Auto merge of rust-lang#100085 - RalfJung:op-ty-len, r=oli-obk

interpret: use new OpTy::len for Len rvalue

This avoids a `force_allocation`.

Author: bors

compiler/rustc_const_eval/src/interpret/step.rs

@@ -251,8 +251,8 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
 
             Len(place) => {
                 let src = self.eval_place(place)?;
-                let mplace = self.force_allocation(&src)?;
-                let len = mplace.len(self)?;
+                let op = self.place_to_op(&src)?;
+                let len = op.len(self)?;
                 self.write_scalar(Scalar::from_machine_usize(len, self), &dest)?;
             }
 

src/tools/clippy/tests/ui/indexing_slicing_index.rs

@@ -3,7 +3,7 @@
 // We also check the out_of_bounds_indexing lint here, because it lints similar things and
 // we want to avoid false positives.
 #![warn(clippy::out_of_bounds_indexing)]
-#![allow(const_err, clippy::no_effect, clippy::unnecessary_operation)]
+#![allow(const_err, unconditional_panic, clippy::no_effect, clippy::unnecessary_operation)]
 
 const ARR: [i32; 2] = [1, 2];
 const REF: &i32 = &ARR[idx()]; // Ok, should not produce stderr.