Fix clippy::ref_as_ptr for non-temporary references in let/const (#16214)

Fix `ref_as_ptr` false positives for temporary values and
let/static/const initializers.

Fixes #16220

changelog: [`ref_as_ptr`]: Only lint on non-temporary expressions)

Author: Jarcho

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 let ExprKind::AddrOf(_, _, addr_inner) = cast_expr.kind
+            && is_expr_temporary_value(cx, addr_inner)
+            && matches!(
+                use_cx.use_node(cx),
+                ExprUseNode::LetStmt(_) | ExprUseNode::ConstStatic(_)
+            )
+        {
+            return;
+        }
+
         let fn_name = match to_mutbl {
             Mutability::Not => "from_ref",
             Mutability::Mut => "from_mut",

tests/ui/ref_as_ptr.fixed

@@ -86,6 +86,16 @@ fn main() {
     f(std::ptr::from_mut::<[usize; 9]>(&mut std::array::from_fn(|i| i * i)));
     //~^ ref_as_ptr
 
+    let x = (10, 20);
+    let _ = std::ptr::from_ref(&x);
+    //~^ ref_as_ptr
+    let _ = std::ptr::from_ref(&x.0);
+    //~^ ref_as_ptr
+
+    let x = Box::new(10);
+    let _ = std::ptr::from_ref(&*x);
+    //~^ ref_as_ptr
+
     let _ = &String::new() as *const _;
     let _ = &mut String::new() as *mut _;
     const FOO: *const String = &String::new() as *const _;

tests/ui/ref_as_ptr.rs

@@ -86,6 +86,16 @@ fn main() {
     f(&mut std::array::from_fn(|i| i * i) as *mut [usize; 9]);
     //~^ ref_as_ptr
 
+    let x = (10, 20);
+    let _ = &x as *const _;
+    //~^ ref_as_ptr
+    let _ = &x.0 as *const _;
+    //~^ ref_as_ptr
+
+    let x = Box::new(10);
+    let _ = &*x as *const _;
+    //~^ ref_as_ptr
+
     let _ = &String::new() as *const _;
     let _ = &mut String::new() as *mut _;
     const FOO: *const String = &String::new() as *const _;

tests/ui/ref_as_ptr.stderr

@@ -200,70 +200,88 @@ LL |     f(&mut std::array::from_fn(|i| i * i) as *mut [usize; 9]);
    |       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `std::ptr::from_mut::<[usize; 9]>(&mut std::array::from_fn(|i| i * i))`
 
 error: reference as raw pointer
-  --> tests/ui/ref_as_ptr.rs:109:7
+  --> tests/ui/ref_as_ptr.rs:90:13
+   |
+LL |     let _ = &x as *const _;
+   |             ^^^^^^^^^^^^^^ help: try: `std::ptr::from_ref(&x)`
+
+error: reference as raw pointer
+  --> tests/ui/ref_as_ptr.rs:92:13
+   |
+LL |     let _ = &x.0 as *const _;
+   |             ^^^^^^^^^^^^^^^^ help: try: `std::ptr::from_ref(&x.0)`
+
+error: reference as raw pointer
+  --> tests/ui/ref_as_ptr.rs:96:13
+   |
+LL |     let _ = &*x as *const _;
+   |             ^^^^^^^^^^^^^^^ help: try: `std::ptr::from_ref(&*x)`
+
+error: reference as raw pointer
+  --> tests/ui/ref_as_ptr.rs:119:7
    |
 LL |     f(val as *const i32);
    |       ^^^^^^^^^^^^^^^^^ help: try: `std::ptr::from_ref::<i32>(val)`
 
 error: reference as raw pointer
-  --> tests/ui/ref_as_ptr.rs:111:7
+  --> tests/ui/ref_as_ptr.rs:121:7
    |
 LL |     f(mut_val as *mut i32);
    |       ^^^^^^^^^^^^^^^^^^^ help: try: `std::ptr::from_mut::<i32>(mut_val)`
 
 error: reference as raw pointer
-  --> tests/ui/ref_as_ptr.rs:116:7
+  --> tests/ui/ref_as_ptr.rs:126:7
    |
 LL |     f(val as *const _);
    |       ^^^^^^^^^^^^^^^ help: try: `std::ptr::from_ref(val)`
 
 error: reference as raw pointer
-  --> tests/ui/ref_as_ptr.rs:118:7
+  --> tests/ui/ref_as_ptr.rs:128:7
    |
 LL |     f(val as *const [u8]);
    |       ^^^^^^^^^^^^^^^^^^ help: try: `std::ptr::from_ref::<[u8]>(val)`
 
 error: reference as raw pointer
-  --> tests/ui/ref_as_ptr.rs:123:7
+  --> tests/ui/ref_as_ptr.rs:133:7
    |
 LL |     f(val as *mut _);
    |       ^^^^^^^^^^^^^ help: try: `std::ptr::from_mut(val)`
 
 error: reference as raw pointer
-  --> tests/ui/ref_as_ptr.rs:125:7
+  --> tests/ui/ref_as_ptr.rs:135:7
    |
 LL |     f(val as *mut str);
    |       ^^^^^^^^^^^^^^^ help: try: `std::ptr::from_mut::<str>(val)`
 
 error: reference as raw pointer
-  --> tests/ui/ref_as_ptr.rs:133:9
+  --> tests/ui/ref_as_ptr.rs:143:9
    |
 LL |         self.0 as *const _ as *const _
    |         ^^^^^^^^^^^^^^^^^^ help: try: `std::ptr::from_ref(self.0)`
 
 error: reference as raw pointer
-  --> tests/ui/ref_as_ptr.rs:138:9
+  --> tests/ui/ref_as_ptr.rs:148:9
    |
 LL |         self.0 as *const _ as *const _
    |         ^^^^^^^^^^^^^^^^^^ help: try: `std::ptr::from_ref(self.0)`
 
 error: reference as raw pointer
-  --> tests/ui/ref_as_ptr.rs:147:9
+  --> tests/ui/ref_as_ptr.rs:157:9
    |
 LL |         self.0 as *const _ as *const _
    |         ^^^^^^^^^^^^^^^^^^ help: try: `std::ptr::from_ref(self.0)`
 
 error: reference as raw pointer
-  --> tests/ui/ref_as_ptr.rs:152:9
+  --> tests/ui/ref_as_ptr.rs:162:9
    |
 LL |         self.0 as *const _ as *const _
    |         ^^^^^^^^^^^^^^^^^^ help: try: `std::ptr::from_ref(self.0)`
 
 error: reference as raw pointer
-  --> tests/ui/ref_as_ptr.rs:157:9
+  --> tests/ui/ref_as_ptr.rs:167:9
    |
 LL |         self.0 as *mut _ as *mut _
    |         ^^^^^^^^^^^^^^^^ help: try: `std::ptr::from_mut(self.0)`
 
-error: aborting due to 44 previous errors
+error: aborting due to 47 previous errors