Fixes #5405: redundant clone false positive with arrays

Check whether slice elements implement Copy before suggesting to drop
the clone method

clippy_lints/src/redundant_clone.rs

@@ -341,16 +341,21 @@ fn base_local_and_movability<'tcx>(
  let mut deref = false;
  // Accessing a field of an ADT that has `Drop`. Moving the field out will cause E0509.
  let mut field = false;
+ // If projection is a slice index then clone can be removed only if the
+ // underlying type implements Copy
+ let mut slice = false;
 
  let PlaceRef { local, mut projection } = place.as_ref();
  while let [base @ .., elem] = projection {
  projection = base;
  deref |= matches!(elem, mir::ProjectionElem::Deref);
  field |= matches!(elem, mir::ProjectionElem::Field(..))
  && has_drop(cx, mir::Place::ty_from(local, projection, &mir.local_decls, cx.tcx).ty);
+ slice |= matches!(elem, mir::ProjectionElem::Index(..))
+ && !is_copy(cx, mir::Place::ty_from(local, projection, &mir.local_decls, cx.tcx).ty);
  }
 
- Some((local, deref || field))
+ Some((local, deref || field || slice))
 }
 
 struct LocalUseVisitor {

tests/ui/redundant_clone.fixed

@@ -160,3 +160,11 @@ fn not_consumed() {
  println!("{}", x);
  }
 }
+
+fn issue_5405() {
+ let a: [String; 1] = [String::from("foo")];
+ let _b: String = a[0].clone();
+
+ let c: [usize; 2] = [2, 3];
+ let _d: usize = c[1].clone();
+}

tests/ui/redundant_clone.rs

@@ -160,3 +160,11 @@ fn not_consumed() {
  println!("{}", x);
  }
 }
+
+fn issue_5405() {
+ let a: [String; 1] = [String::from("foo")];
+ let _b: String = a[0].clone();
+
+ let c: [usize; 2] = [2, 3];
+ let _d: usize = c[1].clone();
+}

tests/ui/redundant_clone.stderr

@@ -167,5 +167,13 @@ note: cloned value is neither consumed nor mutated
 LL | let y = x.clone().join("matthias");
  | ^^^^^^^^^
 
-error: aborting due to 14 previous errors
+error: using `clone` on a `Copy` type
+ --> $DIR/redundant_clone.rs:169:21
+ |
+LL | let _d: usize = c[1].clone();
+ | ^^^^^^^^^^^^ help: try removing the `clone` call: `c[1]`
+ |
+ = note: `-D clippy::clone-on-copy` implied by `-D warnings`
+
+error: aborting due to 15 previous errors