mir: Improve size_of handling when arg is unsized

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

@@ -127,6 +127,8 @@ pub enum InvalidProgramInfo<'tcx> {
     Layout(layout::LayoutError<'tcx>),
     /// An invalid transmute happened.
     TransmuteSizeDiff(Ty<'tcx>, Ty<'tcx>),
+    /// SizeOf of unsized type was requested.
+    SizeOfUnsizedType(Ty<'tcx>),
 }
 
 impl fmt::Display for InvalidProgramInfo<'_> {
@@ -144,6 +146,7 @@ impl fmt::Display for InvalidProgramInfo<'_> {
                 "transmuting `{}` to `{}` is not possible, because these types do not have the same size",
                 from_ty, to_ty
             ),
+            SizeOfUnsizedType(ty) => write!(f, "size_of called on unsized type `{}`", ty),
         }
     }
 }

compiler/rustc_mir/src/interpret/step.rs

@@ -270,6 +270,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                         self.frame().current_span(),
                         &format!("SizeOf nullary MIR operator called for unsized type {}", ty),
                     );
+                    throw_inval!(SizeOfUnsizedType(ty));
                 }
                 self.write_scalar(Scalar::from_machine_usize(layout.size.bytes(), self), dest)?;
             }

src/test/ui/mir/issue-80742.stderr

@@ -1,3 +1,17 @@
+error[E0080]: evaluation of constant value failed
+  --> $SRC_DIR/core/src/mem/mod.rs:LL:COL
+   |
+LL |     intrinsics::size_of::<T>()
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |     |
+   |     size_of called on unsized type `dyn Debug`
+   |     inside `std::mem::size_of::<dyn Debug>` at $SRC_DIR/core/src/mem/mod.rs:LL:COL
+   | 
+  ::: $DIR/issue-80742.rs:23:10
+   |
+LL |     [u8; size_of::<T>() + 1]: ,
+   |          -------------- inside `Inline::<dyn Debug>::{constant#0}` at $DIR/issue-80742.rs:23:10
+
 error[E0599]: no function or associated item named `new` found for struct `Inline<dyn Debug>` in the current scope
   --> $DIR/issue-80742.rs:31:36
    |
@@ -21,6 +35,20 @@ LL |   pub trait Debug {
    = note: the method `new` exists but the following trait bounds were not satisfied:
            `dyn Debug: Sized`
 
+error[E0080]: evaluation of constant value failed
+  --> $SRC_DIR/core/src/mem/mod.rs:LL:COL
+   |
+LL |     intrinsics::size_of::<T>()
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |     |
+   |     size_of called on unsized type `dyn Debug`
+   |     inside `std::mem::size_of::<dyn Debug>` at $SRC_DIR/core/src/mem/mod.rs:LL:COL
+   | 
+  ::: $DIR/issue-80742.rs:15:10
+   |
+LL |     [u8; size_of::<T>() + 1]: ,
+   |          -------------- inside `Inline::<dyn Debug>::{constant#0}` at $DIR/issue-80742.rs:15:10
+
 error[E0277]: the size for values of type `dyn Debug` cannot be known at compilation time
   --> $DIR/issue-80742.rs:31:15
    |
@@ -36,7 +64,7 @@ help: consider relaxing the implicit `Sized` restriction
 LL | struct Inline<T: ?Sized>
    |                ^^^^^^^^
 
-error: aborting due to 2 previous errors
+error: aborting due to 4 previous errors
 
-Some errors have detailed explanations: E0277, E0599.
-For more information about an error, try `rustc --explain E0277`.
+Some errors have detailed explanations: E0080, E0277, E0599.
+For more information about an error, try `rustc --explain E0080`.