Add more UI tests for swap

These tests make sure that the swap warning will not be triggered
for expressions that will cause multiple mutable references of the
same owner

tests/ui/swap.rs

@@ -3,6 +3,25 @@
 
 struct Foo(u32);
 
+#[derive(Clone)]
+struct Bar {
+    a: u32,
+    b: u32,
+}
+
+fn field() {
+    let mut bar = Bar { a: 1, b: 2 };
+
+    let temp = bar.a;
+    bar.a = bar.b;
+    bar.b = temp;
+
+    let mut baz = vec![bar.clone(), bar.clone()];
+    let temp = baz[0].a;
+    baz[0].a = baz[1].a;
+    baz[1].a = temp;
+}
+
 fn array() {
     let mut foo = [1, 2];
     let temp = foo[0];
@@ -32,6 +51,7 @@ fn vec() {
 
 #[rustfmt::skip]
 fn main() {
+    field();
     array();
     slice();
     vec();

tests/ui/swap.stderr

@@ -1,5 +1,5 @@
 error: this looks like you are swapping elements of `foo` manually
-  --> $DIR/swap.rs:8:5
+  --> $DIR/swap.rs:27:5
    |
 LL | /     let temp = foo[0];
 LL | |     foo[0] = foo[1];
@@ -9,23 +9,23 @@ LL | |     foo[1] = temp;
    = note: `-D clippy::manual-swap` implied by `-D warnings`
 
 error: this looks like you are swapping elements of `foo` manually
-  --> $DIR/swap.rs:17:5
+  --> $DIR/swap.rs:36:5
    |
 LL | /     let temp = foo[0];
 LL | |     foo[0] = foo[1];
 LL | |     foo[1] = temp;
    | |_________________^ help: try: `foo.swap(0, 1)`
 
 error: this looks like you are swapping elements of `foo` manually
-  --> $DIR/swap.rs:26:5
+  --> $DIR/swap.rs:45:5
    |
 LL | /     let temp = foo[0];
 LL | |     foo[0] = foo[1];
 LL | |     foo[1] = temp;
    | |_________________^ help: try: `foo.swap(0, 1)`
 
 error: this looks like you are swapping `a` and `b` manually
-  --> $DIR/swap.rs:45:7
+  --> $DIR/swap.rs:65:7
    |
 LL |       ; let t = a;
    |  _______^
@@ -36,7 +36,7 @@ LL | |     b = t;
    = note: or maybe you should use `std::mem::replace`?
 
 error: this looks like you are swapping `c.0` and `a` manually
-  --> $DIR/swap.rs:54:7
+  --> $DIR/swap.rs:74:7
    |
 LL |       ; let t = c.0;
    |  _______^
@@ -47,7 +47,7 @@ LL | |     a = t;
    = note: or maybe you should use `std::mem::replace`?
 
 error: this looks like you are trying to swap `a` and `b`
-  --> $DIR/swap.rs:42:5
+  --> $DIR/swap.rs:62:5
    |
 LL | /     a = b;
 LL | |     b = a;
@@ -57,7 +57,7 @@ LL | |     b = a;
    = note: or maybe you should use `std::mem::replace`?
 
 error: this looks like you are trying to swap `c.0` and `a`
-  --> $DIR/swap.rs:51:5
+  --> $DIR/swap.rs:71:5
    |
 LL | /     c.0 = a;
 LL | |     a = c.0;