Add ref_as_ptr lint

Author:    Marcin Serwin <marcin.serwin0@protonmail.com>

clippy_lints/src/casts/mod.rs

@@ -18,6 +18,7 @@ mod fn_to_numeric_cast_any;
 mod fn_to_numeric_cast_with_truncation;
 mod ptr_as_ptr;
 mod ptr_cast_constness;
+mod ref_as_ptr;
 mod unnecessary_cast;
 mod utils;
 mod zero_ptr;
@@ -689,6 +690,30 @@ declare_clippy_lint! {
     "using `0 as *{const, mut} T`"
 }
 
+declare_clippy_lint! {
+    /// ### What it does
+    /// Checks for casts of references to pointer using `as`
+    /// and suggests `std::ptr::from_ref` and `std::ptr::from_mut` instead.
+    ///
+    /// ### Why is this bad?
+    /// Using `as` casts may result in silently changing mutability or type.
+    ///
+    /// ### Example
+    /// ```no_run
+    /// let a_ref = &1;
+    /// let a_ptr = a_ref as *const _;
+    /// ```
+    /// Use instead:
+    /// ```no_run
+    /// let a_ref = &1;
+    /// let a_ptr = std::ptr::from_ref(a_ref);
+    /// ```
+    #[clippy::version = "1.77.0"]
+    pub REF_AS_PTR,
+    pedantic,
+    "using `as` to cast a reference to pointer"
+}
+
 pub struct Casts {
     msrv: Msrv,
 }
@@ -724,6 +749,7 @@ impl_lint_pass!(Casts => [
     AS_PTR_CAST_MUT,
     CAST_NAN_TO_INT,
     ZERO_PTR,
+    REF_AS_PTR,
 ]);
 
 impl<'tcx> LateLintPass<'tcx> for Casts {
@@ -771,7 +797,9 @@ impl<'tcx> LateLintPass<'tcx> for Casts {
 
             as_underscore::check(cx, expr, cast_to_hir);
 
-            if self.msrv.meets(msrvs::BORROW_AS_PTR) {
+            if self.msrv.meets(msrvs::PTR_FROM_REF) {
+                ref_as_ptr::check(cx, expr, cast_expr, cast_to_hir);
+            } else if self.msrv.meets(msrvs::BORROW_AS_PTR) {
                 borrow_as_ptr::check(cx, expr, cast_expr, cast_to_hir);
             }
         }

clippy_lints/src/casts/ref_as_ptr.rs

@@ -0,0 +1,55 @@
+use clippy_utils::diagnostics::span_lint_and_sugg;
+use clippy_utils::is_no_std_crate;
+use clippy_utils::source::snippet_with_applicability;
+use clippy_utils::sugg::Sugg;
+use rustc_errors::Applicability;
+use rustc_hir::{Expr, Mutability, Ty, TyKind};
+use rustc_lint::LateContext;
+use rustc_middle::ty::{self, TypeAndMut};
+
+use super::REF_AS_PTR;
+
+pub(super) fn check(cx: &LateContext<'_>, expr: &Expr<'_>, cast_expr: &Expr<'_>, cast_to_hir_ty: &Ty<'_>) {
+    let (cast_from, cast_to) = (
+        cx.typeck_results().expr_ty(cast_expr),
+        cx.typeck_results().expr_ty(expr),
+    );
+
+    if matches!(cast_from.kind(), ty::Ref(..))
+        && let ty::RawPtr(TypeAndMut { mutbl: to_mutbl, .. }) = cast_to.kind()
+    {
+        let core_or_std = if is_no_std_crate(cx) { "core" } else { "std" };
+        let fn_name = match to_mutbl {
+            Mutability::Not => "from_ref",
+            Mutability::Mut => "from_mut",
+        };
+
+        let mut app = Applicability::MachineApplicable;
+        let turbofish = match &cast_to_hir_ty.kind {
+            TyKind::Infer => String::new(),
+            TyKind::Ptr(mut_ty) => {
+                if matches!(mut_ty.ty.kind, TyKind::Infer) {
+                    String::new()
+                } else {
+                    format!(
+                        "::<{}>",
+                        snippet_with_applicability(cx, mut_ty.ty.span, "/* type */", &mut app)
+                    )
+                }
+            },
+            _ => return,
+        };
+
+        let cast_expr_sugg = Sugg::hir_with_applicability(cx, cast_expr, "_", &mut app);
+
+        span_lint_and_sugg(
+            cx,
+            REF_AS_PTR,
+            expr.span,
+            "reference as raw pointer",
+            "try",
+            format!("{core_or_std}::ptr::{fn_name}{turbofish}({cast_expr_sugg})"),
+            app,
+        );
+    }
+}

clippy_lints/src/declared_lints.rs

@@ -96,6 +96,7 @@ pub(crate) static LINTS: &[&crate::LintInfo] = &[
     crate::casts::FN_TO_NUMERIC_CAST_WITH_TRUNCATION_INFO,
     crate::casts::PTR_AS_PTR_INFO,
     crate::casts::PTR_CAST_CONSTNESS_INFO,
+    crate::casts::REF_AS_PTR_INFO,
     crate::casts::UNNECESSARY_CAST_INFO,
     crate::casts::ZERO_PTR_INFO,
     crate::checked_conversions::CHECKED_CONVERSIONS_INFO,

clippy_lints/src/only_used_in_recursion.rs

@@ -252,7 +252,7 @@ impl<'tcx> LateLintPass<'tcx> for OnlyUsedInRecursion {
                 {
                     (
                         trait_item_id,
-                        FnKind::ImplTraitFn(cx.tcx.erase_regions(trait_ref.args) as *const _ as usize),
+                        FnKind::ImplTraitFn(std::ptr::from_ref(cx.tcx.erase_regions(trait_ref.args)) as usize),
                         usize::from(sig.decl.implicit_self.has_implicit_self()),
                     )
                 } else {
@@ -390,7 +390,6 @@ fn has_matching_args(kind: FnKind, args: GenericArgsRef<'_>) -> bool {
             GenericArgKind::Type(ty) => matches!(*ty.kind(), ty::Param(ty) if ty.index as usize == idx),
             GenericArgKind::Const(c) => matches!(c.kind(), ConstKind::Param(c) if c.index as usize == idx),
         }),
-        #[allow(trivial_casts)]
-        FnKind::ImplTraitFn(expected_args) => args as *const _ as usize == expected_args,
+        FnKind::ImplTraitFn(expected_args) => std::ptr::from_ref(args) as usize == expected_args,
     }
 }