Refactor ptr_offset_with_cast (#15613)

Putting this lint in `/methods` is simpler and probably slightly more
efficient.

changelog: [`ptr_offset_with_cast`]: respect MSRV when suggesting fix,
and lint even more cases

Author: samueltardieu

clippy_lints/src/declared_lints.rs

@@ -448,6 +448,7 @@ pub static LINTS: &[&::declare_clippy_lint::LintInfo] = &[
     crate::methods::OR_THEN_UNWRAP_INFO,
     crate::methods::PATH_BUF_PUSH_OVERWRITE_INFO,
     crate::methods::PATH_ENDS_WITH_EXT_INFO,
+    crate::methods::PTR_OFFSET_WITH_CAST_INFO,
     crate::methods::RANGE_ZIP_WITH_LEN_INFO,
     crate::methods::READONLY_WRITE_LOCK_INFO,
     crate::methods::READ_LINE_WITHOUT_TRIM_INFO,
@@ -624,7 +625,6 @@ pub static LINTS: &[&::declare_clippy_lint::LintInfo] = &[
     crate::ptr::MUT_FROM_REF_INFO,
     crate::ptr::PTR_ARG_INFO,
     crate::ptr::PTR_EQ_INFO,
-    crate::ptr_offset_with_cast::PTR_OFFSET_WITH_CAST_INFO,
     crate::pub_underscore_fields::PUB_UNDERSCORE_FIELDS_INFO,
     crate::pub_use::PUB_USE_INFO,
     crate::question_mark::QUESTION_MARK_INFO,

clippy_lints/src/lib.rs

@@ -302,7 +302,6 @@ mod permissions_set_readonly_false;
 mod pointers_in_nomem_asm_block;
 mod precedence;
 mod ptr;
-mod ptr_offset_with_cast;
 mod pub_underscore_fields;
 mod pub_use;
 mod question_mark;
@@ -593,7 +592,6 @@ pub fn register_lint_passes(store: &mut rustc_lint::LintStore, conf: &'static Co
     store.register_late_pass(|_| Box::new(unwrap::Unwrap));
     store.register_late_pass(move |_| Box::new(indexing_slicing::IndexingSlicing::new(conf)));
     store.register_late_pass(move |tcx| Box::new(non_copy_const::NonCopyConst::new(tcx, conf)));
-    store.register_late_pass(|_| Box::new(ptr_offset_with_cast::PtrOffsetWithCast));
     store.register_late_pass(|_| Box::new(redundant_clone::RedundantClone));
     store.register_late_pass(|_| Box::new(slow_vector_initialization::SlowVectorInit));
     store.register_late_pass(move |_| Box::new(unnecessary_wraps::UnnecessaryWraps::new(conf)));

clippy_lints/src/methods/mod.rs

@@ -91,6 +91,7 @@ mod or_fun_call;
 mod or_then_unwrap;
 mod path_buf_push_overwrite;
 mod path_ends_with_ext;
+mod ptr_offset_with_cast;
 mod range_zip_with_len;
 mod read_line_without_trim;
 mod readonly_write_lock;
@@ -1725,6 +1726,43 @@ declare_clippy_lint! {
     "Check for offset calculations on raw pointers to zero-sized types"
 }
 
+declare_clippy_lint! {
+    /// ### What it does
+    /// Checks for usage of the `offset` pointer method with a `usize` casted to an
+    /// `isize`.
+    ///
+    /// ### Why is this bad?
+    /// If we’re always increasing the pointer address, we can avoid the numeric
+    /// cast by using the `add` method instead.
+    ///
+    /// ### Example
+    /// ```no_run
+    /// let vec = vec![b'a', b'b', b'c'];
+    /// let ptr = vec.as_ptr();
+    /// let offset = 1_usize;
+    ///
+    /// unsafe {
+    ///     ptr.offset(offset as isize);
+    /// }
+    /// ```
+    ///
+    /// Could be written:
+    ///
+    /// ```no_run
+    /// let vec = vec![b'a', b'b', b'c'];
+    /// let ptr = vec.as_ptr();
+    /// let offset = 1_usize;
+    ///
+    /// unsafe {
+    ///     ptr.add(offset);
+    /// }
+    /// ```
+    #[clippy::version = "1.30.0"]
+    pub PTR_OFFSET_WITH_CAST,
+    complexity,
+    "unneeded pointer offset cast"
+}
+
 declare_clippy_lint! {
     /// ### What it does
     /// Checks for `FileType::is_file()`.
@@ -4665,6 +4703,7 @@ impl_lint_pass!(Methods => [
     UNINIT_ASSUMED_INIT,
     MANUAL_SATURATING_ARITHMETIC,
     ZST_OFFSET,
+    PTR_OFFSET_WITH_CAST,
     FILETYPE_IS_FILE,
     OPTION_AS_REF_DEREF,
     UNNECESSARY_LAZY_EVALUATIONS,
@@ -4960,10 +4999,7 @@ impl Methods {
         // Handle method calls whose receiver and arguments may not come from expansion
         if let Some((name, recv, args, span, call_span)) = method_call(expr) {
             match (name, args) {
-                (
-                    sym::add | sym::offset | sym::sub | sym::wrapping_offset | sym::wrapping_add | sym::wrapping_sub,
-                    [_arg],
-                ) => {
+                (sym::add | sym::sub | sym::wrapping_add | sym::wrapping_sub, [_arg]) => {
                     zst_offset::check(cx, expr, recv);
                 },
                 (sym::all, [arg]) => {
@@ -5334,6 +5370,11 @@ impl Methods {
                     },
                     _ => iter_nth_zero::check(cx, expr, recv, n_arg),
                 },
+                (sym::offset | sym::wrapping_offset, [arg]) => {
+                    zst_offset::check(cx, expr, recv);
+
+                    ptr_offset_with_cast::check(cx, name, expr, recv, arg, self.msrv);
+                },
                 (sym::ok_or_else, [arg]) => {
                     unnecessary_lazy_eval::check(cx, expr, recv, arg, "ok_or");
                 },

clippy_lints/src/methods/ptr_offset_with_cast.rs

@@ -0,0 +1,82 @@
+use clippy_utils::diagnostics::span_lint_and_then;
+use clippy_utils::msrvs::{self, Msrv};
+use clippy_utils::sym;
+use rustc_errors::Applicability;
+use rustc_hir::{Expr, ExprKind};
+use rustc_lint::LateContext;
+use rustc_span::Symbol;
+use std::fmt;
+
+use super::PTR_OFFSET_WITH_CAST;
+
+pub(super) fn check(
+    cx: &LateContext<'_>,
+    method: Symbol,
+    expr: &Expr<'_>,
+    recv: &Expr<'_>,
+    arg: &Expr<'_>,
+    msrv: Msrv,
+) {
+    // `pointer::add` and `pointer::wrapping_add` are only stable since 1.26.0. These functions
+    // became const-stable in 1.61.0, the same version that `pointer::offset` became const-stable.
+    if !msrv.meets(cx, msrvs::POINTER_ADD_SUB_METHODS) {
+        return;
+    }
+
+    let method = match method {
+        sym::offset => Method::Offset,
+        sym::wrapping_offset => Method::WrappingOffset,
+        _ => return,
+    };
+
+    if !cx.typeck_results().expr_ty_adjusted(recv).is_raw_ptr() {
+        return;
+    }
+
+    // Check if the argument to the method call is a cast from usize.
+    let cast_lhs_expr = match arg.kind {
+        ExprKind::Cast(lhs, _) if cx.typeck_results().expr_ty(lhs).is_usize() => lhs,
+        _ => return,
+    };
+
+    let ExprKind::MethodCall(method_name, _, _, _) = expr.kind else {
+        return;
+    };
+
+    let msg = format!("use of `{method}` with a `usize` casted to an `isize`");
+    span_lint_and_then(cx, PTR_OFFSET_WITH_CAST, expr.span, msg, |diag| {
+        diag.multipart_suggestion(
+            format!("use `{}` instead", method.suggestion()),
+            vec![
+                (method_name.ident.span, method.suggestion().to_string()),
+                (arg.span.with_lo(cast_lhs_expr.span.hi()), String::new()),
+            ],
+            Applicability::MachineApplicable,
+        );
+    });
+}
+
+#[derive(Copy, Clone)]
+enum Method {
+    Offset,
+    WrappingOffset,
+}
+
+impl Method {
+    #[must_use]
+    fn suggestion(self) -> &'static str {
+        match self {
+            Self::Offset => "add",
+            Self::WrappingOffset => "wrapping_add",
+        }
+    }
+}
+
+impl fmt::Display for Method {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            Self::Offset => write!(f, "offset"),
+            Self::WrappingOffset => write!(f, "wrapping_offset"),
+        }
+    }
+}

clippy_lints/src/ptr_offset_with_cast.rs

@@ -73,7 +73,7 @@ msrv_aliases! {
     1,29,0 { ITER_FLATTEN }
     1,28,0 { FROM_BOOL, REPEAT_WITH, SLICE_FROM_REF }
     1,27,0 { ITERATOR_TRY_FOLD }
-    1,26,0 { RANGE_INCLUSIVE, STRING_RETAIN }
+    1,26,0 { RANGE_INCLUSIVE, STRING_RETAIN, POINTER_ADD_SUB_METHODS }
     1,24,0 { IS_ASCII_DIGIT, PTR_NULL }
     1,18,0 { HASH_MAP_RETAIN, HASH_SET_RETAIN }
     1,17,0 { FIELD_INIT_SHORTHAND, STATIC_IN_CONST, EXPECT_ERR }

clippy_utils/src/msrvs.rs

@@ -1,4 +1,4 @@
-#![allow(clippy::unnecessary_cast, clippy::useless_vec)]
+#![expect(clippy::unnecessary_cast, clippy::useless_vec, clippy::needless_borrow)]
 
 fn main() {
     let vec = vec![b'a', b'b', b'c'];
@@ -18,5 +18,25 @@ fn main() {
         //~^ ptr_offset_with_cast
         let _ = ptr.wrapping_offset(offset_isize as isize);
         let _ = ptr.wrapping_offset(offset_u8 as isize);
+
+        let _ = S.offset(offset_usize as isize);
+        let _ = S.wrapping_offset(offset_usize as isize);
+
+        let _ = (&ptr).add(offset_usize);
+        //~^ ptr_offset_with_cast
+        let _ = (&ptr).wrapping_add(offset_usize);
+        //~^ ptr_offset_with_cast
+    }
+}
+
+#[derive(Clone, Copy)]
+struct S;
+
+impl S {
+    fn offset(self, _: isize) -> Self {
+        self
+    }
+    fn wrapping_offset(self, _: isize) -> Self {
+        self
     }
 }