Fix a wrong suggestion of ref_in_deref

clippy_lints/src/reference.rs

@@ -1,3 +1,4 @@
+use crate::utils::sugg::Sugg;
 use crate::utils::{in_macro, snippet_opt, snippet_with_applicability, span_lint_and_sugg};
 use if_chain::if_chain;
 use rustc_ast::ast::{Expr, ExprKind, Mutability, UnOp};
@@ -124,14 +125,19 @@ impl EarlyLintPass for RefInDeref {
             if let ExprKind::Paren(ref parened) = object.kind;
             if let ExprKind::AddrOf(_, _, ref inner) = parened.kind;
             then {
-                let mut applicability = Applicability::MachineApplicable;
+                let applicability = if inner.span.from_expansion() {
+                    Applicability::MaybeIncorrect
+                } else {
+                    Applicability::MachineApplicable
+                };
+                let sugg = Sugg::ast(cx, inner, "_").maybe_par();
                 span_lint_and_sugg(
                     cx,
                     REF_IN_DEREF,
                     object.span,
                     "creating a reference that is immediately dereferenced",
                     "try this",
-                    snippet_with_applicability(cx, inner.span, "_", &mut applicability).to_string(),
+                    sugg.to_string(),
                     applicability,
                 );
             }

tests/ui/unnecessary_ref.fixed

@@ -1,7 +1,7 @@
 // run-rustfix
 
 #![feature(stmt_expr_attributes)]
-#![allow(unused_variables)]
+#![allow(unused_variables, dead_code)]
 
 struct Outer {
     inner: u32,
@@ -12,3 +12,12 @@ fn main() {
     let outer = Outer { inner: 0 };
     let inner = outer.inner;
 }
+
+struct Apple;
+impl Apple {
+    fn hello(&self) {}
+}
+struct Package(pub *const Apple);
+fn foobar(package: *const Package) {
+    unsafe { &*(*package).0 }.hello();
+}

tests/ui/unnecessary_ref.rs

@@ -1,7 +1,7 @@
 // run-rustfix
 
 #![feature(stmt_expr_attributes)]
-#![allow(unused_variables)]
+#![allow(unused_variables, dead_code)]
 
 struct Outer {
     inner: u32,
@@ -12,3 +12,12 @@ fn main() {
     let outer = Outer { inner: 0 };
     let inner = (&outer).inner;
 }
+
+struct Apple;
+impl Apple {
+    fn hello(&self) {}
+}
+struct Package(pub *const Apple);
+fn foobar(package: *const Package) {
+    unsafe { &*(&*package).0 }.hello();
+}

tests/ui/unnecessary_ref.stderr

@@ -10,5 +10,13 @@ note: the lint level is defined here
 LL | #[deny(clippy::ref_in_deref)]
    |        ^^^^^^^^^^^^^^^^^^^^
 
-error: aborting due to previous error
+error: creating a reference that is immediately dereferenced
+  --> $DIR/unnecessary_ref.rs:22:16
+   |
+LL |     unsafe { &*(&*package).0 }.hello();
+   |                ^^^^^^^^^^^ help: try this: `(*package)`
+   |
+   = note: `-D clippy::ref-in-deref` implied by `-D warnings`
+
+error: aborting due to 2 previous errors