Add new lint dangling_ptr

Author: aaron-ang

CHANGELOG.md

@@ -5501,6 +5501,7 @@ Released 2018-09-13
 [`create_dir`]: https://rust-lang.github.io/rust-clippy/master/index.html#create_dir
 [`crosspointer_transmute`]: https://rust-lang.github.io/rust-clippy/master/index.html#crosspointer_transmute
 [`cyclomatic_complexity`]: https://rust-lang.github.io/rust-clippy/master/index.html#cyclomatic_complexity
+[`dangling_ptr`]: https://rust-lang.github.io/rust-clippy/master/index.html#dangling_ptr
 [`dbg_macro`]: https://rust-lang.github.io/rust-clippy/master/index.html#dbg_macro
 [`debug_assert_with_mut_call`]: https://rust-lang.github.io/rust-clippy/master/index.html#debug_assert_with_mut_call
 [`decimal_literal_representation`]: https://rust-lang.github.io/rust-clippy/master/index.html#decimal_literal_representation

clippy_lints/src/casts/dangling_ptr.rs

@@ -0,0 +1,41 @@
+use clippy_utils::diagnostics::span_lint_and_sugg;
+use clippy_utils::source::SpanRangeExt;
+use clippy_utils::{expr_or_init, is_expr_positive_literal, std_or_core};
+use rustc_errors::Applicability;
+use rustc_hir::{Expr, Mutability, Ty, TyKind};
+use rustc_lint::LateContext;
+
+use super::DANGLING_PTR;
+
+pub(super) fn check(cx: &LateContext<'_>, expr: &Expr<'_>, from: &Expr<'_>, to: &Ty<'_>) {
+    if let TyKind::Ptr(ref mut_ty) = to.kind {
+        let init_expr = expr_or_init(cx, from);
+        if is_expr_positive_literal(init_expr)
+            && let Some(std_or_core) = std_or_core(cx)
+            && let Some(var) = from.span.get_source_text(cx)
+        {
+            let (msg, sugg_fn) = match mut_ty.mutbl {
+                Mutability::Not => (format!("`{var} as *const _` detected"), "ptr::dangling"),
+                Mutability::Mut => (format!("`{var} as *mut _` detected"), "ptr::dangling_mut"),
+            };
+
+            let sugg = if let TyKind::Infer = mut_ty.ty.kind {
+                format!("{std_or_core}::{sugg_fn}()")
+            } else if let Some(mut_ty_snip) = mut_ty.ty.span.get_source_text(cx) {
+                format!("{std_or_core}::{sugg_fn}::<{mut_ty_snip}>()")
+            } else {
+                return;
+            };
+
+            span_lint_and_sugg(
+                cx,
+                DANGLING_PTR,
+                expr.span,
+                msg,
+                "try",
+                sugg,
+                Applicability::MachineApplicable,
+            );
+        }
+    }
+}

clippy_lints/src/casts/mod.rs

@@ -14,6 +14,7 @@ mod cast_sign_loss;
 mod cast_slice_different_sizes;
 mod cast_slice_from_raw_parts;
 mod char_lit_as_u8;
+mod dangling_ptr;
 mod fn_to_numeric_cast;
 mod fn_to_numeric_cast_any;
 mod fn_to_numeric_cast_with_truncation;
@@ -754,6 +755,28 @@ declare_clippy_lint! {
     "detects `as *mut _` and `as *const _` conversion"
 }
 
+declare_clippy_lint! {
+    /// ### What it does
+    /// Catches casts from a positive integer literal to some pointer type
+    ///
+    /// ### Why is this bad?
+    /// This creates a pointer with no provenance which might cause incorrect compiler optimizations.
+    /// It is better expressed as {`std`, `core`}`::ptr::`{`dangling`, `dangling_mut`}.
+    ///
+    /// ### Example
+    /// ```no_run
+    /// let a = 1 as *const u32;
+    /// ```
+    /// Use instead:
+    /// ```no_run
+    /// let a = std::ptr::dangling::<u32>();
+    /// ```
+    #[clippy::version = "1.86.0"]
+    pub DANGLING_PTR,
+    pedantic,
+    "casting a positive integer literal to a pointer with no provenance"
+}
+
 pub struct Casts {
     msrv: Msrv,
 }
@@ -792,6 +815,7 @@ impl_lint_pass!(Casts => [
     ZERO_PTR,
     REF_AS_PTR,
     AS_POINTER_UNDERSCORE,
+    DANGLING_PTR,
 ]);
 
 impl<'tcx> LateLintPass<'tcx> for Casts {
@@ -819,6 +843,7 @@ impl<'tcx> LateLintPass<'tcx> for Casts {
             fn_to_numeric_cast::check(cx, expr, cast_from_expr, cast_from, cast_to);
             fn_to_numeric_cast_with_truncation::check(cx, expr, cast_from_expr, cast_from, cast_to);
             zero_ptr::check(cx, expr, cast_from_expr, cast_to_hir);
+            dangling_ptr::check(cx, expr, cast_from_expr, cast_to_hir);
 
             if cast_to.is_numeric() {
                 cast_possible_truncation::check(cx, expr, cast_from_expr, cast_from, cast_to, cast_to_hir.span);

clippy_lints/src/declared_lints.rs

@@ -93,6 +93,7 @@ pub static LINTS: &[&crate::LintInfo] = &[
     crate::casts::CAST_SLICE_DIFFERENT_SIZES_INFO,
     crate::casts::CAST_SLICE_FROM_RAW_PARTS_INFO,
     crate::casts::CHAR_LIT_AS_U8_INFO,
+    crate::casts::DANGLING_PTR_INFO,
     crate::casts::FN_TO_NUMERIC_CAST_INFO,
     crate::casts::FN_TO_NUMERIC_CAST_ANY_INFO,
     crate::casts::FN_TO_NUMERIC_CAST_WITH_TRUNCATION_INFO,

clippy_utils/src/lib.rs

@@ -2219,6 +2219,15 @@ pub fn is_expr_used_or_unified(tcx: TyCtxt<'_>, expr: &Expr<'_>) -> bool {
     )
 }
 
+pub fn is_expr_positive_literal(expr: &Expr<'_>) -> bool {
+    if let ExprKind::Lit(spanned) = expr.kind {
+        if let LitKind::Int(v, _) = spanned.node {
+            return v > 0;
+        }
+    }
+    false
+}
+
 /// Checks if the expression is the final expression returned from a block.
 pub fn is_expr_final_block_expr(tcx: TyCtxt<'_>, expr: &Expr<'_>) -> bool {
     matches!(tcx.parent_hir_node(expr.hir_id), Node::Block(..))

tests/ui/dangling_ptr.fixed

@@ -0,0 +1,15 @@
+#![warn(clippy::dangling_ptr)]
+
+pub fn foo(_const: *const f32, _mut: *mut i64) {}
+
+fn main() {
+    let _ = std::ptr::dangling::<usize>();
+    let _ = std::ptr::dangling_mut::<f64>();
+    let _: *const u8 = std::ptr::dangling();
+
+    foo(0 as _, 0 as _);
+    foo(std::ptr::dangling(), std::ptr::dangling_mut());
+
+    let z = 1;
+    let _ = std::ptr::dangling::<usize>();
+}

tests/ui/dangling_ptr.rs

@@ -0,0 +1,15 @@
+#![warn(clippy::dangling_ptr)]
+
+pub fn foo(_const: *const f32, _mut: *mut i64) {}
+
+fn main() {
+    let _ = 1 as *const usize;
+    let _ = 1 as *mut f64;
+    let _: *const u8 = 1 as *const _;
+
+    foo(0 as _, 0 as _);
+    foo(1 as *const _, 1 as *mut _);
+
+    let z = 1;
+    let _ = z as *const usize;
+}

tests/ui/dangling_ptr.stderr

@@ -0,0 +1,41 @@
+error: `1 as *const _` detected
+  --> tests/ui/dangling_ptr.rs:6:13
+   |
+LL |     let _ = 1 as *const usize;
+   |             ^^^^^^^^^^^^^^^^^ help: try: `std::ptr::dangling::<usize>()`
+   |
+   = note: `-D clippy::dangling-ptr` implied by `-D warnings`
+   = help: to override `-D warnings` add `#[allow(clippy::dangling_ptr)]`
+
+error: `1 as *mut _` detected
+  --> tests/ui/dangling_ptr.rs:7:13
+   |
+LL |     let _ = 1 as *mut f64;
+   |             ^^^^^^^^^^^^^ help: try: `std::ptr::dangling_mut::<f64>()`
+
+error: `1 as *const _` detected
+  --> tests/ui/dangling_ptr.rs:8:24
+   |
+LL |     let _: *const u8 = 1 as *const _;
+   |                        ^^^^^^^^^^^^^ help: try: `std::ptr::dangling()`
+
+error: `1 as *const _` detected
+  --> tests/ui/dangling_ptr.rs:11:9
+   |
+LL |     foo(1 as *const _, 1 as *mut _);
+   |         ^^^^^^^^^^^^^ help: try: `std::ptr::dangling()`
+
+error: `1 as *mut _` detected
+  --> tests/ui/dangling_ptr.rs:11:24
+   |
+LL |     foo(1 as *const _, 1 as *mut _);
+   |                        ^^^^^^^^^^^ help: try: `std::ptr::dangling_mut()`
+
+error: `z as *const _` detected
+  --> tests/ui/dangling_ptr.rs:14:13
+   |
+LL |     let _ = z as *const usize;
+   |             ^^^^^^^^^^^^^^^^^ help: try: `std::ptr::dangling::<usize>()`
+
+error: aborting due to 6 previous errors
+