Return FieldIdx from non_1zst_field

Author: scottmcm

compiler/rustc_codegen_cranelift/src/vtable.rs

@@ -53,7 +53,7 @@ pub(crate) fn get_ptr_and_method_ref<'tcx>(
                     .layout()
                     .non_1zst_field(fx)
                     .expect("not exactly one non-1-ZST field in a `DispatchFromDyn` type");
-                arg = arg.value_field(fx, FieldIdx::new(idx));
+                arg = arg.value_field(fx, idx);
             }
         }
 

compiler/rustc_codegen_ssa/src/mir/block.rs

@@ -1019,7 +1019,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                             let (idx, _) = op.layout.non_1zst_field(bx).expect(
                                 "not exactly one non-1-ZST field in a `DispatchFromDyn` type",
                             );
-                            op = op.extract_field(bx, idx);
+                            op = op.extract_field(bx, idx.as_usize());
                         }
 
                         // now that we have `*dyn Trait` or `&dyn Trait`, split it up into its
@@ -1051,7 +1051,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                             let (idx, _) = op.layout.non_1zst_field(bx).expect(
                                 "not exactly one non-1-ZST field in a `DispatchFromDyn` type",
                             );
-                            op = op.extract_field(bx, idx);
+                            op = op.extract_field(bx, idx.as_usize());
                         }
 
                         // Make sure that we've actually unwrapped the rcvr down

compiler/rustc_const_eval/src/interpret/terminator.rs

@@ -793,7 +793,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                             let (idx, _) = receiver.layout.non_1zst_field(self).expect(
                                 "not exactly one non-1-ZST field in a `DispatchFromDyn` type",
                             );
-                            receiver = self.project_field(&receiver, idx)?;
+                            receiver = self.project_field(&receiver, idx.as_usize())?;
                         }
                     }
                 };

compiler/rustc_target/src/abi/mod.rs

@@ -279,7 +279,7 @@ impl<'a, Ty> TyAndLayout<'a, Ty> {
 
     /// Finds the one field that is not a 1-ZST.
     /// Returns `None` if there are multiple non-1-ZST fields or only 1-ZST-fields.
-    pub fn non_1zst_field<C>(&self, cx: &C) -> Option<(usize, Self)>
+    pub fn non_1zst_field<C>(&self, cx: &C) -> Option<(FieldIdx, Self)>
     where
         Ty: TyAbiInterface<'a, C> + Copy,
     {
@@ -293,8 +293,12 @@ impl<'a, Ty> TyAndLayout<'a, Ty> {
                 // More than one non-1-ZST field.
                 return None;
             }
-            found = Some((field_idx, field));
+
+            // Arrays are the only things with more than FieldIdx::MAX fields,
+            // but only 1-element arrays can ever return non-None here.
+            found = Some((FieldIdx::from_usize(field_idx), field));
         }
+
         found
     }
 }