Fix clippy::ref_as_ptr for non-temporary references in let/const

src/tools/clippy/clippy_lints/src/casts/ref_as_ptr.rs

@@ -1,9 +1,9 @@
 use clippy_utils::diagnostics::span_lint_and_sugg;
 use clippy_utils::source::snippet_with_applicability;
 use clippy_utils::sugg::Sugg;
-use clippy_utils::{ExprUseNode, expr_use_ctxt, std_or_core};
+use clippy_utils::{ExprUseNode, expr_use_ctxt, is_expr_temporary_value, std_or_core};
 use rustc_errors::Applicability;
-use rustc_hir::{Expr, Mutability, Ty, TyKind};
+use rustc_hir::{Expr, ExprKind, Mutability, Ty, TyKind};
 use rustc_lint::LateContext;
 use rustc_middle::ty;
 
@@ -23,10 +23,18 @@ pub(super) fn check<'tcx>(
     if matches!(cast_from.kind(), ty::Ref(..))
         && let ty::RawPtr(_, to_mutbl) = cast_to.kind()
         && let use_cx = expr_use_ctxt(cx, expr)
-        // TODO: only block the lint if `cast_expr` is a temporary
-        && !matches!(use_cx.use_node(cx), ExprUseNode::LetStmt(_) | ExprUseNode::ConstStatic(_))
         && let Some(std_or_core) = std_or_core(cx)
     {
+        if matches!(
+            use_cx.use_node(cx),
+            ExprUseNode::LetStmt(_) | ExprUseNode::ConstStatic(_)
+        ) {
+            if let ExprKind::AddrOf(_, _, addr_inner) = cast_expr.kind
+                && is_expr_temporary_value(cx, addr_inner)
+            {
+                return;
+            }
+        }
         let fn_name = match to_mutbl {
             Mutability::Not => "from_ref",
             Mutability::Mut => "from_mut",

src/tools/clippy/tests/ui/ref_as_ptr.fixed

@@ -3,6 +3,8 @@
 
 fn f<T>(_: T) {}
 
+static STATIC_I32: i32 = 42;
+
 fn main() {
     f(std::ptr::from_ref(&1u8));
     //~^ ref_as_ptr
@@ -63,6 +65,9 @@ fn main() {
     f(std::ptr::from_ref::<i32>(&val) as *const f64);
     //~^ ref_as_ptr
 
+    let _ptr_from_local: *const i32 = std::ptr::from_ref(&val);
+    //~^ ref_as_ptr
+
     let mut val: u8 = 2;
     f(std::ptr::from_mut::<u8>(&mut val));
     //~^ ref_as_ptr
@@ -86,6 +91,9 @@ fn main() {
     f(std::ptr::from_mut::<[usize; 9]>(&mut std::array::from_fn(|i| i * i)));
     //~^ ref_as_ptr
 
+    let _ptr_from_static: *const i32 = std::ptr::from_ref(&STATIC_I32);
+    //~^ ref_as_ptr
+
     let _ = &String::new() as *const _;
     let _ = &mut String::new() as *mut _;
     const FOO: *const String = &String::new() as *const _;

src/tools/clippy/tests/ui/ref_as_ptr.rs

@@ -3,6 +3,8 @@
 
 fn f<T>(_: T) {}
 
+static STATIC_I32: i32 = 42;
+
 fn main() {
     f(&1u8 as *const _);
     //~^ ref_as_ptr
@@ -63,6 +65,9 @@ fn main() {
     f(&val as *const i32 as *const f64);
     //~^ ref_as_ptr
 
+    let _ptr_from_local: *const i32 = &val as *const _;
+    //~^ ref_as_ptr
+
     let mut val: u8 = 2;
     f(&mut val as *mut u8);
     //~^ ref_as_ptr
@@ -86,6 +91,9 @@ fn main() {
     f(&mut std::array::from_fn(|i| i * i) as *mut [usize; 9]);
     //~^ ref_as_ptr
 
+    let _ptr_from_static: *const i32 = &STATIC_I32 as *const _;
+    //~^ ref_as_ptr
+
     let _ = &String::new() as *const _;
     let _ = &mut String::new() as *mut _;
     const FOO: *const String = &String::new() as *const _;