Add option_and_then_some lint

tests/ui/option_and_then_some.fixed

@@ -0,0 +1,21 @@
+// run-rustfix
+#![deny(clippy::option_and_then_some)]
+
+// need a main anyway, use it get rid of unused warnings too
+pub fn main() {
+    let x = Some(5);
+    // the easiest cases
+    let _ = x;
+    let _ = x.map(|o| o + 1);
+    // and an easy counter-example
+    let _ = x.and_then(|o| if o < 32 { Some(o) } else { None });
+
+    // Different type
+    let x: Result<u32, &str> = Ok(1);
+    let _ = x.and_then(Ok);
+}
+
+pub fn foo() -> Option<String> {
+    let x = Some(String::from("hello"));
+    Some("hello".to_owned()).and_then(|s| Some(format!("{}{}", s, x?)))
+}

tests/ui/option_and_then_some.rs

@@ -0,0 +1,21 @@
+// run-rustfix
+#![deny(clippy::option_and_then_some)]
+
+// need a main anyway, use it get rid of unused warnings too
+pub fn main() {
+    let x = Some(5);
+    // the easiest cases
+    let _ = x.and_then(Some);
+    let _ = x.and_then(|o| Some(o + 1));
+    // and an easy counter-example
+    let _ = x.and_then(|o| if o < 32 { Some(o) } else { None });
+
+    // Different type
+    let x: Result<u32, &str> = Ok(1);
+    let _ = x.and_then(Ok);
+}
+
+pub fn foo() -> Option<String> {
+    let x = Some(String::from("hello"));
+    Some("hello".to_owned()).and_then(|s| Some(format!("{}{}", s, x?)))
+}

tests/ui/option_and_then_some.stderr

@@ -0,0 +1,20 @@
+error: using `Option.and_then(Some)`, which is a no-op
+  --> $DIR/option_and_then_some.rs:8:13
+   |
+LL |     let _ = x.and_then(Some);
+   |             ^^^^^^^^^^^^^^^^ help: use the expression directly: `x`
+   |
+note: lint level defined here
+  --> $DIR/option_and_then_some.rs:2:9
+   |
+LL | #![deny(clippy::option_and_then_some)]
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: using `Option.and_then(|x| Some(y))`, which is more succinctly expressed as `map(|x| y)`
+  --> $DIR/option_and_then_some.rs:9:13
+   |
+LL |     let _ = x.and_then(|o| Some(o + 1));
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try this: `x.map(|o| o + 1)`
+
+error: aborting due to 2 previous errors
+