Warn about explicit self-assignment

Warn about assignments where left-hand side place expression is the same
as right-hand side value expression. For example, warn about assignment in:

```rust
pub struct Event {
    id: usize,
    x: i32,
    y: i32,
}

pub fn copy_position(a: &mut Event, b: &Event) {
    a.x = b.x;
    a.y = a.y;
}
```

1 files changed, 7 insertions, 0 deletions

diff --git a/src/lintlist/mod.rs b/src/lintlist/mod.rs
index 3229c8da507..bf58c117aaa 100644
--- a/src/lintlist/mod.rs
+++ b/src/lintlist/mod.rs
@@ -1957,6 +1957,13 @@ pub static ref ALL_LINTS: Vec<Lint> = vec![
         module: "methods",
     },
     Lint {
+        name: "self_assignment",
+        group: "correctness",
+        desc: "explicit self-assignment",
+        deprecation: None,
+        module: "self_assignment",
+    },
+    Lint {
         name: "serde_api_misuse",
         group: "correctness",
         desc: "various things that will negatively affect your serde experience",