1 files changed, 74 insertions, 0 deletions
diff --git a/tests/ui/structs-enums/enum-null-pointer-opt.rs b/tests/ui/structs-enums/enum-null-pointer-opt.rs
new file mode 100644
index 00000000000..85fa1eac2e2
--- /dev/null
+++ b/tests/ui/structs-enums/enum-null-pointer-opt.rs
@@ -0,0 +1,74 @@
+// run-pass
+#![feature(transparent_unions)]
+
+use std::mem::size_of;
+use std::num::NonZeroUsize;
+use std::ptr::NonNull;
+use std::rc::Rc;
+use std::sync::Arc;
+
+trait Trait { fn dummy(&self) { } }
+trait Mirror { type Image; }
+impl<T> Mirror for T { type Image = T; }
+struct ParamTypeStruct<T>(#[allow(unused_tuple_struct_fields)] T);
+struct AssocTypeStruct<T>(#[allow(unused_tuple_struct_fields)] <T as Mirror>::Image);
+#[repr(transparent)]
+union MaybeUninitUnion<T: Copy> {
+    _value: T,
+    _uninit: (),
+}
+
+fn main() {
+    // Functions
+    assert_eq!(size_of::<fn(isize)>(), size_of::<Option<fn(isize)>>());
+    assert_eq!(size_of::<extern "C" fn(isize)>(), size_of::<Option<extern "C" fn(isize)>>());
+
+    // Slices - &str / &[T] / &mut [T]
+    assert_eq!(size_of::<&str>(), size_of::<Option<&str>>());
+    assert_eq!(size_of::<&[isize]>(), size_of::<Option<&[isize]>>());
+    assert_eq!(size_of::<&mut [isize]>(), size_of::<Option<&mut [isize]>>());
+
+    // Traits - Box<Trait> / &Trait / &mut Trait
+    assert_eq!(size_of::<Box<dyn Trait>>(), size_of::<Option<Box<dyn Trait>>>());
+    assert_eq!(size_of::<&dyn Trait>(), size_of::<Option<&dyn Trait>>());
+    assert_eq!(size_of::<&mut dyn Trait>(), size_of::<Option<&mut dyn Trait>>());
+
+    // Pointers - Box<T>
+    assert_eq!(size_of::<Box<isize>>(), size_of::<Option<Box<isize>>>());
+
+    // The optimization can't apply to raw pointers or unions with a ZST field.
+    assert!(size_of::<Option<*const isize>>() != size_of::<*const isize>());
+    assert!(Some(std::ptr::null::<isize>()).is_some()); // Can't collapse None to null
+    assert_ne!(size_of::<fn(isize)>(), size_of::<Option<MaybeUninitUnion<fn(isize)>>>());
+    assert_ne!(size_of::<&str>(), size_of::<Option<MaybeUninitUnion<&str>>>());
+    assert_ne!(size_of::<NonNull<isize>>(), size_of::<Option<MaybeUninitUnion<NonNull<isize>>>>());
+
+    struct Foo {
+        _a: Box<isize>
+    }
+    struct Bar(#[allow(unused_tuple_struct_fields)] Box<isize>);
+
+    // Should apply through structs
+    assert_eq!(size_of::<Foo>(), size_of::<Option<Foo>>());
+    assert_eq!(size_of::<Bar>(), size_of::<Option<Bar>>());
+    // and tuples
+    assert_eq!(size_of::<(u8, Box<isize>)>(), size_of::<Option<(u8, Box<isize>)>>());
+    // and fixed-size arrays
+    assert_eq!(size_of::<[Box<isize>; 1]>(), size_of::<Option<[Box<isize>; 1]>>());
+
+    // Should apply to NonZero
+    assert_eq!(size_of::<NonZeroUsize>(), size_of::<Option<NonZeroUsize>>());
+    assert_eq!(size_of::<NonNull<i8>>(), size_of::<Option<NonNull<i8>>>());
+
+    // Should apply to types that use NonZero internally
+    assert_eq!(size_of::<Vec<isize>>(), size_of::<Option<Vec<isize>>>());
+    assert_eq!(size_of::<Arc<isize>>(), size_of::<Option<Arc<isize>>>());
+    assert_eq!(size_of::<Rc<isize>>(), size_of::<Option<Rc<isize>>>());
+
+    // Should apply to types that have NonZero transitively
+    assert_eq!(size_of::<String>(), size_of::<Option<String>>());
+
+    // Should apply to types where the pointer is substituted
+    assert_eq!(size_of::<&u8>(), size_of::<Option<ParamTypeStruct<&u8>>>());
+    assert_eq!(size_of::<&u8>(), size_of::<Option<AssocTypeStruct<&u8>>>());
+}