Rollup merge of #106047 - uweigand:s390x-test-bigendian-ui, r=oli-obk

[rust.git] / src / tools / clippy / clippy_lints / src / transmute / mod.rs

diff --git a/src/tools/clippy/clippy_lints/src/transmute/mod.rs b/src/tools/clippy/clippy_lints/src/transmute/mod.rs
index 83e651aba8e89b15ed99db9dfcf768afece1431f..691d759d7739dbea81c65ab12c1a12855cda657e 100644 (file)
--- a/src/tools/clippy/clippy_lints/src/transmute/mod.rs
+++ b/src/tools/clippy/clippy_lints/src/transmute/mod.rs
@@ -3,6 +3,7 @@
 mod transmute_int_to_bool;
 mod transmute_int_to_char;
 mod transmute_int_to_float;
+mod transmute_null_to_fn;
 mod transmute_num_to_bytes;
 mod transmute_ptr_to_ptr;
 mod transmute_ptr_to_ref;
@@ -409,6 +410,34 @@
     "transmutes from a null pointer to a reference, which is undefined behavior"
 }
 
+declare_clippy_lint! {
+    /// ### What it does
+    /// Checks for null function pointer creation through transmute.
+    ///
+    /// ### Why is this bad?
+    /// Creating a null function pointer is undefined behavior.
+    ///
+    /// More info: https://doc.rust-lang.org/nomicon/ffi.html#the-nullable-pointer-optimization
+    ///
+    /// ### Known problems
+    /// Not all cases can be detected at the moment of this writing.
+    /// For example, variables which hold a null pointer and are then fed to a `transmute`
+    /// call, aren't detectable yet.
+    ///
+    /// ### Example
+    /// ```rust
+    /// let null_fn: fn() = unsafe { std::mem::transmute( std::ptr::null::<()>() ) };
+    /// ```
+    /// Use instead:
+    /// ```rust
+    /// let null_fn: Option<fn()> = None;
+    /// ```
+    #[clippy::version = "1.67.0"]
+    pub TRANSMUTE_NULL_TO_FN,
+    correctness,
+    "transmute results in a null function pointer, which is undefined behavior"
+}
+
 pub struct Transmute {
     msrv: Msrv,
 }
@@ -428,6 +457,7 @@ pub struct Transmute {
     TRANSMUTES_EXPRESSIBLE_AS_PTR_CASTS,
     TRANSMUTE_UNDEFINED_REPR,
     TRANSMUTING_NULL,
+    TRANSMUTE_NULL_TO_FN,
 ]);
 impl Transmute {
     #[must_use]
@@ -461,6 +491,7 @@ fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) {
                 let linted = wrong_transmute::check(cx, e, from_ty, to_ty)
                     | crosspointer_transmute::check(cx, e, from_ty, to_ty)
                     | transmuting_null::check(cx, e, arg, to_ty)
+                    | transmute_null_to_fn::check(cx, e, arg, to_ty)
                     | transmute_ptr_to_ref::check(cx, e, from_ty, to_ty, arg, path, &self.msrv)
                     | transmute_int_to_char::check(cx, e, from_ty, to_ty, arg, const_context)
                     | transmute_ref_to_ref::check(cx, e, from_ty, to_ty, arg, const_context)