Error out of layout calculation if a non-last struct field is unsized

Fixes an ICE that occurs when a struct with an unsized field
at a non-last position is const evaluated.

1 files changed, 37 insertions, 1 deletions

diff --git a/compiler/rustc_ty_utils/src/layout.rs b/compiler/rustc_ty_utils/src/layout.rs
index 331970ac362..44390c1624d 100644
--- a/compiler/rustc_ty_utils/src/layout.rs
+++ b/compiler/rustc_ty_utils/src/layout.rs
@@ -8,7 +8,9 @@ use rustc_middle::ty::layout::{
     IntegerExt, LayoutCx, LayoutError, LayoutOf, TyAndLayout, MAX_SIMD_LANES,
 };
 use rustc_middle::ty::print::with_no_trimmed_paths;
-use rustc_middle::ty::{self, AdtDef, EarlyBinder, GenericArgsRef, Ty, TyCtxt, TypeVisitableExt};
+use rustc_middle::ty::{
+    self, AdtDef, EarlyBinder, FieldDef, GenericArgsRef, Ty, TyCtxt, TypeVisitableExt,
+};
 use rustc_session::{DataTypeKind, FieldInfo, FieldKind, SizeKind, VariantInfo};
 use rustc_span::sym;
 use rustc_span::symbol::Symbol;
@@ -506,6 +508,40 @@ fn layout_of_uncached<'tcx>(
                 ));
             }
 
+            let err_if_unsized = |field: &FieldDef, err_msg: &str| {
+                let field_ty = tcx.type_of(field.did);
+                let is_unsized = tcx
+                    .try_instantiate_and_normalize_erasing_regions(args, cx.param_env, field_ty)
+                    .map(|f| !f.is_sized(tcx, cx.param_env))
+                    .map_err(|e| {
+                        error(
+                            cx,
+                            LayoutError::NormalizationFailure(field_ty.instantiate_identity(), e),
+                        )
+                    })?;
+
+                if is_unsized {
+                    cx.tcx.dcx().span_delayed_bug(tcx.def_span(def.did()), err_msg.to_owned());
+                    Err(error(cx, LayoutError::Unknown(ty)))
+                } else {
+                    Ok(())
+                }
+            };
+
+            if def.is_struct() {
+                if let Some((_, fields_except_last)) =
+                    def.non_enum_variant().fields.raw.split_last()
+                {
+                    for f in fields_except_last {
+                        err_if_unsized(f, "only the last field of a struct can be unsized")?;
+                    }
+                }
+            } else {
+                for f in def.all_fields() {
+                    err_if_unsized(f, &format!("{}s cannot have unsized fields", def.descr()))?;
+                }
+            }
+
             let get_discriminant_type =
                 |min, max| Integer::repr_discr(tcx, ty, &def.repr(), min, max);