Rollup merge of #145941 - Urgau:int_to_ptr_transmutes-unsized, r=lcnr

Disable `integer_to_ptr_transmutes` suggestion for unsized types

This PR disables the machine-applicable `integer_to_ptr_transmutes` lint suggestion for unsized types, as [`std::ptr::with_exposed_provenance`](https://doc.rust-lang.org/std/ptr/fn.with_exposed_provenance.html) requires sized types.

We should probably mention [`std::ptr::from_raw_parts`](https://doc.rust-lang.org/std/ptr/fn.from_raw_parts.html) when it becomes stable.

Related to #145935

Author: Zalathar

compiler/rustc_lint/src/lints.rs

@@ -1554,7 +1554,7 @@ impl<'a> LintDiagnostic<'a, ()> for DropGlue<'_> {
 #[help(lint_help_exposed_provenance)]
 pub(crate) struct IntegerToPtrTransmutes<'tcx> {
     #[subdiagnostic]
-    pub suggestion: IntegerToPtrTransmutesSuggestion<'tcx>,
+    pub suggestion: Option<IntegerToPtrTransmutesSuggestion<'tcx>>,
 }
 
 #[derive(Subdiagnostic)]

compiler/rustc_lint/src/transmute.rs

@@ -169,19 +169,25 @@ fn check_int_to_ptr_transmute<'tcx>(
         expr.hir_id,
         expr.span,
         IntegerToPtrTransmutes {
-            suggestion: if dst.is_ref() {
-                IntegerToPtrTransmutesSuggestion::ToRef {
-                    dst: *inner_ty,
-                    suffix,
-                    ref_mutbl: mutbl.prefix_str(),
-                    start_call: expr.span.shrink_to_lo().until(arg.span),
-                }
+            suggestion: if layout_inner_ty.is_sized() {
+                Some(if dst.is_ref() {
+                    IntegerToPtrTransmutesSuggestion::ToRef {
+                        dst: *inner_ty,
+                        suffix,
+                        ref_mutbl: mutbl.prefix_str(),
+                        start_call: expr.span.shrink_to_lo().until(arg.span),
+                    }
+                } else {
+                    IntegerToPtrTransmutesSuggestion::ToPtr {
+                        dst: *inner_ty,
+                        suffix,
+                        start_call: expr.span.shrink_to_lo().until(arg.span),
+                    }
+                })
             } else {
-                IntegerToPtrTransmutesSuggestion::ToPtr {
-                    dst: *inner_ty,
-                    suffix,
-                    start_call: expr.span.shrink_to_lo().until(arg.span),
-                }
+                // We can't suggest using `with_exposed_provenance` for unsized type
+                // so don't suggest anything.
+                None
             },
         },
     );

tests/ui/lint/int_to_ptr-unsized.rs

@@ -0,0 +1,23 @@
+// Checks for the `integer_to_pointer_transmutes` lint with unsized types
+//
+// Related to https://github.com/rust-lang/rust/issues/145935
+
+//@ check-pass
+
+#![allow(non_camel_case_types)]
+#![allow(unused_unsafe)]
+
+#[cfg(target_pointer_width = "64")]
+type usizemetadata = i128;
+
+#[cfg(target_pointer_width = "32")]
+type usizemetadata = i64;
+
+unsafe fn unsized_type(a: usize) {
+    let _ref = unsafe { std::mem::transmute::<usizemetadata, &'static str>(0xff) };
+    //~^ WARN transmuting an integer to a pointer
+    let _ptr = unsafe { std::mem::transmute::<usizemetadata, *const [u8]>(0xff) };
+    //~^ WARN transmuting an integer to a pointer
+}
+
+fn main() {}

tests/ui/lint/int_to_ptr-unsized.stderr

@@ -0,0 +1,27 @@
+warning: transmuting an integer to a pointer creates a pointer without provenance
+  --> $DIR/int_to_ptr-unsized.rs:17:25
+   |
+LL |     let _ref = unsafe { std::mem::transmute::<usizemetadata, &'static str>(0xff) };
+   |                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: this is dangerous because dereferencing the resulting pointer is undefined behavior
+   = note: exposed provenance semantics can be used to create a pointer based on some previously exposed provenance
+   = help: if you truly mean to create a pointer without provenance, use `std::ptr::without_provenance_mut`
+   = help: for more information about transmute, see <https://doc.rust-lang.org/std/mem/fn.transmute.html#transmutation-between-pointers-and-integers>
+   = help: for more information about exposed provenance, see <https://doc.rust-lang.org/std/ptr/index.html#exposed-provenance>
+   = note: `#[warn(integer_to_ptr_transmutes)]` on by default
+
+warning: transmuting an integer to a pointer creates a pointer without provenance
+  --> $DIR/int_to_ptr-unsized.rs:19:25
+   |
+LL |     let _ptr = unsafe { std::mem::transmute::<usizemetadata, *const [u8]>(0xff) };
+   |                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: this is dangerous because dereferencing the resulting pointer is undefined behavior
+   = note: exposed provenance semantics can be used to create a pointer based on some previously exposed provenance
+   = help: if you truly mean to create a pointer without provenance, use `std::ptr::without_provenance_mut`
+   = help: for more information about transmute, see <https://doc.rust-lang.org/std/mem/fn.transmute.html#transmutation-between-pointers-and-integers>
+   = help: for more information about exposed provenance, see <https://doc.rust-lang.org/std/ptr/index.html#exposed-provenance>
+
+warning: 2 warnings emitted
+