Auto merge of rust-lang#10454 - Alexendoo:transmutes-expressible-as-ptr-casts-parens, r=Jarcho

Wrap `transmutes_expressible_as_ptr_casts` suggestions in parentheses

changelog: [`transmutes_expressible_as_ptr_casts`]: Fix suggestion missing wrapping parentheses

Fixes rust-lang#10449

r? `@Jarcho`

Is this the best way to go about this? `unused_parens` will catch the unnecessary ones but emitting them in the first place isn't ideal

Author: bors

clippy_lints/src/transmute/transmutes_expressible_as_ptr_casts.rs

@@ -2,8 +2,9 @@ use super::utils::check_cast;
 use super::TRANSMUTES_EXPRESSIBLE_AS_PTR_CASTS;
 use clippy_utils::diagnostics::span_lint_and_sugg;
 use clippy_utils::sugg::Sugg;
+use rustc_ast::ExprPrecedence;
 use rustc_errors::Applicability;
-use rustc_hir::Expr;
+use rustc_hir::{Expr, Node};
 use rustc_lint::LateContext;
 use rustc_middle::ty::{cast::CastKind, Ty};
 
@@ -19,7 +20,7 @@ pub(super) fn check<'tcx>(
 ) -> bool {
     use CastKind::{AddrPtrCast, ArrayPtrCast, FnPtrAddrCast, FnPtrPtrCast, PtrAddrCast, PtrPtrCast};
     let mut app = Applicability::MachineApplicable;
-    let sugg = match check_cast(cx, e, from_ty, to_ty) {
+    let mut sugg = match check_cast(cx, e, from_ty, to_ty) {
         Some(PtrPtrCast | AddrPtrCast | ArrayPtrCast | FnPtrPtrCast | FnPtrAddrCast) => {
             Sugg::hir_with_context(cx, arg, e.span.ctxt(), "..", &mut app)
                 .as_ty(to_ty.to_string())
@@ -39,6 +40,12 @@ pub(super) fn check<'tcx>(
         _ => return false,
     };
 
+    if let Node::Expr(parent) = cx.tcx.hir().get_parent(e.hir_id)
+        && parent.precedence().order() > ExprPrecedence::Cast.order()
+    {
+        sugg = format!("({sugg})");
+    }
+
     span_lint_and_sugg(
         cx,
         TRANSMUTES_EXPRESSIBLE_AS_PTR_CASTS,

tests/ui/transmutes_expressible_as_ptr_casts.fixed

@@ -4,7 +4,7 @@
 // would otherwise be responsible for
 #![warn(clippy::useless_transmute)]
 #![warn(clippy::transmute_ptr_to_ptr)]
-#![allow(dead_code, unused_unsafe, clippy::borrow_as_ptr)]
+#![allow(unused, clippy::borrow_as_ptr)]
 
 use std::mem::{size_of, transmute};
 
@@ -77,3 +77,9 @@ fn cannot_be_expressed_as_pointer_cast(in_param: Single) -> Pair {
 
     unsafe { transmute::<Single, Pair>(in_param) }
 }
+
+fn issue_10449() {
+    fn f() {}
+
+    let _x: u8 = unsafe { *(f as *const u8) };
+}

tests/ui/transmutes_expressible_as_ptr_casts.rs

@@ -4,7 +4,7 @@
 // would otherwise be responsible for
 #![warn(clippy::useless_transmute)]
 #![warn(clippy::transmute_ptr_to_ptr)]
-#![allow(dead_code, unused_unsafe, clippy::borrow_as_ptr)]
+#![allow(unused, clippy::borrow_as_ptr)]
 
 use std::mem::{size_of, transmute};
 
@@ -77,3 +77,9 @@ fn cannot_be_expressed_as_pointer_cast(in_param: Single) -> Pair {
 
     unsafe { transmute::<Single, Pair>(in_param) }
 }
+
+fn issue_10449() {
+    fn f() {}
+
+    let _x: u8 = unsafe { *std::mem::transmute::<fn(), *const u8>(f) };
+}

tests/ui/transmutes_expressible_as_ptr_casts.stderr

@@ -58,5 +58,11 @@ error: transmute from a reference to a pointer
 LL |     unsafe { transmute::<&[i32; 1], *const u8>(in_param) }
    |              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `in_param as *const [i32; 1] as *const u8`
 
-error: aborting due to 9 previous errors
+error: transmute from `fn()` to `*const u8` which could be expressed as a pointer cast instead
+  --> $DIR/transmutes_expressible_as_ptr_casts.rs:84:28
+   |
+LL |     let _x: u8 = unsafe { *std::mem::transmute::<fn(), *const u8>(f) };
+   |                            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `(f as *const u8)`
+
+error: aborting due to 10 previous errors