Add check for illegal accessing known length array with a constant index

Author: cocodery

clippy_lints/src/indexing_slicing.rs

@@ -170,7 +170,23 @@ impl<'tcx> LateLintPass<'tcx> for IndexingSlicing {
  return;
  }
  // Index is a constant uint.
- if constant(cx, cx.typeck_results(), index).is_some() {
+ if let Some(constant) = constant(cx, cx.typeck_results(), index) {
+ // only `usize` index is legal in rust array index
+ // leave other type to rustc
+ if let Constant::Int(off) = constant
+ && let ty::Uint(utype) = cx.typeck_results().expr_ty(index).kind()
+ && *utype == ty::UintTy::Usize
+ && let ty::Array(_, s) = ty.kind()
+ && let Some(size) = s.try_eval_target_usize(cx.tcx, cx.param_env)
+ {
+ // get constant offset and check whether it is in bounds
+ let off = usize::try_from(off).unwrap();
+ let size = usize::try_from(size).unwrap();
+
+ if off >= size {
+ span_lint(cx, OUT_OF_BOUNDS_INDEXING, expr.span, "index is out of bounds");
+ }
+ }
  // Let rustc's `const_err` lint handle constant `usize` indexing on arrays.
  return;
  }