Recomend .as_ref()? in certain situations

Author: fuerstenau

clippy_lints/src/question_mark.rs

@@ -84,6 +84,8 @@ impl Pass {
                             replacement_str = format!("Some({}?)", receiver_str);
                         }
                     }
+                } else if Self::moves_by_default(cx, subject) {
+                        replacement_str = format!("{}.as_ref()?;", receiver_str);
                 } else {
                         replacement_str = format!("{}?;", receiver_str);
                 }
@@ -105,6 +107,12 @@ impl Pass {
         }
     }
 
+    fn moves_by_default(cx: &LateContext<'_, '_>, expression: &Expr) -> bool {
+        let expr_ty = cx.tables.expr_ty(expression);
+
+        expr_ty.moves_by_default(cx.tcx, cx.param_env, expression.span)
+    }
+
     fn is_option(cx: &LateContext<'_, '_>, expression: &Expr) -> bool {
         let expr_ty = cx.tables.expr_ty(expression);
 

tests/ui/question_mark.rs

@@ -37,11 +37,11 @@ fn returns_something_similar_to_option(a: SeemsOption<u32>) -> SeemsOption<u32>
     a
 }
 
-pub struct SomeStruct {
+pub struct CopyStruct {
     pub opt: Option<u32>,
 }
 
-impl SomeStruct {
+impl CopyStruct {
     #[rustfmt::skip]
     pub fn func(&self) -> Option<u32> {
         if (self.opt).is_none() {
@@ -62,12 +62,49 @@ impl SomeStruct {
     }
 }
 
+#[derive(Clone)]
+pub struct MoveStruct {
+    pub opt: Option<Vec<u32>>,
+}
+
+impl MoveStruct {
+    pub fn ref_func(&self) -> Option<Vec<u32>> {
+        if self.opt.is_none() {
+            return None;
+        }
+
+        self.opt.clone()
+    }
+
+    pub fn mov_func_reuse(self) -> Option<Vec<u32>> {
+        if self.opt.is_none() {
+            return None;
+        }
+
+        self.opt
+    }
+
+    pub fn mov_func_no_use(self) -> Option<Vec<u32>> {
+        if self.opt.is_none() {
+            return None;
+        }
+        Some(Vec::new())
+    }
+}
+
 fn main() {
     some_func(Some(42));
     some_func(None);
 
-    let some_struct = SomeStruct { opt: Some(54) };
-    some_struct.func();
+    let copy_struct = CopyStruct { opt: Some(54) };
+    copy_struct.func();
+
+    let move_struct = MoveStruct {
+        opt: Some(vec![42, 1337]),
+    };
+    move_struct.ref_func();
+    move_struct.clone().mov_func_reuse();
+    move_struct.clone().mov_func_no_use();
 
     let so = SeemsOption::Some(45);
     returns_something_similar_to_option(so);

tests/ui/question_mark.stderr

@@ -35,5 +35,29 @@ error: this block may be rewritten with the `?` operator
 59 | |         };
    | |_________^ help: replace_it_with: `Some(self.opt?)`
 
-error: aborting due to 4 previous errors
+error: this block may be rewritten with the `?` operator
+  --> $DIR/question_mark.rs:72:9
+   |
+72 | /         if self.opt.is_none() {
+73 | |             return None;
+74 | |         }
+   | |_________^ help: replace_it_with: `self.opt.as_ref()?;`
+
+error: this block may be rewritten with the `?` operator
+  --> $DIR/question_mark.rs:80:9
+   |
+80 | /         if self.opt.is_none() {
+81 | |             return None;
+82 | |         }
+   | |_________^ help: replace_it_with: `self.opt.as_ref()?;`
+
+error: this block may be rewritten with the `?` operator
+  --> $DIR/question_mark.rs:88:9
+   |
+88 | /         if self.opt.is_none() {
+89 | |             return None;
+90 | |         }
+   | |_________^ help: replace_it_with: `self.opt.as_ref()?;`
+
+error: aborting due to 7 previous errors