Auto merge of #5453 - rabisg0:fix/redundant_clone, r=phansch

Fixes #5405: redundant clone false positive with arrays

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

changelog: add a check for slice indexing on redundant_clone lint

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

@@ -51,6 +51,7 @@ fn main() {
  cannot_move_from_type_with_drop();
  borrower_propagation();
  not_consumed();
+ issue_5405();
 }
 
 #[derive(Clone)]
@@ -160,3 +161,12 @@ fn not_consumed() {
  println!("{}", x);
  }
 }
+
+#[allow(clippy::clone_on_copy)]
+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

@@ -51,6 +51,7 @@ fn main() {
  cannot_move_from_type_with_drop();
  borrower_propagation();
  not_consumed();
+ issue_5405();
 }
 
 #[derive(Clone)]
@@ -160,3 +161,12 @@ fn not_consumed() {
  println!("{}", x);
  }
 }
+
+#[allow(clippy::clone_on_copy)]
+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

@@ -108,61 +108,61 @@ LL | let _t = tup.0.clone();
  | ^^^^^
 
 error: redundant clone
- --> $DIR/redundant_clone.rs:60:22
+ --> $DIR/redundant_clone.rs:61:22
  |
 LL | (a.clone(), a.clone())
  | ^^^^^^^^ help: remove this
  |
 note: this value is dropped without further use
- --> $DIR/redundant_clone.rs:60:21
+ --> $DIR/redundant_clone.rs:61:21
  |
 LL | (a.clone(), a.clone())
  | ^
 
 error: redundant clone
- --> $DIR/redundant_clone.rs:120:15
+ --> $DIR/redundant_clone.rs:121:15
  |
 LL | let _s = s.clone();
  | ^^^^^^^^ help: remove this
  |
 note: this value is dropped without further use
- --> $DIR/redundant_clone.rs:120:14
+ --> $DIR/redundant_clone.rs:121:14
  |
 LL | let _s = s.clone();
  | ^
 
 error: redundant clone
- --> $DIR/redundant_clone.rs:121:15
+ --> $DIR/redundant_clone.rs:122:15
  |
 LL | let _t = t.clone();
  | ^^^^^^^^ help: remove this
  |
 note: this value is dropped without further use
- --> $DIR/redundant_clone.rs:121:14
+ --> $DIR/redundant_clone.rs:122:14
  |
 LL | let _t = t.clone();
  | ^
 
 error: redundant clone
- --> $DIR/redundant_clone.rs:131:19
+ --> $DIR/redundant_clone.rs:132:19
  |
 LL | let _f = f.clone();
  | ^^^^^^^^ help: remove this
  |
 note: this value is dropped without further use
- --> $DIR/redundant_clone.rs:131:18
+ --> $DIR/redundant_clone.rs:132:18
  |
 LL | let _f = f.clone();
  | ^
 
 error: redundant clone
- --> $DIR/redundant_clone.rs:143:14
+ --> $DIR/redundant_clone.rs:144:14
  |
 LL | let y = x.clone().join("matthias");
  | ^^^^^^^^ help: remove this
  |
 note: cloned value is neither consumed nor mutated
- --> $DIR/redundant_clone.rs:143:13
+ --> $DIR/redundant_clone.rs:144:13
  |
 LL | let y = x.clone().join("matthias");
  | ^^^^^^^^^