!("{x:?}"));
+}
+
+fn make_dyn_star() {
+    fn make_dyn_star_coercion(i: usize) {
+        let _dyn_i: dyn* Debug = i;
+    }
+
+    fn make_dyn_star_explicit(i: usize) {
+        let _dyn_i: dyn* Debug = i as dyn* Debug;
+    }
+
+    make_dyn_star_coercion(42);
+    make_dyn_star_explicit(42);
+}
+
+fn method() {
+    trait Foo {
+        fn get(&self) -> usize;
+    }
+    
+    impl Foo for usize {
+        fn get(&self) -> usize {
+            *self
+        }
+    }
+    
+    fn invoke_dyn_star(i: dyn* Foo) -> usize {
+        i.get()
+    }
+    
+    fn make_and_invoke_dyn_star(i: usize) -> usize {
+        let dyn_i: dyn* Foo = i;
+        invoke_dyn_star(dyn_i)
+    }
+    
+    assert_eq!(make_and_invoke_dyn_star(42), 42);
+}
+
+fn box_() {
+    fn make_dyn_star() -> dyn* Display {
+        Box::new(42) as dyn* Display
+    }
+    
+    let x = make_dyn_star();
+    assert_eq!(format!("{x}"), "42");
+}
+
+fn dispatch_on_pin_mut() {
+    use std::future::Future;
+
+    async fn foo(f: dyn* Future<Output = i32>) {
+        println!("dispatch_on_pin_mut: value: {}", f.await);
+    }
+
+    async fn async_main() {
+        foo(Box::pin(async { 1 })).await
+    }
+
+    // ------------------------------------------------------------------------- //
+    // Implementation Details Below...
+
+    use std::pin::Pin;
+    use std::task::*;
+
+    pub fn noop_waker() -> Waker {
+        let raw = RawWaker::new(std::ptr::null(), &NOOP_WAKER_VTABLE);
+
+        // SAFETY: the contracts for RawWaker and RawWakerVTable are upheld
+        unsafe { Waker::from_raw(raw) }
+    }
+
+    const NOOP_WAKER_VTABLE: RawWakerVTable = RawWakerVTable::new(noop_clone, noop, noop, noop);
+
+    unsafe fn noop_clone(_p: *const ()) -> RawWaker {
+        RawWaker::new(std::ptr::null(), &NOOP_WAKER_VTABLE)
+    }
+
+    unsafe fn noop(_p: *const ()) {}
+
+    let mut fut = async_main();
+
+    // Poll loop, just to test the future...
+    let waker = noop_waker();
+    let ctx = &mut Context::from_waker(&waker);
+
+    loop {
+        match unsafe { Pin::new_unchecked(&mut fut).poll(ctx) } {
+            Poll::Pending => {}
+            Poll::Ready(()) => break,
+        }
+    }
+}

tests/pass/dyn-star.stdout

@@ -0,0 +1 @@
+dispatch_on_pin_mut: value: 1