Auto merge of #12403 - samueltardieu:issue-12402, r=blyxyas

Pointers cannot be converted to integers at compile time

Fix #12402

changelog: [`transmutes_expressible_as_ptr_casts`]: do not suggest invalid const casts

Author: bors

clippy_lints/src/transmute/mod.rs

@@ -592,7 +592,7 @@ impl<'tcx> LateLintPass<'tcx> for Transmute {
                 | (eager_transmute::check(cx, e, arg, from_ty, to_ty));
 
             if !linted {
-                transmutes_expressible_as_ptr_casts::check(cx, e, from_ty, from_ty_adjusted, to_ty, arg);
+                transmutes_expressible_as_ptr_casts::check(cx, e, from_ty, from_ty_adjusted, to_ty, arg, const_context);
             }
         }
     }

clippy_lints/src/transmute/transmutes_expressible_as_ptr_casts.rs

@@ -18,10 +18,12 @@ pub(super) fn check<'tcx>(
     from_ty_adjusted: bool,
     to_ty: Ty<'tcx>,
     arg: &'tcx Expr<'_>,
+    const_context: bool,
 ) -> bool {
     use CastKind::{AddrPtrCast, ArrayPtrCast, FnPtrAddrCast, FnPtrPtrCast, PtrAddrCast, PtrPtrCast};
     let mut app = Applicability::MachineApplicable;
     let mut sugg = match check_cast(cx, e, from_ty, to_ty) {
+        Some(FnPtrAddrCast | PtrAddrCast) if const_context => return false,
         Some(PtrPtrCast | AddrPtrCast | ArrayPtrCast | FnPtrPtrCast | FnPtrAddrCast) => {
             Sugg::hir_with_context(cx, arg, e.span.ctxt(), "..", &mut app)
                 .as_ty(to_ty.to_string())

tests/ui/transmutes_expressible_as_ptr_casts.fixed

@@ -82,3 +82,10 @@ fn issue_10449() {
 
     let _x: u8 = unsafe { *(f as *const u8) };
 }
+
+// Pointers cannot be cast to integers in const contexts
+const fn issue_12402<P>(ptr: *const P) {
+    unsafe { transmute::<*const i32, usize>(&42i32) };
+    unsafe { transmute::<fn(*const P), usize>(issue_12402) };
+    let _ = unsafe { transmute::<_, usize>(ptr) };
+}

tests/ui/transmutes_expressible_as_ptr_casts.rs

@@ -82,3 +82,10 @@ fn issue_10449() {
 
     let _x: u8 = unsafe { *std::mem::transmute::<fn(), *const u8>(f) };
 }
+
+// Pointers cannot be cast to integers in const contexts
+const fn issue_12402<P>(ptr: *const P) {
+    unsafe { transmute::<*const i32, usize>(&42i32) };
+    unsafe { transmute::<fn(*const P), usize>(issue_12402) };
+    let _ = unsafe { transmute::<_, usize>(ptr) };
+}