Fix checking transmutes with adjusted types

clippy_lints/src/transmute/mod.rs

@@ -415,7 +415,8 @@ impl<'tcx> LateLintPass<'tcx> for Transmute {
                 // And see https://github.com/rust-lang/rust/issues/51911 for dereferencing raw pointers.
                 let const_context = in_constant(cx, e.hir_id);
 
-                let from_ty = cx.typeck_results().expr_ty(arg);
+                let from_ty = cx.typeck_results().expr_ty_adjusted(arg);
+                // Adjustments for `to_ty` happen after the call to `transmute`, so don't use them.
                 let to_ty = cx.typeck_results().expr_ty(e);
 
                 // If useless_transmute is triggered, the other lints can be skipped.

tests/ui/transmute_undefined_repr.rs

@@ -106,5 +106,7 @@ fn main() {
 
         let _: MaybeUninit<Ty2<u32, u32>> = transmute(value::<Ty2<u32, u32>>()); // Ok
         let _: Ty2<u32, u32> = transmute(value::<MaybeUninit<Ty2<u32, u32>>>()); // Ok
+
+        let _: Ty<&[u32]> = transmute::<&[u32], _>(value::<&Vec<u32>>()); // Ok
     }
 }