Add size information

Author: oli-obk

compiler/rustc_const_eval/src/const_eval/type_info.rs

@@ -85,6 +85,22 @@ impl<'tcx> InterpCx<'tcx, CompileTimeMachine<'tcx>> {
                     };
                     self.write_discriminant(variant_index, &field_dest)?
                 }
+                sym::size => {
+                    let variant_index = if layout.is_sized() {
+                        let (variant, variant_place) = downcast(sym::Some)?;
+                        let size_field_place =
+                            self.project_field(&variant_place, FieldIdx::ZERO)?;
+                        self.write_scalar(
+                            ScalarInt::try_from_target_usize(layout.size.bytes(), self.tcx.tcx)
+                                .unwrap(),
+                            &size_field_place,
+                        )?;
+                        variant
+                    } else {
+                        downcast(sym::None)?.0
+                    };
+                    self.write_discriminant(variant_index, &field_dest)?;
+                }
                 other => span_bug!(self.tcx.span, "unknown `Type` field {other}"),
             }
         }

library/core/src/mem/type_info.rs

@@ -11,6 +11,8 @@ use crate::any::TypeId;
 pub struct Type {
     /// Per-type information
     pub kind: TypeKind,
+    /// Size of the type. `None` if it is unsized
+    pub size: Option<usize>,
 }
 
 /// Compute the type information of a concrete type.

tests/ui/reflection/dump.run.stdout

@@ -17,4 +17,7 @@ Type {
             ],
         },
     ),
+    size: Some(
+        2,
+    ),
 }