fix: borrow_deref_ref suggests wrongly when coerce to mut

Author: profetia

clippy_lints/src/borrow_deref_ref.rs

@@ -73,6 +73,9 @@ impl<'tcx> LateLintPass<'tcx> for BorrowDerefRef {
                 }
             })
             && !is_from_proc_macro(cx, e)
+            && let e_ty = cx.typeck_results().expr_ty_adjusted(e)
+            // check if the reference is coercing to a mutable reference
+            && !matches!(e_ty.kind(), ty::Ref(_, _, Mutability::Mut))
             && let Some(deref_text) = deref_target.span.get_source_text(cx)
         {
             span_lint_and_then(

tests/ui/borrow_deref_ref.fixed

@@ -81,3 +81,41 @@ fn issue_13584() {
     let p = &raw const *s;
     let _ = p as *const i8;
 }
+
+mod issue_9905 {
+    use std::{fs, io};
+
+    pub enum File {
+        Stdio,
+        File(fs::File),
+    }
+
+    impl io::Read for &'_ File {
+        fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
+            match self {
+                File::Stdio => io::stdin().read(buf),
+                File::File(file) => (&*file).read(buf),
+            }
+        }
+    }
+}
+
+mod issue_11346 {
+    struct Struct;
+
+    impl Struct {
+        fn foo(self: &mut &Self) {}
+    }
+
+    trait Trait {
+        fn bar(&mut self) {}
+    }
+
+    impl Trait for &Struct {}
+
+    fn bar() {
+        let s = &Struct;
+        (&*s).foo();
+        (&*s).bar();
+    }
+}

tests/ui/borrow_deref_ref.rs

@@ -81,3 +81,41 @@ fn issue_13584() {
     let p = &raw const *s;
     let _ = p as *const i8;
 }
+
+mod issue_9905 {
+    use std::{fs, io};
+
+    pub enum File {
+        Stdio,
+        File(fs::File),
+    }
+
+    impl io::Read for &'_ File {
+        fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
+            match self {
+                File::Stdio => io::stdin().read(buf),
+                File::File(file) => (&*file).read(buf),
+            }
+        }
+    }
+}
+
+mod issue_11346 {
+    struct Struct;
+
+    impl Struct {
+        fn foo(self: &mut &Self) {}
+    }
+
+    trait Trait {
+        fn bar(&mut self) {}
+    }
+
+    impl Trait for &Struct {}
+
+    fn bar() {
+        let s = &Struct;
+        (&*s).foo();
+        (&*s).bar();
+    }
+}