From 0e5b1b19f540936fa12f89ae307ab129485a3d86 Mon Sep 17 00:00:00 2001
From: Ada Alakbarova <ada.alakbarova@proton.me>
Date: Wed, 13 Aug 2025 17:12:33 +0200
Subject: [PATCH] clean-up `ptr_cast_constness`

use `Mutability::ptr_str`

replace `matches!` with an equality check

avoid always allocating a `String`

s/cast_expr/cast_from_expr -- for more consistency with the naming in `mod.rs`
---
 clippy_lints/src/casts/ptr_cast_constness.rs | 27 ++++++++------------
 1 file changed, 11 insertions(+), 16 deletions(-)

diff --git a/clippy_lints/src/casts/ptr_cast_constness.rs b/clippy_lints/src/casts/ptr_cast_constness.rs
index c0c0a47f8551..5ab399152519 100644
--- a/clippy_lints/src/casts/ptr_cast_constness.rs
+++ b/clippy_lints/src/casts/ptr_cast_constness.rs
@@ -1,9 +1,10 @@
 use clippy_utils::diagnostics::span_lint_and_sugg;
 use clippy_utils::msrvs::{self, Msrv};
+use clippy_utils::source::snippet_with_applicability;
 use clippy_utils::sugg::Sugg;
 use clippy_utils::{std_or_core, sym};
 use rustc_errors::Applicability;
-use rustc_hir::{Expr, ExprKind, Mutability, QPath};
+use rustc_hir::{Expr, ExprKind, QPath};
 use rustc_lint::LateContext;
 use rustc_middle::ty::{self, Ty, TypeVisitableExt};
 
@@ -12,26 +13,23 @@ use super::PTR_CAST_CONSTNESS;
 pub(super) fn check<'tcx>(
     cx: &LateContext<'_>,
     expr: &Expr<'_>,
-    cast_expr: &Expr<'_>,
+    cast_from_expr: &Expr<'_>,
     cast_from: Ty<'tcx>,
     cast_to: Ty<'tcx>,
     msrv: Msrv,
 ) {
     if let ty::RawPtr(from_ty, from_mutbl) = cast_from.kind()
         && let ty::RawPtr(to_ty, to_mutbl) = cast_to.kind()
-        && matches!(
-            (from_mutbl, to_mutbl),
-            (Mutability::Not, Mutability::Mut) | (Mutability::Mut, Mutability::Not)
-        )
+        && from_mutbl != to_mutbl
         && from_ty == to_ty
         && !from_ty.has_erased_regions()
     {
-        if let ExprKind::Call(func, []) = cast_expr.kind
+        if let ExprKind::Call(func, []) = cast_from_expr.kind
             && let ExprKind::Path(QPath::Resolved(None, path)) = func.kind
             && let Some(defid) = path.res.opt_def_id()
             && let Some(prefix) = std_or_core(cx)
             && let mut app = Applicability::MachineApplicable
-            && let sugg = format!("{}", Sugg::hir_with_applicability(cx, cast_expr, "_", &mut app))
+            && let sugg = snippet_with_applicability(cx, cast_from_expr.span, "_", &mut app)
             && let Some((_, after_lt)) = sugg.split_once("::<")
             && let Some((source, target, target_func)) = match cx.tcx.get_diagnostic_name(defid) {
                 Some(sym::ptr_null) => Some(("const", "mutable", "null_mut")),
@@ -53,11 +51,8 @@ pub(super) fn check<'tcx>(
 
         if msrv.meets(cx, msrvs::POINTER_CAST_CONSTNESS) {
             let mut app = Applicability::MachineApplicable;
-            let sugg = Sugg::hir_with_context(cx, cast_expr, expr.span.ctxt(), "_", &mut app);
-            let constness = match *to_mutbl {
-                Mutability::Not => "const",
-                Mutability::Mut => "mut",
-            };
+            let sugg = Sugg::hir_with_context(cx, cast_from_expr, expr.span.ctxt(), "_", &mut app);
+            let constness = to_mutbl.ptr_str();
 
             span_lint_and_sugg(
                 cx,
@@ -73,8 +68,8 @@ pub(super) fn check<'tcx>(
 }
 
 pub(super) fn check_null_ptr_cast_method(cx: &LateContext<'_>, expr: &Expr<'_>) {
-    if let ExprKind::MethodCall(method, cast_expr, [], _) = expr.kind
-        && let ExprKind::Call(func, []) = cast_expr.kind
+    if let ExprKind::MethodCall(method, cast_from_expr, [], _) = expr.kind
+        && let ExprKind::Call(func, []) = cast_from_expr.kind
         && let ExprKind::Path(QPath::Resolved(None, path)) = func.kind
         && let Some(defid) = path.res.opt_def_id()
         && let method = match (cx.tcx.get_diagnostic_name(defid), method.ident.name) {
@@ -84,7 +79,7 @@ pub(super) fn check_null_ptr_cast_method(cx: &LateContext<'_>, expr: &Expr<'_>)
         }
         && let Some(prefix) = std_or_core(cx)
         && let mut app = Applicability::MachineApplicable
-        && let sugg = format!("{}", Sugg::hir_with_applicability(cx, cast_expr, "_", &mut app))
+        && let sugg = snippet_with_applicability(cx, cast_from_expr.span, "_", &mut app)
         && let Some((_, after_lt)) = sugg.split_once("::<")
     {
         span_lint_and_sugg(