allow explicit deref method call in deref or deref_mut impl of Deref trait

Author: relaxcn

clippy_lints/src/dereference.rs

@@ -945,6 +945,19 @@ fn report<'tcx>(
             is_ufcs,
             mutbl,
         } => {
+            // Skip when inside a `deref` or `deref_mut` implementation of the `Deref` trait.
+            let fn_def_id = cx.tcx.hir_enclosing_body_owner(expr.hir_id).to_def_id();
+            if !cx.tcx.is_closure_like(fn_def_id)
+                && matches!(cx.tcx.item_name(fn_def_id), sym::deref | sym::deref_mut)
+                && let Some(impl_defid) = cx.tcx.impl_of_assoc(fn_def_id)
+                && let Some(impl_trait_ref) = cx.tcx.impl_trait_ref(impl_defid)
+                && cx
+                    .tcx
+                    .is_diagnostic_item(sym::Deref, impl_trait_ref.skip_binder().def_id)
+            {
+                return;
+            }
+
             let mut app = Applicability::MachineApplicable;
             let (expr_str, expr_is_macro_call) =
                 snippet_with_context(cx, expr.span, data.first_expr.span.ctxt(), "..", &mut app);

tests/ui/explicit_deref_methods.fixed

@@ -50,6 +50,36 @@ impl DerefMut for Aaa {
     }
 }
 
+mod issue_15392 {
+    use std::ops::{Deref, DerefMut};
+
+    struct Inner;
+
+    struct WrapperA(Inner);
+
+    impl Deref for WrapperA {
+        type Target = Inner;
+        fn deref(&self) -> &Inner {
+            &self.0
+        }
+    }
+
+    enum MyEnum {
+        A(WrapperA),
+    }
+
+    impl Deref for MyEnum {
+        type Target = Inner;
+
+        fn deref(&self) -> &Inner {
+            // forwarding is ok
+            match self {
+                MyEnum::A(wrap_a) => Deref::deref(wrap_a),
+            }
+        }
+    }
+}
+
 fn main() {
     let a: &mut String = &mut String::from("foo");
 

tests/ui/explicit_deref_methods.rs

@@ -50,6 +50,36 @@ impl DerefMut for Aaa {
     }
 }
 
+mod issue_15392 {
+    use std::ops::{Deref, DerefMut};
+
+    struct Inner;
+
+    struct WrapperA(Inner);
+
+    impl Deref for WrapperA {
+        type Target = Inner;
+        fn deref(&self) -> &Inner {
+            &self.0
+        }
+    }
+
+    enum MyEnum {
+        A(WrapperA),
+    }
+
+    impl Deref for MyEnum {
+        type Target = Inner;
+
+        fn deref(&self) -> &Inner {
+            // forwarding is ok
+            match self {
+                MyEnum::A(wrap_a) => Deref::deref(wrap_a),
+            }
+        }
+    }
+}
+
 fn main() {
     let a: &mut String = &mut String::from("foo");
 

tests/ui/explicit_deref_methods.stderr

@@ -1,5 +1,5 @@
 error: explicit `deref` method call
-  --> tests/ui/explicit_deref_methods.rs:58:19
+  --> tests/ui/explicit_deref_methods.rs:88:19
    |
 LL |     let b: &str = a.deref();
    |                   ^^^^^^^^^ help: try: `&*a`
@@ -8,73 +8,73 @@ LL |     let b: &str = a.deref();
    = help: to override `-D warnings` add `#[allow(clippy::explicit_deref_methods)]`
 
 error: explicit `deref_mut` method call
-  --> tests/ui/explicit_deref_methods.rs:61:23
+  --> tests/ui/explicit_deref_methods.rs:91:23
    |
 LL |     let b: &mut str = a.deref_mut();
    |                       ^^^^^^^^^^^^^ help: try: `&mut **a`
 
 error: explicit `deref` method call
-  --> tests/ui/explicit_deref_methods.rs:65:39
+  --> tests/ui/explicit_deref_methods.rs:95:39
    |
 LL |     let b: String = format!("{}, {}", a.deref(), a.deref());
    |                                       ^^^^^^^^^ help: try: `&*a`
 
 error: explicit `deref` method call
-  --> tests/ui/explicit_deref_methods.rs:65:50
+  --> tests/ui/explicit_deref_methods.rs:95:50
    |
 LL |     let b: String = format!("{}, {}", a.deref(), a.deref());
    |                                                  ^^^^^^^^^ help: try: `&*a`
 
 error: explicit `deref` method call
-  --> tests/ui/explicit_deref_methods.rs:69:20
+  --> tests/ui/explicit_deref_methods.rs:99:20
    |
 LL |     println!("{}", a.deref());
    |                    ^^^^^^^^^ help: try: `&*a`
 
 error: explicit `deref` method call
-  --> tests/ui/explicit_deref_methods.rs:73:11
+  --> tests/ui/explicit_deref_methods.rs:103:11
    |
 LL |     match a.deref() {
    |           ^^^^^^^^^ help: try: `&*a`
 
 error: explicit `deref` method call
-  --> tests/ui/explicit_deref_methods.rs:78:28
+  --> tests/ui/explicit_deref_methods.rs:108:28
    |
 LL |     let b: String = concat(a.deref());
    |                            ^^^^^^^^^ help: try: `&*a`
 
 error: explicit `deref` method call
-  --> tests/ui/explicit_deref_methods.rs:81:13
+  --> tests/ui/explicit_deref_methods.rs:111:13
    |
 LL |     let b = just_return(a).deref();
    |             ^^^^^^^^^^^^^^^^^^^^^^ help: try: `just_return(a)`
 
 error: explicit `deref` method call
-  --> tests/ui/explicit_deref_methods.rs:84:28
+  --> tests/ui/explicit_deref_methods.rs:114:28
    |
 LL |     let b: String = concat(just_return(a).deref());
    |                            ^^^^^^^^^^^^^^^^^^^^^^ help: try: `just_return(a)`
 
 error: explicit `deref` method call
-  --> tests/ui/explicit_deref_methods.rs:124:31
+  --> tests/ui/explicit_deref_methods.rs:154:31
    |
 LL |     let b: &str = expr_deref!(a.deref());
    |                               ^^^^^^^^^ help: try: `&*a`
 
 error: explicit `deref` method call
-  --> tests/ui/explicit_deref_methods.rs:154:14
+  --> tests/ui/explicit_deref_methods.rs:184:14
    |
 LL |     let _ = &Deref::deref(&"foo");
    |              ^^^^^^^^^^^^^^^^^^^^ help: try: `*&"foo"`
 
 error: explicit `deref_mut` method call
-  --> tests/ui/explicit_deref_methods.rs:156:14
+  --> tests/ui/explicit_deref_methods.rs:186:14
    |
 LL |     let _ = &DerefMut::deref_mut(&mut x);
    |              ^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `&mut **&mut x`
 
 error: explicit `deref_mut` method call
-  --> tests/ui/explicit_deref_methods.rs:157:14
+  --> tests/ui/explicit_deref_methods.rs:187:14
    |
 LL |     let _ = &DerefMut::deref_mut((&mut &mut x).deref_mut());
    |              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `&mut ***(&mut &mut x)`