1 files changed, 52 insertions, 31 deletions

diff --git a/src/test/ui/consts/const-eval/ub-enum.rs b/src/test/ui/consts/const-eval/ub-enum.rs
index 483285aa4e1..1922d59891f 100644
--- a/src/test/ui/consts/const-eval/ub-enum.rs
+++ b/src/test/ui/consts/const-eval/ub-enum.rs
@@ -1,34 +1,36 @@
+#![feature(const_transmute, never_type)]
 #![allow(const_err)] // make sure we cannot allow away the errors tested here
 
+use std::mem;
 
 #[repr(transparent)]
 #[derive(Copy, Clone)]
 struct Wrap<T>(T);
 
+#[derive(Copy, Clone)]
+enum Never {}
+
+// # simple enum with discriminant 0
+
 #[repr(usize)]
 #[derive(Copy, Clone)]
 enum Enum {
     A = 0,
 }
-#[repr(C)]
-union TransmuteEnum {
-    in1: &'static u8,
-    in2: usize,
-    out1: Enum,
-    out2: Wrap<Enum>,
-}
 
-const GOOD_ENUM: Enum = unsafe { TransmuteEnum { in2: 0 }.out1 };
+const GOOD_ENUM: Enum = unsafe { mem::transmute(0usize) };
 
-const BAD_ENUM: Enum = unsafe { TransmuteEnum { in2: 1 }.out1 };
+const BAD_ENUM: Enum = unsafe { mem::transmute(1usize) };
 //~^ ERROR is undefined behavior
 
-const BAD_ENUM_PTR: Enum = unsafe { TransmuteEnum { in1: &1 }.out1 };
+const BAD_ENUM_PTR: Enum = unsafe { mem::transmute(&1) };
 //~^ ERROR is undefined behavior
 
-const BAD_ENUM_WRAPPED: Wrap<Enum> = unsafe { TransmuteEnum { in1: &1 }.out2 };
+const BAD_ENUM_WRAPPED: Wrap<Enum> = unsafe { mem::transmute(&1) };
 //~^ ERROR is undefined behavior
 
+// # simple enum with discriminant 2
+
 // (Potentially) invalid enum discriminant
 #[repr(usize)]
 #[derive(Copy, Clone)]
@@ -36,39 +38,58 @@ enum Enum2 {
     A = 2,
 }
 
-#[repr(C)]
-union TransmuteEnum2 {
-    in1: usize,
-    in2: &'static u8,
-    in3: (),
-    out1: Enum2,
-    out2: Wrap<Enum2>, // something wrapping the enum so that we test layout first, not enum
-    out3: Option<Enum2>,
-}
-const BAD_ENUM2: Enum2 = unsafe { TransmuteEnum2 { in1: 0 }.out1 };
+const BAD_ENUM2: Enum2 = unsafe { mem::transmute(0usize) };
 //~^ ERROR is undefined behavior
-const BAD_ENUM2_PTR: Enum2 = unsafe { TransmuteEnum2 { in2: &0 }.out1 };
+const BAD_ENUM2_PTR: Enum2 = unsafe { mem::transmute(&0) };
 //~^ ERROR is undefined behavior
-const BAD_ENUM2_WRAPPED: Wrap<Enum2> = unsafe { TransmuteEnum2 { in2: &0 }.out2 };
+// something wrapping the enum so that we test layout first, not enum
+const BAD_ENUM2_WRAPPED: Wrap<Enum2> = unsafe { mem::transmute(&0) };
 //~^ ERROR is undefined behavior
 
 // Undef enum discriminant.
-const BAD_ENUM2_UNDEF : Enum2 = unsafe { TransmuteEnum2 { in3: () }.out1 };
+#[repr(C)]
+union MaybeUninit<T: Copy> {
+    uninit: (),
+    init: T,
+}
+const BAD_ENUM2_UNDEF : Enum2 = unsafe { MaybeUninit { uninit: () }.init };
 //~^ ERROR is undefined behavior
 
 // Pointer value in an enum with a niche that is not just 0.
-const BAD_ENUM2_OPTION_PTR: Option<Enum2> = unsafe { TransmuteEnum2 { in2: &0 }.out3 };
+const BAD_ENUM2_OPTION_PTR: Option<Enum2> = unsafe { mem::transmute(&0) };
 //~^ ERROR is undefined behavior
 
+// # valid discriminant for uninhabited variant
+
+// An enum with 3 variants of which some are uninhabited -- so the uninhabited variants *do*
+// have a discriminant.
+enum UninhDiscriminant {
+    A,
+    B(!),
+    C,
+    D(Never),
+}
+
+const GOOD_INHABITED_VARIANT1: UninhDiscriminant = unsafe { mem::transmute(0u8) }; // variant A
+const GOOD_INHABITED_VARIANT2: UninhDiscriminant = unsafe { mem::transmute(2u8) }; // variant C
+
+const BAD_UNINHABITED_VARIANT1: UninhDiscriminant = unsafe { mem::transmute(1u8) };
+//~^ ERROR is undefined behavior
+const BAD_UNINHABITED_VARIANT2: UninhDiscriminant = unsafe { mem::transmute(3u8) };
+//~^ ERROR is undefined behavior
+
+// # other
+
 // Invalid enum field content (mostly to test printing of paths for enum tuple
 // variants and tuples).
-#[repr(C)]
-union TransmuteChar {
-    a: u32,
-    b: char,
-}
 // Need to create something which does not clash with enum layout optimizations.
-const BAD_OPTION_CHAR: Option<(char, char)> = Some(('x', unsafe { TransmuteChar { a: !0 }.b }));
+const BAD_OPTION_CHAR: Option<(char, char)> = Some(('x', unsafe { mem::transmute(!0u32) }));
+//~^ ERROR is undefined behavior
+
+// All variants are uninhabited but also have data.
+const BAD_UNINHABITED_WITH_DATA1: Result<(i32, Never), (i32, !)> = unsafe { mem::transmute(1u64) };
+//~^ ERROR is undefined behavior
+const BAD_UNINHABITED_WITH_DATA2: Result<(i32, !), (i32, Never)> = unsafe { mem::transmute(1u64) };
 //~^ ERROR is undefined behavior
 
 fn main() {