fix null pointer error messages

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

@@ -170,22 +170,25 @@ impl fmt::Display for InvalidProgramInfo<'_> {
 /// Details of why a pointer had to be in-bounds.
 #[derive(Debug, Copy, Clone, TyEncodable, TyDecodable, HashStable)]
 pub enum CheckInAllocMsg {
+    /// We are access memory.
     MemoryAccessTest,
+    /// We are doing pointer arithmetic.
     PointerArithmeticTest,
+    /// None of the above -- generic/unspecific inbounds test.
     InboundsTest,
 }
 
 impl fmt::Display for CheckInAllocMsg {
     /// When this is printed as an error the context looks like this
-    /// "{test name} failed: pointer must be in-bounds at offset..."
+    /// "{msg}pointer must be in-bounds at offset..."
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         write!(
             f,
             "{}",
             match *self {
-                CheckInAllocMsg::MemoryAccessTest => "memory access",
-                CheckInAllocMsg::PointerArithmeticTest => "pointer arithmetic",
-                CheckInAllocMsg::InboundsTest => "inbounds test",
+                CheckInAllocMsg::MemoryAccessTest => "memory access failed: ",
+                CheckInAllocMsg::PointerArithmeticTest => "pointer arithmetic failed: ",
+                CheckInAllocMsg::InboundsTest => "",
             }
         )
     }
@@ -299,18 +302,18 @@ impl fmt::Display for UndefinedBehaviorInfo<'_> {
             }
             PointerOutOfBounds { ptr, msg, allocation_size } => write!(
                 f,
-                "{} failed: pointer must be in-bounds at offset {}, \
+                "{}pointer must be in-bounds at offset {}, \
                            but is outside bounds of {} which has size {}",
                 msg,
                 ptr.offset.bytes(),
                 ptr.alloc_id,
                 allocation_size.bytes()
             ),
-            DanglingIntPointer(_, CheckInAllocMsg::InboundsTest) => {
-                write!(f, "null pointer is not allowed for this operation")
+            DanglingIntPointer(0, CheckInAllocMsg::InboundsTest) => {
+                write!(f, "null pointer is not a valid pointer for this operation")
             }
             DanglingIntPointer(i, msg) => {
-                write!(f, "{} failed: 0x{:x} is not a valid pointer", msg, i)
+                write!(f, "{}0x{:x} is not a valid pointer", msg, i)
             }
             AlignmentCheckFailed { required, has } => write!(
                 f,

src/test/ui/consts/const-eval/ub-wide-ptr.32bit.stderr

@@ -296,7 +296,7 @@ error[E0080]: could not evaluate static initializer
   --> $DIR/ub-wide-ptr.rs:135:5
    |
 LL |     mem::transmute::<_, &dyn Trait>((&92u8, 0usize))
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ null pointer is not allowed for this operation
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ null pointer is not a valid pointer for this operation
 
 error[E0080]: could not evaluate static initializer
   --> $DIR/ub-wide-ptr.rs:139:5

src/test/ui/consts/const-eval/ub-wide-ptr.64bit.stderr

@@ -296,7 +296,7 @@ error[E0080]: could not evaluate static initializer
   --> $DIR/ub-wide-ptr.rs:135:5
    |
 LL |     mem::transmute::<_, &dyn Trait>((&92u8, 0usize))
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ null pointer is not allowed for this operation
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ null pointer is not a valid pointer for this operation
 
 error[E0080]: could not evaluate static initializer
   --> $DIR/ub-wide-ptr.rs:139:5

src/test/ui/consts/offset_from_ub.stderr

@@ -74,7 +74,7 @@ error: any use of this value will cause an error
 LL |           unsafe { intrinsics::ptr_offset_from(self, origin) }
    |                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |                    |
-   |                    null pointer is not allowed for this operation
+   |                    null pointer is not a valid pointer for this operation
    |                    inside `ptr::const_ptr::<impl *const u8>::offset_from` at $SRC_DIR/core/src/ptr/const_ptr.rs:LL:COL
    |                    inside `OFFSET_FROM_NULL` at $DIR/offset_from_ub.rs:36:14
    |