Auto merge of #3922 - RalfJung:box-custom-alloc, r=RalfJung

add tests for validity of Box with custom allocator
Ensure that the validity visitor visits both parts of a box with custom allocator using the right types.

Author: bors

src/tools/miri/tests/fail/validity/box-custom-alloc-dangling-ptr.rs

@@ -0,0 +1,32 @@
+//! Ensure that a box with a custom allocator detects when the pointer is dangling.
+#![feature(allocator_api)]
+// This should not need the aliasing model.
+//@compile-flags: -Zmiri-disable-stacked-borrows
+use std::alloc::Layout;
+use std::ptr::NonNull;
+
+#[allow(unused)]
+structMyAlloc(usize,usize);// make sure `Box<T, MyAlloc>` is an `Aggregate`
+
+unsafeimpl std::alloc::AllocatorforMyAlloc{
+fnallocate(&self,_layout:Layout) -> Result<NonNull<[u8]>, std::alloc::AllocError>{
+unimplemented!()
+}
+
+unsafefndeallocate(&self,_ptr:NonNull<u8>,_layout:Layout){
+unimplemented!()
+}
+}
+
+#[repr(C)]
+structMyBox<T>{
+ptr:NonNull<T>,
+alloc:MyAlloc,
+}
+
+fnmain(){
+let b = MyBox{ptr:NonNull::<i32>::dangling(),alloc:MyAlloc(0,0)};
+let _b:Box<i32,MyAlloc> = unsafe{
+ std::mem::transmute(b)//~ERROR: dangling box
+};
+}

src/tools/miri/tests/fail/validity/box-custom-alloc-dangling-ptr.stderr

@@ -0,0 +1,15 @@
+error: Undefined Behavior: constructing invalid value: encountered a dangling box (0x4[noalloc] has no provenance)
+ --> tests/fail/validity/box-custom-alloc-dangling-ptr.rs:LL:CC
+ |
+LL | std::mem::transmute(b)
+ | ^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value: encountered a dangling box (0x4[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
+ = note: BACKTRACE:
+ = note: inside `main` at tests/fail/validity/box-custom-alloc-dangling-ptr.rs:LL:CC
+
+note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
+
+error: aborting due to 1 previous error
+

src/tools/miri/tests/fail/validity/box-custom-alloc-invalid-alloc.rs

@@ -0,0 +1,37 @@
+//! Ensure that a box with a custom allocator detects when the allocator itself is invalid.
+#![feature(allocator_api)]
+// This should not need the aliasing model.
+//@compile-flags: -Zmiri-disable-stacked-borrows
+use std::alloc::Layout;
+use std::mem::MaybeUninit;
+use std::ptr::NonNull;
+
+// make sure `Box<T, MyAlloc>` is an `Aggregate`
+#[allow(unused)]
+structMyAlloc{
+my_alloc_field1:usize,
+my_alloc_field2:usize,
+}
+
+unsafeimpl std::alloc::AllocatorforMyAlloc{
+fnallocate(&self,_layout:Layout) -> Result<NonNull<[u8]>, std::alloc::AllocError>{
+unimplemented!()
+}
+
+unsafefndeallocate(&self,_ptr:NonNull<u8>,_layout:Layout){
+unimplemented!()
+}
+}
+
+#[repr(C)]
+structMyBox<T>{
+ptr:NonNull<T>,
+alloc:MaybeUninit<MyAlloc>,
+}
+
+fnmain(){
+let b = MyBox{ptr:NonNull::from(&42),alloc:MaybeUninit::uninit()};
+let _b:Box<i32,MyAlloc> = unsafe{
+ std::mem::transmute(b)//~ERROR: uninitialized memory
+};
+}

src/tools/miri/tests/fail/validity/box-custom-alloc-invalid-alloc.stderr

@@ -0,0 +1,15 @@
+error: Undefined Behavior: constructing invalid value at .1.my_alloc_field1: encountered uninitialized memory, but expected an integer
+ --> tests/fail/validity/box-custom-alloc-invalid-alloc.rs:LL:CC
+ |
+LL | std::mem::transmute(b)
+ | ^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value at .1.my_alloc_field1: encountered uninitialized memory, but expected an integer
+ |
+ = 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
+ = note: BACKTRACE:
+ = note: inside `main` at tests/fail/validity/box-custom-alloc-invalid-alloc.rs:LL:CC
+
+note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
+
+error: aborting due to 1 previous error
+