new lint for as *const _ and as *mut _ casting

Author: Soveu

CHANGELOG.md

@@ -5193,6 +5193,7 @@ Released 2018-09-13
 <!-- begin autogenerated links to lint list -->
 [`absolute_paths`]: https://rust-lang.github.io/rust-clippy/master/index.html#absolute_paths
 [`absurd_extreme_comparisons`]: https://rust-lang.github.io/rust-clippy/master/index.html#absurd_extreme_comparisons
+[`accidental_double_ref_into_flat_addr_cast`]: https://rust-lang.github.io/rust-clippy/master/index.html#accidental_double_ref_into_flat_addr_cast
 [`alloc_instead_of_core`]: https://rust-lang.github.io/rust-clippy/master/index.html#alloc_instead_of_core
 [`allow_attributes`]: https://rust-lang.github.io/rust-clippy/master/index.html#allow_attributes
 [`allow_attributes_without_reason`]: https://rust-lang.github.io/rust-clippy/master/index.html#allow_attributes_without_reason

clippy_lints/src/casts/as_pointer_underscore.rs

@@ -0,0 +1,24 @@
+use rustc_errors::Applicability;
+use rustc_lint::LateContext;
+use rustc_middle::ty::Ty;
+
+pub fn check<'tcx>(cx: &LateContext<'tcx>, ty_into: Ty<'_>, cast_to_hir: &'tcx rustc_hir::Ty<'tcx>) {
+    if let rustc_hir::TyKind::Ptr(rustc_hir::MutTy { ty, .. }) = cast_to_hir.kind
+        && matches!(ty.kind, rustc_hir::TyKind::Infer)
+    {
+        clippy_utils::diagnostics::span_lint_and_then(
+            cx,
+            super::AS_POINTER_UNDERSCORE,
+            cast_to_hir.span,
+            "using inferred pointer cast",
+            |diag| {
+                diag.span_suggestion(
+                    cast_to_hir.span,
+                    "use explicit type",
+                    ty_into,
+                    Applicability::MachineApplicable,
+                );
+            },
+        );
+    }
+}

clippy_lints/src/casts/mod.rs

@@ -1,3 +1,4 @@
+mod as_pointer_underscore;
 mod as_ptr_cast_mut;
 mod as_underscore;
 mod borrow_as_ptr;
@@ -717,6 +718,33 @@ declare_clippy_lint! {
     "using `as` to cast a reference to pointer"
 }
 
+declare_clippy_lint! {
+    /// ### What it does
+    /// Checks for the usage of `as *const _` or `as *mut _` conversion using inferred type.
+    ///
+    /// ### Why restrict this?
+    /// The conversion might include a dangerous cast that might go undetected due to the type being inferred.
+    ///
+    /// ### Example
+    /// ```no_run
+    /// fn as_usize<T>(t: &T) -> usize {
+    ///     // BUG: `t` is already a reference, so we will here
+    ///     // return a dangling pointer to a temporary value instead
+    ///     &t as *const _ as usize
+    /// }
+    /// ```
+    /// Use instead:
+    /// ```no_run
+    /// fn as_usize<T>(t: &T) -> usize {
+    ///     t as *const T as usize
+    /// }
+    /// ```
+    #[clippy::version = "1.81.0"]
+    pub AS_POINTER_UNDERSCORE,
+    restriction,
+    "detects `as *mut _` and `as *const _` conversion"
+}
+
 pub struct Casts {
     msrv: Msrv,
 }
@@ -753,6 +781,7 @@ impl_lint_pass!(Casts => [
     CAST_NAN_TO_INT,
     ZERO_PTR,
     REF_AS_PTR,
+    AS_POINTER_UNDERSCORE,
 ]);
 
 impl<'tcx> LateLintPass<'tcx> for Casts {
@@ -795,6 +824,7 @@ impl<'tcx> LateLintPass<'tcx> for Casts {
             }
 
             as_underscore::check(cx, expr, cast_to_hir);
+            as_pointer_underscore::check(cx, cast_to, cast_to_hir);
 
             if self.msrv.meets(msrvs::PTR_FROM_REF) {
                 ref_as_ptr::check(cx, expr, cast_expr, cast_to_hir);

clippy_lints/src/declared_lints.rs

@@ -78,6 +78,7 @@ pub(crate) static LINTS: &[&crate::LintInfo] = &[
     crate::cargo::NEGATIVE_FEATURE_NAMES_INFO,
     crate::cargo::REDUNDANT_FEATURE_NAMES_INFO,
     crate::cargo::WILDCARD_DEPENDENCIES_INFO,
+    crate::casts::AS_POINTER_UNDERSCORE_INFO,
     crate::casts::AS_PTR_CAST_MUT_INFO,
     crate::casts::AS_UNDERSCORE_INFO,
     crate::casts::BORROW_AS_PTR_INFO,

tests/ui/as_pointer_underscore.fixed

@@ -0,0 +1,17 @@
+#![warn(clippy::as_pointer_underscore)]
+#![crate_type = "lib"]
+#![no_std]
+
+struct S;
+
+fn f(s: &S) -> usize {
+    &s as *const &S as usize
+    //~^ ERROR: using inferred pointer cast
+    //FIXME: idk how to get this help working ~| HELP: use explicit type: `*const &S`
+}
+
+fn g(s: &mut S) -> usize {
+    s as *mut S as usize
+    //~^ ERROR: using inferred pointer cast
+    //FIXME: idk how to get this help working ~| HELP: use explicit type: `*mut S`
+}

tests/ui/as_pointer_underscore.rs

@@ -0,0 +1,17 @@
+#![warn(clippy::as_pointer_underscore)]
+#![crate_type = "lib"]
+#![no_std]
+
+struct S;
+
+fn f(s: &S) -> usize {
+    &s as *const _ as usize
+    //~^ ERROR: using inferred pointer cast
+    //FIXME: idk how to get this help working ~| HELP: use explicit type: `*const &S`
+}
+
+fn g(s: &mut S) -> usize {
+    s as *mut _ as usize
+    //~^ ERROR: using inferred pointer cast
+    //FIXME: idk how to get this help working ~| HELP: use explicit type: `*mut S`
+}

tests/ui/as_pointer_underscore.stderr

@@ -0,0 +1,17 @@
+error: using inferred pointer cast
+  --> tests/ui/as_pointer_underscore.rs:8:11
+   |
+LL |     &s as *const _ as usize
+   |           ^^^^^^^^ help: use explicit type: `*const &S`
+   |
+   = note: `-D clippy::as-pointer-underscore` implied by `-D warnings`
+   = help: to override `-D warnings` add `#[allow(clippy::as_pointer_underscore)]`
+
+error: using inferred pointer cast
+  --> tests/ui/as_pointer_underscore.rs:14:10
+   |
+LL |     s as *mut _ as usize
+   |          ^^^^^^ help: use explicit type: `*mut S`
+
+error: aborting due to 2 previous errors
+