cast_slice_from_raw_parts: check for implicit cast to raw slice pointer

zihan0822 · zihan0822 · commit 02111a4d30fa · 2025-08-23T18:53:59.000-04:00
changelog: [`cast_slice_from_raw_parts`]: check for implicit cast to raw slice pointer

Signed-off-by: Zihan &lt;zihanli0822@gmail.com&gt;
diff --git a/clippy_lints/src/casts/cast_slice_from_raw_parts.rs b/clippy_lints/src/casts/cast_slice_from_raw_parts.rs
@@ -1,10 +1,12 @@
 use clippy_utils::diagnostics::span_lint_and_sugg;
+use clippy_utils::get_parent_expr;
 use clippy_utils::msrvs::{self, Msrv};
 use clippy_utils::source::snippet_with_context;
 use rustc_errors::Applicability;
 use rustc_hir::def_id::DefId;
 use rustc_hir::{Expr, ExprKind};
 use rustc_lint::LateContext;
+use rustc_middle::ty::adjustment::{Adjust, Adjustment, AutoBorrow};
 use rustc_middle::ty::{self, Ty};
 use rustc_span::sym;
 
@@ -53,3 +55,40 @@ pub(super) fn check(cx: &LateContext<'_>, expr: &Expr<'_>, cast_expr: &Expr<'_>,
         );
     }
 }
+
+/// Checks for implicit cast from slice reference to raw slice pointer.
+pub(super) fn check_implicit_cast(cx: &LateContext<'_>, expr: &Expr<'_>) {
+    if let ExprKind::Call(fun, [ptr_arg, len_arg]) = expr.peel_blocks().kind
+        && let ExprKind::Path(ref qpath) = fun.kind
+        && let Some(fun_def_id) = cx.qpath_res(qpath, fun.hir_id).opt_def_id()
+        && let Some(rpk) = raw_parts_kind(cx, fun_def_id)
+        && !matches!(get_parent_expr(cx, expr).map(|e| e.kind), Some(ExprKind::Cast(..)))
+        && let [deref, borrow] = cx.typeck_results().expr_adjustments(expr)
+        && matches!(deref.kind, Adjust::Deref(..))
+        && let Adjustment {
+            kind: Adjust::Borrow(AutoBorrow::RawPtr(..)),
+            target,
+        } = borrow
+        && let ty::RawPtr(pointee_ty, _) = target.kind()
+        && pointee_ty.is_slice()
+        && !expr.span.from_expansion()
+    {
+        let func = match rpk {
+            RawPartsKind::Immutable => "from_raw_parts",
+            RawPartsKind::Mutable => "from_raw_parts_mut",
+        };
+        let mut applicability = Applicability::MachineApplicable;
+        let ctxt = expr.span.ctxt();
+        let ptr = snippet_with_context(cx, ptr_arg.span, ctxt, "ptr", &mut applicability).0;
+        let len = snippet_with_context(cx, len_arg.span, ctxt, "len", &mut applicability).0;
+        span_lint_and_sugg(
+            cx,
+            CAST_SLICE_FROM_RAW_PARTS,
+            expr.span,
+            format!("implicitly casting the result of `{func}` to `{target}`"),
+            "replace_with",
+            format!("core::ptr::slice_{func}({ptr}, {len})"),
+            applicability,
+        );
+    }
+}
diff --git a/clippy_lints/src/casts/mod.rs b/clippy_lints/src/casts/mod.rs
@@ -910,6 +910,9 @@ impl<'tcx> LateLintPass<'tcx> for Casts {
         if self.msrv.meets(cx, msrvs::RAW_REF_OP) {
             borrow_as_ptr::check_implicit_cast(cx, expr);
         }
+        if self.msrv.meets(cx, msrvs::PTR_SLICE_RAW_PARTS) {
+            cast_slice_from_raw_parts::check_implicit_cast(cx, expr);
+        }
         cast_ptr_alignment::check(cx, expr);
         char_lit_as_u8::check(cx, expr);
         ptr_as_ptr::check(cx, expr, self.msrv);
diff --git a/tests/ui/cast_raw_slice_pointer_cast.fixed b/tests/ui/cast_raw_slice_pointer_cast.fixed
@@ -1,6 +1,7 @@
 #![warn(clippy::cast_slice_from_raw_parts)]
 
-#[allow(unused_imports, unused_unsafe)]
+const fn require_raw_slice_ptr<T>(_: *const [T]) {}
+
 fn main() {
     let mut vec = vec![0u8; 1];
     let ptr: *const u8 = vec.as_ptr();
@@ -27,4 +28,26 @@ fn main() {
         let _: *const [u8] = core::ptr::slice_from_raw_parts(ptr, 1);
         //~^ cast_slice_from_raw_parts
     }
+
+    // implicit cast
+    {
+        let _: *const [u8] = unsafe { core::ptr::slice_from_raw_parts(ptr, 1) };
+        //~^ cast_slice_from_raw_parts
+        let _: *mut [u8] = unsafe { core::ptr::slice_from_raw_parts_mut(mptr, 1) };
+        //~^ cast_slice_from_raw_parts
+        require_raw_slice_ptr(unsafe { core::ptr::slice_from_raw_parts(ptr, 1) });
+        //~^ cast_slice_from_raw_parts
+    }
+
+    // implicit cast in const context
+    const {
+        const PTR: *const u8 = std::ptr::null();
+        const MPTR: *mut u8 = std::ptr::null_mut();
+        let _: *const [u8] = unsafe { std::ptr::slice_from_raw_parts(PTR, 1) };
+        //~^ cast_slice_from_raw_parts
+        let _: *mut [u8] = unsafe { std::ptr::slice_from_raw_parts_mut(MPTR, 1) };
+        //~^ cast_slice_from_raw_parts
+        require_raw_slice_ptr(unsafe { std::ptr::slice_from_raw_parts(PTR, 1) });
+        //~^ cast_slice_from_raw_parts
+    };
 }
diff --git a/tests/ui/cast_raw_slice_pointer_cast.rs b/tests/ui/cast_raw_slice_pointer_cast.rs
@@ -1,6 +1,7 @@
 #![warn(clippy::cast_slice_from_raw_parts)]
 
-#[allow(unused_imports, unused_unsafe)]
+const fn require_raw_slice_ptr<T>(_: *const [T]) {}
+
 fn main() {
     let mut vec = vec![0u8; 1];
     let ptr: *const u8 = vec.as_ptr();
@@ -27,4 +28,26 @@ fn main() {
         let _: *const [u8] = unsafe { one::from_raw_parts(ptr, 1) } as *const [u8];
         //~^ cast_slice_from_raw_parts
     }
+
+    // implicit cast
+    {
+        let _: *const [u8] = unsafe { std::slice::from_raw_parts(ptr, 1) };
+        //~^ cast_slice_from_raw_parts
+        let _: *mut [u8] = unsafe { std::slice::from_raw_parts_mut(mptr, 1) };
+        //~^ cast_slice_from_raw_parts
+        require_raw_slice_ptr(unsafe { std::slice::from_raw_parts(ptr, 1) });
+        //~^ cast_slice_from_raw_parts
+    }
+
+    // implicit cast in const context
+    const {
+        const PTR: *const u8 = std::ptr::null();
+        const MPTR: *mut u8 = std::ptr::null_mut();
+        let _: *const [u8] = unsafe { std::slice::from_raw_parts(PTR, 1) };
+        //~^ cast_slice_from_raw_parts
+        let _: *mut [u8] = unsafe { std::slice::from_raw_parts_mut(MPTR, 1) };
+        //~^ cast_slice_from_raw_parts
+        require_raw_slice_ptr(unsafe { std::slice::from_raw_parts(PTR, 1) });
+        //~^ cast_slice_from_raw_parts
+    };
 }
diff --git a/tests/ui/cast_raw_slice_pointer_cast.stderr b/tests/ui/cast_raw_slice_pointer_cast.stderr
@@ -1,5 +1,5 @@
 error: casting the result of `from_raw_parts` to *const [u8]
-  --> tests/ui/cast_raw_slice_pointer_cast.rs:8:35
+  --> tests/ui/cast_raw_slice_pointer_cast.rs:9:35
    |
 LL |     let _: *const [u8] = unsafe { std::slice::from_raw_parts(ptr, 1) as *const [u8] };
    |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: replace with: `core::ptr::slice_from_raw_parts(ptr, 1)`
@@ -8,40 +8,76 @@ LL |     let _: *const [u8] = unsafe { std::slice::from_raw_parts(ptr, 1) as *co
    = help: to override `-D warnings` add `#[allow(clippy::cast_slice_from_raw_parts)]`
 
 error: casting the result of `from_raw_parts_mut` to *mut [u8]
-  --> tests/ui/cast_raw_slice_pointer_cast.rs:10:35
+  --> tests/ui/cast_raw_slice_pointer_cast.rs:11:35
    |
 LL |     let _: *const [u8] = unsafe { std::slice::from_raw_parts_mut(mptr, 1) as *mut [u8] };
    |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: replace with: `core::ptr::slice_from_raw_parts_mut(mptr, 1)`
 
 error: casting the result of `from_raw_parts` to *const [u8]
-  --> tests/ui/cast_raw_slice_pointer_cast.rs:12:26
+  --> tests/ui/cast_raw_slice_pointer_cast.rs:13:26
    |
 LL |     let _: *const [u8] = unsafe { std::slice::from_raw_parts(ptr, 1) } as *const [u8];
    |                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: replace with: `core::ptr::slice_from_raw_parts(ptr, 1)`
 
 error: casting the result of `from_raw_parts` to *const [u8]
-  --> tests/ui/cast_raw_slice_pointer_cast.rs:16:30
+  --> tests/ui/cast_raw_slice_pointer_cast.rs:17:30
    |
 LL |         let _: *const [u8] = unsafe { slice::from_raw_parts(ptr, 1) } as *const [u8];
    |                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: replace with: `core::ptr::slice_from_raw_parts(ptr, 1)`
 
 error: casting the result of `from_raw_parts` to *const [u8]
-  --> tests/ui/cast_raw_slice_pointer_cast.rs:19:30
+  --> tests/ui/cast_raw_slice_pointer_cast.rs:20:30
    |
 LL |         let _: *const [u8] = unsafe { one::from_raw_parts(ptr, 1) } as *const [u8];
    |                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: replace with: `core::ptr::slice_from_raw_parts(ptr, 1)`
 
 error: casting the result of `from_raw_parts` to *const [u8]
-  --> tests/ui/cast_raw_slice_pointer_cast.rs:24:30
+  --> tests/ui/cast_raw_slice_pointer_cast.rs:25:30
    |
 LL |         let _: *const [u8] = unsafe { slice::from_raw_parts(ptr, 1) } as *const [u8];
    |                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: replace with: `core::ptr::slice_from_raw_parts(ptr, 1)`
 
 error: casting the result of `from_raw_parts` to *const [u8]
-  --> tests/ui/cast_raw_slice_pointer_cast.rs:27:30
+  --> tests/ui/cast_raw_slice_pointer_cast.rs:28:30
    |
 LL |         let _: *const [u8] = unsafe { one::from_raw_parts(ptr, 1) } as *const [u8];
    |                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: replace with: `core::ptr::slice_from_raw_parts(ptr, 1)`
 
-error: aborting due to 7 previous errors
+error: implicitly casting the result of `from_raw_parts` to `*const [u8]`
+  --> tests/ui/cast_raw_slice_pointer_cast.rs:34:39
+   |
+LL |         let _: *const [u8] = unsafe { std::slice::from_raw_parts(ptr, 1) };
+   |                                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: replace_with: `core::ptr::slice_from_raw_parts(ptr, 1)`
+
+error: implicitly casting the result of `from_raw_parts_mut` to `*mut [u8]`
+  --> tests/ui/cast_raw_slice_pointer_cast.rs:36:37
+   |
+LL |         let _: *mut [u8] = unsafe { std::slice::from_raw_parts_mut(mptr, 1) };
+   |                                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: replace_with: `core::ptr::slice_from_raw_parts_mut(mptr, 1)`
+
+error: implicitly casting the result of `from_raw_parts` to `*const [u8]`
+  --> tests/ui/cast_raw_slice_pointer_cast.rs:38:40
+   |
+LL |         require_raw_slice_ptr(unsafe { std::slice::from_raw_parts(ptr, 1) });
+   |                                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: replace_with: `core::ptr::slice_from_raw_parts(ptr, 1)`
+
+error: implicitly casting the result of `from_raw_parts` to `*const [u8]`
+  --> tests/ui/cast_raw_slice_pointer_cast.rs:46:39
+   |
+LL |         let _: *const [u8] = unsafe { std::slice::from_raw_parts(PTR, 1) };
+   |                                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: replace_with: `std::ptr::slice_from_raw_parts(PTR, 1)`
+
+error: implicitly casting the result of `from_raw_parts_mut` to `*mut [u8]`
+  --> tests/ui/cast_raw_slice_pointer_cast.rs:48:37
+   |
+LL |         let _: *mut [u8] = unsafe { std::slice::from_raw_parts_mut(MPTR, 1) };
+   |                                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: replace_with: `std::ptr::slice_from_raw_parts_mut(MPTR, 1)`
+
+error: implicitly casting the result of `from_raw_parts` to `*const [u8]`
+  --> tests/ui/cast_raw_slice_pointer_cast.rs:50:40
+   |
+LL |         require_raw_slice_ptr(unsafe { std::slice::from_raw_parts(PTR, 1) });
+   |                                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: replace_with: `std::ptr::slice_from_raw_parts(PTR, 1)`
+
+error: aborting due to 13 previous errors
 
