const-eval: better wording for errors involving maybe-null pointers

compiler/rustc_const_eval/messages.ftl

@@ -476,14 +476,20 @@ const_eval_validation_invalid_vtable_trait = {$front_matter}: wrong trait in wid
 const_eval_validation_mutable_ref_in_const = {$front_matter}: encountered mutable reference in `const` value
 const_eval_validation_mutable_ref_to_immutable = {$front_matter}: encountered mutable reference or box pointing to read-only memory
 const_eval_validation_never_val = {$front_matter}: encountered a value of the never type `!`
-const_eval_validation_null_box = {$front_matter}: encountered a null box
+const_eval_validation_null_box = {$front_matter}: encountered a {$maybe ->
+    [true] maybe-null
+    *[false] null
+  } box
 const_eval_validation_null_fn_ptr = {$front_matter}: encountered a null function pointer
-const_eval_validation_null_ref = {$front_matter}: encountered a null reference
-const_eval_validation_nullable_ptr_out_of_range = {$front_matter}: encountered a potentially null pointer, but expected something that cannot possibly fail to be {$in_range}
+const_eval_validation_null_ref = {$front_matter}: encountered a {$maybe ->
+    [true] maybe-null
+    *[false] null
+  } reference
+const_eval_validation_nonnull_ptr_out_of_range = {$front_matter}: encountered a maybe-null pointer, but expected something that is definitely non-zero
 const_eval_validation_out_of_range = {$front_matter}: encountered {$value}, but expected something {$in_range}
 const_eval_validation_partial_pointer = {$front_matter}: encountered a partial pointer or a mix of pointers
 const_eval_validation_pointer_as_int = {$front_matter}: encountered a pointer, but {$expected}
-const_eval_validation_ptr_out_of_range = {$front_matter}: encountered a pointer, but expected something that cannot possibly fail to be {$in_range}
+const_eval_validation_ptr_out_of_range = {$front_matter}: encountered a pointer with unknown absolute address, but expected something that is definitely {$in_range}
 const_eval_validation_ref_to_uninhabited = {$front_matter}: encountered a reference pointing to uninhabited type {$ty}
 const_eval_validation_unaligned_box = {$front_matter}: encountered an unaligned box (required {$required_bytes} byte alignment but found {$found_bytes})
 const_eval_validation_unaligned_ref = {$front_matter}: encountered an unaligned reference (required {$required_bytes} byte alignment but found {$found_bytes})

compiler/rustc_const_eval/src/errors.rs

@@ -668,7 +668,7 @@ impl<'tcx> ReportErrorExt for ValidationErrorInfo<'tcx> {
             MutableRefInConst => const_eval_validation_mutable_ref_in_const,
             NullFnPtr => const_eval_validation_null_fn_ptr,
             NeverVal => const_eval_validation_never_val,
-            NullablePtrOutOfRange { .. } => const_eval_validation_nullable_ptr_out_of_range,
+            NonnullPtrMaybeNull { .. } => const_eval_validation_nonnull_ptr_out_of_range,
             PtrOutOfRange { .. } => const_eval_validation_ptr_out_of_range,
             OutOfRange { .. } => const_eval_validation_out_of_range,
             UnsafeCellInImmutable => const_eval_validation_unsafe_cell,
@@ -696,8 +696,8 @@ impl<'tcx> ReportErrorExt for ValidationErrorInfo<'tcx> {
             }
             UnalignedPtr { ptr_kind: PointerKind::Box, .. } => const_eval_validation_unaligned_box,
 
-            NullPtr { ptr_kind: PointerKind::Box } => const_eval_validation_null_box,
-            NullPtr { ptr_kind: PointerKind::Ref(_) } => const_eval_validation_null_ref,
+            NullPtr { ptr_kind: PointerKind::Box, .. } => const_eval_validation_null_box,
+            NullPtr { ptr_kind: PointerKind::Ref(_), .. } => const_eval_validation_null_ref,
             DanglingPtrNoProvenance { ptr_kind: PointerKind::Box, .. } => {
                 const_eval_validation_dangling_box_no_provenance
             }
@@ -804,9 +804,7 @@ impl<'tcx> ReportErrorExt for ValidationErrorInfo<'tcx> {
             | InvalidFnPtr { value } => {
                 err.arg("value", value);
             }
-            NullablePtrOutOfRange { range, max_value } | PtrOutOfRange { range, max_value } => {
-                add_range_arg(range, max_value, err)
-            }
+            PtrOutOfRange { range, max_value } => add_range_arg(range, max_value, err),
             OutOfRange { range, max_value, value } => {
                 err.arg("value", value);
                 add_range_arg(range, max_value, err);
@@ -822,10 +820,13 @@ impl<'tcx> ReportErrorExt for ValidationErrorInfo<'tcx> {
                 err.arg("vtable_dyn_type", vtable_dyn_type.to_string());
                 err.arg("expected_dyn_type", expected_dyn_type.to_string());
             }
-            NullPtr { .. }
-            | MutableRefToImmutable
+            NullPtr { maybe, .. } => {
+                err.arg("maybe", maybe);
+            }
+            MutableRefToImmutable
             | MutableRefInConst
             | NullFnPtr
+            | NonnullPtrMaybeNull
             | NeverVal
             | UnsafeCellInImmutable
             | InvalidMetaSliceTooLarge { .. }

compiler/rustc_const_eval/src/interpret/validity.rs

@@ -511,7 +511,7 @@ impl<'rt, 'tcx, M: Machine<'tcx>> ValidityVisitor<'rt, 'tcx, M> {
                 CheckInAllocMsg::Dereferenceable, // will anyway be replaced by validity message
             ),
             self.path,
-            Ub(DanglingIntPointer { addr: 0, .. }) => NullPtr { ptr_kind },
+            Ub(DanglingIntPointer { addr: 0, .. }) => NullPtr { ptr_kind, maybe: false },
             Ub(DanglingIntPointer { addr: i, .. }) => DanglingPtrNoProvenance {
                 ptr_kind,
                 // FIXME this says "null pointer" when null but we need translate
@@ -538,8 +538,10 @@ impl<'rt, 'tcx, M: Machine<'tcx>> ValidityVisitor<'rt, 'tcx, M> {
         );
         // Make sure this is non-null. We checked dereferenceability above, but if `size` is zero
         // that does not imply non-null.
-        if self.ecx.scalar_may_be_null(Scalar::from_maybe_pointer(place.ptr(), self.ecx))? {
-            throw_validation_failure!(self.path, NullPtr { ptr_kind })
+        let scalar = Scalar::from_maybe_pointer(place.ptr(), self.ecx);
+        if self.ecx.scalar_may_be_null(scalar)? {
+            let maybe = !M::Provenance::OFFSET_IS_ADDR && matches!(scalar, Scalar::Ptr(..));
+            throw_validation_failure!(self.path, NullPtr { ptr_kind, maybe })
         }
         // Do not allow references to uninhabited types.
         if place.layout.is_uninhabited() {
@@ -757,6 +759,11 @@ impl<'rt, 'tcx, M: Machine<'tcx>> ValidityVisitor<'rt, 'tcx, M> {
                 } else {
                     // Otherwise (for standalone Miri), we have to still check it to be non-null.
                     if self.ecx.scalar_may_be_null(scalar)? {
+                        let maybe =
+                            !M::Provenance::OFFSET_IS_ADDR && matches!(scalar, Scalar::Ptr(..));
+                        // This can't be a "maybe-null" pointer since the check for this being
+                        // a fn ptr at all already ensures that the pointer is inbounds.
+                        assert!(!maybe);
                         throw_validation_failure!(self.path, NullFnPtr);
                     }
                 }
@@ -819,10 +826,7 @@ impl<'rt, 'tcx, M: Machine<'tcx>> ValidityVisitor<'rt, 'tcx, M> {
                 if start == 1 && end == max_value {
                     // Only null is the niche. So make sure the ptr is NOT null.
                     if self.ecx.scalar_may_be_null(scalar)? {
-                        throw_validation_failure!(
-                            self.path,
-                            NullablePtrOutOfRange { range: valid_range, max_value }
-                        )
+                        throw_validation_failure!(self.path, NonnullPtrMaybeNull)
                     } else {
                         return interp_ok(());
                     }

compiler/rustc_middle/src/mir/interpret/error.rs

@@ -499,10 +499,7 @@ pub enum ValidationErrorKind<'tcx> {
     MutableRefInConst,
     NullFnPtr,
     NeverVal,
-    NullablePtrOutOfRange {
-        range: WrappingRange,
-        max_value: u128,
-    },
+    NonnullPtrMaybeNull,
     PtrOutOfRange {
         range: WrappingRange,
         max_value: u128,
@@ -544,6 +541,8 @@ pub enum ValidationErrorKind<'tcx> {
     },
     NullPtr {
         ptr_kind: PointerKind,
+        /// Records whether this pointer is definitely null or just may be null.
+        maybe: bool,
     },
     DanglingPtrNoProvenance {
         ptr_kind: PointerKind,

src/tools/compiletest/src/runtest.rs

@@ -2655,7 +2655,7 @@ impl<'test> TestCx<'test> {
 
             // The alloc-id appears in pretty-printed allocations.
             normalized = static_regex!(
-                r"╾─*a(lloc)?([0-9]+)(\+0x[0-9]+)?(<imm>)?( \([0-9]+ ptr bytes\))?─*╼"
+                r"╾─*a(lloc)?([0-9]+)(\+0x[0-9a-f]+)?(<imm>)?( \([0-9]+ ptr bytes\))?─*╼"
             )
             .replace_all(&normalized, |caps: &Captures<'_>| {
                 // Renumber the captured index.

tests/ui/consts/const-eval/ub-nonnull.rs

@@ -57,4 +57,8 @@ const NULL_FAT_PTR: NonNull<dyn Send> = unsafe {
     mem::transmute((0_usize, meta))
 };
 
+static S: u32 = 0; // just a static to construct a maybe-null pointer off of
+const MAYBE_NULL_PTR: NonNull<()> = unsafe { mem::transmute((&raw const S).wrapping_add(4)) };
+//~^ ERROR invalid value
+
 fn main() {}

tests/ui/consts/const-eval/ub-nonnull.stderr

@@ -9,7 +9,7 @@ LL | const NULL_PTR: NonNull<u8> = unsafe { mem::transmute(0usize) };
                HEX_DUMP
            }
 
-error[E0080]: in-bounds pointer arithmetic failed: attempting to offset pointer by 255 bytes, but got ALLOC1 which is only 1 byte from the end of the allocation
+error[E0080]: in-bounds pointer arithmetic failed: attempting to offset pointer by 255 bytes, but got ALLOC2 which is only 1 byte from the end of the allocation
   --> $DIR/ub-nonnull.rs:22:29
    |
 LL |     let out_of_bounds_ptr = &ptr[255];
@@ -37,7 +37,7 @@ LL | const NULL_USIZE: NonZero<usize> = unsafe { mem::transmute(0usize) };
                HEX_DUMP
            }
 
-error[E0080]: reading memory at ALLOC2[0x0..0x1], but memory is uninitialized at [0x0..0x1], and this operation requires initialized memory
+error[E0080]: reading memory at ALLOC3[0x0..0x1], but memory is uninitialized at [0x0..0x1], and this operation requires initialized memory
   --> $DIR/ub-nonnull.rs:36:38
    |
 LL | const UNINIT: NonZero<u8> = unsafe { MaybeUninit { uninit: () }.init };
@@ -80,6 +80,17 @@ LL | const NULL_FAT_PTR: NonNull<dyn Send> = unsafe {
                HEX_DUMP
            }
 
-error: aborting due to 8 previous errors
+error[E0080]: constructing invalid value: encountered a maybe-null pointer, but expected something that is definitely non-zero
+  --> $DIR/ub-nonnull.rs:61:1
+   |
+LL | const MAYBE_NULL_PTR: NonNull<()> = unsafe { mem::transmute((&raw const S).wrapping_add(4)) };
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ it is undefined behavior to use this value
+   |
+   = note: the rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rustc repository if you believe it should not be considered undefined behavior.
+   = note: the raw bytes of the constant (size: $SIZE, align: $ALIGN) {
+               HEX_DUMP
+           }
+
+error: aborting due to 9 previous errors
 
 For more information about this error, try `rustc --explain E0080`.

tests/ui/consts/const-eval/ub-ref-ptr.rs

@@ -4,7 +4,7 @@
 //@ normalize-stderr: "([0-9a-f][0-9a-f] |__ |╾─*ALLOC[0-9]+(\+[a-z0-9]+)?(<imm>)?─*╼ )+ *│.*" -> "HEX_DUMP"
 //@ dont-require-annotations: NOTE
 //@ normalize-stderr: "0x[0-9](\.\.|\])" -> "0x%$1"
-
+#![feature(rustc_attrs)]
 #![allow(invalid_value)]
 
 use std::mem;
@@ -27,6 +27,11 @@ const NULL: &u16 = unsafe { mem::transmute(0usize) };
 const NULL_BOX: Box<u16> = unsafe { mem::transmute(0usize) };
 //~^ ERROR invalid value
 
+const MAYBE_NULL_BOX: Box<()> = unsafe { mem::transmute({
+//~^ ERROR maybe-null
+    let ref_ = &0u8;
+    (ref_ as *const u8).wrapping_add(10)
+}) };
 
 // It is very important that we reject this: We do promote `&(4 * REF_AS_USIZE)`,
 // but that would fail to compile; so we ended up breaking user code that would
@@ -57,13 +62,27 @@ const DANGLING_FN_PTR: fn() = unsafe { mem::transmute(13usize) };
 //~^ ERROR invalid value
 const DATA_FN_PTR: fn() = unsafe { mem::transmute(&13) };
 //~^ ERROR invalid value
-
+const MAYBE_NULL_FN_PTR: fn() = unsafe { mem::transmute({
+//~^ ERROR invalid value
+    fn fun() {}
+    let ptr = fun as fn();
+    (ptr as *const u8).wrapping_add(10)
+}) };
 
 const UNALIGNED_READ: () = unsafe {
     let x = &[0u8; 4];
     let ptr = x.as_ptr().cast::<u32>();
     ptr.read(); //~ ERROR accessing memory
 };
 
+// Check the general case of a pointer value not falling into the scalar valid range.
+#[rustc_layout_scalar_valid_range_start(1000)]
+pub struct High {
+    pointer: *const (),
+}
+static S: u32 = 0; // just a static to construct a pointer with unknown absolute address
+const INVALID_VALUE_PTR: High = unsafe { mem::transmute(&S) };
+//~^ ERROR invalid value
+
 
 fn main() {}