new lint: option_as_ref_cloned

tests/ui/option_as_ref_cloned.fixed

@@ -0,0 +1,21 @@
+#![warn(clippy::option_as_ref_cloned)]
+#![allow(clippy::clone_on_copy)]
+
+fn main() {
+    let mut x = Some(String::new());
+
+    let _: Option<String> = x.clone();
+    let _: Option<String> = x.clone();
+
+    let y = x.as_ref();
+    let _: Option<&String> = y.clone();
+
+    macro_rules! cloned_recv {
+        () => {
+            x.as_ref()
+        };
+    }
+
+    // Don't lint when part of the expression is from a macro
+    let _: Option<String> = cloned_recv!().cloned();
+}

tests/ui/option_as_ref_cloned.rs

@@ -0,0 +1,21 @@
+#![warn(clippy::option_as_ref_cloned)]
+#![allow(clippy::clone_on_copy)]
+
+fn main() {
+    let mut x = Some(String::new());
+
+    let _: Option<String> = x.as_ref().cloned();
+    let _: Option<String> = x.as_mut().cloned();
+
+    let y = x.as_ref();
+    let _: Option<&String> = y.as_ref().cloned();
+
+    macro_rules! cloned_recv {
+        () => {
+            x.as_ref()
+        };
+    }
+
+    // Don't lint when part of the expression is from a macro
+    let _: Option<String> = cloned_recv!().cloned();
+}

tests/ui/option_as_ref_cloned.stderr

@@ -0,0 +1,37 @@
+error: cloning an `Option<_>` using `.as_ref().cloned()`
+  --> $DIR/option_as_ref_cloned.rs:7:31
+   |
+LL |     let _: Option<String> = x.as_ref().cloned();
+   |                               ^^^^^^^^^^^^^^^
+   |
+   = note: `-D clippy::option-as-ref-cloned` implied by `-D warnings`
+   = help: to override `-D warnings` add `#[allow(clippy::option_as_ref_cloned)]`
+help: this can be written more concisely by cloning the `Option<_>` directly
+   |
+LL |     let _: Option<String> = x.clone();
+   |                               ~~~~~
+
+error: cloning an `Option<_>` using `.as_mut().cloned()`
+  --> $DIR/option_as_ref_cloned.rs:8:31
+   |
+LL |     let _: Option<String> = x.as_mut().cloned();
+   |                               ^^^^^^^^^^^^^^^
+   |
+help: this can be written more concisely by cloning the `Option<_>` directly
+   |
+LL |     let _: Option<String> = x.clone();
+   |                               ~~~~~
+
+error: cloning an `Option<_>` using `.as_ref().cloned()`
+  --> $DIR/option_as_ref_cloned.rs:11:32
+   |
+LL |     let _: Option<&String> = y.as_ref().cloned();
+   |                                ^^^^^^^^^^^^^^^
+   |
+help: this can be written more concisely by cloning the `Option<_>` directly
+   |
+LL |     let _: Option<&String> = y.clone();
+   |                                ~~~~~
+
+error: aborting due to 3 previous errors
+